Power System Planning

1

POW£R S~ST£M PLANNING ...N

INDIA POWER GRID REGIONS .:-., ,,' _/ ,-

.- ,

LEGEND_. _. -

International Boundary State.90undary

]0 •

Country Capital

State Capital

.+7-5 Prepared by I ANILKUMAR K.M., Assistant Professor in E&EE, BIET, . Davangere-04. ..L E XC U}SI VtL 'I XcRcl'/(PP A-T R R.,~ ~eyveJ 94-4-.9850sgS

®

HNA eUIC-I(.PR..INI"{ . Ogo 2.3.3 2633

+~ J1:d_ ..

4dY }41Cfj\.:t~-:::..

'~o.b:

-~~

2aJ\1~cl.@cr-a\ .C<

2

-'-_

. AS PER VTU SYLLABUS SUBJECT - POWER SYSTEM PLANNING Subject Code: 10~E761 IA Marla: 25 No. of Lecture Hrs.1 Week: 04 Total No. of Lecture Hrs. 52

Exam Hours: 03 Exam Marks: 100

PART-A

UNIT~ 1 INTRODUCTION

OF POWER PLANNING, National and regional planning, structure of

power system, planning tools, electricity regulation, Load forecasting, forecasting techniques, modeling.

8 Hours

UNIT-2 &3 GENERATION

PLANNING, Integrated power generation, co-generation I captive power, ..

power pooling and power trading, transmission & distribution planning, power system economics, power sector finance, financial planning, private participation, rural. electrification

10 lIotirs

investment, concept of rational tariffs..

UNIT-4 COMPUTER

AIDED PLANNING: Wheeling, environmental effects, green house effect,

technological impacts, insulation co-ordination, and reactive compensation.

8 Hours

PART-B:

UNIT-5 & 6 POWER SUPPLY

RELIABILITY,

reliability planning, system operation planning, load

management, load prediction, reactive power balance, online power flow studies, test estimation, computerized management. Power system simulator.

10 Hours

UNIT-7 & 8 Optimal Power system expansion planning, formulation of least cost optimization problem

incorporating the capital, operating and maintenance cost of candidate plants of different types (thermal hydro nuclear non conventional etc), Optimization techniques for solution by

16 Hours

programming. TEXT BOOK REFERRED FOR NOTES: 1. ElectriCal Power System Planning, A.S.Pabla, Macmillan India Ltd, 1998 2. Electrical Power Distribution System, AS.Pabla, Macmillan India Ltd, 1983

ANILKUMAR K.M., Assistant Professor in E&EE, B.I.E.T, Davangere.

Krishna Xerox 9008281471

..,

3

UNIT -1: INTRODUCTION OF POWER PLANNING

V.T.U.Syllabus

-

-

ANIT.KUMAR KJv!. Assistant Professor,E&EE, BIET,DavangeD! . ..•-.<. ......~~

National and regional planning, structure of power system, planning tools, electricity regulation, Load forecasting, forecasting techniques, modeling.

SYNOPSIS The basic process of planning & its application to the power system has been illustrated. The history of the planning & its increasing importance in present & future scenarios of power system has been analyzed. The power growth & national & regional planning & development of national grids ?ave been brought out. Least cost planning is discussed, the regulatory process of power .. development which includes various rules, acts & policies are illustrated. The various techniques for forecasting & its modeling are explained.

4

... "" ".- ....

UNlT-l~ INTRODUCTION

_._.-_ ..._ - -

-'-

OF POWER PLANNING

1. INTRODUCTION 1.1 POWER PLANNING Electricity plays -; key-role in the modem society because of its versatility ;W;respect

to input

~nergy form. The annual per capita consumption in India is about 335 kWh (1996). A rise in this consumption to three times the value is likely to substantially raise the standard of living of the people in the country with respect to education, health, transport,

communication,

media,

productivity etc. Electricity can be produced with coal, nuclear fuels, oil, gas, hydro power, diesel, geothermal energy, biomass, wind -energy, solar energy or fuel cells. Electrical supply also offers the opportunity

of total environmental enhancement

compared to other energy use patterns.

For increasing the supply of electricity, new power projects will have to be installed. Expansion, modernization, and maintenance of the electricity utility industry will require increased capital costs, financial and environmental restraints, increasing fuel costs and regulatory delays. AU these factors lead to the necessity for a more comprehensive understanding and analysis of electric power systems. Recent developments in system analysis and synthesis as well as in related. Digital, analog, and hybrid computer techniques provide important tools which will aid the planning engineer in meeting these challenges. Some of the questions to be-explored are: 1. Where and how much generating capacity should be added? 2. What should be the optimum size of the generating units? 3, what types or combinations of generation types should be used - nuclear, gas turbine, conventional steam, pumped hydro, solar, wind etc. 4. What will be the environmental impact of various generation alternatives? 5. What should be the size of the interconnections with neighboring systems? 6. What voltage levels are most economical and what transmission lines should be constructed? 7. What will be the impact of major facility additions upon the financial structure Of the utility? 8. How will utility requirements affect targets of performance for new technologies? 9. How will the energy conservation and load management measures help to reduce generation capacity requirements? 10. How much reliability of power supply to consumer is required? 1.2 PLANNING PROCESS ./' Planning is the process of taking a careful decision. The main input in Planning is the quality of systematic thought that goes into a decision . ./' The process of establishing the power industry is capital intensive and time Planning saves project time and ensures that resources are used most economically.

ANlLKUMAR K.M., AssistantProfessor in E&EE, B.l.E.T, Davangere.

5

POWERSYST$)f PLANNING

../ Planning is the process of selecting vision, values. m!SSk'Al and objectives and decIding what -" should be done to attain them. ../ Planning should take into account: uncertainty about the future, many alternative action choices and many goals and constraints. Planning can be seen asconsisttng-of three cyclical componenents 1 Learning about the environment, the relevant issues and possible future scenarios in order to identify: i

(i) Strategically goals (ii) The decision criteria and constraints (iiij.Technological needs and opportunities

2 Thinking about available strategic options, the associated costs and risks and their implications. This involves: (i) Investment of resources . (ii) Possible unforeseen factors (ifi) Reliability of outcome.

3 Action that involves choosing preferred plans or strategies on the basis of supporting analysis. Once an action has been selected and the process of implementation begins, the cycle is renewed. The following characteristics.make this planning process particularly challenging for power systems. 1. The power system is highly capital intensive. 2. Rationales and experiences developed in advanced countries are difficult to apply for expanding a large system with diverse options in developing countries. 3. The learning and thinking activitiesoften tend to diverge broadly before finallyconverging. • NEW PLANS

~.':

.

" 1~ ...-

,

t

!~f~.

~

,

Implementation of Plans

-

,

t..

">

,

-_.,,---._-;>

.

-

r;1f:TiT::i~'J11: ':,_,:up:.-

,

" ~

/,' - , ~ '

ft~I.,;!nf~\""f}..( r.'r'·'~:.f.Jrf1r;-_ > ,/

•

"',,'

-

.....

~ -

•

6 POWER SYSTb. ...l11J!LAJVJV1N
1.3 POWER SYSTEMS ./

Ever since electrification began in the world around 1880, electrical utilities have gradually consolidated into larger units to generate, transmit and distribute electricity. In India, electrification started with the commissioning of small ~ydro-el~ctric station (I3v....!~,-I-.(1I--1lDarjeeling in 1897. Followed by commissioning of a hydropower station at Sivasarnudrarn in Karnataka during 1902 •

./

The regulatory systems have consequently changed over time~ The planning of power systems

•

must fit with the overall energy policy with due respect to public opinion and reliability of power supply. This makes power system planning difficult. The problem of ensuring adequate future electricity supply varies from country to country depending on the peoples' expectations, technological development; and availabilities of resources . ./

Under the Electricity Supply Act, it is the duty of the Central Electricity Authority to adopt a systematic approach to formulate policy and optimize resources.

./

Planning should consider the needs of the system - existing, new or refurbished generation, new transmission or upgrades, demand-side management and so on - and the resources that maybe available to meet them. Where additional generation is required, like site, size, the fuel type including back-up fuel requirements (if any), technical and environmental characteristics and mode of dispatch (base load, intermediate, peaking), should be identified .

./

Environmental and resource constraints are forcing us to approach the future with better planned and researched projects. The major goals for the future are to develop least cost projects, identify new primary resources, find better means of distribution, transmission and generation, emphasize on better and less wasteful use of electricity, and develop demand side management.' Pumped hydro power and superconducting magnetic coils represent a possible solution for storage of electricity Planning should identify the project with decision & clarity. Power aspects in developed and developing countries • ,114' :,1:-,,\', 1.,-,"'1 "'('" , ....', :i _-''\';! ,

'(If:''0~~i;;~~ J,,~ !,~_-;.~ .:~.:.. "-

""_

.

ANILKUMAR K.M ••AssistantProfessor inE&EE. BJ.E.T. Davangere.

•

7 POWER SYSTEM PLANNING

1.4 STRATEGIC PLANNING 1.4.1 Strategies & its classification v' Strategy is a unified, comprehensive and. integrated plan. v' His designed to ensure that the corporate goals are achieved.·Comprehensive intelligence about the nature and extent of the likely trends of power development and demand is essential for a

i

successful strategy. v' Strategic planning.is the process of determining the long-term goals and courses of action and the allocation of resources necessary to accomplish these goals.

v' The broader planning horizon of strategic planning has significant implications for resource planning, for example, planning to influence demand in order to reduce the need to build new generating capacity. There are many means available to reduce demand, such as by (i) Changing the tariff structure, e.g., time-of-day tariff.

(ii) Demand billing. (iii) Implementation ofload control by shifting peak load to

?~ peak period.

(iv) Encouraging eo-generation/captive generation. (v) Promotion of conservation of energy.

Functions of planning . ......

. C).l'Et')!(Zt'~ttjfl.>;i f.,.<\,-\,~'-l . .

.

.

•

-.

.-

..

.

.. The first step in developing a strategy is the identification of the problems and opportunities that exist. A successful utility win have a fertile idea generating environment. To attain the vision, perform strengths, weaknesses opportunities and threats (SWOT) analysis and benchmarking exercises within the power utility. The second step is to set goals (objectives). Goal setting is not independent from identification of opportunities- The next step is to have a procedure for providing possible solutions. Tactical and operational planning involves this step. The fourth step in strategic planning is to choose the best solution, given possible solutions and the objectives. On what the solutions be chosen is a difficult job, depending upon various constraints. The planning are shown in the next page.

t4I...

Al'lTT VTl1\JI AV TC M

A ",,;M<>,..t l>rnfl><:<.:nT ;n

F&F'R HJ.E.T. Davaneere.

8

-

-

__- -VISION - ..-

_.

POLICIES, ,

~A"

STRATEGIES . PROCEOURl:S' . " ... ~

..,

. .:

'

".

~, ~ )

BUDGETS.; •

'_

4' _;

- -~,.

't ••

v

•

Flow chart showing the Components of Planning The last step is to have some type of review procedure to check how the best solution has actually performed. The nature of this review function will depend on the performance and style of management. To implement a strategy, develop the specific action plan.

Long-Term Strategy Some technological,

managerial

and geopolitical

issues require long-term

policy and

administrative decisions and include, among others: (i) Directions for capacity augmentation to meet the projected demand need for accelerating hydro development. (ii) Environmental issues in power development. (iii) Inter (state/regional issues in water resources development. (iv) Functional and commercial issues in integrated operation. (v) Land and water availability for thermal power development. (vi) Fuel (coal, oil etc.) quality and transport in thermal power development. (vii) Energy costs and prices and resource mobilization. (viii) Organizational deficiencies in power development, i.e., re-engineering of power industry to bring efficiency in the management process. (ix) Private participation in power generation, transmission and distribution.

Medium-Term Strategy The broad aims are:

(i) Renovation, modernization, upgrading and extension in the life of existing ageing power plants. (ii) Reduction of transmission and distribution losses. (iii) Construction of shorter gestation power plants like gas turbine based combined cycle, generation schemes etc. (iv) Energy conservation and load management.

ANll..KUMAR K.M., Assistant Professor inE&EE, B.I.E.T, Davangere.

,..

9 POWER SYSTEM PLANNING

(v) Adoption of non-conventional energy sources particularly for rural decentralized energy systems. Short-Term Development Strategy Short-term strategies aim "at:

.- -

(i) Improving the performance of existing power plant capacity and maximizing its utilization. (ii) Seeking even power sharing over circuits of similar ratings. (iii) Establishing new circuit connection as required, if possible without recourse to displacing. lower voltage circuits, and at the highest possible capacity.

..

(iv) Routing new circuits so that they may readily be used for connection of future power stations, or for supply points to regional grids. (iI) Reducing the number of levels of system voltage used. (vi) Maintaining uniformly high, but acceptable fault levels. (vii) Installing capacitors at various voltage levels (HT and LT.) (viii) Computerizing work management system for tracking recurring problems, materials movement and maintenance history and to forecast maintenance schedule. The planning engineer's contribution to a project is to prepare a detailed project report giving a time frame for site clearance, and for starting, completing, and finishing construction of a project. The report sets the limits of resources and sequence of activities and phases etc. 1.4;2 Detailed project report (DPR) Planning of power project facilities undergoes the following stages: (i) Preliminary investigations for establishment' of need proposed to be achieved through the implementation of a project. (ii) Project identification and formulation which involves examination of various options to meet desired needs and selection of one for preparation of feasibility report. (iii) Detailed

Feasibility Report (DFR.) regarding

technical, demand, organization,

and

environmental aspects, and financial and economic viabilities. (iv) Appraisal of Detailed Feasibility Report keeping in mind the following aspects: (a) Technical analysis to determine whether the specifications of technical parameters chosen are realistic and optimal. (b) Demand analysis to determine the demand availability gap_of power for a particular region/state/site and arrangement for evacuation of power thus generated. (c) Organizational aspects to determine whether the organization has the managerial capability to implement and operate the project. (d) To check ifthe environmental guidelines are fully covered in theproject cost (e) Financial analysis to determine whether financial costs are properly estimated, ensured and the project is financially viable. ANaKUMAR

K.M., Assistant Professor in E&EE, B.I.E.T, Davangere,

10 POWER SYSTEM PLANNING

(f) Economic analysis to determine the cost generation/transmission and whether the project is e~~no;nically worthwhile . .(v) _Preparation of Detailed Project Report: It comprises technical details running into severa! . volumes for large projects. After the appraisal ofDFR, detailed engineering cqnducted, A Detailed Project Report indicating the firmed-up cost estimates and project implementation schedule is prepared. Between the DFR and DPR stage, there may be some further studies required to improve information about site conditions and other project parameters. (vi) Implementation involves implementation planning as per detailed project report, obtaining various clearances, getting investment approval or financial close, detailed designs and drawings, specifications, tendering/contracting, execution of various activities leading to commissioning of the project and monitoring throughout. 1.4.3 Project implementation Good project management is necessary to avoid time and cost over runs. Rigorous project planning and management practices should be applied for the project to be completed in time and within budget. PERT must define an overall project management framework under which all implementation activities will have to be performed. It should contain: (i) A detailed schedule of all project activities and their estimated durations. (ii) A statement on the methods to be used to complete all the project activities. (iii) A quality statement which identifies a11quality control and quality assurance steps to be applied. (iv) A statement on the organizational requirement and impact within the utility organization, so that it can be managed effectively. Well researched, clear and good quality Detailed Project Reports (DPRs) for power development are important. Research and Development should be an in-built part of the project for the entire duration of the project. The one important reason for the present conditions of power supply in India is the delays in the addition of power generating, and transmission and distribution capacity mainly due to DPR deficiencies. 1.4.4 Role of consultants Consultants have important role in Power industry. The consultant can take up the tum-key projects and' Consultancy services such as feasibility reports, detailed project reports, detailed engineering, total project management, commissioning, financial systems, manpower management, R&D etc. The primary business of a consultant is; (i) To provide solution to their client's problems. The consultant should be able to define the problems and constraints and analyze them to. arrive at a solution. (ii) To help the client to accept and implement the solution. (iii) Consolidate consultants' knowledge base. ANILKUMAR K.M., AssistantProfessor in E&EE,B.I.E.T,Davangere.

•

11

POWERSYSTEM PLANNING

1.5 POWER DEVELOPMENT The development of power is closely linked with the growth of gross national product. The economic strength of a region in the next century will be greatly dependent on the availability of power, In the planning of power system development, priority is given to regional-systems and generation lead balances are maintained. Also, keeping in view that different transmission lines are not too 'reduadant' but are sufficiently robust regional links, there must be strategic planning to i

foresee, evahaate and co-ordinate future requirements and concentrate resources to dovetail with medium andshort-term objectives. The overa n'time leads to th e vanous plannmg activities are given below, Activity Plannlna Time ahead Vision, values, mission, load forecasting regional system Long-term planning 5-20 years and National grid expansions scheme '. Medium-term utility generation schemes such as coal, Medium-term 2-5 years thermal, gas turbines, hydro etc. Renovation and planning modernization of existing generating plants System improvement of transmission and distribution Short-term planning 1-2 years systems, Small generation schemes, small hydro, gas turbines diesel power projects, non-conventional sources of generation Maintenance scheduling of units and fuel requirements 15days-l year Operational planning Generation scheduling and network switching Operational planning 1-1 days Economic dispatching instruction and power purchases I Operational planning 2-12 hours selling Network switching Economic Dispatch Control Operational planning 0-2 hours The starting point in the planning process is to develop clear vision, good values and mission. The other processes follow, such as to develop load forecasts in terms of annual peaks and energy needs for the entire utility area as well as for each region consisting of many utilities. The system expansion is determined by load-flow studies under steady state and abnormal conditions. The load-flow studies are made for calculation of currents, voltages, and real and reactive power flows taking into account the voltage regulating capability of generators and transformers, capacitors, generation schedules, power interchange etc. By changing the location, size and number of transmission lines, the planner can achieve. To design an economical system that meets the operating, design, environmental and cost criteria. After determining the best system configuration from the load-flow studies, the planning engineer studies system behavior under fault conditions by carrying out Short-circuit studies as a short-term plan to determine design parameters of protection systems. Finally the planner performs the stability studies to ensure that the power system will remain stable following severe fault.

ANILKUMAR K.M., AssistantProfessor in E&EE,B.I.E.T,Davangere.

12 POWER SYSTEM PLANNING

1.6 PO'VER GROWTH ./ The electricity generation capacity in India is the fifth largest in the world. India is also the sixth largest consumer of electricity, and accounts for 3.4 -per cent of the global energy consumptiQn. Over the pasUhirty years, the country's energy demand has grown at an average of 3.6 per cent per annum. Growth in the installed capacity of power generation has been spectacular, having risen from 1,712MW in 1950 to 84,087MW ending 1995-96. During the financial year 2011-12, the highest ever capacity addition of 20,501 MW (thermal, nuclear and hydro) was achieved (CEA). A capacity addition of 17,956 MW during the year 2012-13comprising 15,154 Mw of thermal, 802 MW of hydro and 2000

MW

of nuclear power-has

been envisaged . ./

India's Installed Generation Capacity stands at 210,95Ln the electricity

sector

in India had an installed

MWas on December 31,2012. And

capacity of 225.133· OW as of May

2013. Captive power plants generate an additional 34.444 GW. Non Renewable Power Plants constitute 87.55% of the installed capacity, and Renewable- Power Plants constitute the remaining 12.45% of total installed Capacity. India generated

8~~su

(855 000 MU i.e.

855 TWh) electricity during 2011-12 fiscal. ./

In terms of fuel, coal-fired plants account for 57% of India's installed electricity capacity, compared

to South Africa's

92%; China's

77%;

and Australia's

76%.

After coal,

renewal hydropower accounts for 19%, renewable energy for 12% and natural gas for about 9%. -/ The Power Ministry has also proposed an outlay of Rs 37 crores for the Central Electricity Authority (CEA) for various initiatives of strengthening its institutional framework. Sixty-three per cent will be spent on new and ongoing projects while twenty-nine per cent is on renovation and modernization, and the rest is on renewable energy projects. The overall investment required for the power sector in the 12th Plan is about 12 to 14 lakh crores of rupees. The investment pattern should focus on generation, transmission and distribution segments in order to achieve balanced growth in the power sector . ./

The Central Electricity Authority (CEA), in its fifteenth Electric power Survey has estimated that the gross energy generation required by the year 2020 is to the order of 1325TWhlannum and the corresponding generation capacity requirement is 3,85,770MW .

./

The transmission network comprises of about 98,367 circuit kilometers of transmission lines at 8001765kV, 400kV, 220kV and 132kV EHVAC and +500kV HYDC lev~ls and 160 substations. A new transmission line of 1200 KV has become operational in India whereas the highest transmission voltage level in China is only 1100 KV. The capacity is about 1,57, 158 MVA as on January 31,2013. This gigantic transmission ~"'.,,,~.~""

ANILKUMAR K.M., AssistantProfessorin E&EE, B.l.E.T,Davangere.

•

13 POWER SYSTEM PLANNING

spread over the length and breadth of the country is consistently maintained at an availability of over ninetynine per cent (pGCIL) . ./' The transmission and distribution less is another ill afflicting the power sector in the country. --The

main reasons for high transmission and distribution losses are weak and inadequate sub-

transmission and distribution system, improper load management, inadequate reactive load compensation

at load points, low quality of construction, inadequate maintenance

of

equipments, and unmetered supply of agricultural pump-sets and pilferage/theft of energy . ./' India's network losses exceeded 32% in 2010 including non-technical losses, compared to world average of less than 15%. Both technical and non-technical factors contribute to these

•

losses, but quantifying t~~ir proportions is difficult: But the Government pegs the national T &D losses at around 24% for the year 2011 & has set a target of reducing it to 17.1% by 2017 & to 14.1% by 2022. Some experts estimate that technical losses are about 15% to 20%.

2. NATIONAL AND REGIONAL PLANNING 2.1 ADVANTAGES

& DISADVANTAGES OF NATIONAL AND REGIONAL

PLANNING There is a lot of diversity in the country in topography, daily peak due to day time differences, annual peak load timings (winter or summer) & resources in the various regions. Hence five electricity regions have been established. The economic argument in support of regional coordination is - Advantages, ../

Such coordination allows joint planning & operation of facilities,

../

It makes the exchange of economical energy easier,

../ It prevents the constructions of unnecessary facilities by isolated systems & increases reliabilities . ../

More specifically, as a result of transmission interconnections, coordination offers distinct economic & the non coincidental occurrence of the peak of the participation systems .

../

It might be possible to reduce the total generating capacity requirements that would otherwise

apply if each utility system were to fully meet its needs . ../

By combining the existing capacity of generation in the region & to make economic use of the generating resources such as hydro & fossil fuels etc ... Disadvantage,

../

One of the problems in regional planning relates to coordination among the various utilities in the region with respect to tariff and backing down Of generating units in merit order. _ links for transfer of power between various regions is desirable in order to utilize power in some regions and for stable grid operation.

ANILKUMAR K.M., AssistantProfessor inE&EE, B.I.E.T,Davangere.

14 POWER SYSTEM PLANNING

2.2 INTEGRATED RESOURCES PLANNING This is an aspect of least cost planning. The utilities have to evaluate all the Supply side and

time of use pricing and system improvement

demand side options like energy conservationprogrammes,

direct load control: interruptible or

.

..SUPPLYSIDE OPTIONS 1. The technology related to conventional fossil fuels is predominant at present. Many utilities have turned to combustion turbines fueled with natural gas with new capacity which are highly efficient, have low emission, and are well adapted for intermittent use. Moreover, as the focus is now.on cleaner, more efficiently cost-effective, Goal-fired generation technologies, washed coal, gasification based generation options like Integrated Gasification-Combined

Cycle

(lGCC), etc., are found more effective over applying Flue Gas Desulfurization units and Fluidized Bed Combustion because the former have a potential to minimize solid waste in addition to cutting airborne emissions. 2. Increasing role of renewable: While technological advancement continues in the use of fossil fuels, several new options have started to emerge which broaden the scope of non-conventional sources of energy in the future. Wind power generation costs have fallen dramatically, by a factor of 10, and photovoltaics by a factor of 4, over the last two decades. 3. Increase in the availability of generating station. 4. Efficient operation of the regional and national grid. S. Strengthening the existing transmission and distribution system such as by adding new links

and capacitor banks at suitable points and thus reducing system losses and improving voltage profiles. DEMAND SIDE OPTIONS 1. Taking energy conservation 111£asureTs:here is a potential for energy saving to the extent of 30 per cent in agriculture pump-sets, 25 per cent in industrial motors, and 10-15 per cent in commercial and domestic lighting. 2. Minimum consumer power factor of not less than 0.95 lagging. 3. Consumer load management such as rural, agriculture and urban load staggering, individual large consumer load control, and thereby improvement in generating stations load factor. 4. Time-of-day metering with three tariffs for peak time (higher rate), night time (lower rate) and other times ofthe day (medium rate). 2.3 LEAST COST UTILITY PLANNING ../ There are two fundamental problems inherent in traditional planning. The first is that forecasting and investment planning are treated as sequential steps in planning, interdependent aspects of the planning process. The second problem is that planning ANILKUMAR K.M., AssistantProfessor in E&EE,B.I.E.T, Davangere.

..

15 POWER S¥':''1'bM J'LAiV1V./.JVb

inadequately directed at the main constraintsfacing the sector, namely, the serious shortage of resources. ./' Demand forecastsare little more than extrapolations of past trends of consumption;no attempt is made-te-uederstendneither the extent ofunmet demand, nor the-eeeentto which price would influence demand .growth. Greater attention should be paid to end-use efficiency, plant rehabilitation, loss reduction programme etc as these have a potential for much more economic use of investmentresources. -/' Least cost planningis least cost utility planning strategy to provide reliable electrical services •

at the lowest overallcost with a mix of supplyside and demandside resources. -/' The Leup uses various options like end-useenergy efficiency,load management, transmission and distribution options, alternative tariff options, decentralized non-conventional sources power generation and conventional centralized generation sources. The magnitude. of the various componentsdepends upon the detailedoutcome of the exercise. ./ This planning process can yield enormousbenefits to consumersand societybecause it affords acquisition of resourcesthat meet consumerenergy service needs in ways that are low in cost, environmentally benign, and acceptable to the public. Such benefits occur because of the diversity of resourcesconsidered, public involvement in the planning process and cooperation among interestedparties. ./' Least costs utility planning as a planning and a regulatory process can greatly reduce the uncertainties and risks faced by utilities. System expansion detailed project reports (DPRs) must be based on least cost planning and need to be made mandatory by amending the Electricity (Supply)Act, 1948.The logic for least-cost planningis shown in below Figure. lEAST COST -to

AlTAI8UTES:

IlEMTCOST. EN'liltON. BE... GM. soc;lALlY

A.CU:PTAaLE. ETC.}

./ For an investmentto be least cost, the lifetimecosts are considered.These include capital cost, interest on capital,fuel costs, and operationaland maintenance cost. ./ To fully realize the benefits, a complete analysis of the options is necessary and simulation study according to a programming can be necessary and simulation study according to a programming can be helpful for a complete analysis of attributes. The process of least cost planning is shownin next page.

ANll.KUMAR K.M., AssistantProfessorin E&EE,B.I.E.T,Davangere.

16 POWER SYSTEM PLANlVING

..

The process of least cost planning Evaluation 1. All options, whether supply or demand, should be assessed in a comparable and consistent manner. 2. Once the initial evaluation has been completed, other factors (economic, environmental, and societal) should be considered individually. Such revaluation prevents the rejection of options with high costs in one set of factors, such as economics, but strong benefits in others, such as environmental impacts. 3. The evaluation and integration of options can also be accomplished through the use of various commercially available computer programs. 4. A linear programming model (India ELITE) based on an earlier version of a power planning model developed in Canada has been prepared. It has been used in identifying least cost electric power system development options for India for the 1991-2021time frame. S. EGEAS packages have been used by CEA for preparing the National Power Plans. . 6. Other software's. or packages available for simulation or least cost planning are PROMOD, ELFIN, MIDAS, EGEAS, UPLAN, MARKAL-ELGEM etc which are used in different countries.

3. STRUCTURE OF POWER SYSTEM ,/

An electrical" power system can be considered to consist of generation, transmission, sub transmission systems and distribution parts. In general, the generation and

,

systems are considered as bulk power supply and the sub transmission and distribution are considered to be the final means to transfer the electric power to the ultimate

ANILKUMAR K.M., AssistantProfessor in E&EE,B.I.E.T,Davangere.

£,AT,,'Ulrn"

17

The standard system voltages used in India for transmission and distribution are as per IS: 123601988are given in the below table.

Standard system KV Volt.ag~ (IS: 12360) Nominal Voltage in KV

•

--

Maximum SystemVoltage

Remarks

0.240

0.264

Distribution

0.415

0.457

3.3

3.6

6.6

7.2

11.0 22.0

.

12.0 .

'. 24.0

33.0

36.0

Distribution & Sub

66.0

72.5

transmission

132.0

145.0

Sub transmission &

220.0

245.0

400.0

420.0

765.0

800.0

..

Transmission Transmission & Tie

.

line

v' The basic system consists of energy resources such as hydro, coal, gas etc., a prime mover, a

generator and a load. Some sort of control system is required for supervising it. v' The prime mover may be a steam driven turbine, a hydraulic turbine or an internal combustion

engine. Each one of these prime movers has the ability to convert energy in the form of heat, falling water or fuel into rotation of the shaft which in turn drives the generator. v' The generator may be are alternator or a d.c. machine. The Electrical load on the generator may

be lights, motors, heat or other devices, alone or in combination etc. ,

The con.ol system functions to keep the speed of the machine constant, the voltage within prescribed limits to meet varying conditions of the load by adjusting fuel/water, and generator excitatien within the generator capability .

../' The active power (MW) is regulated by frequency (speed) control. The reactive power (MVAr) and voltage is regulated by excitation control. ../' TIle components of an electric power system include generators designed to convert mechanical energy into electricity, transformers, which change the voltage or current of electric po~~r suppl~, tr~~ission

lines used to itr~sfer power from on~ location to another,

auxiliary equipment intended to vary the system controls.

~j, ,,,:,~<.'}i

18 POWER SYSTEM PLANNING v" System performance is determined at an instant of time and is characterized by

its functional

parameters such as levels of power, voltage, frequency, wave shape, phase balance> and amperes. Physical properties of interconnected systems are characterized by resistance of .

.

components, inertia moments and...JiIne constants determining the change of electrical and mechanical quantities, The electric power system is closely connected to other systems by tie lines or links. llEUtolti

$tJi"t..

tAAHS·

. UII~.::'" l(Y[l

t f/rm I~R<~

a:N.

SJl&I':'

Power System Components The power transmission and distribution network may be of the following types 1. The radial system is as in Figure shown in next page. Here the lines form a 'tree' spreading out from the generator. Opening any line results in interruption of power to one or more of the loads. 2. The loop system is as in Figure shown in next page. With this arrangement all loads will continue to be served even if one line section' is put out of service. In normal operation the loop may be open at some point at A as shown in the figure. In case a line section is to be taken out, the loop is first closed at A and the line section is put on shut down. In this way no service interruption occurs.

Radial System

Loop System

Network of Lines

19 POWER SYSTEM PLANNING

3. In Network of lines the same loads being served by a network. This arrangement has a higher reliability as each load has two or more circuits of supply. -/' The sub transmission and distribution circuits are"commonly designed as radial or loop circuits. - The-high voltage transmission lines are generally laid as interconnected or networks .

./' In this case interconnection of major power stations creates networks made of many line sections. As the demand for load grows, generating capacity and transmission and distribution must grow as well. Transmission and distribution are distinguished by their voltage levels. In general, transmission systems have bulk power handling capability, and relatively long lines connecting generating stations to.load centres of the utilities. -/' The model of transfer of powe!. (P) by transmission line (having line reactance XI) between two distance buses, (1 and 2) fed by generating machines with terminal bus voltage VI and V2 . respectively with phase angle

e difference is generally represented

as,

p = I V. II V; I sin B XL ../ Distribution systems including sub transmissions, branch out from" and Under lie the transmission systems. They handle lower levels and have relatively short lines. The power level that transmission and distribution systems are being called upon to handle, are increasing with time. The economies of scale need large generating stations and higher voltage levels for transmission and distribution. Electricity cannot be stored and has to be supplied instantly. -/' The component installed capacity, say in MVA p.u., expands progressively as one moves from generation to transmission, sub transmission, distribution and the consumer end. Typical value for the Indian power system is, Generation

capacity

(1 p.u.) =Transmission

capacity (1.5 p.u.) + Sub transmission

capacity (2p.u.) + Distribution capacity (3 p.u.) + Connected load (6p.u.) -/' The reduced p.u. values on the right hand will indicate better electricity efficiency of the system but in the interest of reliability and future expansion p.u. values may be higher for some sectors. With rapid advancements in the field of electronics and its applications in innumerable domestic, commercial and industrial sectors, the demand for quality power supply has increased. 'Computers and other high-tech electronic process technologies require clean, precise, transient free and uninterrupted power supply. -/' Rule

54 of the Indian Electricity

Rules, 1956, states that a supplier shall not permit deviation in

=::;I:~~eb::o:e:~c~:::~ :ighersideorbymore,~~~

voltage at the point of supply in consumer premises

~::::; c:o:~o:;

percent on the lower SIde, or

ANILKUMAR K.M., AssistantProfessor in E&EE,B.I.E.T, Davangere.

:"(io:'yt!{'.:;

20 POWER SYSTEM PLANNING

3. In the case of extra high voltage, by more than 10 percent on the higher side Or by more than 12.5 percent on the lower side. 4. Rule 55 states that the frequency of the alternating current should not vary from the declared frequency by m0x:.ethan 3 percent.

4. POWERRESOURCES ./ The electricity

sector

in India had an installed capacity of 225.133 GW as of May

2013. Captive power plants generate an additional 34.444 OW. Non Renewable Power Plants constitute 87.55% of the installed capacity, and Renewable Power Plants constitute the remaining 12.45% of total installed Capacity . ../' The share of electrical energy in total energy consumption in India is 13.0% which is at 10th place in world ranking . ../ India is endowed with economically exploitable and viable hydro potential assessed to be about 84,000 MW at 60010 load factor. In addition, 6,780 MW in terms of installed capacity from Small, Mini, and Micro Hydel schemes have been assessed . ./' India's coal reserves will outlast other fuels for there are known coal reserves for another 200 years. India is the third major coal producing country in the world. Coal and '·1 ignite accounted

-

for about 57% of India's installed capacity. However,. since wind energy ~epends on wind speed, and hydropower energy on water levels, thermal power plants account for over 65% of India's generated electricity. India's electricity sector consumes about 80% of the coal produced in the country . ./' India's share of nuclear power plant generation capacity is just 1.2% of worldwide nuclear power production capacity, making it the 15th largest nuclear power producer. Nuclear power provided 3% of the country's total electricity generation in 2012 .

. ./' In India, the known reserves of oil will last for about 30 years & the Natural Gas can last up to AD 2050 at the present rate of consumption. Natural gas is basically methane which contains one carbon atom for every four hydrogen atoms. Therefore, after combustion it gives out less C02 for every energy unit derived. Besides, gas has little or no sulfur compounds or suspended particulate matter, & the percentage of nitrogen is much less than in coal or oil. As a natural policy, the use of oil & gas has been allowed for power generation.

,,._

-:

21 YUW.l!.l( ,Sr':HbM

l'LAJVIV1Jv(:i

5. PLANNING TOOLS y'

Planning engineer's primary requirement is to give power supply to consumers in a reliable manner at a minimum cost with due flexibility for future expansion.

y'

The criteria and constraints in planning an energy system are reliabi~

environment,

economics and electricity pricing, financial constraints, and society impacts and value of electricity. y'

Reliability, economic; financial and environmental factors can be quantified. However, societal effects are evaluated qualitatively.

Some of these criteria conflict, ~aking

the planning

decisions more complex. For example, meeting higher reliability levels may be constrained by

•

financial limitations to build new facilities. Achieving lower environmental impact is likely to increase the cost of electricity to consumers (economic factor). y'

The system must be optimal over a time period from first day of operation through the planned lifetime. Today, the planner numerous analysis and synthesis tools at his disposal.

y'

Various computer programs are available and are used for fast screening of alternate plans with respect to technical, economic and environmental performance of power system.

The available tools for power system planning can be split into three basic techniques: simulation, optimization and scenario Techniques,

r. ./

Simulation ToolsThese simulate the behavior of the system under certain conditions andlor calculate relevant indices. Examples of (simulation tools) are load flow models, short-circuit-models, transient stability models etc., in transmission; production costing, adequacy calculations, estimation of environmental impact etc .

./

In power generation, corporate models can simulate the impact of various decisions on the financial performance of the power utility company.

y'

The use of simulation tools for strategic planning need voluminous data and requires the results from various models to be integrated such typical simulation programs is shown.

2. OptimizationToolsy'

These minimize or maximize an objective function by choosing adequate values for decision variables. Examples of these are optimum power, least cost expansion planning, generation expansion planning.

3. The Scenario Techniquesy'

This is a method for viewing the future in a quantitative fashion.

y'

All possible outcomes are investigated. The sO,rtof decision or assurnp~ions which might

~,l

made by a utility developing such a scenario .~ight be: should we Computeri~e and a~~~~l~l the management of power system after a certain date.

ANll-KUMAR K.M., Assistant Professorin E&EE, B.I.E.T, Davangere.

.".'; -c

'.;;;';"

22 POWER SYSTEM PLANNING

./

The process of Planning Electric Energy Systems consist of generating a set of planning Scenario,

./

Scenario can.be optimistic/ambitious or optimum or Pessimistic .

./ In India, the various types of scenarios for electric power are drawn by the Pla~ing Commission, CEA, State Electricity Boards, research organizations, individual research workers Etc . ./

Electrical utilities should prepare integrated resource plans. These Long term plans seek to develop the best mix of demand and supply options to meet consumer needs for electric energy services -, Simulation programs for system planning •~;~:< .: 1_ " .';;_i B " .

-

..:

. ' .. '"!t!, '-~~~J~ /~\":~

Optimum generation

mix

Best combination ofdifferenttypes

and sizes of generating units

cohsideIirig capit(il and production costs and minimizingrevenue requirements

~KUMAR

K.M., AssistantProfessor in E&EE, B.lE.T, Davangere.

23 POWER SYSTEM PLANNING

6. THE ELECTRICITY REGULATIONS -I Regulations shape and influence the functions and processes. The regulations generally concern, 1. Price setting: consumer tariff, wheeling charges, long-term-bulk-power Purchase agreeiiieiits.

2. Quality of'service standard and monitoring. 3. Compliance with public service obligations. 4. Dealing with consumer complaints. 5. Ensuringfair and open competition or the harnessing of competitive forces, as appropriate.

6. Monitoring investment in and repair of infrastructure. 7. Third party use of networks. -/' The current regulations enacted by the Government of India are primarily administered by CEA in its role as technical and economic advisor to the Minister of Power, with input from state, regional and central government entities. -/' For example, there is need for rules regarding transmission access to private generators and for checking the potential for anticompetitive use of monopoly power . ../' Tariff regulations at the bulk power level are primarily "covered under section 43A of the Electricity (Supply) Act of 1948. ELECTRICITY

ACTS

INDIAN TELEGRAPHICACT,

1885

This act covers the privileges and powers of the government to place the telegraphic lines and posts. Penalties and certain other supplementary provisions regarding electric power lines. INDIAN ELECTRICITY

ACT, 1910

This is an act to amend the law relating to the supply and use of electrical energy. It regulates:

..

1. Licences: Grant of licences; revocation or amendment of licences; purchase of undertakings; annual account of licensees. 2. Works: Provision as to opening and breaking up of streets, railways and tramways; notice of . new works; laying of supply lines; notice to telegraph authority; overhead lines; compensation for damage. 3. Supply: Point of supply; powers of lincences to enter premises, restrictions on licensees; obligation on licensees to supply energy; powers of the state governments to give direction to a licensee, power to control the distribution and consumption of energy; discontinuance of supply to consumers; meters. 4. Transmission and Use of Energy by Non-licensees: sanctions required by non-licensees incertain cases; control of transmission and use of energy.

ANILKUMAR K.M.• Assistant Professor in E&EE, B.I.E.T, Davangere.

24

5. General Protective Clause: Protection of railways, aerodromes, canals, docks and piers; protection of telegraphicand electric signal lines; notice of accidentsand enquiries; prohibition of connection ~ith earthand power to governmentto interfere in certaincases of default.I 6. Administration andRules: AdvisoryQ_oards; 'lPpointment of electricalinspectors. 7. criminal Offences and Procedure: Theft of energy; penalty for maliciously wasting energy or injuring works; penalty for unauthorized supply of energy by non-licensees;penalty for illegal or defective supply or for non-compliance with order, penalty for interference with meters or licensee's works andfor improper use of energy; offences by companies;institution of prosecution. 8. supplementaryProvisions: Exercise in'certain cases of power of telegraph authority;'arbitration; recovery of sums; delegation of certain functions of the state government to the inspection staff; protection for acts done in good faith; amendment of Land Acquisition Act, 1884;repeals and savings. THE ELECTRICITY (SUPPLY ACT) ACT, 1948 This act rationalizes the production and supply of electricity and generally provides for taking measures conduciveto its development. It provides for: 1. The Central Electricity Authority: Constitution ; powers to requ~re accounts, statistics and returns; direction of central government.to the Authority; power of central government to make rules; powers of Authorityto make regulations. 2. State electricity boards, generating companies; state electricity consultative councils and local advisory committees;constitution and compositionof state electricityboards; interstate agreement to extend board'sjurisdiction to another state; formation, objects,jurisdiction etc., of generating or transmission companies. 3. Power and duties of state electricity boards and generating or transmission company, coordination with regionalelectricity boards and regional load dispatchcentres. 4. The board's financeaccounts and audit. S..Miscellaneous items such as effects of other laws; water power concessions to be granted only to the board or a generatingcompany; coordinationbetween the boards and multipurpose schemes; powers of entry; annualreports, statistics and returns arbitration; penalties; cognizance of offences; direction by the state government; provision relating to income-tax; members officers and other employees of the board to be public servant; protection of persons acting under this act; saving of application of Act. THE INDIANELECTRICITYRULES, 1956 It contains 143 rules alongwith detailed annexure and covers:

1. Authorization to perform duties 2. Inspection of electric installations: Creation of inspection agency; entry inspection fees; appealagainst an order, submission of records by supplier or owner. ANn~KUMAR K.M.. AssistantProfessorin E&EE,RI.E.T, Davangere.

25 POWER SYSTEM Pl..ANN1N(J

3. Licensing: Application, contents and form of draft license; advertisement of application and contents thereof; approval of draft licence and a notification for grant of licence; commencement of licence; amendments of licence; preparation ant! submission of accounts and model conditions .. of supply. -

4. General safety precautions: Regarding construction, installation, Protection, operation and maintenance of electric supply lines and apparatus; service lin~s and apparatus on consumer's

..

premises; identification

of earthed conductors;

accessibility of bare conductors; provisions

applicable to protective equipment; instructions for restoration of persons suffering from electric shocks; intimation of accidents; precautions to be adopted by consumers, owners, electrical contractors, electrical workmen and suppliers; periodical inspection and testing of consumer's installations. S. General conditions relating to supply end use of energy: Testing of consumer's installation; precaution against leakage; declared voltage and frequency of supply; placing and sealing of energy and demand meters; point of supply; precautions against failure of supply...

6. Electric supply lines, system and apparatus for low, medium, high and extra high voltages: Testing of insulation resistance; connection with earth; voltage tests systems; general conditions as to transformation and control of energy; approval by inspector;. use of energy;" pole-type substations; discharge of capacitors; supply to neo-signs; supply to HVelectrode boiler; supply of X-ray and high frequency installations. 7. Over headlines: Materials and strength; joints; clearances and supports, erection of or alteration of buildings; structures; conditions to apply where telecommunication lines and power-lines can be carried on the same supports; lines crossing; service lines; protection against lightening; unused overhead lines.

8. Electric traction: Additional rules for electric traction; voltage of supply; difference of potential on return; current density in rails.: size and strengths of trolley wires; records.

9. Additional precaution for mines and oil fields. 10. Miscellaneous Provisions. Rules relaxation by the government; relaxation by the inspector; supply and use of energy by non licensees and others; penalty for breaking seal and other penalties for breach of rules; repeal FOREST (CONSERVATION)

ACT, 1980

The Act stipulates the forest clearance requirement for the forest area where hydro plants (reservoir etc.), and transmission lines are planned. The guidelines for taking power lines through the forest area are, 1. Where routing of power lines through the forest areas cannot be avoided, these shoul aligned in such a way that it involves the least amount of tree cutting.

-c

"

2. As far as possible, the route alignment through forest areas should not have any 1i~~lt:~'i:;;>I'\;Mi.",~ ANTI .KHMAR K.M.. AssistantProfessor in E&EE. B.I.E.T,Davangere.

26 POWER SYSTEM PLAiVNING

3. The maximum width of right-of-way for the power lines on forest land shall be as follows: Line Voltage (KV)

Width of Right Of Way

11

7

-

_lS_ --

33 66

18

IHT

22

132

27

220

35

400

52

800

85

_._

. 4. Below each conductor, width clearance of 3m would be permitted for taking the swinging of stringing equipment. 5. In the remaining width, right-of-way up to a maximum of 8.5 metres (for 800kV lines), trees

WIll be felled or looped to the extent required, for preventing electrical hazards by maintaining the Following, The sag and swing of the conductors are to be kept in view while working out the minimum clearance mentioned below. Line Voltage (KV) Minimum clearance between conductors & trees (m)

-

11

2.6

33

2.8

66

3.4

110

3.7

132

4.0

220

4.6

400

5.5

6. In the case of lines to be constructed in hilly areas, where adequate Clearance is already available, trees will not be cut. 7. Where the forest growth consists of coconut groves or similar tall trees, widths of right-of-way greater than those indicated above may be permitted in consultation with the CEA. TOWN AND COUNTRY PLANNING ACTS These acts are of interest before erecting a plant, a substation or overhead line. It is necessary to seek approval of planning authorities whenever these acts are applicable ENVIRONMENT

LAWS

Environment laws such as Water (Prevention and Control of Pollution) Act, 1974; Air and Control of Pollution) Act, 1981; Environment (Protection) Act, 1986are important for pollution clearance from the competent authorities in case of generating plants

ANlT.KUMAR K.M.•Assistant Professor in E&EE, B.I.E.T, Davangere.

..

27

POWER SYSTEM PLA1VNING

7. LOAD FORECASTING 7.1 LOADS

...

-

v' Throughout the world, electrification is an ongoing process. The reason for this phenomenon is . -:---Ule preference for electrical energy..

-

v' The increasing demand in the Asian region is due to severa] factors such as popu]ation growth, growth of per capita income, migration to urban areas and increase in energy using product. v' Demand forecasts are used to determine the capacity of generation, transmission

and

distribution v' System and energy forecast to determine the type of generation facilities required. v' There are five broad categories of loads-domestic, commercial, industrial, agricultural and residential. Commercial and agricultural loads are characterized by seasonal variations. Industrial loads are considered base loads that contain little weather dependent variation. Their generation characteristics are given below, 1

Domestic - This type of load consists mainly of lights, fans, domestic appliances such as heaters, refrigerators, air conditioners, mixers, ovens, heating ranges and small motors for pumping, and various other small household appliances. The various factors are: demand factor 100 percent, diversity factor 1.2-1.3 and load factor 10-15 percent.

2

Commercial

- This type of load consists mainly lighting for shops and advertisement

boarding's, fans, air conditioning;" heating and ofher electrical appliances used in commercial establishments, such as shops, restaurants, market places, etc. The demand factor is usually 90100 percent, diversity factor is 1.1-1.2 and load factor is 25-30 per cent. 3

Industrial - These loads may be of the following typical power range, Small Scale Industries

0-20kW

Medium Scale Industries

20-I00kW

Large Scale Industries

100kW & above

The last type of loads needs power over a longer period and which remains fairly uniform throughout the day. For large-scale industrial loads the demand factor may be taken as 70-80 percent and the load factor 60-65 per cent. For heavy industries the demand factor may be taken as 85-90 per cent with a load factor of70-80 per cent. 4

Agriculture

- This type of load is required for supplying water for irrigation by means of

suitable pumps driven by electric motors. The load factor is generally taken as 15-25 percent, the diversity factor is 1-1.5 and the demand factor is 90-100 per cent.

5

i

Other loads - Apart. from the loads mentioned above, there are othe~ loads such as bul(~t supplies, street light, traction and governmenL loads which have their own i

characteristics.

ANll..KUMAR K.M., Assistant Professor in E&EE,B.I.E.T, Davangere.

PiC /' " .

28

7.2 ELECTRICITY FORECASTING ~ Forecasting of electric load basically consists of, o Long-teIm..forecasting which is connected with load growth and supply I demand side resource

o

management adjustments. Mid- / short-term forecasting which is connected with seasonal or weather variations in a year,

weekly or daily load forecast etc. ..;' The planning for the addition of new generation, transmission and distribution facilities is "based on long-term "load forecasts and must begin 2-25 years in advance of the actual in service. ..;' In India, electricity load forecasts at the national, the Annual Power Survey Cornmittee under Central Electricity Authority prepares regional and state levels. . ..;' Load demand of states and regions must be forecasted. The pattern of Their typical monthly load curves must be determined and the mix of base load and peaking power stations for efficient integrated operation must be fixed. Locations and power station capacities must also be identified to give optimum results. ~ Tie-up of all necessary inputs; and marching transmission and distribution systems must also be a part of the full plan . ..;'. Forecasting techniques must be used as tools to aid the planner, along with good judgment and experience.

7.3 FORECASTING HORIZON Load forecasting is required in all three facets of power system operation, viz., long-range system planning, operational planning and operational control, generally in the following time frames, (i) Long-term forecasting (periods ranging 245.years).

(ii) Medium-term forecasting (periods from one month to two years) for operational planning. (iii) Short term forecasting (periods from one day to a few weeks) for operational planning. (iv) Very short term forecasting (a few minutes to 24 hours) for operational control.

7.4 TYPES OF FORECAST~ & THEIR IMPORTANCE Long Range Forecasts Long-range forecasts involve Identification of both energy and demand forecasts for a utility over a period exceeding two years. Whereas the energy requirements decide the type of generating units (i.e., peaking or intermediate or base-load units), expansion and the demand of peak power requirements decide the utility'S investment in generation andthe resultant transmission capacity" additions. Long-term forecasts are used for,

(i) Exploration of natural fuel and water resources. ANn.KUMAR K.M., AssistantProfessor inE&EE, B.I.E.T, Davangere.

29 POWER SYSTEM PLANNING

(ii) Development of trained human power. (iii) Reinforcement planning of generation transmission and distribution equipment. (iv) Establishing future fuel requirement. Forecasts based on either past

trends-oI

011 Vety broad

based factors do not provide suffici

confidence level for long-range planning. Forecasting in today's environment has increased in complexity due to rapid and random changes in the factors that influence load consumption.

•

Tne following factors are relevant for their impact on utility's growth, (i) The country's economic policy, developmental plans, technological development in production of products and services. (ii) Growth pattern in domestic, commercial, industrial and agricultural loads. (iii) Population growth and electrification plan (urban and rural). (iv) Political, developmental and environmental decisions. Statistical methods with adaptive techniques are employed to forecast long-range requirements, as the method chosen shall have to use

load

past data, growth patterns and human

judgment. Mid:..Term Forecasts These forecasts are aimed to determine yearly or monthly peak, minimum load and energy requirements for one to few years for the purpose of: (i) Decidingrat--structure

for billing of different consumer categories.

(ii) Power exchange contract with neighboring utilities and interchange schedules. (Hi) annual planning and budgeting for fuel requirements and other operational requirements. (iv) Maintenance scheduling of generation and transmission equipment. (v) Scheduling of captive plants.

°

(vi) Scheduling of multi-purpose hydro plans for irrigation, flood control, cooling water requirements etc., apart from generation. Short-Term Forecasts Short-term load forecasting is required for operational planning for, (i) Unit commitment and economic dispatch calculations. (ii) Maintenance scheduling updates. (iii) On-line load flows. (iv) Spinning reserve calculations. (v) Short-term interchange schedules with neighboring system. (vi) System security analysis. (vii) Scheduling of pumped storage units. (viii) Load management scheduling. (ix) Optimization of fuel stocking. ANILKUMAR K.M .. AssistantProfessor in E&EE. B.I.E.T. Davanzere.

30 r._"',L:..l\,.,.I....,~.£.:...I,...A

..&.I...AI.&.I.'~."""_

Utilities use past normalized data, weather data, and information on known random phenomena like popular TVprograromes, school vacations, factory strikes etc., for short-term forecasting of,

(i) Peak load conditions for system in a day.

... .

(ii) System Joad at various intervals of time (half hour /hour) in a day. (iii) Hourly or half-hourly energy requirements. . (iv) Individual bus load prediction. (v) A few minutes to several hours ahead for~cast and is useful in utility's systems operations to deal with economic load dispatching & security assessment. 7.5 FORECASTS TECHNIQUES ./

Theneed to understand the proper use of forecasting techniques has increased as the computing capability has moved out

./

WITH EXAMPLES

0

the hands of the experts in to those of the users in an organization .

Forecasting continues to gain in importance due to the increasing scarcity of electrical energy along with the availability of lower cost and more powerful computing equipment and softwares .

./

Here techniques used are called Deterministic and Statistical.

../ Deterministic techniques are further classified as extrapolating, econometric; "end use and strategic. For example 1. For extrapolation,

Sheer's formula is used which is based on the hypothesis that for everyone

hundredfold increase. In per capita generation, half will reduce the rate of growth of power generation. The following relation was developed after studying load growth in a number of countries.

IOC G = U0.l5 Where G is annual percentage growth in power generation, U is per capita generation, and C is constant which is 0.02 multiplied by population growth rate plus 1.33. The formula is used iteratively to forecast power consumption growth for each year with the preceding value used to forecast the next year's growth. 2. In the end use method, the consumption of each category is projected, based on expected changes in production (industrial), traction, irrigation, water works and sewerage pumping etc. This technique is adopted where sufficient data regarding the programme

for future is

available.

3. Trend method, is suitable in case of other sectors such as domestic, commercial and public lighting. For example, an exponented trend using energy consumption data in India the calculated regression equation is shown below: Y

=- 3411.39+

8555.05

x eO.0988X

X =time in years with 1950-51 as base year, Y= GWh requirement for the

ANILKUMAR K.M., Assistant Professor in E&EE, B.lE.T, Davangere.

""'
•

31 rows»

SYSTej~PLANNING

Trends identified nowadays are, (i) Industrial to information society

(ii) national to world economy

(iii) Short-term to long-term thinking

(iv) centralization to decentralization

(v) Either/or to multiple options 4. Time series analysis, is a good tec~que

involving the necessity of Using sound judgments

along with an analysis of past history. The history of past loads might be forecasted by a utility •

Using a time series analysis program, which uses monthly data and yields an analysis of trend, cyclical variation, seasonal variation, and irregular movement. A recomposition of these four .: factors into future months would involve considerable judgement as to the future course of the cyclical and' irregular elements and, if these elements were well formulated, would produce . usable forecast of electrical energy demand.

5. Moving average, Here each point of a moving average of a time series is the arithmetic or weighted average of a number of consecutive points of the series, where the number of data points is chosen so that the effects of season or irregularity or both are eliminated. A minimum of two years of past energy consumption is desirable, if seasonal effects are present. Otherwise, there will be less data. (Of course, more the history, the better.) The moving average must be specified.

..

6. Trend projections, This technique fits a trend line to a mathematical equation and then projects it into the future by means of 'this equation. There are several variations, the slopecharacteristic method, polynomials, iogarithms, and so on. Trend analysis is the study of the behavior of a process in the past and its mathematics modeling so #1 at future behavior can be extrapolated from it. Two general approaches' followed for trend analysis are, (i) The fitting of continuous mathematical functions through actual data to achieve the least overall error, known as regression analysis; and (ii) The fitting of a sequence on discontinuous lines or curves to the data. The second approach in the short term forecasting. A time varying event such as power system load can be broken down into the following four major components, (i) Basic trend (ii) Seasonal variation (iii) Cyclic variation which includes influences of periods longer than the above and causes the load pattern to be repeated for two or three years (or even longer cycles) (iv) Random ;'ariations which occur on account of the day-to-day changes are in the case of power systems, are usually dependent on the time of the week, e.g., weekend, weak day, weather, etc. Th~"

, /~j

last three variations have a long-term mean ~f zero ~s in figures shown in next page.

';:,:.j.,'

~~:~F:

ANTI,1{1TMARK.M .• Assistant professor inE&EE. B.lE.T, Davangere.

32 POWER SYSTEM PLANNll'.'G

-

-

(.a)

•

Decomposition of typical load growth curve (a) Total process (b) Decomposition EXAMPLES FOR ABOVE TECHNIQUES Linear trend. This is a pasttrend where the increase in consumption from Year to year is more or less constant. Tabulate the past consumption data and plot it on an arithmetical graph which will give a straight li?e. The projection of this line can give a forecast of future demands. But in real life, such a growth trend is unlikely in the power supply industry. Such a growth trend in the power industry can be mathematically expressed as Ct = a+bt where, Let Ct =electricity consumption in any year t , a = consumption for base year t =0,

b = constant

annual increase in energy consumption, t =cardinal number of year t with reference to the base year, i.e., equal to T - 1 + n, where T is the number of years for which the forecast is required. a=40Wh, b =0.180Wh, n=5, t=T-1+n, t = 11- 1+5 = 15, Then, CIS

= 4 + (0.18 x l S) =4+2.7 =6.7GWh

Analysis of Time Series. Typical power system load curves can be represented by the equation, Y=T*C*S*I Where, T = long-term trend, C

=

cyclical trend (often over several years), S = seasonal trend (1 year

cycle), I = irregular movements (noise). The 'noise' component is due, in part, to temperature effects. A reasonable correlation demand and temperature has been found in most power systems. represented by a sum of these factors, i.e. Y=T+C+S+I.

ANILKUMAR K.M., Assistant Professor in E&EE, B.l.E.T, Davangere.

,",0,,,,7<'0'"

33

CORRELATION OF DEMAND WITH TEMPERATURE ./' There is a fair amount of correlation the power system demand with temperature. The random . variations left in demand after deseasonalizing and removal of the Trend effect are largely due to temperature ·variations. There are two portions of the power system load which are . temperature dependent: domestic and commercial loads which increase with cold on account of the use of heating devices, and with heat which necessitates the use of fans, coolers, air conditioner etc. resulting in load increase . ./

The correlation between the seasonal demand and temperature variations is in fact high. e removal of temperature affects from load readings, however, still leaves cyclic and random effects. This is because similar weather conditions at different times of the year do not cause similar human response. Other factors, such as wind and rain seem important, but are hard to account for, as the repetition of a certain set of exact weather conditions (e.g., cold night, rain) . is unlikely. Typical temperature demand relationship is shown below

7.6 FORECASTING MODELLING 7.6.1 Factors Affecting the Forecasting There are many factors which influence the prediction of load, and their influence vary from area to area and from country to country. The impact of any factor on load of a utility needs to be properly examined before building a forecasting model. The factors found to affect a variety of utilities' load are time dependent, weather dependent, random, and other.

Time dependent factors ./' Power systems exhibit a time dependent pattern of electric load demand. At times, these factors are regular, irregular or random in nature . ./' Regular pattern is exhibited during the time of day, day of week and week of the year, anqi!

\

yearly growth.

?6... :.

,.

ANTT.1{1TMARK_M_ A~~i~t::mtProfessor in E&EE. B.I.E.T. Davanzere.

,

",f'"

. y.,

34 POWER SYSTEM PLANNING

-/' Irregular pattern is exhibited on holidays, weekends, special days etc., and load requirements tend to differ on these days than on other days. Sometimes, load requirements do not follow any pattern because of weather or other factors. -/' Electric load requirements tend to depend <_on work rest style of our set-l1lLaS there can be different possibilities of electric power consumption if people are at home during the day than -if they are away at work. This implies that load patterns are different on weekdays and weekends, with the -/' Possibilities of2-4 groups, namely, weekdays, weekends, and pre and Post-respectively. -/' An analysis of past data can reveal two or more pattern ofload consumption for a week. On the same lines, load consumption also differs on holidays, special holidays preceding and <

following the weekends), and special days of national or social importance which may require excessive lighting loads etc. -/' The impact of these holidays and special days on load demand would depend on the extent of public participation, impact on industrial activity, and state-level celebrations requiring excessive lighting load. There are seasonal variations In hourly or daily load, due to change in daylight hours, change in heating to cooling load or vice-versa, typicality of load pattern of some months etc. From the past data (typically 2-5 years), periods in a year can be divided into time-scales (hourly, daily etc.) which exhibit an established load curve and others with a comparatively variable load curve. Weather Dependent Factors .,/ \Veather is one of the principal causes of load variations as it affects domestic load, public lighting, commercial loads etc. Therefore, it is essential to choose relevant weather variables and model their influence on power consumption. Principal weather variables found to affect the power consumption include temperature, cloud cover, visibility, and precipitation . .,/ The first two factors affect the domestic/office (e.g., heating, cootin g) loads, whereas the others affect lighting loads as they affect daylight illumination . .,/ Average temperature is considered to be the most significant dependent factor that influences load variations. However, temperature and load are not linearly related, and variations in temperature in one temperature range may not have any effect on the load, whereas in other temperature ranges and/or other seasons a 1°C change can change load demand by over one per cent. This non-linear relation is further complicated by the influence of humidity and by the effects of extended periods of extreme heat or cold spell.

ANaKUMAR K.M., AssistantProfessorinE&EE, B.I.E.T, Davangere.

•

35 POWER SYSTEM PLAIVNING

Random Factors "

There are random phenomena which affect load consumption and can cause large errors in load forecast.

"

It is difficult to-accurately model their-actual iI~pact on load demand. These include school holidays, factory strikes, and influence of popular TV programmes.

"

Influence of these Phenomena can be studied .ifpast data on these occurrences are available.

Other Factors Other factors that influence the load demand include, (i) Effects ofDSEs (Distributedgenerating devices). (ii) Effects of rate tariff (time-of-day pricing, change in industrial tariffs). (iii) Change over to winter time or summer time. Impact of these factors in past data should be identified. The model should be selected based on these factors and other considerations, and should be fitted to the data. Before use, the model should be checked to discover possible lack of fit or any inadequacy, and necessary correction should be applied as required. 7.6.3 Forecasting Models Regression Model. ./

This functionally relates load to other economic, competitive or weather variables and estimates an equation using the least squares technique. Relationships are primarily analyzed statistically, alt~ough any relationship should be selected for testing on a rational ground .

./

Regression analysis involves the necessity of using judgment along with statistical analysis whenever forecasting takes place.

./

Regression of time series data is a common occurrence in utilities where tracking important measures of performance on a weekly, monthly, or quarterly basis is conducted. As autocorrelation is a common problem in such studies, an understanding of this condition and its cure becomes vital if the results of such analyses are to be valid in the decision-making process.

Econometric Model. An econometric model is a system of interdependent regression equations that describes energy sales. The parameters of the regression equations are usually estimate simultaneously. As a rule, these models are relatively expensive to develop. However, due to the system of equations inherent in such models, they will better express the casualties involved than an ordinary regression equation and hence, will predict turning-points more accurately.

Strategic Forecasting. ANILKUMAR K.M., Assistant Professor in E&EE,B.I.E.T,Davangere.

36 POJYEll SYSTEM PLANNING -I' Strategic forecasting is becoming increasingly important and involves the explicit examination

of the factors and issues affecting future growth, It recognizes the impact that policy decisions can have on future loads.

-

This requires details of consumer operations, their current and potentili I' demand for electricity, their competitiveness in me market place and their options with respect to production processes, -I' Switching alternatives, e~ergy conservation technologies, etc. -I' In the industrial sector, this implies combining elements of the econometric approach with the

technology detail found in end use/process models. Strategic models must be capable of doing more thari merely forecasting future requirements.. They must be able to provide planners with additional information to help shape the future demand. Mathematical

Modelling-Simulation

-I' In modelling, the total load is considered to be the sum total of various components due to

various factors. -/' These factors need to be measured and interrelated with load requirements. Thus, this technique

requires. individual

modelling

of

each

load' type,

and identifying

their

interrelationship to arrive at future load requirements. -/' This is mathematical modelling. Mathematics is a language that allows us to represent physical problems in a form that a computer can understand. -/' The strength of a method lies in the accuracy of the results it gives. Errors in predicted loads are found mainly in peak periods, transitional phase (from peak to off peak and vice-versa), and on weekends and special days. -/' In extrapolation, future load is treated as an extension of the past and the load curve based on past data is suitably adjusted to reflect growth trend. Thus, this technique involves the detection of trends in the past data for various parameters, fitting a trend curve-which could be a straight o

line, a parabola, exponential or a polynomial of other orders or a mix of the above-and finding coefficients of these curves as given below, Straight line Y=a+bx Parabola Y=a + bx+ cx2 S. curve Y=a + bx +cx2+dx3 Exponential Y=becx Modified exponential Y =a + beel: Logistics Y =1 / (a + beC.:l) Where Y is a variable to be fitted, x is time in assigned frame (in day, week, year etc.), and.a,': ", c, d are coefficients be calculated. Extrapolation could be deterministic or probabilistic..

~~~ .• e

~!!!!'!!!!~ANIL~~KUMAR=~~K=:.M~.,!!!Ass~i!!!st!!!an!!!t!!!Pr!!!!'!!!!o!!!fe!!!sso~r!!!in!!!E!!!&~E!!!E!!!, !!!B!!!.I!!!.E!!!.!!!T!!!. Da!!!!'!!!!v!!!an~_ge!!!r!!!e!!!. ~~

t

,~,;:~,~¢~

.,.,~fi.:C~~

37 POWER SYSTEM PLArY'NING

accuracy of results quantified using statistics (i.e., standard deviation, variance etc.) in the letter case. The'Tnathematical models for domestic, commercial and other sectors have been determined by the CEA as given below. Domestic sector -/ Energy in the domestic sector is mainly used for cooking, lighting, heating and other household appliances like TV, refrigerators etc. -/ Increase in the family income and the resultant increased expenditure on household effects, consisting of electrical appliances among other things has pushed up the demand for electrical energy in the domestic sector. -/ There is a close relationship between the private final consumption expenditure (PFCE) and the demand for energy in the domestic sector. PFCE data is available from Basic Statistics y"

Of Indian Economy from the Ministry of Planning, Government of India.

-/ The following model has been adopted for projecting the anticipated demand in the domestic sector as it gave the most consistent results, log Y ";'a+ blogX Where Y = Energy consumption, a and b =Constant to be determined by Regression Analysis. X=Private Final Consumption Expenditure. Commercial and Other sectors y"

The increased commercial activity has resulted in increasing use of energy. The use of electricity for illumination, weather comforts, refrigerators, air-conditioning and water heating is being increasingly resorted to.

y"

There is a strong relationship between the number of urban households and energy consumption in the commercial sector.

y"

The other sectors, which mainly consist of public lighting, public water works and miscellaneous segments of energy consumption, are also expected to maintain the present temp; of energy consumption in the foreseeable future due to expected industrial development, increasing urbanization, migration of population from rural to urban areas, electrification of villages and expansion of water facilities in the rural area. The public lighting system in the urban areas is also likely to develop further due to increased demand for energy. The increase in the number of urban households has, therefore, a close relationship with the increase in energy demand relating to other sectors. As such, a. similar model has been adopted for projecting the energy demand is these sectors separately. log Y =a +b log X

y =rrJ\::r:~); consumption, a and b=Constants to be determined by Regression Analysis fcr

Sb-.[,X, X=Number

of urban households

A.NUJKUMAR K.M., AssistantProfessorinE&EE, B.lE.T, Davangere.

38 POWER SYSTEM PLANNING

Typical requirements of a good load forecast programme are in terms of, Where, (i) Accuracy of results (in real-time operation for a long period of time) . (ii) Its adaptive nature (e.g., model parameters can be changed on-line to track seasonal load variations or zariation.of impact of different components of load etc.) _ (iii) Being computationally efficient (in terms of data requirements, processing time and memory requirements) (iv) Its being easy to implement and use. Econometrics Certain economic factors which influence the system load growth are, (i) Business and economic cycle (cyclic variations) (ii) Growth of gross national product (GNP) (long-term variations) (iii) Growth in population "(long-termtrend). Most of these factors only affect the long-term trend which will not be picked up in a normal model based on, say, a past history of 10 years (i.e Nyquist condition): Of course, changes in government" p6.li.cy·.in, say, population,

railway traction

and

integrated socio-economic

development of rural areas, will result in a change in the long-term trend. For example, an examination of various electrical energy forecasts in India reveals that the energy demand with regard to population and GNP leads to a satisfactory linear regression model. The regression model is of the form In Y =20.74773+2.8815Inxl+

1.3695lnx2

Where, Y =electrical energy demand in GWh, xl =population in millions, x2=GNP lOx millions.of rupees Xl and x2 are graphical projections based on data available from planning Commission or the concerned ministry, such as Finance or social welfare. Single factor modelling Single Factor Model indication may be defective because of the following reasons, I. It is too general. 2. A sector like industry occupies a far larger share in the consumption of electricity (45%) as compared to its contribution to GNP which is only 30 per cent. On the other hand, agriculture may have a larger share in the GNP (50%) but a lower share in electricity consumption (28%)(1996) 3. It is known that the rate of growth of various sectors of the economy is not the same. It is, therefore, preferable to have separate single factor models for electricity consumption domestic, commercial, industrial, agricultural and other uses. Domestic The forecast of domestic consumption by use of population forecast aIid other variable number of domestic consumers and per capita consumption can be a good model of t{"" _:/r:~'.

ANILKUMAR K.M., AssistantProfessor inE&EE, B.I.E.T, Davangere.

fo.r

39 POWER SYSTEM PLANNING

the UK, GDP and average temperature gave a reliable model for energy forecasts. The model fitted is of the form: ~t =K+ O.71671ogGDP

...

=-O.708'Z1ogCt - 1- 0.4957 log Tt Where, K =constant (can be calculated by the regression method), Tt=average temperature over a period t in of, GDP =Gross domestic product. Industrial For industrial projection, the following two trends are important, 1. The growth in industry as represented by the index of production and growth in the sale of electricity. by the utility per unit growth ill industry. Two' separate graphs can be drawn. For any point of time, if the two quantities are multiplied, then the total electricity consumption for the industrial sector can be arrived at. For example, for a forecast, say for 1998, index of production as projected from graph = 180 (say) Electricity sold per unit of industrial index (from the graph) = 37 GWh, say (projected) Hence, total electricity sales = 180 x37GWh =6660GWh 2. The growth in number of workers employed .i~ industry and electrical energy consumed per worker. It should be possible to obtain data regarding industrial workers from either the Central Statistical Organization or the Ministry of Labour. A trend graph can be established to show a forecast of industrial workers employed in industry at any point of time. A second trend graph has to be plotted for the electrical energy consumed per worker. From these two trend graphs, a forecast can be made for the requirement of electrical energy for the industrial sector. For example. for a forecast, say, for 1998, (i) Number of industrial workers projected = 0.86 million, say (ii) Industrial electrical energy sales per worker projected =7750kWh, say (iii) Forecast of electrical energy sales for industrial sector = 7750

x 0.86 GWh

=6665 GWh Agriculture ../' The electricity demand for agriculture can be processed in the same manner as industrial consumption, the independent variable being the agricultural output or added value . ../' Alternatively, the trend of installation of irrigation pumps can be established keeping in view the targets fixed by the Planning Commission and perspective plan envisaged by the Ministry of Agriculture and Irrigation. A second trend graph can be established for the consumption of electricity per pump. From these two graphs a trend graph can be established for electricity,-':{?j: consumption by the agricultural sec~r. Other Sectors

ANILKUMAR K.M., AssistantProfessor in E&EE, B.I.E.T, Davangere.

40 POWER SYSTEM PLANNING

..;' Forecast for street lighting,

water works, sewerage, railways, auxiliary consumption,

transmission and distribution losses, etc., can be made by establishing trend graphs based on time series study. Alternately, these projections may be made on the basis of plan targets, wherever deemed feasible . ..;' In each of these sectors of energy consumption, the relevant economic Variable may be identified and an econometric model built. For example, national income in India is a function of energy consumption. Based on the actual past energy consumption and national income, both the log-log and linear forms as given below gave a very good fit relation, Y =68.90 + 0.592 E Where, Y is national income in billion of rupees, E =Total energy consumption in million tons of coal replacement. The Central Electricity Authority carried out a long-term power planning exercise using sophisticated computer models like EGEAS and ISPLAN for evolving a need based power plan covering the time horizon of 15 years.

ANILKUMAR K.M., Assistant Professor inE&EE, B.I.E.T,Davangere.

41 POWER SYSTEM PLANNING

QUESTIONS BANK 1) Explain the Power systemplanning. 2) Explain the Strategic planning, long term planning and short term planning. 3) Explain integrated resourceplanning with respeet-te-pewergenerationplanning. 4) Explain the structure of power system with types of transmission and distribution networks. 5) Mention and explain the different types of power resources. 6) List and explain power systemplanning tools. . 7) List and explain the differenttypes of loads. 8) Explain electricity forecastingand its types. 9) Mention and explain factors affecting the load of utility in forecastingmodeling. 10)List the challenges facedby power system planning engineers. 11)Explain the power system planning process. Enumerate the cyclical components of planning. 12)Discuss different stages of preparation of Detailed Project Report (DPR) for planning of power projects. 13)With the help of a neat diagram,explain least cost utility planning. 14)Explain different time-framesof load forecasting. 15)Explain, in detail, the trend projection method used in load forecasting. Use necessary diagrams.

Note - Questions are collected from previous year Q.P, & Model Q.P .

..

42

POWER SYSTEM PLANNING

UNIT-2&3: GENERATION PLANNING

ANll.KUMAR K.lVI. Assistant Professor,E&EE, BIEI,Davangere .

. V.T:U:Syllabus . Integrated power generation, co-generationI captive power, power pooling and power trading, transmission & distribution planning, power system economics, power sector finance, financial planning, private participation, rural electrificationinvestment, concept of rational tariffs.

SYNOPSIS Integrated generation planning involves centralized generation along with the distributed generation for least cost of supply. The various options for planning of generation schemes & their optimal analysis is given. The national electricity policies are discussed. Importance of cogeneration is illustrated & importance of power pooling & power trading ,isexplained. The planning of transmission and distribution of power to the consumers is as important as generation. About 50 per cent of the total budget needs to be spent in this sector. The voltage level selection for transmission and distribution, and their development criteria have been presented. The high voltage dc for power transfer between the.regions and stable working of power system is important. To save generation capacity and to reduce losses, flexible ac transmission including advance series compensationhas been found to be a more suitable option. The development options of substations in the urban and rural area and the development of reactive power requires proper planning for system efficiency. National power grid is necessary for efficient and reliable operation of the power system. Rural electrification is important for social benefits to about 70 per cent of the rural population in India. Cost-benefit analysis should be applied to rural electrification. For rural load growth decentralized generation with growth of agro-industries is need to be encouraged. Rationaltariff's are discussed. The investment analysis of the power project is important for decision making. About 20 per cent of the national budget is spent on the power sector. The power industry being capital intensive, involves capital risks and for that good bankable project reports are desirable. Private sector participation is important for mobilization of capital and various incentives for that are necessary, Modes of private participation and methods of bidding has been explained. The pattern and structure of the investment needs to be risked are covered. The various methods of mobilizing the financial resources from the state funds, from public or from the international bodies and banks have been-discussed.

43 POWER SYSTEM PLANNING

UNIT-2 & 3: GENERATION PLANNING 1. IN'I,EGRATED POWER GENERATION 1.1 INTRODUCTION Today plannersmust deal with problemshaving three characteristics, (i) Multiple conflicting objectives, e.g., minimizing 'costs, monitoring environmental impact and maximizing reliability. (ii) A broad range of options (including demand side options! non-conventional and traditional generation, and transmission alternatives). (iii) Pervasiveuncertainty. Sorlie factors which can have a major influence on a utility are not under its control o~.cannot be .predicted with certainty.These are calleduncertainties. Risk is the hazard to which a utility is exposed because of uncertainty. Attributes like cost of electricity, capital requirements, and environmental effects constitute risk. Risk as a characteristic of decisions has two dimensions:

(9 The·likelihoodof making a regrettabledecision, (ii) The amountby which the decisionis regrettable. ./ Historically there have been two general approaches to dealing with uncertainty in power utility planning-(i}probabilistic analysis,and {ii) contingencyanalysis. . ./ The first is used frequently in establishing generation reserve requirements and the second in transmission planning and operations. Both share a common initial step: they deal with particular uncertainties and plans. Uncertainties in the probabilistic method are modelled using probability distributions for unit availability-capacity functions, expected loads, etc. In generation planning applications, we use such well-known attributes as the loss of load expectation, expected unsupplied energy, the probability distribution of emergency power requirementsand the expected cost of power production. ./ In transmissionplanning and the investigation of certain system Operating questions such as transfer capability, probabilistic methods are - not widely used. Instead, most transmission planners use contingency analysis methods to study the system under preselected normal and emergencyconditions. 1.2 PLAN FORMULATION & DISTRIBUTED POWER GENERATION ./ Power utilities should-give increasing attention to the distributed utility concept. A distributed utility integrates the central station power with distributed generation and demand side management applications that are strategically located within the utility network to lower overall cost of serving consumers.

ANll.KUMAR K.M., Assistant Professor inE&EE, B.I.E.T, Davanzere,

44 PO"WERSYSTEM PLANNING

-/' This model integrates a variety of energy options into a "power generation portfolio" consisting of conventional options as well as advanced renewable, PV technology, clean coal, waste-toenergy and nuclear technologies. The distributed utility concept has several strategic operating advantages ~-the-Central

station model.

-/' The smaller modular nature of this design allows planning flexibility and short construction lead time. Furthermore, transmission losses are reduced by locating the power generation source near the consumer. This also allows gr~ater operating flexibility through the utilization efficiency of existing transmission and distribution assets. -/' Distributed power generation can avoid the need for substantial improvements in transmission systems by better utilization of existing transmission and distribution assets. -/' Decentralized power generation (Captive, CCGT, Small hydro, wind, photovo!taic etc.) located close to the loads can follow the local load, minimizing the heavy loading of the transmission grid and saving the cost of substantial system losses for the utility or the power consumer. -/' The addition of central power generation source can create stability problems or load flow and voltage problems. Line compensation can be expensive and can introduce additional losses on the system. Distributed' power generation can actually improve the existing transmission

.

network capability by adding real and reactive power to the local load and the-network .

../ This interest in non-traditional power sources stems from the emerging reality that traditional approaches to rural electrification are both costly and difficult. Line extensions are frequently unreliable are characterized by low loading ratios and high losses . ../ The planning formulation includes three elements as shown in below figure Variety of options, irreducible uncertainties, and objectives (attributes).

ATInWTeS

I"OWa\ til ~ITY

PWHHO

PAOOESS

Options ../ 'The list of options available includes non-utility supply sources, conservation and demand side management (DSM), A variety of institutional means can be used to develop the options with scenarios. The scenarios of various options are developed by various agencies in India after careful studies. Such agencies are-the Planning Commission, CEA, SEBs, R&D in power Research workers I individual thinkers etc. Planning options includes -/' Type of Generation station plants selection, Packaged plants, DSM, Pumped hydro Existing plants renovation, reduction ofT &D losses etc ..

ANILKUMAR K.M., Assistant Professor in E&EE, B.I.E.T, Davangere,

45 POWER SYSTEM PLANNING

Uncertainties

..

./ It seems impossible to eliminate uncertainty altogether. A goal is a plan which is robust or ..

flexible in the presence of uncertainty,perhaps because hedges against adverse outcomeshave been carefully designed. ../ Some of Uncertainties may be load growth, Fuel prices and water availability in hydro stations, Consumerresponse to demandside options, Potentialsupply of non-utilitygeneration, Construction costs of planning options, Longevity and performance of Life extended or converted plants,Market for off pealesales,Technological developments, Regulatorychanges. Objectives v"

Objectives are expressed in terms of attributes or measures of goodness. In the past, utility economic evaluationswere based on minimizing the present worth of the revenues required. Reliability and certain other attributeswere taken as constraints. When a problem has multiple attributes, there is usually no single solutionwhich simultaneouslyoptimizes all of them. What

a

is sought is compromisewhichrepresentsa reasonable tradeoff among the attributes. ../' Some of the Attributes (measures of goodness) are Economic, Quality, Reliability, Financial, Environmental,and Societal. 1.3 GOALS-NATIONAL

ACTION PLAN

According the studies by CEA and World Bank the desirableoptions in India for the next 25 years are, 1. Accelerate hydro capacity development:hydro share shouldbe at least around40 per cent of the whole generation for optimum operationof the system. The site locations need to be identifiedon a long-term basis in advance and Detailed Project Report shouldbe prepared as need based. Hydro power is urgent for developingpeaking capability. 2. Accelerated nuclear power development India is the only developing country in the world •

having a mature nuclear technology and a long-term power generation programme based on PHWRs using natural uranium in the first phase and FBRs or LW thorium reactor in the second phase around 2010ADusingthorium and plutoniumresources. 3. Reduction in T&D losses from about 23 per cent to 15 per cent will save the generationcapacity of about 6000MWatthe rate of about 0.35 per cent reduction in T&D losses per year. About onef~urth of these losses are attributed to theft of energy. The otherreasons are bad design of system: use of long LT lines,low voltage, low load densit:rand long linesin rural areas;introductionof flat rate for agricultural consumers etc. The losses can be reduced by executing the system

,cl

.improvement sch~es and ~y ~e~ermanagem~nt.. . . _4. The energy savmgpotential m mdustry,agriculture,and m the Commercial z domesticsect~Ft:~~;

,··.··'1

been identified as 25, 30 and 10 per cent respectively. With a modest overall 10 perce "/.,,-,;:;.,, .. ';,1 mission, about thousandsMW installedcapacitycan be savedby energy conservatio~~ji~lt~j:j~(f.Z: ANILKUMAR K.M., Assistant Professor in E&EE, B.I.E.T. Davanzere.

46

5. Studies show that demand management in regional systems will reduce system installed capacity requirement by about ten to twenty thousand MW by improving the regional system load factors from 3 to 11 per cent by shifting load from peak hours to off peak hours. The country should .switch to two time zones with one hour difference, i.e..One.for the eastern states and ooe-for-thewestern state, to reduce the clock related peak demand in the country. 6. Renovation ~d modernization of existing thermal units and hydro units will add capacity to the tune ofMW capacities. The scheme will improve the plant load factors and will result in extended life of the plants. 7. Formation and operation of the National Power Grid, according to Simulation studies will have the advantage of an overall saving of about 10,000 MW generation capacity in reserve margin or peaking capacity. Feasible improvement in grid discipline will contribute about 5 per cent of the saving in installed capacity. All the five regions at present are deficit in meeting peak load requirements, even though a substantial amount of energy resources remain unutilized at certain time of the day/season. Generating units in one region often have to be backed down while simultaneously there is perceptible power shortage in a neighboring region. Installation of inter regional links (HVDC/HVAC) will improve hydro-thermal mix of combined regions and enable transmission of surplus energy. 8. There is a lot of scope for .co-generation in large industries such as sugar, textile, alcohol, paper, petro-chemical and metallurgical works. Cogeneration potential in the country is to the order of 10,000 MW in the sugar industry. It should be mandatory for cement, steel, fertilizer and chemical plants having load above 15MWto install captive power. The Indian Electricity (Supply) Act 1948 must be amended to make the installation of captive power by such plants mandatory. There is need for comprehensive legislation towards compulsory co-generation and feeding into the grid for the sake of conserving natural energy resources.

"

9. In the rural areas only, there is scope for wind farm generation of up to 20,OOOMW. Solar photovoltaic has great potential for rural street lighting, home lighting, operating pumps etc. The Ministry of Non-conventional Energy Sources has drawn an ambitious programme touching at least 1,00,000 villages through photovoltaic's. At 1996 about (}.25million modules are installed in the country and this number is likely to exceed 50 millions by the year 2020. 2. COGENERATION

/ CAPTIVE POWER

./' There is large scope for cogeneration of nearly 50000MW in India in industries such as sugar, textile, alcohol, paper, petro-chemicals and metallurgical. It should be made mandatory for cement, steel, aluminium, fertilizers, chemical plants and other heavy industry to install captive power, Consumers could utilize the waste heat produced in heavy power-intensive . having load more than 5. MW, such as steel, aluminium plants or group of

ANILKUMAR K.M., AssistantProfessor inE&EE,B.I.E.T, Davangere.

II'

lU'LtLU'

47 POWER SYSTEM PLANNIlvG ~

~

furnaces: They must install cogeneration plants/captive power generation plants for the sake of economical power generation. "../' A cogeneration facility produces electrical energy and other forms of useful thermal energy ,

(such asneafaiidSteam)

'

used for industrial, commercial, heatingorcooling

purposes through

the sequential use of energy from a single source. ill the combustion of fuel, energy is released which is used for heating or to perform some useful form of work. Not all of the energy that is produced can he used; some of it is wasted. A cogeneration facility recaptures some of the waste energy that otherwise would escape and puts it to useful purpose . ./' The modem technology is more efficient having steam pressure of minimum 45 kg/ cm2 and high temperature up to 500°c. Cogeneration can be used in almost any industry with some type, , of thermal need. -./' Large energy consuming industries such as steel, paper, distilleries, sugar mills, textiles, cement (dry process), chemicals and petroleum refining, led the way in building cogeneration facilities. With the availability of small packaged cogeneration units such as for hospitals, shopping complexes and small manufacturing firms are becoming involved in cogeneration. -./' To determine the feasibility of cogeneration, economic and energy factors must be considered. Rates for purchase and sale of electrical energy are important as are fuel prices. The cost of the equipment in relation to the energy saved is a major e~onomic factor. Cogeneration systems are more expensive and cost more to operate and maintain than systems that produce only thermal energy. Degree of waste recovery, duty cycle, capital cost, fuel and electricity' prices, taxes, reliability and size are all important factors to consider in deciding on cogeneration . ../ There are two basic processes a cogeneration facility may utilize. The first process, and the most common, is the "topping cycle process". The second one is called the "bottoming cycle process". (i) In the topping cycle process, electricity is produced first and the waste energy being recovered is in the form of thermal energy. There are several different configurations for a topping cycle facility hut -two of the most common are: (a) A boiler produces steam that is used to power a steam turbine generator set to make electricity. The steam required for the process is extracted from the exhaust of the turbine or from an intermediate stage. (b) A gas turbine or diesel engine bums fuel to spin

shaft connected to a generator produce

electricity. Heat is given from the burning of fuel. This is recaptured in a waste heat recovery

, t

boiler which Produces steam from the hot exhaust gas, or the hot exhaust is used directly in ~.. thermal process, . (iiJIn the bottoming cycle, the thermal energy is ~ ~ recovered from that process

IS

.. ~sed in a process and the ~~s1if.

"~ ..." .f:

.•.•

a

used to produce electricity. For example, a fumac~J~jl~SiM~fi~Z~~',.f

~~~~~~~~~!,,!!!!!!!!,,!!!!!!!~~~!,,!!!!!!!~~~~!"!!!!!!!!!'!!!'!!!!!!'!!!'!!!!!!'!!!'!!!!!"!!!!!!!!!'!!!'!!!!~=~~=~~i~! "'I

·it. I1

ANILKUMAR K.M., Assistant ProfessorinE&EE. B.I.E.T.Davanzere.

4,%~~'zyi~~~~~~I~fl

48 POWER SYSTEM PLANNING

smelting or forming process. A waste heat recovery boiler recaptures the unused energy and uses it to produce steam to drive steam turbine generator which in turn produces electricity .

./ The choice of configuration facilities is dictated by the needs of the plant for electrical and thermal..energies and the nature of the fuels available. Typically, in the bottoming cycle configuration, the thermal energy (process) steam or (process) heat is required at a very high temperature and the attempt is to recover part of the exhaust heat from the process to generate electricity. In contrast, the topping cycle configuration is suitable where the thermal energy required (process steam) is ata comparatively lower temperature . ../ As 'of now, there is need for comprehensive legislation in India with regard to cogeneration systems in order to conserve national energy resources generation should be free of tax

&.

& -to encourage the cogeneration,

government should offer best prices for the energy

production . ../ In this regard it is worthwhile to study the legislations measures adopted in the countries, especially in the USA called Public Utilities Regulatory Policies Act (PURP A) to serve as guidelines for any possible legislation . ./' However, in order to derive the .economic benefits associated with the sale of cogenerated power, the cogeneration system configurations being evaluated must satisfy basic criteria identified in the legislation. To distinguish new cogeneration facilities that will provide meaningful energy conservation from those that will be "token" facilities producing trivial amounts of useful heat and power, the PURPA regulation sets three separate qualifying criterion-efficiency, standard and ownership . ./

The operating standard requires that a new topping cycle facility must produce at least 5 per cent of the total energy output as useful thermal energy. The efficiency standard, which is applicable only if oil or natural gas is used, requires that the annual electric power plus half the useful thermal energy must be at least 42.Sper cent of the total natural gas and oil energy input (on the LHV basis) except that if the thermal energy output is less than 15per cent of the total energy output, the requirement becomes 45 per cent. For new bottoming cycle facilities, the annual useful power output must be at least 45 per cent of the energy input of oil and. ~ used for supplementary firing {heating of water or steam before entering the electricity generating cycle from the thermal energy cycle}.

Deciding purchase price for cogeneration Decision on purchase price involves consideration of three costs'of generation, ie.. (i) Unit cost of generation from a new power plant based on relevant conventional source (i.e. thermal power plants based on coal in most cases) (ii) Unit costof generation from the relevant conventional alternative in cases of DG sets/in most cases) ANn .K1TMARK.M .. Assistant Professor in E&EE. B.I.E.T.Davanzere,

49 POJYERSYSTEM PLANNING

(iii) Unit cost of generation from biomass based power generation system. Brief and simplified formulations for each are: 1. Unit cost of generation from thermal power plants In a simplified case, this can be seen to consist of three major components-fuel costS~ capital charges and O&M charges. Fuel charges can be represented in terms of specific coal consumption

.

(with a multiplier to account for oil input etc.), and the other two can be represented in terms of a

percentage charge on capital investment divided by the average annual generation. A typical correlation could be: Unit cost of generation =1.2 x (Delivered cost of 0.70 kg of coal) + 0.2x (Capital investmentlkW) 8760x (plant Load Factor) This is based on a specific fuel consumption-of 0.70 kg of coaVkWh, other fuel costs etc., and being 20 per cent of coal cost and capital charges (interest, depreciation) as well as O~M charges put together being approximately 20 percent of the capital investment. 2: Unit cost of generation from DG sets .Unit cost of Generation == 1.2x (delivered cost of 330cc ofHSD) + 0.3 x (Capital investment /kW) 3. Unit cost of generation through biomass gasification Unit cost of generation = Delivered cost of 1 kg of prepared through bjomass biomass + Delivered cost of 100 cc of gasification HSD.+ [0.2x (Delivered Cost of 330cc of HSD)]+ (O.3x (Capital investment/kwj]

3. POWER POOLING ANDTRADING ./

The electric power cannot be stored and power demand must equal power generation at any time. Therefore, power pooling is an important consideration for power supply in the 21 st century.

../

This is the wholesale market in bulk supply, the pool, in which spot price is determined for every half-an-hour in the national power load curve period through competitive bidding by individual generators .

./

The pool itself exists as a mechanism to allow trading or sharing between power utilities and power generators. Long-term contracts in sales and purchases of electricity are made between participating utilities and generating companies according to a set of rules evolved .

./

This is supplemented by spot trading in a short-term market with prices reflecting supply and demand on short-term basis .

./

In order to improve the prospects for the electricity trade, it will be necessary to formulate commercial guidelines for wheeling of power and a rational tariff structure to encourage selling and buying of energy for mutual benefit. .Suitable measures have also to be discourage high frequency operation of the grid.

ANILKUMAR K.M., Assistant Professor inE&EE, B.I.E.T,Davangere.

so POWER SYSTEM PLANNING

~ The settlement system in UK grid calculates the prices and payments due under the poolwheeling arrangements, while the grid operator seeks to schedule and dispatch generating units, subject to certain technical constraints, to meet demand, including a margin for reserve. ·This is done principally on the basis of a merit order which is constructed from the generators' offers of prices and the availability of their generating units . ._,- Generating capacity scheduled for energy in the revised unconstrained schedule receives the Pool Purchase Price (PPP) which is a single price determined for each half hour and ·comprising two elements-Systems Marginal Price (SMP) and the Capacity Element. SMP is the price derived from the offer prices of the marginal generating .sets scheduled in the ·unconstrained schedule for the relevant period, the capacity element is calculated according to Loss of Load Probability (LOLP) . ../ The pool is a spot market which operates in real time. The tariff making for retail market takes signal and messages obtained in pool output price system. These messages are passed to the consumers for efficiency and load management. ._,- To encourage the generation from renewable energy sources, the consumers are obliged to purchase electricity from such generators under Non-Fossil Fuel Obligations. Under this arrangement, the Public Electricity Suppliers will purchase electricity from the generators which do not use fossil fuel for electricity production. The additional cost to be incurred will be recovered from the consumers through the Fossil Fuel Levy.

4. TRANSMISSION AND DISTRIBUTION PLANNING 4.1 NETWORK ../ Transmission of electric power is one of the most important elements of electric power system planning. The transmission system transfers bulk power from the generating plant to the areas of consumption from which distribution systems supply to the consumers . ._,- Sub transmission is an intermediate network between transmission and distribution that is able to transfer & segregate the electrical power efficiently and economically in those cases where distribution networks are not connected directly to the transmission networks ._,- The transmission system also interconnects the electric utilities to permit power exchange when it is of economic advantage and to assist the power utilities when their generating plants are out of service for some reason . ../ The planning of ac transmission involves power flow requirements, systems stability, selection of voltage levels, voltage and reactive power flow, conductor selection, losses, insulation levels, selection of type of structure and rights of way. The criteria for network Planning' generally depends on such factors as availability of generation for the load demand voltl:1~) _

'

~t~;;'~r(t0tt) .,;.\.:.;?!'~i':';r';&;

levels, size and configuration of systems, distance, right-of-ways, resource constrain:s

~~~~~~~~~~~~~~~~~ ....... ~ "\Nfl .KTTM"\RK.M._ Assistant Professor in E&EE.

",~\!:;i::;~

B.I.E.T. Davangere.

51 POWER SYSTEM PLANNING y'

Practices vary from Country to country. Due to increasing demand and increasing requirement of high reliability, the neighboring utility networks are interconnected.

-/' In healthy systems, the networks are loaded normally up to 50-60 per cent of their designed - capm!ity. At present in India transmission network is mostly loaded above 90 per cent, Operating always at alert conditions during peak period. A small any point is capable of causing a major collapse in the grid network.

Distribution In general, distribution of power is a part of ~e system between the transmission and consumer services. In general, a typical distribution system consists of the following network. y'

Sub-transmission circuits in Voltage ratings usually between 33 kV and 220 kV which delivers energy to distribution substations.

y'

The distribution substation which converts the energy to lower primary system voltage for local distribution and usually improves facilities for voltage regulation of the primary voltage.

-/' Primary circuits of feeders usually operating in the range of llkV to 33 kV supplying the load in well defined geographical areas. -/' The distribution transformer in rating from 10 to 2500 kVA which may be installed on poles or on pads or in.underground vaults near the consumer sites and transform the primary voltage to the utilization voltage at usually 11Oto440 volt. ./

Secondary circuits at utilization voltage which carry energy from the distribution transformer along the street etc.

.-/' Service lines which deliver the energy from secondary circuits to the consumer premises by service lines. It is desirable to rationalize and standardize the voltage levels employed in supply systems and to limit the number of voltage levels. Several studies showed that an optimal supply situation would have only three voltage levels beyond the low-voltage system. These studies indicated, that no extra intermediate voltage levels are necessary. However when loads are unevenly distributed (spot-wise), a two-voltage level system can be very suitable. The six basic distribution systems used by utilities are discussed below sections. 1. RADIAL -/' A radial system is connected to only one source of supply. -/' It is exposed to many interruption possibilities, the most important of which are those due to overhead line or underground cable failure or transformer failure. -/' Each event may be accompanied by a long interruption. It has lower reliability. Both, components (feeder and transformer) have finite failure rates and such expected and statistically predictable.

ANILKUMAR K.M., Assistant Professor in E&EE, B.I.E.T, Davangere.

"'i .,'*:l

.52 POWER SYSTEM PLAlVlVING

../ Feeder breaker reclosing or temporary faults are likely to affect sensitive loads. This system is suitable for small loads. 2. PRIMARY LOOP ../ A great improvement over a radial system-is-obtained by arranging a primary loop, which provides power from two feeders. ../ Power flow to consumers is by way of single path at anyone time from either side of the loop depending upon the open/close status of sectionalisers and reclosers . ../ The loop is normally operated with the tie sectionaliser switch open. Any section of the feeder can be isolated without interruption and primary faults _arereduced in duration to the time required to locate a fault and do the necessary switching to restore service. Each line of the loop must have sufficient capacity to carry all the load . ../ The additional line exposure tends to increase the frequency of faults, but not necessarily the number of faults per consumer. Sensitive loads are affected by reclosing under temporary fault conditions.

~"-.,

Figs showing the Radial & Primary loop type of distribution systems.

fEt!)!EH-l

IIRs:,w,I(ER rWoN:;.F<;.tN(A I

_{'~~i " ?iI()

IO"'(~l

1,01.0.7

Figs showing the Primary Selective & secondary selective type of distribution systems. 3. PRIMARYSELECTIVE ../ It uses the same basic components as in the primary loop.

Each transformer can have supply

loss. of feeder, transfer to second feeder is automatic and the interruption duration-j I

limited to two or three seconds. ANILKUMAR K.M., AssistantProfessor inE&EE, B.I.E.T, Davangere.

.."",

f,:Y£~}

53 POWERSYSTEM PLANNING

./' System reliability is high here. It also offers a little advantage to sensitive loads like computer problems caused by temporary faults. This scheme is normally used for large essential or continuous process industrial consumers.

·4. SECONDARYSEI;ECTIVE /

'.-

----

This system uses two transformers, each from separate primary feeders and with low voltage switching .

•

./' The load is generally divided between two LT buses with both transformers continuously energized. The tie switch on secondary tie bus is normally open and is interlocked with secondary feeder switches . ./' This system is commonly used for industrial plants and institutions like hospitals . ./' Primary operational switching is eliminated. Duplicate transformer virtually eliminate the possibility of a long interruption due to failure. Each transformer and feeder must have sufficient capacity to supply the entire load. ./' Transfer is automatic upon loss of voltage on either feeder with static switching equipment. Sensitive equipment can be effectively served. Reliability is better than in the primary selective system because of additional redundancy of transformers.

5. SPOT NETWORK ./' Maximum services reliability and operating flexibility for most loads are obtained by use of the network using two or more transformer units in parallel. ./' The low voltage bus (spot network bus) is continuously energized by all units operating in parallel. ./' Automatic disconnection of any unit is obtained by sensitive reverse power relays in the protection. If there is a fault in one feeder, it is isolated by the network protection on that feeder. ./' Maintenance switching of primary feeders can be done without con~Fer

interruption. Spot

networks are used generally in metropolitan high-load density areas, for large continuous process industries and essential services loads such as water works etc.

6. GRID NETWORK ./' Grid networks provide maximum reliability and operating flexibility . ./' These networks are the most economical and effective methods to serve the high density loads in metropolitan cities. The network grid is simultaneously supplied from several feeders . ./' In grid network, no consumer outage is caused by switching off primary feeder for scheduled maintenance. Voltage regulation is improved since power flow to the consumers is several transformers operating in parallel,

ANll.KUMAR K.M., AssistantProfessor inE&EE, B.I.E.T, Davangere.

54

POJJlERSYSTEM PLANNING

./

The grid can handle abrupt load changes and disturbances associated with large motor starting without severe voltage dips or surges. A strong grid network is sufficiently stiff and a fault on one,unit does not disrupt voltage outside of sensitive load tolerance limits.

•

Figs showing the spot & grid network type of distribution

systems.

4.2 HIGH VOLTAGE TRANSMI$SION The sources of hydro and thermal power are often situated far·away from the load centres. This ..

.

necessitates transfer of power from one area to another o.ver long distance, on the other hand increasing requirement of bulk power transfer over long distances has resulted in the adoption of higher voltages of ac transmission all over the world. The policy of generating power at pit heads having high ash content and transmitting bulk power to load centres, even across long distances, has found favour for economic and ecological reasons. The voltage level at which power is to be transmitted depends primarily on the quantity of power to be transmitted and the distance over which it is to be transmitted. An approximate

an

'"

re Ia tiIon fcor power h an mg capacity

IS

given as P

= O.5y2_

XD Where P is the total power in megawatts, Y is the line to line voltage in kV, D is the distance in kilometer and X is reactance in ohm/km (X=21tjL) where

f

is the frequency of ac supply, L is

inductance which is an inertial property of an ac circuit. The transmission loss PL is given by PL =

53.6r Wh

-X-·

ere r

Transmission

"

.

IS resistance III

ohms / km. Typical values are given in below table.

line losses

VoltagekV

Reactance X ohmslkm

Resistance r ohmslkm

400

0.327

0.031

800

0.272

0.0136

1000

0.231

0.0036

1200

0.231

O~0027

Percentage loss

ANILKUMAR K.M., AssistantProfessorinE&EE, B.I.E.T, Davangere.

55

POWER SYSTEM PLANNING

Observations, ../' The capital cot per MW-km decreases with higher voltage . ../' One 800 kV line can normally carry as much power as four 400 kV circuits for equal distance of transmission. "Y'

One 1200 kV circuit can carry the power of three 800 kV circuits .a.'1dtwelve 400 kV circuits for the same transmission distance.

..

y'

In comparison to the percentage power loss at 400 kV, if the same power is transmitted at 800 kV, the line losses are reduced to one-tenth .

../' There is an overall power shortage in the country. There are pockets of surplus but the same cannot be transferred to distance. deficit because of the absence of transmission

links.

Experience has shown that transmission links will have to be asynchronous HVDC/back-toback links as the frequency of the connecting system widely differs and ac mode of connection . is practically impossible. 4.2.1 HVDe Transmission ../' High voltage DC (HVDC)' Transmission system consists of three basic parts: I) .converter station to convert AC to DC 2) transmission line 3) second converter station to convert back to AC. HVDC transmission systems can be configured in many ways on the basis of cost, flexibility, and operational requirements . ../' The simplest one is the back-to-back interconnection, and it has two converters on the same site and there is no transmission line. This type of connection is used as an inter tie between two different AC transmission systems . ../' The mono-polar link connects two converter stations by a single conductor line of usually negative polarity and earth or sea is used as a returned path. The most common HVDC link is bipolar, where two converter stations are connected by bipolar (±) conductors and each conductor has its own ground return. The third link is homopolar link which is having two or more conductors having the same polarity & always operated with ground or metallic return the multi-terminal HVDC transmission systems have more than two converter stations, which could be connected is series or parallel. DC liM r-.... ,

~~~

Block diagram of monopole system with earth as return.

56 POWER SYSTEM PLANNING

... liMa

u-"~, J

LC:::.:J-.J~

SmooIhiDg"";'--

~Il

I

I8l1C1CJ

III

i~

•

1111-----1

Schematic diagram of HVDC back to back converter station. CONFIGURATION

OF HVDC TRANSMISSION

SYSTEM Transmision cable

ACbllS

Block diagram showing the HYDe system configuration. The most relevant components that comprise a HVDC system are the following -/ The Thyristor or IOBT (Insulated Gate Bipolar Transistor) valves make the Conversion from AC to DC and thus are the main component of any HVDC converter. Each single valve consists of a certain amount of series connected thyristors (or IGBTs) with their auxiliary circuit, conventional thyristor valves are replaced by IOBT & OTO valves and these are actually called as VSC (voltage source converters) ofHVDC. -/ The Converter Transformers transform the voltage level of the AC busbar to the required entry voltage level of the converter.

v:

The Smoothing reactor, which main functions are (i) Prevention of the intermittent current (ii) Limitation of the DC fault currents (iii)Prevention of resonance in the DC circuits

,/ The Harmonic Filters, on the AC side of a HVDe converter station, which have two main duties (i) To absorb harmonic currents generated by the HVDC converter (ii) To supply reactive power, Also DC filter circuits have to be used. Besides Active Harmonic filters can be a supplement to passive filters due- to their better performances; Surge arrester's which main task is to protect the equipment of over-voltages

ANILKUMAR K.M., Assistant ProfessorinE&EE, B.I.E.T, Davangere.

)Y~li~

57 POWER SYSTEil-JPLANNING

../ DC Transmission circuit, which include DC Transmission line, cable, high speed DC switches and earth electrode. Converter stations require reactive power supply that is depending upon the active power loading fortunately part of this is fulfilled by active filters. In addition static VAR compensators & shunt capacitors are provided . ../ Control and Protection. - Control of firing angle is accomplished by the optic fiber. based hardware circuitry; power transmitted over the de link is always controlled. Converter stations are controlled in such a way that a rectifier end controls the current while the inverter end contr~ls the voltage allowing the link to maintain th~ constant power. In HVDC there is a need to convert power from ac to de and reconvert it to ac to the end. HVDC transmission brings with. it a considerable cost. Transmission cost in HVDC, on the other . hand, is lower than that in UHVAC There is, therefore, a minimum distance or break-even distance beyond which HVDC may be economical. A diagram representing the cost with distance for both DC and AC transmission is given below

Investment Cost In Rupees

200 400 iSOO goo

ieee

IMt-...nC"lt 1200 1400

(km)

Graph of cost along with losses as a function of distance for HVAC &HVDC. Situation promoting for HVDC in India are ../ The surplus and short regions during peak and off-peak periods of various regions are identified. Based on these exercises, inter-regional ties are planned to interconnect the regions at suitable points/or transport of surplus energy. ../' There is wide variation in the surplus/deficit generation conditions in the five regions in India resulting in mismatch between the frequencies and operating voltages of these regions, making it almost impossible to run these regions in synchronism . ../

There is a need to have controlled power flow between these regions .

./

An asynchronous HVDC link would further enhance the stability of these regions due to its ability to control the tie line power flows fast

,/t~i

../ With an ac.tie, the disturbances in one region may be transmitted to other regions, ther" increasing the chances of a wider effect.

&

.....

T....-w'

... ,....-Ta

........

.",.

..

_

•

••

• -

".

58

POWERSYSTEM PLANNING

../' Asynchronous links, being electronically controlled, ca."}reduce the spinning reserves required to a great extent. The total MW spinning reserve requirement therefore, can be maintained at a nationallevel rather than at the individual regional level in case of national grid . ../' With the HYDC' inter-regional links, the overall stabiiity ef-beth the regions shall increase. Due to this, the power carrying capability of some o/the ac lines shall increase and the dlances of state/region level grid collapse 'shall also be reduced. In case of an unavoidable grid collapse, the links shall reduce the region's restart time by transmission of large amount of power at the earliest from the adjoining region. The total saving on this account itself are considered to be adequate to justify these links. ../ The HVDC links can operate with different frequencies on either sIde, thereby allowing a region to serve a greater number of consumers by operating at a relatively lower frequency. In case of ac links, however, considerably power may flow over the link only to equalize the frequency of the two regions. ../' In case of a synchronous tie between the regions, the flow on the tie line behaves in an uncontrolled manner and is mainly dependent upon the two region's load-generation balance. Because of strong dependence of loads on the system's voltage and frequency, the tie line flow shall also be influenced by the variations in the voltage/frequency of these regions. In order to

-

properly control the flow on the tie line and limit them below the capacity of the Jine under such circumstances, it becomes necessary to keep some generating capacity in reserve in both the regions so as to take care of the relatively fast variations in the load/generation baJance and/or voltage, frequency variations. This would also mean loss in revenue and underutilization of the generating capacity and thus will defeat the very purpose of connecting the two regions . ./ The asynchronous links can control the power flow in any direction irrespective of the voltage/frequency conditions on either side. This feature may be helpful in solving some power issues. ../ Within its capability, the HYDe links can be used to control the frequency of a region to a given target value. It is concluded that HVDC inter-regional link facilitate optimal utilization of the existing resources, provides reliable and secure supply to some important load centre, and supply a share of power from generating stations in one region to another. There are, however, some major technical advantages of an HVDe system which may be summarized as follows ./ Power flow can be controlled independent of system operating conditions . ../' Systems operating at different frequencies may be interlinked. , ../ It helps to improve stability.

ANILKUMAR K.M., AssistantProfessor in E&EE,B.I.E.T, Davangere.

A~ft~1\X€#?~~~~ifJf~l~£~

•

59

POWER SYSTEM PLANNlNG

The most common reasons for HVDe system are -/' lower line costs- A de line with two conductors is more economical to build than an ac with

three conductors . ./

lower losses- With HYIJC"'thereiSno

reactive power transmitted. This is one onhe'reasons

why the line losses are lower with de than with ac. The losses in the converter terminals are approximately 1-1.5 percent of the transmitted power, which is low compared with the line losses. -/' Asynchronous connection- Sometimes it may be impossible to connect two ac networks due to stability reasons or because they operate at different ac frequencies. In such cases the solution is HVDe since it is an asynchronous connection.

0

-/' Controllability- Today's advanced semiconductor technology, utilized both in power thyristcrs and microprocessors for the control system, has yielded a substantial improvement in reliability and controllability of HVDe system. In an ac system it is not possible to control the power flow while in an HVDe system, the power flow can be controlled with regard to both amount and direction very quickly. This characteristic has often been used to stabilize different all networks. HVDC offers several advantages -/' DC cables are cheaper compared to ac.

-/' One single cable can take up to 500-1 OOOMW. -/' A de cable does not contribute to the short-circuit power. -/' Costly and difficult overhead line paths in a city centre can be avoided by cabling. -/' It ensures better conductor utilization. -/' It provides for three times the capacity, using the same conductors.

-/' It has an even higher capacity with new towers in an existing right-of-way. -/' It makes it possible to control reactive power in a city centre.

-/' It ensures increased ac system stability. -/' It provides for increased power capacity in parallel ac lines. -/' Itprovides for controlled power flow.

-/' It provides for double circuit performance of a converted single circuit ac line. -/' There is higher power without increased short-circuit power. -/' There is better control of the line load factor. Disadvantages of HYDC transmission system are -/' Costly terminal equipments - converters are expensive, converters require power & generate harmonics so they require filters, and converters have capability. -/' Inability to use the transformers to change the voltage levels. ANll.,KUMAR K.M., Assistant Professor in E&EE, B.lE.T, Davangere.

60 POfYER SYSTEM PLAIVNING

../ The difficulty of breaking the D.C currents which results in high cost ofD.C breakers . ../ Generation of harmonics- which require A.C & D.C filters, adding to the cost of converter stations. ../ Difficult for maintenance, need skilled technicians for operating. Application of HVDC transmission system ../ Control & stabilization of power flows in A.C ties in an integrated power system . ../ For. the cables crossing bodies of water wider than 20ml (32km). ../ For interconnecting the AC systems having different frequencies or where asynchronous operation is desired . ../ For transmitting the large amount of power o~er the long distances by overhead lines. -/' In congested urban areas or elsewhere where it is difficult to acquire right of way for overhead lines & where the lengths involved make the A.C cable impracticable. -/' Increasing the capacity of existing AC. transmission by conversion to D.C transmission. New transmission rights-of-way may be impossible to obtain. Existing overhead AC transmission lines if upgraded to or overbuilt with D.C. transmission can substantially increase the power transfer capability on the existing right-of-way. 4.2.2 FLEXIBLE AC TRANSMISSION SYSTEM (FACTS) -/' For economic reasons electric power systems are interconnected within utilities and- interutilities. -/' The purpose of transmission network is to pool power plants and load centres in order to minimize the number of power generation sources needed, taking advantage of diversity of loads, availability, of sources and in order to supply the load at required reliability . ../ As power transfers grow, the power system becomes increasingly more complex to operate and the system can become more insecure with large power flows with inadequate control and inability to utilize the full potential of transmission interconnections. The concept of Flexible AC -/' Transmission System has great potential, using thyristor based controllers to offer the utilities the ability to control power flows on their trans..nission lines, allow secure loading of transmission lines to their full thermal capacity. -/' The relevant technologies based on thyristor based controls are-SSR" damping, static V Ar. compensator (SVC), series capacitor, phase angle regulator, static condenser, dynamic load brake, dynamic voltage limiter, series reactor, fault current limiter, circuit breaker, load tap changer, and ferro resonance damper . ../ Static VAr compensators, fast controllable phase shifters, and series compensation, all significant role in FACTS. Although the equipment which comes under this existed for many years, what is new about FACTS is that these power comeonentss ANILKUMAR K.M., AssistantProfessor in E&EE. RI.E.T, Davangere.

61

't

special features are systematically evaluated with the goal of increasing the power transfer limits of ac networks. ./ An important property of the FACTS components is their ability to control the power flow,

. both active and reactive power flows or the power in feed to a certain node. The Controi ,..~.

r

be used either to regulate the power flows in the steady state, or to damp power swings dynamically. . Advanced series compensation(ASq •

./ Advanced Series Compensation is a way of further improving the efficiency of the transmission line or network by reducing power losses and so saving energy.By making better use of existing line capacity, the need for additional transmission lines couldbe obviated and in extremecases, the need for extra generating capacitycurtailed. ../' The first three-phase ASe system has been operational since Autumn 1992 at the Kayenta substation.in northeast Arizona, USA. By providing direct control of transmission line impedance, this scheme offers many' advantages over conventional fixed series-capacitors installations .

./ Advanced Series Compensation combines high-power electronics devices along with these essentially comprises a reactor (an inductive reactance) in parallel with a series capacitor. The net series compensation 'seen' by the power transmission line is the combined impedance of the reactor. In varying the impedance of the reactor, the total impedance of the compensation circuit changes. The ASe system regulates the current flowing through the reactor and so the current along the transmission line. It can control the apparent line impedance over a wide range by varying the firing angle of the thyristor. This allows ASe to operated not just as a series capacitor but also as a series reactor which in turn allows changes in transmission line impedanceto be readily made. ./ The main features offered by such a system are-direct and continuous flexible control of the transmission line compensation levels, increased stability, reduction of short-circuit current achieved by changing from a controlled capacitive reactance to a controlled inductive reactance, better overload flexibility by adapting the thyristor firing angle to the accumulated capacitor and arrester energy, improved protection of series capacitor banks, reduction of de offset voltage, sub-synchronousresonance mitigation, and power swing damping. 4.2.3. Underground transmission ./ Underground cables or underwater (submarine) cables are used for electrical energy transport where overhead constructionis impracticable, unsafe, costly or environmentaHyunacceptable... : .

.~

,,/ The main applications are in urban areas, where th,ereare long water crossings, across isl'md"~/ or where overheadrights-of-way are unav~ila~leor not possible or ~ery costly, or w.~y~;,~

it '

laws dictate underground cabling such as 10 arrport approaches, stations and subst~i.o~~7~!i~~:; rt ~ ANIT ,ll1lM AR K.M .. A~<:;dl:mt "Professor in F&F.E. BJ.RT. Davanzere.

E~T;ri

62 POWER SYSTEM PLANNING

areas of unusual scenic. value or with extreme vulnerability to damage by natural forces or vandalism . ./' There are many systems of cables depending upon the voltage, power requirements, length, ___ cost and reliability considerations, Underground transmission cables up to 8-00 kV are in operation . ./' Some common cable systems are-high pressure oil filled (typical voltage level 132-500 kV), low pressure oil filled (110-132 kV), extruded dielectric cable (132 kV to 400 ~V), compressed gas system (up to 800 kV). Up to the 66 kV level, solid cables are used such as paper impregnated insulated cables, plastic insulated (PE, PVC etc.) cables, and rubber insulated cables. 4.2.4 Development of transmission

voltage levels

./' In order to develop strong regional systems, it is important to strengthen the existing 400 kV network with 800kV ac and HVDe compensation,

links and use such modem techniques as series

static VAr systems, and phase shifting transformers with a possible future

application of flexible ac transmission systems . ./' In order to supply the growing demand for power, there has been a continuing trend towards adoption of higher voltages for transmission of power economically & also to reduce the losses throughout the world. 4.2.5 Selection of voltage levels ../' The economy of electrical power supply is determined essentially by the selection of the voltages in the distribution and transmission systems . ../' Fundamental considerations that determine the voltages to be used in the medium high, and high voltage ranges and also for their stepping are-load density; transmission distance and transmission power on the voltage to be selected . ../' The steady growth of loads also makes it necessary that consideration be given to the load development which may not only vary with respect to the time but also geographically. Matching of the voltages to the standardized values is also important. Voltage application range is given in table Voltage application range Voltage

Designation


Low Voltage (LV)

1-36kV

Medium Voltage (MY)

36-150kV

High Voltage (HV)

Range of application Distribution systems for feeding low voltage consumers such as houses, small workshops, commercial shops, hotels etc. Distribution systems for feeding low voltage systems & large consumers such as shopping complexes, schools, , hospitals, industrial plants, administration buildings etc~J;K.3 Distribution & sub transmission systems for feedin medium voltage system, for cities, large industria,J:.:'_~

ANILKUMAR K.M., Assistant Professor in E&EE, B.I.E.T, Davangere,

h~~~~l~~~.~Y.J

..

63 POWER SYSTEM PLANNING

railways, main substations. >150kV Extra High Voltage Transmission systems for large blocks of power & for (EHV) interconnected system operation . . ./ In the selection. of extra high voltages, other special problems arise in the dimensioning of the -

-

insulation and design of the overhead lines. ¥' At present high voltages, the influence of the insulation on the costs may be of great

importance, particularly where there is danger of contamination or other special c1imatic conditions such as mountain climate. Recommendations are made for the dimensioning of the insulation, these being based on the applicable standards . ./

Also important is the economical design of high voltage overhead lines, since in long distance . transmission lines, the proportion of the line costs to the total costs is very high. 4.3 PLANNING CRITERIA 4.3.1 Strategy for transmission expansion

./

While SEBs are responsible for providing the transmission systems for their respective state grids, POWER GRID has been entrusted with the responsibility for laying transmission system' network. for facilitating

transfer of power generated by the central sector to various

constituents as also for laying necessary transmission network for augmentation/strengthening of regional power grids and formation of national power grid to facilitate transfer of power not only within a region but also across various regions in the country. ¥' With the latest amendment (1997-ordinance)

to the Indian Electricity Act 1910and the

Electricity Supply Act 1948, private transmission companies can be entrusted for developing any transmission system . ./

Keeping in view long- and medium-term perspective planning, the transmission system needs to be evolved taking an integrated approach for evacuating power from different generating sources, irrespective of their ownership, and delivering it to the beneficiaries over an optimally designed power transmission system with reliability, security and economy .

./

In other words, the state/regional power systems have to be planned in such a manner that the power received from all the power plants can be transmitted without constraints to different beneficiaries as per their allocated shares, maintaining a reasonably good voltage profile, stability conditions and redundancy criteria.

¥' The power system so planned should also integrate well within the region. Hence, the

requirement of individual states as well as the possibilities ofjnter-state

and inter regional

exchanges must be kept in mind during the planning exercises . ./

Regional grids are developed for substantial inter-regional transfers and limited cross exchanges can.be attached to achieve optimized utilization of available generation and high standard of supply to beneficiaries with reliability and at reasonable cost.

64

4.3.2 Thermal loading ~ Thennalloadings are generally decided by design practice on the basis of ambient temperature and maximum permissibleconductor temperature. y'

In India, the ambient temperatures obtained in the varieus-perts-ef-thecountry are different and vary considerably during the various seasons of the year. It is, therefore, difficult to specify conductor loadings based on uniform ambienttemperature conditions.

v"

The maximum permissible line loading with respect to standard sizes of ACSR employed in 220 kV and 400 kV lines for ambient temperature of 40°C, 45°C, 48°C and 50°C, are different.

../' For the purpose of system planning studies, the line loadings should not exceed the values corresponding to appropriate ambient temperature conditions and maximum permissible conductor temperature, or those dictated by the stability criterion,whichever are lower. 4.3.3 Dispatchability Loading & Outage Capability -/' The transmission system should be planned on the basis of regional self-sufficiency. Wherever. inter-regional power transfer are allowed, the system should also be suitable for specific quantum of assistance from neighbouring regions, The maximum power angular separation between any two important buses should not normally exceed 40° for load flow under steady state conditions. -/' The transmission system should be capable of transmitting, the states shares from the central sector common projects. -/' The transmission system should be planned to withstand outage of two circuits of 220 kV system, or one circuit of 400 kV or higher voltage system, or one pole of HYDC bipole, or an EHV transformer without the necessity ofload shedding or reschedulingof generation. ../' The transmission system should be planned to ensure full transferring of

the maximum

possible output fromgenerating stations even under forced outage of a transmission outlet. ../' There should be sufficient redundancy to ensure that there is no transmission constraint on rescheduling generationunder the conditions of outage in any of the generating plants. -/' Reactive compensation should be provided as far as possible in lower voltage systems with a view to meet the reactive power requirement ofloads close to load points. 4.3.4 Security -/' The system should be able to survive without losing synchronism, the-single contingency of single line-to-ground fault, or line-to-line fault close to a bus on a trunk transmission link cleared by three pole opening of the circuit breakers on either end within 100 initiation of fault, or a fault in HVDC converterstation equipment resulting in a

.

of one of the poles ofan HYDe bipole.

IDS

from .th~.

perman¢.h\'l~J~~,

.f}f!;if;l '_ ~:.

~:. ')e,'; "':'/.;

1'1.

L;·.~),;l;';~,;:rf ~

65 POWER SYSTEM PLANNING ~

~

./

The above criterion is proposed since single-line-to-ground (SLG) or line-to-line (LLG) faults are more common and frequent as compared to the other types. Three-phase clearance has been adopted since it is more commonly practiced as compared to single-pole clearance. In the case ,. of 800 kV system, the SLG-fault-for-transient stability with a fault clearance time CJfj-"tycles (100 ms for 50 cycle systems) is to be adopted. The same criterion for security should be adopted with respect to the 800kV system .

./ In the event of a double contingency of single-line-to-ground fault or line-to-line fault with the primary protection failing to operate and fault being cleared by second zone protection, the system should return to stable operation after resorting to load shedding. In the event of an . extreme contingency of outage of two circuits emanating from same generating station, it should be possible to revert to stable operation with protection being coordinated to island the zones. 4.3.5 Right-Of-Way In view of increasing difficulty in obtaining right-of-way for transmission lines, and on account of problems associated with the clearance for routing transmission lines in forest area, transmission lines should be constructed as double circuit or multi-circuit lines wherever feasible. 4.3.6 Economic Evaluation Economic evaluation should take into account the cost of the total system including terminal equipment. The cost of energy should be based on marginal cost. 4.3.7 Planning of distribution

networks

../ The basic parameters considered are-load density, expected load growth, voltage level and circuit ../ configuration, number of feeding points etc. ../ In order to select the most advantageous investments from different alternatives, costlbenefit studies must be carried out taking into account system voltage, system losses, estimated non distributed energy due to system faults, annual maintenance costs, safety etc., for one or two years. Suitable account should be taken of future long-term period unknown factor by some form of sensitivity analysis. -/" The existing distribution system network arrangement is a natural starting point for planning for future developments. Good system planning requires sound knowledge of the existing system to provide a firm base on which to assess the projects for future network development from the technical and economic point of view . ../ At HV (subtransmission) level, the technical studies can be complex. HV systems an~. ,,;£...

introduced to deal with longer distances and increased power requirements. The use of a sin~J·~:· higher voltage system of 33-220 kV to supply local LV networks directly unacceptably high costs and amenity problems. Thus, another voltage level ANILKUMAR K.M .• Assistant Professor in E&EE. B.lE.T. Davanzere.

WOul~'1\1;

~~t~iim~"")

jt~~i£fI~~~.~4w~~1

66 POWER SYSTEM PLANNING

level), is used to interlink, i.e., 22 kV or 11 kV. Material & construction costs of 11-22 kV over head lines are only slightly higher than those for a 400 V line of the same length, but are approximately-one-tenth

the costs of a 110 kV line. It is this large cost differential which

economically justifies the inclusion of an MV network between the EHV, HV and LV systems, even when the costs of HVIMV substations have been taken into account. Medium voltage system also provides a convenient voltage for connecting substantial industrial loads, large buildings or office blocks. The decision for selecting the voltage level must be based on longterm studies. 4.3.8 Substation development ./. For planning the density and size of substations in the power system, the following technical and economic aspects are considered-load density (e.g., MW per km2), load growth, utilization of transformer capacity, maximum fault levels, flexibility and siting . ./. Normally, the city areas have higher load densities and the size of substations will be higher than in rural areas. This is mainly because of-the fact that the cost of distributing the power in general is lower when the load density is high .: ./. The size and number or density of substations is determined by technical-economic analysis. The average distance between substation, It is given by TOlalAreas ( NumberofSubstations y'

)"2

Due to the scarcity of available sites and other local environmental aspects, it may be impossible to respect the optimal technical-economic

solutions alone. Nevertheless, these

solutions should be looked for so that the cost consequences are known and the optimum conditions may be approached as near as possible . ./. From the economic point of view the optimal successive transformer sizes, between the same voltage levels, have a ratio of about 1.5 to 2.5. This means, in practical situations, that new . sizes should be envisaged when the loads in substations have been increased by that factor. y'

Load density is a very important determinant of the size of substations. Very big substations can be attractive when the density is high as an increase in demand in the long term is very probable otherwise smaller sizes are preferable .

./. Now SF6technologies make it possible to put HV substations inside buildings or underground. Such substations closer to the load centres are physically smaller and often simpler designed. Modem protection schemes ;ilow a more complex operation to maximize security of supply. This also favors simpler substations.

67 l:'UW.J:!.1( .>.l.>J../!,M r.L/1JYJl.l1YIJ

substation bus bar schemes The arrangement of bus bar and circuit breakers plays an important part in determining the efficiency of power transmission and distribution system. The type of arrangement to be adopted is . . .determined by the degree of flexibility of operation, immunity from totar shutdown. importance and nature of loads, security, capital sectionalization,

cost and minimization

l-

of fault level by way of

maintenance, area of extension, land area etc. The most prevalent bus bar

arrangements are given below

1. Single Bus System -./. 'It is the cheapest arrangement and is used for small substations where power outage for short periods for maintenance and repairs is permissible. «/' The disadvantage of the system is that

in case of contingency' the whole system has to be dosed

down. «/' Improvement to this is possible by sectionalizing the bus by installing isolating switches or a

circuit breaker so 'that different sections can be operated independently.

2. Duplicate Bus System «/' This arrangement is commonly used in large systems with many feeders. «/' There is a coupling switch or circuit breaker between the two bus bars. «/' Isolators and circuit breakers are connected so as to have the power flow without interruption.

This is a comparatively more expensive arrangement. «/' Feeder breaker maintenance is di fficui t without interruption of supply of feeder.

3. Transfer Bus Arrangement «/' With this arrangement line circuit breakers can be taken out for maintenance and repairs without

interruption of supply. «/' This is a very costly scheme but is more flexible.

4. Breaker and A Half System «/' The arrangement is suitable for systems where power outage is not permissible for any reason

whatsoever. «/' The supply has to be kept uninterrupted even in case of bus fault and the bus can be taken out

for «/' maintenance. The cost and the area required are 90 percent and 50 percent as compared to main

bus and transfer breaker schemes.

4.3.9 Reactive power planning ,The planning criteria for reactive power compensation may be adopted as follows, >

«/' Reactive power should not be transported over long distances.

,

,~

,.i.<:' .;

<.:\:,i., •.1·.·•

«/' In normal intact network situations reactive power should be produced and consume~:tlitt:"

",;y(;T'ti:i~~Et·y ,

68

,/ The network should be operated at upper voltage limits in high load conditions to achieve higher stability margins and to reduce active and reactive power transmission losses. ,/ The amount of reactive power reserves should be sufficient to ensure acceptable transmission ~acities

inthe network during sys~emdisturbance sonditions.

There are two important aspects which distinguish reactive power planning from the planning of activepower, ,/ Transmission of reactive power over long distances win have both active and ~eactivepower losses and voltage drop. Compensation to maintain reactive power balance in an area must consequently be provided in the vicinity. Reactive power is in this respect a more local problem than activepower. ,/ Investment cost related to reactive power reach only a few per cent of Corresponding values for active power transmission equipment. Furthermore, reactive power installations have a much shorter constructiontime and very less influence on the environment. Reactive power sources ,/ Reactive power is generated or absorbed by all major components of a power systemgenerators; transformers, HVDC converters, lines, loads; and reactive po~er compensating devices. ,/ Reactive power compensation devices such as capacitors, reactors, synchronous condensers etc., are installed to improve reactive power balance, voltage control, and system stability including dampingof power oscillations. ,/ The future UHV and EHV transmission development will not see much progress of shunt reactors and shunt capacitors and synchronous condensers. Static VAr compensators,based on power electronicswill have large development in this area for transmission level. Series Compensation For long lines, series compensation is used to increase the permissible loadingwhich is limited mainly by the transient stability. The following factors should be considered in the selection of series compensationrequirements ,/ steady state and transient system stability ,/ protection of series capacitors ./ sub synchronousresonance. Shunt Compensation Selection of shunt compensation requirement for EHV & UHV lines requires consideration of the following factors. ,/ steady state over voltages during light load conditions ./ dynamic over voltages. ,/ switching over voltages ANTT _ll1lM & D

1( M

A<:<:i<:t~nt Professor

in F.&ER B.I.E.T. Davanzere.

,.{_j~it*~

69 POWERSYSTEM PLANNING

../ resonance voltagesfrom parallel lines. Capacitor Planning

../ The low voltage nodes can be raised within operating limlts by increasing the generation bus voltage.beyond the-eseal upper steady state limits. The system voltage is allowed to operate above the normal limit for low load since the extra reactive power intake can jeopardize the .generator stability and shunting. To meet the contingency, some of the system nodes may be operating at voltage experiencedduring the low load period. The bus voltageraise produces an effect similar to the transformertap variation. . . ../ Optimum capacitors can be decided considering both the transformers tap setting and the variable voltage ceiling limit. Criteria for planning static VAr system

../ A static VAr compensator (SVC) is an automaticallycontrolledsupply ofVArs. The supply of VArs is regulated by the thyristor switching off reactors or capacitors in shunt with the transmission or distribution system. The result is that the voltage of the bus at the location of the SVC will be controlled. The response time of an SVC is in the range of a few cycles and can be switched as often as the control allows. . ../ Rapidly varying loads cause voltagefluctuationsin the transmission or distributionsystem. Arc . furnaces, welders, steel rolling mills., induction furnaces, cement mills, large pumps and compressors, mining shovels, wood choppers, and electric traction loads are examples of rapidly varying loads. Many times the industry with these loads does not complain, but the other electricity-using consumers in the area do complain. SVCs are fast enough to stabilize voltage for the types of applications listed above and reduce or eliminate the consumer complaintsof voltage fluctuations. ../ Weak transmission and distribution systems with varying loads are one application which could be served by an SVCs. ../ If the load is constant, switched capacitors can usually supply the VArs for the load and the line losses, therebyreducing currentin the line, improvingthe power factorand thus regulating the voltage. If the load varies and the switched banks cannot be dispatched rapidly enough to meet the load, then an SVC mayberequired. 4.3.10 Grid Formulation

The creation of the Power Grid Corporation of India (PGCI) would provide the necessary impetus for establishing efficient power system networks with the ultimate objective of evolving a national power grid by the year AD 2000.1n a regime of shortages, the grid management philosophy has to be different from the advance~ countries where huge reserves are avail

-

enabling considerableflexibility in economicload dispatch.

ANILKUMARK.M., AssistantProfessorin E&EE,B.I.E.T,Davangere.

70

Grid operation

The major problems encounteredby the five regional load dispatchcentres in the five region in the integrated operation of the power grids relate to inadequate capacity, inadequacies in the transmission and distribution system, grid indiscipline leading to indiscriminate and heavy over

-

drawls by the constituents, wide frequency fluctuations, reluctance to back down generation, abnormal voltage levels, commercial disputes; inadequacy of load dispatch and communication facilities. The steps to solve these problems are discussed below,

_, Accelerating the constructionof power generating stations & convertingnowadays Inadequate generating capacity in to adequate capacity. _, perspective plans for transmission and distributionsystem includingHVDC have to be planned for inter-regional power exchanges. ./' Managing the load for avoiding Frequency and voltage fluctuations. ./' Optimizing the-generatingstations for Economicpower generation. ./' Proper hydro-thermal mix is required for evolvingthe most efficient ./' and economical systemfor generation of power. 4.3.11 Compact Lines Up gradation of existing lines and substations

-

Several alternative approaches are available to increase the capability of existing lines. The most obvious method of increasing the capability of an existing line is to increase the operating voltage. This method can sometimes be accomplishedby modifying existing structures on a line, but a large increase in voltage might require replacement of structures,which is usually still more economical and practical than trying to obtain right-of-way for a new transmissionline. Some commonly used practices are,

./' use of aluminum alloy conductors which have low weight to strength ratio for minimization of sag or tension as comparisonto ACSR. ./' use of V-string assembly or polymer insulators to prevent conductor swing and thereby maintain required electricalclearness. ./' Introduction of additionalpanel in tower structure suitably to increaseground clearance. ./' Replacement of X-arm by special shape arms. Reduction in the number of circuits (from double circuit to single circuit) for upgrading system voltage followedby reconductoring. ./' Reinforcing structure legs through attachment of additional steel sections with the existing leg posts. . ./' Another method of making more efficient use of right-of-way involves" compaction"

k

of;

tr~smiSSion lines. By restricting the movement of the conductors at the structure, ri~t>~;..:~~i WIdthcan be reduced. :{

I 111 ~\::i

ANH,KUMAD

K_M._Assist:mt Pmfp..ssor in F~FF.

RTF 't n~v:mop,.p

71 POWER SY..\'TEM PLANN1N(i

~

~ y'

Series compensation is another way to increase power-transfer capability of ac transmission lines. Economic benefits of adding series compensation to long transmission lines are realized . by allowing reliable operation of the system closer to be line's thermal limit. An advanced series compensation (ASC) scneme can be used to evaluate benefits of combining converrtinnal fixed series capacitors with thyristor-controlled reactors and provide direct dynamic control of a transmission line's impedance

y'

With the increasing requests for wheeling and transmission access transmission engineers will be challenged more and more to provide maximum capability on existing lines and to design new lines making the most efficient (optimum) use of right-of-way with the lowest electric and magnetic fields possible. It is feasible to upgrade any existing llkV line to 33 kV line or 33 kV lines to 66 or 132kV lines as compact line.

y'

It will be advantageous to change the delta formation of the conductors to a horizontal (or near horizontal) formation. This can be achieved by fitting a 33 kV "V" type cross arm to the existing llkV pole.

y'

Load leveling in time and area domains is effective for improving the utilization factor of power utilities network.

y'

Uprating/upgrading of transmission system is possible due to innovative approach, to improve transmission capacity such as compaction, FACTS, use of AAAC, use of polymer insulators and insulated X-arms, reduction of air clearances and angle of swings, and deploying Zno lightning arresters.

y'

The dimensions of a transmission line can be compacted by restraining the movement of the conductor at the point of attachment to the insulators by certain arrangements like V string, Horizontal posts," Strut suspension combination, Horizontal V etc. and by installing ZnO arresters.

y'

Multi-circuit lines One solution to the increasing pressure for mere compact right -of-way is to restring existing low-voltage lines onto new towers with new high voltage circuits.

5 & 6 POWER SYSTEM ECONOMICS & POWER SECTOR FINANCE y'

About 20 per cent of the national plan budget is spent on the electric power sector.

y'

Even ignoring possible inflation and cost overruns, the power sector project investment- needs equal 2.5 per cent of the GDP.

y'

Much of this additional capacity will come from coal-fired plants, especially in China and India. But there will also be substantial additional capacity in the amount of hydroelectricity and gas-fired capacity.

..

1

'j

According to estimates, the annual costs to industry in India due to electricity shorta~~"t',~

.

!I;~J;~I

currently one to three percent of the GD P.

, ..••.. ·k

11··· ,i t· /'.l:--"

t." I:

. '.'

rf ~

72

./

It will be impossible for the public sector to make the necessary investment to bridge the gap between the demand and supply of electricity. The increasing role of the private sector in electric power sector-bas three aspects-mobilization of private capital for power development, development of new sources of power generation and improved economic efficiency. Three main points make project finance attractive - (i) Risk Sharing, (Ii) Improvement of Balance Sheet, (iii) Taxation Advantages. 7. FINANCIAL PLANNING

./

Investment requirement of the power sector has increased exponentially over the years and, therefore, a need was left' to mobilize resources to meet this huge requirement by way of foreign assistance, private capital, public borrowings and internal resource generation, to reduce the financial burden on the public .

../' The state electricity boards and the central sector corporation are expected to generate at least 20 per cent of their total investment as internal resources . ../' The capital structure of the state electricity board, is built up with loans from the state governments, financial institutions like banks, LIC, PFC" REC etc. and -market borrowing. They are ~lso expected to generate internal resources from their statutory earnings after meeting the liabilities of operating expenditure, interest on loans, capital-and depreciation . ../' The negative internal resources indicate losses incurred by SEBs due to lack of rational tariff and other reasons . ../' Power being the basic infrastructure required for sustainable economic development, cannot be ignored even in such a situation and ways and means will have to be found to mobilize finances for funding the new schemes . ./

The capital finance debt andlor equity is required for fixed capital (long term) for land, building, machinery, materials, construction etc, and working capital (short term) for raw material such as fuel for two months etc. Working capital has highest interest rates. ,.Competitive financial markets are emerging. The innovative approach by various financial institutions has made funding a complicated process. The broad options available for power sector finance are as follows,

(i) Issue of bonds by the central corporations, electricity boards, (ii) Internal resources generation by utilities, (iii) Subscriptions of shares/debentures from public, (iv) Loans from power finance corporation (PFC), (v) Promoters money, (vi) State plan resources for state e1ectricity boards, (vii) New budgetary support from the government of India, (viii) Joint sector participation between .central and state governments, ANILKUMAR K.M., Assistant Professor in E&EE,B.lE.T, Davangere.

73 POWER SYSTEM PLANNING

(ix) Joint ventures between public and private sectors,. (x) Bilateral assistance on selective basis in terms of grant, equity and loans, (xi) Multilateral assistance from world bank! AOD etc., in terms of grant, equity and loans, (xii) Loans or equity from financial institutions such as LIe, UTI, commercial banks, NABARD, IDBI etc. (xiii) Loans from specialized financial corporations such as IFC, IeIeI, pension funds etc.

..

(xiv) Lease financing to power utilities . Pattern of investment ../ The· Rajadyksha

Committee

on Power appointed

by the Government

of India had

recommended (1980)that the investment ratios in the power sector between generation, transmission, distribution and rural electrification should be 4:2: 1,.1. ../ More than 50 percent system losses are estimated to occur in the lower voltage system below 132 kV which are the sub transmission and distribution system. These need to be strengthened through increasing investment. Plan outlay ../ Much higher outlays have been allocated to generation component than T &0 system or renovation and modernization (R&M)programmes . ../ Inadequate investments in T&0 system is one of the reasons for poor quality of supply of electricity (voltage fluctuations and break downs). Investment on optimum utilization of existing generation plants through R&M programmes has aiso not always been adequate, though large investment in R&M - programmes would probably have resulted in higher average PLF of the power plants . . ./ This plan outlay generally describes the pattern of investment made in the five year plans in the different sector of power & energy. Techno-economic viability '/

One of the basic objectives of the power project report is to determine techno-economic viability for the project identified and also to obtain the investment for construction of generation plants and interconnecting links which ensures an economic and reliable supply.

,/ The evaluation of investment in various subsectors of the power industry such as generation system, transmission linkages, distribution systems, etc., through long-range planning is necessary for a rational and planned growth of the power system as a whole . .. ,l

In ~rge developing countries, such as India and China,' there is, however, another feature of the planning problem that is absent in the developed countries. This arises from the fact that, concomitant with the need for new capacity to meet the rapidly growing demand, there is a~

.

.;.'IT

equally important requirement for the expansion and extension of the transmi;,si9,ll:'~~t

distribution to provide power either to new areas. ANILKUMAR K.M., Assistant ProfessorinE&EE, B.I.E.T,Davangere.

[I,k r

i

J ~~:i" b:

• ,,;.~'

A;{~:rKi~4\

74

../. From the standpoint of analysis of investment alternatives for the system

3S

a whole, this

implies that the analytical tools used should be capable of assessing the options for both capacity and transmission linkage expansion and distribution in an integrated fashion to .achieve an optimal solution for the future evolution of_the~m

.

../. The project must be clear from the point of regulatory clearancesbefore seeking finance from investment agencies. The main choice problems confronting the system planners in case of thermal power are the question of optimal unit size and generation reliability, the locati.onof the plants in relation to the load centre, the coal mines, the transportation network for coal and extension to highervoltage level ofthe transmission grid. ../. Since power systems planning is generally carried out over relatively long time horizons, an important operational consideration given, the large uncertainties inherent in long-term input assumptions is that the suitable analytical methods should be capable of examining a large number of future scenarios within a reasonable time and levelof effort. ../. The Central Electricity Authority has acquired the Integrated System Planning Package (ISPLAN)developedby Mis I.D.E.A.ofUSA. It is an indicativeplanning tool for analyzing the major features of an optimal expansion plan for generation capacity, transmission. and coal transport. Based on an LP formulation, the model can be utilized effectively and quickly with respect to a large number of alternative input assumptions to produce an optimal expansion plan at the regionallevel. ../. Another proprietary package, the Electric Generation ExpansionAnalysis System (EGEAS) is a computer software package which contains five capacity expansion analysis options ranging from preliminary analysis tools based on screening curves and linear programming to sophisticated non linear analysis tools utilizing Generalized Bender's Decomposition Technique and Dynamic ProgrammingAlgorithm. 8. PRlV ATE PARTICIPATION ../. Private power projects are importantas a part of the country'sinvestment resources raising and least cost expansionplan for the supplyof electricity. ../. Under the Indian Electricity (Supply) Act, the private sector generating companies, transmission or distribution companiesare encouraged to participate in power sector. ../. Another advantage of private' sector participation is that it opens up new work and management skills for timely execution of the project and 'delivery of quality in work and service. Some of incentives for private sector versus public sector are given in the below table.

..

75 POWER SYSTEM PLANNING

As notified by the Government of India Private & public sector investment

-

Public sector

Details

Private sector

Debt-Equity RatiO-

1:1

4:1

Minimum rate of retum(ROR) on

12%

16%

Capitalization of Interest

1% above reserve

At actual cost

construction

bank rate

Period of initial validity oflicence

-

equity component

Increased from 20 to 30 years & .... :

further expandable by 20 years on each occasion

Mode of operation as Generation,

Independent

Independently or Association with central or SEBs

T&D companies Foreign participation

-

Single point clearance of application

../ Capitalization of interest during construction is at the actual cost for private sector from the existing schedule interest rate applicable to state electricity boards, and state and central corporations. The interest(%) during construction is =

C*R*N where, C= Cost of project in Rs., R = Rate 2*12*100

of interest, N = Construction and commissioning period in months . ../ With different debt-equity ratios and rate of return as indicated above, private sector cost of energy would go up. ,'I

·,Gvernment has further liberalized the rates of depreciation provision in the

Electricity (Supply) Act, 1948 with respect to assets of power generating companies/boards and licensee companies . ./' The private power generating companies would have to be assured of guarantee by state governments or by the central government or by any legal institution or expanded form of an escrow account and letter of credit or timely payments of the dues on account of power sale to the various electricity boards or timely payment of loan to the lender respectively. Provision of direct supply by private companies to HT consumers or exclusive distribution area may be another option.

ANILKUMAR

K.M .. Assistant Professor in E&EE, B.I.E.T, Davangere.

76 POWER SYSTEM PLANNING 't •

Ownership ./ Power utilities have a natural monopoly . ./ The efforts are to remove this monopoly by creating supply market as in UK [8], USA, Argentina, Australia and some other ~untries . ./ The consumers will be free to choose their suppliers. Rapid decision-making, risk-taking and innovation are needed and these qualities are usually lacking in state-owned undertakings. Privatization will restructure the electricity supply industry in most countries in Asia in the near future. It will break up vertically integrated monopolies in search of lower costs and higher productivities . ./. The public sector and private sector power utilities have different financial structures Various private sector options like ~rnkey (engineering, procurement, construction) contract, BOOT, BOO, BOL, ROL etc., BOO (Build-awn-operate), BOOT (Build-own-operate-transfer) are the most common schemes for new projects, ROL (Rehabilitate-awn-Iease) are common for old plants and BOM (Build-awn-maintenance) for new transmission lines. MI,.IUlJU ANNUAL rlEVI!UIJ12 Il£OUr>lEl.tENT

_iLl r--l Figs showing the finance structure of private & public utilities, Some salient business features of the incentives given by the government

to private

investment are, 1. Private sector units can set up coal/lignite/oil/gas-based thermal, hydel, wind and solar energy projects of any size. 2. Private enterprises can set up units, either as licensees distributing power in a licensed area from own generation or purchased power, or as generating companies, generating power for supply to the grid. 3. Licensee companies holding licence to supply and distribute energy in a specified area under a licence issued by the state government will function under a liberalized economic and legal environment. 4. New licences can be issued by the state governments to private units willing to. enter the electricity sector.

.

c :

.

...•

,.J '#:.;

5. pn~~te enterpnses may be allowed to set up and they can sell or distribute surplus pow~rf~,~titr B,_

electncIty boards (SEEs).

....,

ANILKUMAR K.M., Assistant Professor in E&EE. B.I.E.T.Davanzere.

. t ...•. £ £: ;,•...~.•rf ,,~""~. '"''''

f f7~

.!!~~;';i'r:;y?;i:~;i'

77 POWER SYSTEM PLANNING

6. Promoters' contribution should be at least 11 per cent of the total outlay. Not more than 40 per cent of the total outlay can come from Indian public financial institutions. To ensure that private entrepreneurs bring in additional resources for the sector, they must find 60 per cent of the resources from 'sources other than public financiii[ institutions.

7. Both license ,;'; and g~nerating companies can enjoy the following Benefits, (i) Up to hundred per cent foreign c;~::~i ¥.:~~;cip.:.tioii(:al1(,;" pcJ1iiiUcJ fo- !lr(\j~r.ts set up by .foreign private investors, (ii) With the approval of the government, import of equipment for power project will be permitted. in cases where foreign suppliers or agericies extend concessional credit. (iii) Return for producers.

Debt Equity Hatio The Government of India has stipulated a debt-equity ratio of 4:1. A higher ratio is considered more risky for t1:'

iders. Debt-equity ratio is calculated by dividing long-term debt by the equity.

Debt and equity:

-lefined as follows

Debt . long-tee -.

aeposits (repayable after twelve months) including interest bearing unsecured

loans from ;',' '.,,_ rent agencies, promoters etc. & deferred payments. Equity ordinary i ;,' ,p share capital, premium on issue of shares, amount of central/state subsidy, non-refundab!r .: ,)osits in the case of cooperatives. Modes of U . }.lcipation Given the

I.',

?i~entprovision of electricity laws, the private sector could participate in four

ways. ',' -'

~ the state electricity board would be responsible for transmission and .T while

ST.'" y'"

.ontractual agreement such as PP A.

,,"

ely where private entrants would be granted monopoly rights to supply a

Fr sp :':

y'"

private entrants could own generating companies and sen energy to

,,

B"

~rthrough self-generation or by purchasing the required power. is wheeling

of power where the private sector generating company could sell

directly h :>flV consumer and could have access to the T&D network by paying for it. The

NTP~= ;:; ,.:,.,,,h"ng power to the railways at present by this arrangement. lines could be set up on the basis of norms laid by the central government in .nission tariff, line availability, service agreement, depreciation and return

,

o.

'"

s : ,

.014:"

M

Assistant

Professor inE&EE, B.I.E.T,Davangere.

78 . POWER SYSTEM PLANNING

Bidding for private power entrants ../ The state zovemment will be required. to plan and select projects for offering them to bidders. ../ The planning process woetd include identification of system requirements estimated on the basis of demand projection, power evacuation arrangement, availability of fuel and water, ash disposal/utilization and environmental aspects in the form ofDPR or DFR .

...f. _J>dy~!e.~eneration bidding can be on competitive bidding to set up Power projects through the least cost/price or through Memorandum of Understanding route. Memorandum Of Understanding (Moo) Route ../ This is an initial one-to-one agreement with the state electricity board and the prospective generating company to express intention for under-taking power generation project (MW or prepared under negotiations with certain boundary conditions and time period).

.

../ MoU system is considered suitable at the initial stages of private power sector policy implementation or when no competitive bidders are coming such as for a project in an area having less developed infrastructure where railway, fuel linkage and power dispatchability are difficult. There. is difficulty in arriving at a reasonable price level ill an MoU case. Competitive Bjdding Route Competitive bidding is done for prepared and cleared projects and can be in five phases (i) Issue of RFQ (Request for qualifications) to encourage competent bidders to participate by giving threshold criteria, mainly organization, financial capability, management capability and technical capability for qualifying an applicant for the subsequent RFP process (ii) Issue of RFP (Request for proposals)detailing engineering adequacies, acceptance of SEBs operating requirements, pricing, plant availability, plant load factor, draft power purchase agreement and implementation agreement (IA),evaluation criteria, capacity, timing, sizes of units etc., as in DPR for new capacity or DFR in case of refurbishment (iii) Submission of Bids and evaluation the determining factor for awarding the project could be based on the total project outlay or ultimate single tariff (iv) Signature ofPPA and IA (v) Financial close. Power Purchase Agreement (PPA) ../ It is a type of commitment by the state electricity board to allocate risk and for sale and purchase of energy and power. It is based on the philosophy of keeping a balance between the risk and the price of electricity purchased for an agreed period say of 15 to 30 years. It incorporates plant load factor versus long-term costs and tariff structure, fuel reserves, period. /";!

·1

of

contract,

maintenance

guarantee,banking,

procedures,

billing

insurance, dispatchability,

and

metering,

payments, licences,

agreement termination, arbitration and jurisdiction provision. ANILKUMAR K.M., Assistant Professor inE&EE, BJ.E.T, Davangere.

pollution,

.

79 POWER SYSTEM PLANNING

../ This agreement is between the prospective generator and the state government. The quality of PPA is important for satisfying financere, t.ogether back up for other agreements. Fuel Supply agreement

It is an agreement for the linkage of fuel supply (coal or oil or gas) with concerned department giving details of the costs-annual and monthly, linkages, quality. combustion, transportation, timely delivery of fuel, default and penalty . •

Implementation

Agreement (1Al

It is !ill agreement between the independent power producing (IPP) company or NUG or private owned . utility

generation

company

and the state .government

providing

assurance

on

implementation of PPA, construction, water supply agreement, government approvals, sovereign guarantee by government of India, levy of taxes, foreign exchange, immigration, bank account, exchange risk insurance, political, resettlement, force majure conditions etc. Operation and Maintenance agreement Financial Close Financial close is the date on which banks and financial institutions start lending for the work .

.

on the project. The breakup time up to financial closing in general is shown in below Figure.

21

Fig showing Typical time lead of the private utility up to fmancial close

It takes four to eighteen months for executing the various project agreements including financial agreements for debt andlor equity with lenders to arrive at financial close. The signing of agreements can be simultaneous. or in sequence as shown in Next page.

A NTLKUMAR K.M.,

Assistant Professorin E&EE, B.I.E.T, Davangere.

80 POWER SYSTEM PLANNING

Typical stages of arrangements

of a power project.

Energy purchase agreement with cog en era tors .. ./

Energy purchase agreements bit cogeneration companies & SEBs will require agreement for power purchase & sale tariffs including wheeling & banking of power, billing & pa:yment, parallel operation, interconnection facility owned by state electricity boards, continuity of service, personnel & system safety, metering, permits & licenses, events of defaults & termination indemnification & disputes.

Y" All or portion of value of electricity energy delivered at peak may be designated for peak:

banking or delivered off peak may be designated as off peak banking. This energy may be used by the cogenerators for credit against future energy purchase by the cogenerator from the SEBS. Y" All or portion of value of electricity energy delivered on peak: may be designated for peak

wheeling or delivered off peak may be designated as off peak wheeling. This energy may be used for future credit against energy purchased by third party from the SEBS. Y" Each month, the cogeneration firm should prepare an invoice indicating what quantity of

energy delivered to the SEBs during the previous calendar month is designated as banked, wheeled, sold for on peak & off-peak.

9. RURAL ELECTRIFICATION PLANNING & INVESTMENT Y" It would not, however, be quite correct to judge rural electrification purely on the criterion of

the financial returns-on the investments made. Y" A number of indirect socio-economic advantages like harnessing of groundwater resources

for • :{;C,'

increased food production, promotion of rural industries and rural employment, preventio migration from rural to Y" urban centres, saving in diesel and the like, should not be ignored.

ANILKUMAR K.M., AssistantProfessor in E&EE, B.I.E.T,Davangere.

))!~

81 POWER SYSTEM PLANNING F

~ y"

The real advantages of rural electrification are not limited to the immediate or long-term financialreturns but go far beyondand can be truly evaluatedby the benefit-cost analysis.

y"

The National Council of Applied Economic . . Research (NCAER)carrieB out studies in the impact of rural electrification"in1hePunjab and Kerala villages and after evaluation of the indirect benefits, it was found that the benefit-cost ratio of all the schemes was well above unity proving that there was abundant economic justification for the rural electrification schemes. 9.1 RURAL ELECTRIFICATION

y"

Rural Electrificationprogrammeis mainly funded by Rural Electrification Corporation of India since 1969 for all-round development of village life, agriculture and village industries. The presentconcerns are,

v'

Rural electrification concerns the supply of electricity to low density areas of villages. It is traditionallyachieved in two ways by the installationof generators independentof the grid, i.e., diesel or micro-hydel or wind generation etc., directly at the consumption site (village, farm, small industry, dispersed dwellings),or by the extension of the interconnected electrical grid. This latter technique accounts for 80 per cent of rural electrioity distribution in the world and about 98 per cent in India.

../' For electricity distribution, rural areas are distinguished from urbanized areas by some fundamentalaspects like sites to be electrified are often several kilometers from the existing (H.T.) medium voltage (MV) network, there is lower population density and electricity consumptionis much lower than the average urban consumption. v'

The above characteristics of rural electrification result in an increase in capital costs of rural projects in comparison with urban projects because the great distance of sites to be electrified entails the installation of MV lines from the grid over sometimes significant distances. (2 to 3 Ian on an average in India).

../ The low population density in comparison with urban sites requires to installation of longer low voltage(LV)lines per consumer. As a rule of thumb, stability problems limit extensions of grid to a distance in km of not more than double the line voltage in kV. v'

The rural electrification programme has a useful contribution to the agricultural production, especiallyby the energization of pump sets for irrigation. However, due to non-availability of reliable power supply in rural area, the agro-based industries did not grow and this lead to migrationof rural population to urban area.

../' The rural power system has long lines, low voltage, low power factor, overloaded transformers _ causing damage to the costly equipment and higher transmission and distribution losses. ,J11~{t . ,tl;~~·. consumersdo not install capacitorsin their premises to increase power factorand also h ~.e·nO;!0 inclinationof participate in the energy conservation.

,,/~'~-.;;)i{:~;,t~fJ·;~~! _ '..'

~ r4

.~:1\m~~~~~s~:~~~~%t~€f~~i!.t~

82

POJVERSYSTEM PL4_NNING

9.2 COMPONENTS OF RURAl, ELECTRIFICATION

PLANNL""'lG

1. Village electrification At present millions of villages have been electrified out of a total of 0.579million villages ..

which constitute about 86 per cent in the country. A -yiJIageis deemed to be

__

._._ .

_

electrified even if a single connection is given in the revenue boundary of the village. ,2.

Pump set energization .•..

..;.-

..."....'-~

This is a major scheme' of rural electrification planning. Rural Electrification Corporation of India, NABARD and commercial banks & many rural electrification cooperatives have provided funds in equal ratio for pump sets energii;ti~n.-- . 3. Load development The use of electricity for domestic andother non-farm activities is still limited and the creation ofHT/LT network in the rural areas for industrial development is yet to take place. 4. System improvement planning The existing system has expanded at a fast rate and not strengthened, therefore, making the . overall system inadequate. Continuous system improvement needs to be planned as part of the work culture. "S. Insulated aerial cable system ./

Insulated overhead distribution system has the ability to reduce the environmental impact on overhead system both for new work in difficult areas and retrofitting or-existing bare system. High Voltage ABC (Aerial Bunched Cable) system is used in many countries.

>/' Covered conductor system provides an improved open wire system which can be less

expensive than HV ABC. Two versions of power conductors, namely, covered conductor (CC) and covered conductor thick (CCT) are now used. Decentralized generation >/' The electrification of these villages by conventional means from grid supply is becoming

.Increasingly

expensive and unreliable. It is desirable to, electrify the villages through

decentralized generation schemes like mini-micro hydel, solar, wind, geothermal etc. Also the growth of load in already electrified villages can be accelerated by such small generation .schemes. >/' The small power generation schemes are being given subsidies up to 50 per cent by the

Ministry of Non-conventional Energy Sources to reduce the ultimate cost of supply.. Small hydro and wind generators up to 100 kW should be developed by the local Panchayat at the identified sites for which necessary expertise should be given by the Ministry of Nonconventional Energy Source !Indian Renewable Energy Development Agencies Ltd (IRED

AND..KUMARK.M., AssistantProfessorinE&EE. B.I.E.T,Davangere.

f.."

..,';

83 POWER SYSTEM PLANNING

1. Wind generator These are competitive source of electricity in windy areas and are susceptible to substantial development in India. An assessment of wind energy resources in India indicates a potential of

50,OOOMW. Now commercially India is generating arournt--2(T,OOOMW of power through wind energy. The commercial wind turbines in India are in the range of 1-2 MW for grid connected applications.

2. Small hydro power stations Small hydro power stations have begun to spread in several developing countries in hilly areas and plain terrains. Two problems need to be solved here, the problem of capital cost, which must be kept as low as possible by the use of standardized hardware and local engineering, and the problem of the good load factor, which must be high enough to make the project viable.

3~ Wood fired gasifier micro power stations These seem capable of supplying a kWh at a price comparable to that of a conventional generating set under certain conditions: isolation of the locality to be supplied and availability of raw materials, w.iththe advantage of using a local energy source. 4. Photovoltaic systems Thousands of PV systems are today in operation worldwide, and have proved highly competitive in a range of residential, agricultural, commercial, village level, health, education and smail-scale industry applications. A large number of photovoltaic water pumps are now in service in the country. 5. Biomass electricity generation sets The technology for such biomass based power plants is a proven one. These run exactly on the same principles as a coal-fired plant. These plants are modular in nature and are in the 5-25 MW range. T::cy rim on any combustible material.

10. RATIONAL TARIFFS There are three main objectives of a sound pricing structure/consumer tariff. (i) Financial-Ensuring

that the revenue yield from the application of tariff to the consumer is

sufficient. (ii) Economic-Ensuring

that tariffs charged to consumers enable them to make rational and

optimal choices in the use of energy, discourage waste and promote efficient allocation of resources. (iii) Social-Ensuring that the price structure takes into account fair distribution of costs among various classes of consumers, subsidization of target class etc.

;'

,/ There are two basic tariff-making philosophies recognized- (i) Cost based and (il)

~ill

based. The factors used in developing cost-based tariffs are identified as capaciryi:reif"~ ;', energy-related and consumer-related. These factors vary for different classes, 0 ANILKUMAR K.M., AssistantProfessor in E&EE, B.I.E.T, Davangere.

J

:~,Wt.

84 POWERSYSTEM PLANNING

(residential, agricultural, commercial, industrial etc.), and require an analysis of much data in - ..

.__ -.'.

_..",..

_--:-:.-;_

order to properly allocate costs. ./

Cost based tariffs are generally pseferred -because they are less likely to be criticized by

---consumers.

However, political or social considerations sometimes over-ride the inherent

fairness of cost-based tariffs especially developing economies. When this is done, L'1c tariffs are said to market based. 10.1 COST-BASED TARIFFS ./

The tariff should have sufficient rates to raise adequate revenue to meet the financial requirements of the utility .

./

The tariff should be based on supply cost for each .category of consumer. However, urban consumers will subsidize the rural consumers to some extent.

-./ Peak consumers should pay both capacity and energy costs whereas off peak consumers such as agriculture should pay only the energy costs. -./ Lower the service voltage, the greater the costs consumers impose on the system. Therefore, higher tariff for low voltage consumers is desirable. Tariffs must be based o!l marginal costs of serving demand which varies, (i) for different consumer categories, (ii) for different seasonal industries such as rice shellar; ice industry etc. (iii) for different hours of the day, i.e., higher rate for' peak hours, medium rate for day time and lower rate for off peak hours. (iv) for different voltage levels, i.e., HT or LT supply consumers. (v) for different geographical areas. 10.2 MARKET-BASED TARIFFS -./ Following are some examples of market-based tariffs, They may be more prevalent when sufficient justification can be provided. However, to recover costs, cross-subsidization between various classes of consumers and! or some subsidization by the government is inevitable. -./ Certain industrial rate classes may be subsidized to attract new industry to an area. -./ Residential rates may be subsidized by other classes or Social/Political purposes. -./ Agricultural tube wells services may be subsidized to encourage increased food production -./ Inverted block rates have been used extensively to encourage energy conservation depending upon the analysis of price elasticity.

= %changeinenergyc01'iSumptioninkWhrs

E p

%changeinpriceperk Whrs

10.3 CENTRAL SECTOR GENERATION PROJECTS TARIFFS "As per provision of IE (Supply) Act, 1948,the tariff for sale of electricity by genttr~iihfi company to the state electricity board shall be computed and fixed for a period ANILKUMAR KM., AssistantProfessor in E&EE,B.I.E.T, Davangere.

O~i:~~

!3,:I~;~~t

85 POWER SYSTEM PLANNING

normative basis as per electricity (supply) Act provision. Bulk power supply agreements (BPSA) are usually signed. An ac transmission tariff plus HVDC transmission tariff (if any) are charged in each case and charged on fixed rate/unit basis in each case of agreement. However, the tariff shall be computed and fixed a new for a period of five years each and whenever additional generating capacity is commissioned in the same station. Thermal Power Station

,.

-The two-part tariff for sale of electricity from thermal power generating stations (including gas based stations) .shall comprise the recovery of annual fixed charges consisting of interest on loan capital, depreciation, operation and maintenance expenses (excluding fuel), taxes on income

- reckoned as expenses, return on equity and interest on working capital at a normative level of generation and energy (variable) charges covering fuel cost recoverable for each unit (kilowatt hours) of energy supplied. Hydro Power Station ./ The two-part tariff for sale of electricity from hydro power generating stations shall comprise the recovery of annual capacity charges consisting of operation & maintenance expenses, tax on income reckoned as expenses, return on equity, cessor levy on water charges as actual, & interest on working capital at a nonnative level of generation shall be based on 'the norms as may be applicable . ./ There is a mechanism of incentive specified for improved performance above normative level with respect to project availability & energy generation. Transmission tariff ./ For common interstate projects, the capital cost of construction for the transmission lines and other assets such as generating stations is generally shared in proportion to the power allocation to the state . ./ The power may be in terms of energy drawn for each month or year or for. block of years or

••

over the life of the line or other assets . ./ The cost recovery may be in the form of 'transmission tariff in the shape of fixed charges based on cost contribution plus annual energy charges of kWh supplied. The transmission tariff is the total tariff for transmission of power and is payable by the beneficiary states. It is equal to the annual fixed charges which consists of O&M expenses plus depreciation plus interest on loan and working capital plus return on equity plus any other tax annually payable . ./ Usually O&M charges, depreciation charges and rate of return are levied as per norms notified by the government or regulatory body. The annual fixed charges are based on fixed assets of the transmission system.

ANILKUMAR K.M., Assistant Professor inE&EE. B.I.E.T. Davanzere.

"j

86

Tariff for Renewable resources generation ./ Most of the renewable resources are required to be connected to the grid for selling power to the nearby utility. ./ The cost of supplying...isnormally decided by the avoided cost to-utility....Thcavoided cost to utility is taken as cost of generationwhich is predominantly installed by the utility. ./ If there is no utility generation then the cost may be decided on the basis of opportunity cost. Opportunity cost is the cost that the consumers will be spending per unit of energy, may be in the form of wood, diesel, keroseneetc. ./ It may be notedhowever, that the cost of power of the new private producerswould necessarily

be more than the pooled power provided by the state electricity boards (SEBs),the bulk of which is from old, depreciated plants. Such average low-cost supply should mean that SEBs. can supply power more competitivelythan the private distributors, who are more likely to have a larger proportionof their supplyfrom new plants.

ANILKUMAR K.M .. Assistant Professorin E&EE.B.I.E.T.Davanzere.

87 POWER SYSTEM PLANNING

QUESTIONS BANK 1) 2) 3) 4)

•

..

What are the basic processes of cogeneration? What are its benefits? Explain. Explain the strategies for transmissionsysteffl'expansion in India. Discuss generation characteristics cfbroad categories of loads, MQP Enumerate elaborately on the desirable generation options for next 25 years for India as per CEA and World Bank. 5) Write descriptive notes on (i) Boiler renovation, and (ii) Power policy and trading. 6) Write a descriptive note on selection of voltage levels in India for Transmission and Distributi on. 7) Explain different types of reactive power compensation techniques used in transmission and distribution systems. 8) With the help of necessary graphs, Explain variation of (i) Reliability .vs Investment cost, and (ii) Annual cost vs System reliability. . . 9) Enumerate different trends and issues that planners a.'1doperators have to cope with during reliability plarming. 1O}Describe the two methods of reliability assessment. 11) Write a descriptive note on CEA's reliability planning criteria. 12) Describe different types of disturbances and the devices used to suppress the disturbance. 13) Describe in detail the economic characteristics of generation units. 14) Write a note on reactive load forecast. 15) Explain Power Pooling and trading in India and its role in Power System Planning. 16) What is renovation and Modernization of power plants? Explain Boiler renovation in thermal power plants? . 17) Describe HVDC transmission on planning. 18) Describe substation development planning. 19) Explain grid operation in power system planning. 20) Explain the components of rural electrification planning. 21) Explain basic distribution system used by utilities along with single line diagram. 22) Enumerate elaborately on the desirable generation options for next 25 years for India as per CEA and World Bank. 23) Explain the variation of investment cost with respect to distance in ACIDC systems. 24) Give the merits and demerits ofHVAC and HYDC systems. 25) Explain private participation in generation planning? How it will improve the situation in India? 26) Discuss the tariff making philosophy. 27) Explain with V-T curves the importance insulation coordination in the power system. 28) Explain the concept of Dispatchability in power system planning. 29) Discuss the effect of power generation on environment? How it can be reduced? 30) What are the objectives of sound pricing structure? Explain. 31) Describe reliability planning with reliability versus cost graph.

Note - Questions are collected from previous year Q.P, & Model Q.P.

88 POWER SYSTEM PLANNING

UNIT-5 & 6: POWER SUPPLY RELIABILITIES

ANILKmvIAR K.M. Assistant Professor ,E&EE, BlET ,Davangere. . ""'""" .--...,.~-

V.T.U.Syllabus Reliability planning, system operation planning, load management, load prediction, reactive power balance, online power flow studies, test estimation, computerized management. Power

system simulator.

SYNOPSIS The reliability of the. power system has been discussed with reference to cost, unnerved

..

energy & unnerved demand for various stages of power system. The lead times for operational planning and on line controls of AGC, economic load dispatch, state estimation are given for complete op~rational planning. The operational planning involving hardware and software for various functions of load dispatch, economicdispatch, load dispatch centre, energy management,SCADA, state estimation are disc.ussed.'Generation-load balance prediction studies are necessary one year in advance. The peaking capacity and energy requirement along with medium and short time forecasting based on computer programs are' necessary. The grid code for grid operation at the national and regional levels and the optimum utilization of thermal, hydro, nuclear and other resources is desirable for every utility, dispatch centre and national grid centre. Maintaining frequency by means frequency-basedtariff, keeping automatic load shedding schemes and strengthening of system by capacitors installation is required. The grid frequency control, wheeling and trading of power and grid connection of small generating schemes for future importance are discussed.

89 POWER SYSTEM PLANNING

UNIT-5 & 6: POWERSUPPLYRELIABILITX 1. RELIABILITY PLANNING 1.1 SYSTEM RELIABILITY .,/ Modem society expects that the supply of electricity should be continuously available on demand . ../ Sometimes reliabilities fails due to Random system failures which are generally beyond the control of power system engineers . .,/' The probability of consumers being disconnected, however, can be reduced by increased investment on power systems by providing high quality equipment or redundancy and better maintenance . .,/' The reliability of supply to consumers is judged from the frequency of interruptions, the duration of each interruption and the value a consumer places on the supply of electricity at the time that service is not . ,/' Provided. The value to consumers is determined by the benefits which they can derive from using it.

Uncertainty .,/' The problem of uncertainty consists in devising a system sufficiently robust to withstand the impacts . .,/' At the present time the amplitude and the number of the possible impacts is such that the cost of a robust system becomes prohibitive, if one wants to face most of the uncertainty factors . .,/' Flexibility within the system development. From the planner's point of view a flexible system is a system which will be able to be adapted quickly to any external change. This is achieved either because the planner made provisions to change over to diverse fuels or diverse power "I"

•

•

because he decided to install equipment which makes better use of the existing

system. In recent years the need for flexibility has become particularly apparent because both planners and operators had to cope with more and more significant trends, 1. Industry structure trends _ deregulation, privatization and vertical disaggregation, wheeling for non utility generation, transmission access for consumers for power purchases from other utilities, 2. Financial trends - capital availability and cost uncertainty, rate base incentives and constraints, stockholder risks and uncertain rates of return, construction expenditure recov~

risks.

3. Ted:;: :~':trends _ load management and conservation, generation technology and licensing issu '":'s,t;':1nsmissiontechnology and ROW issues. 4.

,',/ir\):::f:cnt and health issues - emissions limits, power frequency and electromagnetif:!i$l4 , ,,,:;-::'.,,,~',,

,.:"

i Z.:C .is, i ~dioactive

..

waste storage/disposal, endangered species.

,\~;:~,KUMARK.M., AssistantProfessorin E&EE. B.lE.T. Davanzere.

- :-,;

90 POWERSYSTEM PLANNING >/' F'lexibility appears with the improvement in the ability of the power system to adapt itself

quickly to new circumstances. >/' Security affects the operation and the strueture of the system. The system security is defined

here.as.as ability to avoid or limit-major outages which entails the collapse of entire parts of the system. 1.2 SYSTEM ADEQUACY AND SECURITY >/' A simple yet reasonable subdivision of power system reliability, both deterministic

and

probabilistic, is the two basic aspects of system security and system adequacy. >/' Adequacyis

generally defined as the capability of the system to meet the system demand

within major component ratings and in the presence of scheduled and unscheduled outages of generation, transmission and distribution facilities. >/' Security is generally defined as the capability of the system to withstand disturbances arising

from faults and unscheduled removal of equipment without further loss of facilities or cascading. Adequacy therefore, relates to the existence of sufficient facilities within the system, i.e., it relates to static system conditions whereas security relates to dynamic system conditions. >/' The task of power system planning is to configure an electric power system with a compromise

between the requirements perceived by consumers for adequacy and security to achieve continuity and quality of supply, and to keep in mind the economics of the power system in terms of operating and capital costs, so that the benefit of higher levels of adequacy and security are realized by the consumer. 1.3 RELIABILITY

PLANNING

./ The basic function of an electric power system is to meet electricity requirements, with adequate quality and reliability and in an economical manner. >/' There is an emerging recognition that the traditional practice of providing all users with a

uniform and a good level of service reliability merits a re-examination. Given the changes in the electric utility industry's cost structure in recent years, there is a growing feeling that investments related !o the provision of electric service reliability should be more explicitly evaluated with reference to their cost and benefit implications . ./

Cost-benefit analysis provides the basis for answering the fundamental economic question in reliability planning-how much reliability is adequate? A key related question is how and where should a utility spend its 'reliability rupees'.

>/' Because of the changes in technology, consumer needs and lifestyles, economic factors, etc.,

reliability preferences can also shift over time. This may require periodical revision at reliability standards. As the reliability standards changes from time to time.

ANILKUMAR K.M., AssistantProfessor inE&EE, B.I.E.T,Davangere.

{

.tlf~:

ti~~{;~

91 POWER SYSTEM PLANNING

Figs showing the Reliability versus Cost • ../ In contrast, the total cost minimization approach seeks to establish the trade-off that is conceptually depicted in Figure below. The total cost of supplying electricity is the sum of system.G~st and consumer outage 'costs. The lowest point on the total cost curve defines the. optimal balancing of system costs and consumer costs and determines the optimal reliability level, reserve margin, LOLP,EUE . ../ From an implementation standpoint, the following analysis is required under this method. For each of several preselected reserve margins, ail optimum resource mix is first determined. Next, for each such resource mix, production costing, revenue requirements and reliability calculations are performed to estimate total costs as (revenue requirements) + (EVE) (outage cost in Rs/kWh) ../ The lowest point on this curve defines the optimum reserve requirement which can also be . calibrated to an optimal EUE (Expected Unserved Energy) standard or some normalization of EUE such as loss-of-energy probability {LOEP).Especially in situations where the present generation fuel mix is non-optimal, the total cost minimization approach will indicate a higher reliability level because some generating plant will be added to reduce fuel costs. CEA reliability planning criteria The Central Electricity Authority (CEA) uses the following reliability criteria on deterministic and probabilistic basis. For Lines Loading under normal operating conditions with nearly 20% margin for lines. For example 400 kV SIC line: 360-800 MW, 220 kV SIC line: 160-200 MW, 132 kV SIC line: 50-70 MW. For Generation The transmission system configurations for which the transmission planning studies are carried out depending on the generation scenarios worked out by the CEA. The peaking capacities and energy generation capabilities, availabilities of power plant on which the power & energy balance studies are based, would be determined on the basis of the foHowing norms,

.

..

t

Thermal and Nuclear Plants - The norms for availability of peaking capability is ~\yet by Rated capacity - (Maintenance @5% + Parti~1 outage rate @15% + Forced out~g~'~J{e @170/0 + Auxiliary consumption @10%

+ Spinning

reserve @5%)

,<·fit, , >..

..~

. ~"

ANlLKUMAR K.M., Assistant Professor in E&EE, B.I.E.T, Davangere.

92 POWER SYSTEM PLANNING

This norm is not realistic and total reserved margin should not be more than 20 per cent. Hydro plants - Norms for deciding overall peaking capacities of hydro units would be as under,

Rated capacity - (Maintenance

@3%

+

Forced outage rate @9.5% + Auxiliary

consumption @O.5%)--··· --

- --

The peaking capacities and energy generation capabilities of hydro stations shall be determined taking the hydrological conditions, requirements of water for irrigation purposes, etc., into consideration. Generation expansion - LOLP = 1%,2%,

5%.

Reliability evaluation The power system reliability studies are conducted for two purposes, 1. Long-term reliability evaluations may be performed to assist in long range system planning. 2. Short-term reliability predictions may be undertaken to assist in day-to-day operating decisions· including system security. Improvement in system reliability can be effected by using either better components or a system' design incorporating more redundancy. The main steps in reliability studies are, 1. Define the system-list the components and collect the necessary component failure data from field surveys available. 2. Define the criteria for system failure. 3. List the assumptions to be used. 4. Developing the system model. 5. Perform failure effects analysis and compute the system reliability indices. 6. Analyze and evaluate the results.

2. SYSTEM OPERATION PLANNING 2.1 OPERATIONS ../ Operational planning covers the whole period ranging from the implementation stage of system development plans to the point when system operation engineers at area, state, regional and national load dispatch deal with the dispatch of power . ../ It is the matching of generation output with aggregated consumer demand, subject to requirements of economy and security. It covers the maintenance of generation, transmission and distribution facilities . ../ Certain Operational problems. have to be considered at the long-term planning. For example, the Indian power system regional grids are-small in capacity and size, and thus, there is a limitation on installation oflarge sized generation units

i-? the grid.

,

,".

../ Operation planners plan to minimize operating costs within constraints while ensuring -

,.f,.

t

an'.

iJ·

acceptable level of system reliability. Various decisions are required at approP11e.~~iines' ,.2t,%{J ,. ~." ANILKUMARK.M., AssistantProfessor in E&EE, B.I.E.T, Davangere.

93 POWER SYSTEM PLANNING

related to operating policies, operating procedures, maintenance planning, fueling, hydraulic

-

utilization, transaction planning etc. The overall operation is shown in the below figure

St40~T·T£m..

MAIN1Il:NAHCfi

sECONOS - 60

I MINUTES

HOURS

MONTHS

12

OAVS

!!O

ne:AL TIME OPERATION .mOCONlAOL

24

MAINTENI\NCE PlANNING

EXTENDED AE.At. mAE

YEARS

10

OPERATIONALPlANNI;'IG S'ISTEM PlAN~P1G

Fig showing the lead time for operational planning. 2.2 REAl, TIME OPERATION 2.2.1 State Estimation ../' The state of technology of actually existing real time computers allow network data collection -for the period at one to two minutes. after each state estimation, all data identified as bad for 'erroneous and non-telemetered values are replaced by calculated values becoming available to the operator of the programs . ../' The network estimation assumed to be the most important functions for the real time secure operation, include all the principles and computer programs devoted to the permanent 'assessment of security factors for actual or simulated network configurations. "

In the real time program, the comparison of variables in telemetered values to fixed limits is the first step of maximum system loading evaluation .

·.

../' Let n be the number of buses of the network, thus overload checking belongs to "n security" assessment. With an ac load flow calculation, the complete n security can be checked, while changing the values of some data (measurements or indications) which allows the operator to anticipate the evaluation of eventual future situations . ../' Many power systems today have been designed in such-a way that the random failure of the transmission's item or generating unit with the heaviest load does not affect reliability of other equipment, at the same time preserving the quality of supply . ../' The contingency analysis is based on this criterion starting from it toad flow calculation. The

, ~k

program simulates outages and determines the load transferred on the remaining items~f:~i

(')~,rf,~'*'.·;·.~ .-.j.".:.

ANILKUMAR K.M., Assistant Professor in E&EE. B.I.E.T. Davanzere.

94 POWER SYSTEM FLANNING

network. A display of violated constraints informs the operator of the risks occurring in the new operating conditions. 2.2.2 Automatic Generation Control .-/' Automatic Generation Control function (AGC) is on-line computer control and is generally-executed everyone to ten seconds. AGe tracks system load and generation level of each committed unit. In the interconnected power systems, this function also meets an additional objective namely the maintaining of the net interchange contracts in force at each instant. -/' The tie lines are generaliy connected into the transmission network at locations where their specific power flow must be established by adjusting or shifting the power output of generators in order to achieve a desired flow value. -/' To maintain a net interchange of power with its area neighbours, an AGC uses real power flow measurements of all tie lines emanating from the area and subtracts the scheduled interchange to calculate an error value. -/' The net power interchange (together with a gain B (MW/O.1Hz) called the frequency bias) as a multiplier on the frequency deviation is called the area control error (ACE)and is given by .

k

ACE = L (Pk-Ps)+ lOB (fa-fo)MW k=1

'" AGC sensing only ACE does not control the flow on the individual tie lines but is concerned with area net generation. Often, the tie lines transfer power through the area from one neighbor to the next, caned wheeling power. 2.2.3 Economic Load Dispatch It is on-line computer control generally performed everyone two minutes to supply the existing system load demand from each committed units

in the most economical manner in terms of

minimal fuel cost and minimal losses. Even pollution control can be a feature of economic dispatch operation. 2.2.4 Stability ./ Power systems are becoming increasingly complex because of interconnections and faster dynamic response of plant, particularly if equipped with solid state controllers. Also, heavier loading on the existing circuits. to cope with increasing energy transfers without constructing new lines has made the system operate closer to its transient stability limits. ./ New techniques for the on-line evaluation of stability criterion and for detecting in real time operation through many recent techniques & methods are available. Fast transient stability methods are categorized under three main groups (i) Direct and hybrid methods based on energy functions, (ii) New computing hardware including parallel processors,

ANTI..KUMAR K.M., Assistant Professor in E&EE, B.I.E.T, Davangere.

95 POWER SYSTEM PLANNING

(iii)Artificial intelligence approaches (pattern recognition and expert system). 2.3 MAINTENANCE Maintenance needs to be given due priority while protecting capital investment and making sure that the system

IS operative in a cost-effective manner.

-. - ... ---

It has been observed that more than 50 per cent of all the accidents and equipment failures investigated arc caused by either faulty maintenance or operator error. Successful maintenance depends upon: l.The prerequisite for any maintenance programmeis

that well trained and adequate Tools and

Plants equipped maintenance staff is posted. Good quality of spares and materials are used. 2. Manufacturer's instructions should always be given due consideration while carrying out the maintenance of a particular equipment. 3. A correct record of fault investigations, test results, inspections, tripping should be maintained.

4. Required safety precautions must be observed while carrying out the maintenance jobs. 5. Hot line maintenance for important transmission lines and essential supply distribution lines should be carried out. Other latest practices in maintenance of substations and lines such as infr?l~ red thermography in temperature scanning of equipment or lines must be adopted. 6. A good communication between the maintenance staff and operation staff is essential to cut down the shutdown period. The communications can be VHF, paging etc., with desirable features. 7. The ultimate aim should be Total Productive Maintenance (TPM) to achieve zero breakdowns, zero defects and zero accidents. There are THREE types of maintenance

1. Preventive maintenance The aim of preventive maintenance is to find the defects by periodical inspections and replace the unreliable parts or units so as to prevent accidents or damage and keep the equipment efficiency up to the mark. ~

.

The measures taken in preventive maintenance are, 1. Each power station or network region should have an emergency and insurance stock of spare electrical equipment (generator exciter, LP turbine blades, HP/IP rotors, generator rotor, electric motors, circuit-breaker arc chutes, brushes, brush and commutator gear, etc.) which should be checked at regular intervals. 2. All required repairs should be performed at the power stations, lines and substations at convenient periods of time. Lean months are most suitable for thermal power stations. &Tow water period for hydro plants when load is very less & can be easily diverted. 3. Repairs should be planned so that main equipment and its auxiliaries simultaneously in order to avoid the maximum duration of power interruption.

ANll..KUMAR K.M., AssistantProfessorin E&EE. B.I.E.T.Davanzere.

96 POWERSYSTEM PLANNING

4. In order to improve the reliability of the machines and in tum improve the availabiiity of the same, the preventive maintenance schedule should be drawn in advance, for at least a year, on a weekly basis. 5.

No unplanned w~ther

... than emergency repairs should be undertaken.

2. Capital maintenance and modernization ./

The schedule for replacing various ageing equipment in power system such as turbines, boilers, . generating units, transformers, breakers, convertors etc., must be prepared in advance on a rolling basis for the next five years and should be updated on the basis of actual achievements .

./

An engineering declaration should be made before overhaul (Replacement), giving details of the present condition of the units and expected performance levels after overhauling .

./

A performance evaluation test should invariably be conducted on the equipment after overhaul to confirm the achievements of overhaul.

./

The aim of modernization and improvement of various parts is to increase the service-span of electrical equipment and improve its performance and efficiency.

3. Condition Based Maintenance .,/' Condition based maintenance is condition. monitoring for timely prediction and diagnosis of failure in advance . .,/' Condition based maintenance can achieve cost benefits through reduction of 'in-service' failures, reduction of regular preventive maintenance routines and deferral of major overhauls. Points to be considered should include, (i) additional transducers and signal conditioning required, (ii) system architecture--a distributed processing architecture, featuring intelligent

front end

hardware, is preferred as it minimizes the extent of cabling required, (iii) installation and cabling costs, (iv) computer hardware costs,

-.

(v) system interfacing requirements, (vi) system software costs, (vii) on-line/off-line mix. The final stage of the analysis involves a cost-benefit assessment to establish the financial viability of applying condition monitoring to the nominated auxiliary plants. Condition based techniques for power plants Equipment

Technique

Rotating Machines

Vibration monitoring, Performance Monitoring, Acoustic Emission

Steam/Gas turbines

Vibration monitoring, Performance analysis, Oil analysis, Acoustic Emission

ANILKUMAR K.M., AssistantProfessor in E&EE,B.1.E.T,Davangere.

97 POWER SYSTEM PLANNING

Insulation condition checking, Vibration monitoring, Performance

Altemators

analysis Boilers & furnaces

Temperature monitoring, corrosion monitoring, smoke & flue gas composition monitoring, leak monitoring

3. LOAD MANAGEMENT 'I'

,"

The utilization of load management techniques is becoming more important in the operational planning process of indian power system as there is small spinning reserve available .

./' The peak demands are difficultto meet and generally at night after 1O.00PM hours, power stations start experiencing very low demand to the order of 30 per cent or less. This compels the coal-fired thermal stations to resort to costly oil support to the boilers due to back down in most cases . ./' Load management has two aims, one is to bring up economic advantages, especially in the operation of power plants and in the necessary investment in the new plants and transmission capacity. To reach this, the utility has to try to get a flat load curve. The second aim is to avoid the spreading of an emergency in case there is over-loadingor unbalancing

in. the system .

./' The differentiation oftariffs (time-of-day-tariffs) has an influence on filling of load valleys and reducing the peak load.

.. . Fig showing the different Load management measures. 3.1 GENERATION SCHEDULE Figure shown in next page illustrates how a typical utility may meet its daily load demand. The base load is carried by generators that run at !,90percent capacity on a 24-hour basis. Intermediate, or controllable generators run most of the time but are not necessarily fully loaded. Peaking units are kept on-line only for a few hours every day. Reserve capacity is needed to meet unforesee emergencies.

~l!

.i~;M€~~~,?~jl~¥f~~~~i~~i@?

98 FUWl!,K :iXi>.l.l!.M./'L/il'yJV.lHU

1 ..-~.

I Gel)eration to meet typical load demand, Base-Load Units. Nuclear units and thermal power stations typically fall in this category. Due to the need for keeping the nuclear reactor and steamsystem in thermal balance, it is desirable to maintain the megawatt output of such units at as constant a level as possible, Intermediate Units' . When the megawatt output must be regulated, hydro-powered units are the most convenient choice. The power output of a hydro generator is controlled simply by changing the water flow through the turbine. Not all electric utilities have hydropower available and must then use controllable thermal units=coal Drgas. Peaking Units Gas turbine driven generators can pick up load very fast and are therefore often used for peaking purposes, Hydro-powered generators are also an excellent choice when available. Pumped hydro storage is a special type of peaking equipment used for supplying the peak loads. Reserve Units ../ The required generator margin can consist of generators maintained at partial output spinning reserve Dr generators standing by at vario.us levels of readiness . ../ The energy cost, expressed in rupees per megawatt hour, will vary greatly between the above types of units. Peaking units are the most expensive because, on the average, they are greatly underused. If a utility can shave its peak demand by load management, it may be possible to' postpone for years the need for acquiring such units . ../ Maintaining a proper generation mix is a most important requirement for a power utility of

any

size . ../ The problem is not only due to. the hourly shift in power demand All generating units must be .'. ../ regularly maintained and, in case of nuclear units, also. refueled. The op~rating success utility depends to a great extent upon the ability to. optimally match the generation to. I/{ not only over the 24-hour daily time span but over seasons and years. ANll..KUMARK.M., AssistantProfessor in E&EE, BJ.E.T, Davangere.

.

J)t::1 '···1

;':\~J

,)~j~,.~Si~

-

.

99 POWER SYSTEM PLANNING

../ Pooling can benefit the individual utilities in terms of spinning reserve margin need, peak capacity and better use of load and generation diversity. •

Conti_ngency plans Typical plans are, ~. The coal mines tend to flood during monsoon. Therefore, before the onset of monsoon, the railhead non-pit-head and pit-head thermal power stations should have coal stock of 30 days and 15 days respectively. l~

../ Island generation should be allowed for supplying important local loads . ../ Frequency should be maintained constant by balancing the load & supply.

4. LOAD }>REDICTION ../ The total demand may be divided into components with varying time constants-the seasonal and economic factors have large time constants of several months while the variations due to consumer habits and rapid weather fluctuations have small time constants of a few hours . ../ In consequence, the load at any time y (t) can be written in the form of the equation below which is the basis for the prediction techniques discussed here, y (t)=A (t) + B (t) + C (t) A (t) is the long term or base load, B (t) daily variations, C (t) hourly variations. ~

The prediction methods may be broadly classified into two categories, those which require meteorological information and those which require past load data only .

../ The method of weather weighting uses a set of weather dependent weights that act as percentage changes on a base load to form an estimate of the future load . ../ The load is therefore considered as two components,

a fixed or base load and a variable

deviation due to the effect of the weather . .._, The meteorological factors included are temperature, cloud cover, rains and wind velocity. Hence, by estimating the weights associated with varying degrees of each of these weather

..

variables, a base for a given time of the day and week may be derived by subtracting ~ postulated total weather dependent load from the recorded total load . ../ These weights together with the deduced based load can be checked using other data relating to the same period. If poor correlation is found between the predicted load and the actual load then the weights must be revised. After a trial and error period, the...appropriate weather weights for a given time of day and year can be deduced, which may then be used for load estimation in conjunction with weather forecasts. Two important methods of load prediction are as follows Regression analysis

~-t

-

/" ;" A.~~,i\~'

../ It is a more mathematical approach to the load prediction problem, the effects"SJ~~ai3~~~

weather components are obtained by a regression analysis on previous load and w,ellthef~at~. y,S $ _-~':"'. _'<: •.... ;_"

ANlT,KITMAR K_M __A.<:<:i<:t:mtPmfp.<:<:nr

in

F&F.F. AT F T

nllVllnOp.rp.

L_-._.;··JIJ<;.:_·._.; ....-..

100 POWER SYSTEM PL4NNING

-/' The meteorological parameters considered are an effective temperature T, a cooling effect

0/

the wind W, an illumination index L, and a rate o/precipitation P. With the assumption that the weather sensitive component of the load C(t)can be expressed as the sum of functions of the respective meteorological factors, y=y B+YW+YD+A) T+A1W+A3L+A.P .where the long-term base load is given by Y B, and Yw and Y D represent correlation for a particular week and day of the week respectively. -/' The base load Y B is only changed when the average load has increased due to long-term factors such as economic growth. -/' The coefficients Y B, Yw, Y D can be estimated from the load data of the previous year. The Coefficients al, a2, a3, a4 indicate the change in demand per unit change of corresponding meteorological variable and may also be determined from previous load and weather data by regression analysis. Now, from past records ofload and weather conditions Y, T, W, L andP are kn~wn ~d YB is assumed constant. -/' . Thus; the regression analysis consists of estimation of the best values for the coefficients al, a2;a3,a4and the values ofY

D: The values

ofYw are considered to be represented by orthogonal

Polynomials which are constant during each week, given 52 polynomials in total. Using ..a maximum of sixth order polynomials was found to give a good fit to a year's data. Spectral Expansion -/' Only past load data is required in the form ofN discrete load values for each day . ../ If M previous days data is used then any load samples may be denoted as X

rnr»

Where M

indicates the day & N the time of the day. ../ The load variation during any day may be regarded as a time series which has a similar form every day due to the similarity of the load pattern. 5. REACTIVE POWER BALANCE

s.i REACTIVE

POWER SHEDULING

Reactive power scheduling is operational planning of reactive power balance for the coming year with analysis on seasonal, weekly, daily and hourly basis and minimization of power losses in a power system, by control of the VAr devices. The optimization studies are made with the following constraints, (ij.Acceptable voltage profiles (ii) Limiis of VAr devices (iii) Keeping reactive power reserve suitably shared in different areas (iv) Planned maintenance outages of generation and transmission equipment (v) Normal operating regimes and emergency and post-emergency states contingencies. ANlLKUMAR K.M., Assistant Professor in E&EE, B.I.E.T, Davangere.

-

.

101 POWER SYSTEM PLANNING

(vi) Reactive power requirements of the load

Reserve allocations to different areas/regions in a network should be done, considering the aspects of, (i) Response time ofV Ar devices

-_.

-- ._-

(ii) Effect of loss of VAr devices on voltage stability of area as well as on consumer load requirement (iii) Flexibility in re-allocation of reserve under planned or forced outages (iv) Locational distribution of reserve throughout the areas/regions

•

(v) impact of reserve on power transfer capability of transinission lines on tie-lines etc, ../ While deciding reactive reserve,. the response time of reactive device is an important consideration . ../ The function of reactive power scheduling

normally catered to higher levels of priority

controlled utilities, is also referred. to as secondary and tertiary control or regulation in the power utility. 5;2 MAINTAINING THE SYSTEM VOLTAGE ./ The management of MW requirements is far more easy than the management of MV Ar requirement in the sense that the MW capacity to be commissioned has to take care of the MW load requirement, the losses and auxiliaries . ./

The solution is not as straightforward in the case of fulfilling MVAr requirements because' a simple balance of MVAr load requirement and overall MVAr losses in the system with MV Ar generation would, by itself not ensure maintaining of declared voltages all through the system .

./ Maintaining declared voltages within permissible tolerance at each busbar in the system calls for b:

'g the MVAr inputs and outputs at each of the buses keeping the voltage as an don..

oltages due to MW flow still requires to be made good by suitable means by

..

on transformers. This, therefore, puts limits on tolerable voltage regulation on l:ran;j"j ',in;,

lines, sub transmission lines and distribution feeders. The system voltage can be led by properly adjusting the reactive power sources at the suitable places.

5 '/

GRID

'j

U

any other industry, the electric supply industry is one in which there has to be an ;,;·t:,::Ci·,':;balance between supply and demand.

v

..;' The

(,c{motbe stored and therefore the grid must stay balanced at all times . ml"')i~l!

distribution of resources calls of effective interconnections between various

t,,, :,now inter-regional

exchanges of power so as to optimize the economics-of -~-~'d

._~.

······.f···'l

~'

102 POWER SYSTEM PLANNING ~

~

../' Power planning is generally done on a regional basisand efforts are made to make them selfsufficient. ../' In India, five such regions have been recognized: Western, Eastern, Southern, Northern and Northeastern. There -is a-hlg difference between one region and another which results

III

differentpeak load. ../' The operation of each regional grid is controlled by the regional electricityboard. Regional electricity boards promote development of regional grids and establish regional I state load dispatch centres for the following benefits with the support computer programs of EMS and SCADA, (i) optimumutilization of hydro-thermaland nuclear stations. .

.

(ii) reduction in installed capacity requirement due to diversity in peak demand of various

constituentsystems. (iii) reductionin spinning reserve requirement. . (iv) installationof large size units with less cost / MW and less operating cost/kWh. (v) better frequencycontrol and stabilitydue to high inertia. (vi) coordinating optimized maintenance schedules for.generating units, transmission lines and other equipment. (vii) reactivepower planning in the region. 5.4 GRID CODE ../' A grid code is a set of standard rules within the power industry to which the utilities, power producersand grid maintaining companies would need to comply. ../' The grid code includes technical provisions covering planning, connections, metering, schedulingand dispatch, and grid working restrictions. ../' The operating companies keep the grid code to have restorationplans based on their restoration objectives, operating philosophies and practices and for familiarity with the characteristics of peculiarities.

-

../' The provisionsregarding load shedding (u.f. or dfJdtrelaying), island facilitiesat various nodes. in the grid, transaction of power (MW and MVAr) within the grid are covered in the code & the grid codes will remain differentin different countries. ../' In the code the details of interconnection between systems of different countries must also be specified. Typical details for-our countries is, India having interconnection with Bhutan & Nepal, type of the voltage is 220kV3 circuit lines & power exchangethroughradial modes. 5.5 TRADING OF POWER

f other buyers and sellers. wheeling is necessary for any non-utility generation(NUG) ahd:~l~~~~)

../' Wheeling is defined as the use of a utility's transmission facilities to transmit power for tlj~:l

f; J;l'~!J

be an importantproblem over the coming years.

« ". ANILKUMAR K.M .. Assist::mtProfessor in F.RrFF H TF T

n",v:moprp

,,"

'rf

J~7j

.,{(~iJi;";~~ft,iiE¥~~>i;¥>:!,~Jit{" f:i~

.

103 POWER SYSTEM PLANNING

./' Short-run marginal cost (SRMC), long-run incremental .cost (LRIC)and embedded cost methods are generally used for calculating the wheeling cost rate. ~

.

./' Currently bulk power is wheeled from the central sector projects to the heneficiary states on the -./'

basis oflong-term contracts, .

./' With the coming up of private power generation companies and small power generation, wheeling of power in the state or regional grid is becoming increasingly important to operate the power system at adequate security levels and in an economically optimal way . ./' Wheeling is the use of the electric power system of one utility to transmit power to another utility or utilities, the power delivered to the recipient being of like quantity (MW, MVAr) and

.

.

characteristics (duration and time of the day, month, year) as that delivered by the wheeling utility . ./' Energy trading in generation is based on economic, environmental, political and geographical factors. Frequency based tariff for power trading ./' At a given time; the frequency is the same all over the system, and can be"measured precisely ••

•

&

with ease anywhere . ./' Grid frequency and its trend are continuous indicators of generation-load balance . ../' A high frequency invariably means generation-surplus situation in which some costly operating stations may have to back down. A low frequency condition invariably means

a generation

deficit in which more costly generation plants such as diesel generator, gas turbine or storage hydro etc., support may be required . ./' Due to the above, the frequency-linked tariff structure would be incremental cost based, which is ideal for power exchange pricing in the grid, depending upon the grid frequency increment. Regional electricity boards are levying this tariff for average frequency of more than 52.2 Hz on six hours block basis at present.

..

./' There is large variations in system frequency in the range of 47.5 to 51.5 Hz in Indian power grids due to grid indiscipline. Rationalized tariff structure based on system frequency and time of the day metering for bulk power transactions and unscheduled interchanges besides free governor operation of generating unit is desirable. Billing of reactive power drawl is necessary and urgent.

6. ONLINE POWER FLOW STUDIES An interconnected power system represents an electric network with a multitude of branches and nodes, where the transmission lines typically constitute the branches. The nodes are referred to as. I

'buse.§.

.

,

,

A.,...

104 POWER SYSTEM PLANNING

../

Even a power utility serving a mixed urban and rural population operates a network that may contain typically hundreds of buses and thousands of branches, not counting the distribution network .

./' At some of the buses, power is being injeetetl-into--thenetwork, whereas at most other buses it is being tapped by the system loads. In between, the power will flow in the network meshes . ./' A given set of loads can be served from a given set of generators in an infinite number of 'pewer flow'. Or 'load-flow' configurations. Power-flow analysis concerns itself not only with the actual physical mechanism that controls the power flow in the network meshes but also

..

with how to select a 'best' or 'optimum' flow configuration from among the various possibilities for system operations. Some of the important aspects of power-flow analysis are, 1. The total amount of real power in the network arising from the generator stations, the location and size of which are fixed. The generation must equal the demand at each moment, and since this power must be divided between the generators in a unique ratio in order to achieve optimum economic operation, the individual generator outputs must be closely maintained at predetermined set points. It is important to remember that the demand undergoes slow but wide changes throughout the 24 hours of the day and therefore, slowly, either continuously or in discrete steps, these set points must be changed as the hours wear on; This means that a load-flow configuration that fits the demand of a certain hour of the day may look quite different the next hour. 2. Transmission links can carry only certain amounts of power and must not be operated too close to their stability or thermal limits. 3. It is necessary to keep the voltage levels of certain buses within close tolerances. This can be achieved by proper scheduling of reactive powers. 4. If the power system is part of larger grid, it must fulfill certain contractual power-scheduling commitments via its "tie-lines" to neighboring systems.

5.. The disturbances following a massive network fault can cause system outages, the effects of which can be minimized by proper prefault power-flow strategies. 6. Power-flow analyses are very important in the planning stages of new networks or additions to existing ones. The overall power-flow problem can be divided into the following sub problems, for the on-the-line analysis, (i) Formulation of a suitable mathematical network model - +he model must describe adequately the relationships between voltages and powers in the interconnected system. (ii) Specification of the power and voltage constraints that must apply to the various buses network.

ANILKUMAR K.M., Assistant Professor in E&EE, B.I.E.T, Davangere.

-

.

105 POWF..RSYSTEM PLANNING

(iii) Numerical computation of the power-flow equations subject to the above constraints. These computations give us, with sufficient accuracy, the values of all bus voltages. (iv) When all bus voltages have thus been determined, then, finally, the actual power flows in all transmission lines can be computed.

Operational power flow programs ./

_-

Power-flow programs are available and used by electric utilities as a planning tool on-line monitoring mechanism, or a simulation of the real system. The size of the programs in terms of number of buses and lines is set at compilation time and varies with the application .

• •

-./' The power-flow programs of utilities are usually more dedicated in purpose and have fewer diagnostics to assist with difficulties. Virtually all operational power-flow programs have features that facilitate data handling in terms of reading base-case information, storing results, and manipulating power system control variables. The capability to delete lines, change a bus type during iterations, check limits, use a different slack bus, and so on. Some typical features of a program are, ..1. Buses are often identified by a combination name-voltage, for example, KARNAT AKA 110, where the 110 refers to the line-to-line voltage. Bus number referring to this name are internal, changeable program labels. 2. Generation, load, shunt capacitors, and shunt resistors are represented separately, so ratings and limits are available individually. The internal program may combine quantities such as

MW

generation and MW load at a bus, but their external identity is maintained. 3. Bus types are tabulated in below table The slack bus identity is retained because its phase angle is a reference (slightly different from a swing bus). 4. Shunt admittances are usually represented as fixed. admittance, inductive or capacitive, switched capacitor in steps with on and off voltage points, switched reactor in steps with on and off voltage points.

,.

5. Branches (lines or elements) (i) The series element of a branch between two buses may be specified in terms of impedance (R +jX) or admittance (G+jB) in per unit on MV A base or bases as specified by the user. (ii) There are no restrictions on the magnitude or sign of branch impedances. Zero, low-value, or negative impedances are acceptable, but at least one non-zero value per branch. _ (iii) Pi elements having unequal legs are acceptable, with both capacitive or inductive shunt elements. (iv) Parallel lines are permitted with identity retained. Mutual coupling is an input quantity. (v} Branches are identified by terminal bus names. Branch numbers are not reqgired. .

t ~r;r

(vi) Provision is made for line current ratings and transformer MV A ratings for overload checking. ' (vii) Provision is made for calculating line currents at terminals on selected lines. ANILKUMAR K.M .• Assistant Professor in E&EE. RIET

Davanoere.

.~f >'_:.,#:,,~t-..-..

106 POWER SYSTEM PLANNING

TYPES OF BUSES FOR POWER FLO'V Specified

Definition

pWrameters (p.u.) . P,Q(orunregulated)

Scheduled real and reactive power injections into the network. Power flow calculations determine the voltage magnitude and phase angle. High .

and low voltage limits are possible. In the event that a voltage limits is reached, the MVAr rating is converted to a fixed reactive element. P, V (or regulated)

-_ -::----

Scheduled real power injections into the network at fixed voltage

magnitude. The voltage is maintained at a constant level by means of an

"

adjustable internal or remote reactive source, such as a synchronous condenser, generator field excitation, static VAr generator, saturable reactor, or other control device. Both (+} and (-) MV Ar limits are entered. In the event that a MVAr limit is reached, the voltage schedule is no longer held, and the reactive source is fixed MVAr. Remote

Scheduled

MW

and variable MV Ar. The MVAr injection is varied to

maintain constant voltage at a remote bus. MVAr limits are enterable, beyond which the bus becomes a P.Q. type, with Q at the limit. The remote bus changes to a fixed reactive element and specified P. Swing (area)

Variable MW and schedule voltage. The MW injection is varied to maintain the real power part of desired area control error. In the event that a MVAr limit is reached, the voltage schedule is no longer held.

Slack

Scheduled voltage magnitude and fixed phase-angle reference for the power flow calculation but has variable MW, MYAr output.

6. Transformers and phase shifters (i) Fixed tap transformer ratios may be entered in terms of rated kV on each terminal. (ii) OLTC (on-load tap control) transformer voltage range and step size are specified by the program user. (iii) OLTC control on MVAr injection at a remote or adjacent bus specified by user. (iv)-Phase shifters have through power or angle set by means of the user's schedule. Phase shifters have 1:1 voltage ratio. Phase-shifter impedance adjustment with step change is automatic phaseshifter angle range and step size are inputs by the user. 7. STATE ESTIMATION -I' Methods have been developed using measurements from the network to calculate the state

~.~.

at

. ...i. ,<:'

the network such as voltage magnitude, phase angle etc., at every bus.

.

4Jl.k

~ These methods are called state estimators because they are essentially weighed leastsqt.l~res.. .

techniques to find the best state vector to fit scattered of data. ANILKUMAR K.M., AssistantProfessor in E&EE, B.I.E.T,Davangere.


,';'.

.

- .,

107 POWERSYSTEM rLANNING

../ The scattered data is due to imperfect measurements of rapidly changingvoltage or currents on the network in addition to errors in the assumedvalues, and variations in the transmission line linear models, line charging, and so on. ../ Imperfect measurements, the first source of errors, is due to signal noise, metering accuracy and analog-to-digitalconversion. ../ The network topology and parameters are assumed as knownuntil they are 'fitted' to the data in parameter estimation. •

../ The power system is assumed to be operating in a steady-state condition with fixed voltages,

currents, and power flow. TIle remote terminal units (RTUs) which sample network analog variables and convert the signals to digital form are periodically examined for the latest values of the signals. ../ For example showing the block diagram of state estimator, the RTUs are sequentially exaI~ined which causes a 'times skew' in the data from unit I compared to unit N dependingon when the unit was scanne~ and the time when the actual analogsignal was sampled. The set of N measurements is called a snapshot of the power system, even though the data may have a time skew at as much as 2 s. ./' The data collected by the RTUs are often redundant. There may be voltage sensing by stepdown transformers on each phase of the transmission line, whereas only one is needed for a balanced operation. ./' In addition, each transmission line voltage to the substation may be monitored on the line side of a circuit breaker, introducing redundancywhen an lines are in service. There may be singlephase watt and VAr meters in addition to current measurements on all phases. The state estimator should incorporateall measurementsto obtain the greatestpossible accuracy. ./' Because the poor system data are redundant, the state estimator may be used with statistical methods to detectbad or grossly incorrect data. ••

Fig showing the block diagram of state estimation of power system.

108 POWERSYSTEM PLANNING

./' Another purpose of a state estimator is to detect changes in network configuration. If one phase of a transmission line becomes abruptly open circuited, the average power flow on the intact phases will be far less than the values given by the last state estimate. Thcnperator is alerted to this condition at the first data sean-As-ef this data, corrective action by the control computer is not automatic but may be implemented in the future through 'remedial action' programme . ./' Another purpose of a state estimator is to complete a set of measurements in order to replace faulty or missing data. It is possible to estimate power flows and voltages at a bus whose measurements are lost due to a communication line failure or RTU failure. Significant problems in this regard are to determine the minimum number of measurements in order to calculate the state, often called observability, and how to improve state estimates by' additional measurements.

8. COMPUTERIZED MANAGEMENT Computerized management of the power systems is required to ensure a secure and economic operation of the system as well as to facilitate the minute by minute tasks carried out by the operational staff. 1. Secure operation - It includes the following main aspects, (i) State estimate, (ii) Security.analysis, (iii) Optimal'power and water flow / fuel consumption. 2. Economic operation - It signifies the following functions, (i) Automatic Generation Control (AGC), (ii) Economic dispatch, (iii) Unit commitment and load forecasting. The main aim is to computerise all the above functions so that the human operator only interacts for any feedback action if required. Considering the nature and size of the problem, a suitable model is required to envelope the functional modules such as, (i) Main computer system at master station, (ii) Remote terminal unit (RTU) system for controlling the power stations and grid-substations (iii) Storage of data (iv) Mode of output. ./' The main computer would handle the computational activities, accept input, store the desired information, process it and send back the requisite instructions to the respective RTUs. It will perform the task of a decision and maintenance support system.

ANll..KUMARK.M., Ass.istantProfessor in E&EE,B.I.E.T,Davangere.

•

109 POWER SYSTEM PLAN]'.'lNG

./' The RTUs will transmit data and receive the processed information. Storage unit will store information, for retrieval as and when required in future. The mode of output could be printer, console or dynamic map board. Computerconfiguration

...

.

./' Consistent with the principles of high reliability and fail-safe features, electric utilities have almost universally applied a redundant set of dual digital computers for remote supervision

..

data acquisition and control, energy management and system security . ./' Both. computers have their own core memory and. drive an extensive number of input-output devices, such as printers, telemetering, magnetictape

drives, disks, and so on. Usually, one

computer, the on-line unit, monitors and controls the power system . ./' The backup computer may execute off line batch programs such as load forecasting or hydro thermal allocation. The on-line computer periodically updates a disk memory shared between the two computers . ./' Upon a fail over or switch in status command, the stored information of the common disk is inserted in the memory of the oncoming computer. Thus, the information used by the oncoming computer has maximum age of the update cycle (typically 30 seconds).

All the

peripheral equipment is interfaced with the computer through input-output microprocessors that have been programmed to communicate as well as preprocess the analog information, check for limits, convert to another system of units, and so on. ./' The microprocessors can transfer data in and out of computer memory without interrupting the central processing unit. Often, the microprocessors are also redundant, in that equipment interfaces may be switched to spare units upon detecting a malfunction . ./' As a result of these precautions, for all critical hardware functions there is often a guaranteed 99.8 percent or more availability. Software also allow for multilevel hardware failures and initialization of application programs if failures occur. Another feature of the computer system

..

is that critical operating functions are maintained during either preventive or corrective maintenance. Besides hardware, new digital code to control the system may be compiled and tested in the backup computer, then switched to online status. ./' The computers are usually employed in a fixed cycle operating mode with priority interrupts wherein the_computer periodically performs a list of operations. The most critical functions have the fastest scan cycle. Typically, the following categori~ are scanned every two seconds, ~ All status points, such as switchgear position (open or closed), substation loads and voltages, transformer tap positions, and capacitor banks, ~ Tie-line flows and interchange schedules, ~ Generator loads, voltage, operating limits, and boiler capacity,

ANILKUMAR K.M., Assistant Professor in E&EE, B.I.E.T, Davangere,

110

»

Telemetry verification to detect failures and errors in the bilateral communication links between the digital computer and the remote equipment.

../ The turbine generators are often commanded to new power levels every four seconds, sharing the load adjustment based on each unit's response capahlliiy-iB-MW Imin . ../ The absolute power output of each unit is typically adjusted every two minutes by the computer executing an economic dispatch program to determine the base power settings. Many

I

other system operations, such as the recording of load, forecasting of load, determination of which generators to start up or stop, are considered non-critical, so the computer executes these

"

programs on an hourly basis .

.'

../ Most low-priority programs (those run less frequently) maybe executed on demand by the operator for study purposes or to initialize the power system . ../ An operator may also alter the digital computer code in the execution if a parameter changes in the system. For example, the MW/min capability of a generating unit may change if one of its throttle valves is temporarily removed for maintenance, so the unit's share of regulating power must accordingly be decreased by the code. The computer software compilers and data handles are designed to be versatile and readily accept operator inputs.

seADA CC.t.IP,Jli"

~<:,.Lr~ c.(jti?.;ttt"!~

OfH~1l ~r9.U;';'1r.~-t..;Al.

R£MQTc nATA.. COUlSIll()N ~A.TtJ$ Of BRIi'Al<ERS,~WI!CHeS. KW f:tOWS. K'IAR RO'm. VO~1$. ,ll,M'ERES.lfW-ISFOP:MS.A

..

TAPS. PHlIBf-SHlfT£R

POSlTlONETC.

Fig showing the block diagram of configurations of computer management

in power system.

9. POWER SYSTEM SIMULATOR ../ The operation of the power system is a complex task requiring the operator to make splitsecond decisions regarding integrity of the system . ../ It is important for those who operate power systems. to be aware of the potential weak points the system and to provide counter-measures for overcoming the weak points. For this necessary to develop the computer programs to simulate power system behaviour.

AND..KUMARK.M., AssistantProfessorin E&EE, B.I.E.T, Davangere.

111

r------~~~----------------~~~ POWER SYSTEM PLANNING

../' Due to increasing intcrcoruiecticus ~h:,:; power systems are becoming complex. Tl.erc ~.~growing

.-

need for higher operational skills. Trained operators are required urgently to improve system efficiency, reduce down-time and maintenance costs . ../' The .t>.<>wer system- ne~~rk

simul~tor allows the operator to .study b~th ~y

state and

.dynamic behaviour through interactive graphics, menu driven formats and command line inputs . ../' The simulator has a flexible man-machine interface and can easily be configured to any power f'

•

system. The Central Power Research Institute has facilities for development of software for simulators for power systems network .

../' A training simulator is a device which creates the effects of an actual power system including power plant by using a mathematical model. The mathematical model updates the database in the computer (pC based) which is used to drive all indicators, recorders, annunciators etc. on the control panel. ../' Training simulator comprises a processor, control panel and an instructor's console. It solves the mathematical model representing power interactively to continuously predict the behaviour, after taking into account the operator's action from the panel. ../' A math model comprises of differential equations, algebraic equations and Boolean equations . ../' The panel displays- the system parameters dynamically to give feedback to the operator about the system's operating conditions. The operator also uses a panel to start up, shunt down and control the simulated plant and to change the operating condition . ../' The operator can check whether bus voltages are in order, line flows are well within thermal limits, ../' and the generator reactive power limits are not exceeded. The instructor's console is used to create real life disturbances, which the operator is supposed to handle and take remedial action. A schematic arrangement is shown below .

..

../' The mimics prove complete perspective giving the details of various equipments (generator, breakers, lines, transformers, shunt reactors, capacitors, loads etc.) and their interconnections. Interaction with the instructor is minimum. All lining up procedures along with the necessary interlocks and design specifications are available to the trainee through help files . ../' For each operation, explanation of right and wrong operations is provided, help files with essential operational parameters (such as trip setting) are provided . ../' In the operation mode, all the interlocks are logic associated with various equipments incorporated in it. In this mode, the 'help' facility is inhibited and a trainee performan~e1 evaluation package is invoked."

_, ..~;/'~:.'.:;t.' .

-

;(,~~:t~·I

.,/ The operator training simulator is built on a PC with associated peripherals & sofm;'~~{~:u~ making the overall cost very minimal and affordable by the utilities. •• ~

.~

.......

..,. T7 "..

A

~~:~.~~+ "P..,.,fp
F&F.E. B.I.E.T. Davangere.

r'

t:

I( :~;J:l

tJ

.112 POWER SYSTEM PLAlVNTNG

../' Simulators are extensively customerized to a given plant or power system of the power utility for specific operating conditions, down to actual response time. Since the software is user friendly, 'Theoperator can learn many things independently without the help of a supervisor . ../' National Power Training Institute (NPTI), Faridabad, uses such facilities for training engineers., operators and technicians for operation and maintenance in all aspects of power sector-thermal, hydro, power network etc. ../' NPTI has 210MWand 500MWthermal plant simulators at Badarpur in the country. Simulators 4..

are used for similar training in nuclear plants by Nuclear Power Corporation, by CPR! for

•

power system integrated operation. The thermal power station training is compulsory AS PER .,!,HE Indian Electricity Act 'for deployment at the thermal power station of capacity- 100MW & above.

........

- ..

~-.... ---- -----

..

,.---------_ lIA1H·t.IQOEl

It-,--.....;...-.!

($QI'1WAAE)

I

I

.. -----

........

-.,.~

....

- ...

Fig showing the schematic of simulator. 10. SYSTEM FREQUENCY ../' It is technically impossible to store electrical energy in the form of alternate current. ../ This means that there must be continuous balance between the input of mechanical energy in an ac system. If consumption is greater than production, the grid frequency drops. Ifproduction is greater than consumption, the grid frequency rises. In this respect, the power system can be compared to a set of scales, with production in one scale and consumption in the other .

..

../ The speed at which the pointer swings back and forth represents the grid frequency. The transmission grid can be compared to a balance beam . ../ The number of weights in the scale for consumption is determined by a continuously decentralized decision-making process. When an individual consumer turns on a light in the morning, a small weight is placed in the scale. When another consumer turns off a light, a small weight is removed from the scale. Each power utility in the regional power system grid has a production scale and a consumption scale. ."

../' The power utilities in the grid have joint responsibility for putting the weights on the scale and. taking them off so as to obtain a continuous balance between generation and consumption.

.

If'

~~.~..... .t

the balance beams were not interconnected, each subsystem would have to continuously Ill<:iV~! .. . ,;!.

the Weight son and off the scale in order to maintain the pointer at the midpoint. ANll-KUMAR K.M., AssistantProfessor inE&EE, B.I.E.T, Davangere.

'(, ~ ~ r: .

~

113 POWER SYSTEM PLANNING

./ The investment in tie-lines for joint operation is one of the more profitable investments in the power industry. One prerequisite is the difference in structure of the generation systems in the different utiiities, which varies from thermal power system to the mix of hydro and thermal and the hydro system. ./ Grid frequency is normally maintained within a narrow band around 50 Hz. Frequency deviations can be regarded as a measure of the quality of the electrical energy delivered. In normal operation, frequency is maintained within at O.lHz, with standard deviations of about 0.3Hz. This degree of accuracy appears to be quite sufficient for most consumers.

, ¥'

In connection with faults in the transmission grid that result in disconnection of parts of the grid with generation surpluses, grid frequency can drop below 49.9 Hz. In this case, there is a risk thatthe nuclear and thermal power plants must be disconnected in order to avoid damaging vibrations in the steam turbines. Hydro power plants are more robust and normally tolerate a drop in grid frequency to 45 Hz without sustaining damage. Frequency variations

.../ A frequency range between 49.8 and 50.2 Hz is considered safe for generation, transmission, distribution and consumer end equipment, all of which are increasingly using frequencysensitive electronics. ./_. Frequency is influenced by the balance in real power. At present, there

IS

no regulation

.' regarding this in the regional power grids. ./ The generation meant for spinning reserve and regulation reserve is used to meet more load. Also, more load is met at the cost of frequency. Frequency effects Constant r.

j

.' ,

..

1. Most a: 'n

frequency is the primary mark of a normal operating system and the system

,"':31

d A be allowed to deviate outside the strict tolerance values for the following

*.r.: CO"'.

2. Genera: .

at speeds that are related to frequency . . especially steam driven ones, are designed to operate at a very precise speed.

3. The 11,;b: ,:~ s arc ; enerally set for tripping at 51.6 Hz and 47.5 Hz. Turbo rotor, with its many huge t';':::r:c ['::ldes, constitutes a mechanical system of many natural frequencies. These frequencies are quite undamped and are each subject to resonance at various rotor speeds. Hydro h~;hij)c~are not subject to this danger. 4. A !ar~':'

L:>m;hcr

acc\1:';.'Z:Y

5.

of electrically operated clocks are driven by synchronous motors and the

t;;\: dock is a function not only of the frequency error but also of the integral of

is

s.. l;J: ;'ormally related to the real power balance in the overall network. Undb"'the

HOln,ol ""e:·fi(Jjey the power generated is of all loads plus real transmission losses. _\',{ft

){! i!\I:\R

K.M., AssistantProfessorinE&EE, B.I.E.T,Davangere,

114 P(JWl!."JC

J:'LIlIVJVllYl7

docs not exist then the difference would enter into or exit from kinetic

6. in .. '.Sf:

(f

srsrus«

of momentary surplus of generator power over the load, the total speed

.crease, TIle rate of increase in speed would depend upon the- .amount of . . '. . r the running equipmem:-A& load being supplied by the network speeds up, r-:

,...

) ;Ti:~d l)i!?,lH~T load

torques and thus require to puil more power

311i'pinsof megawatts tends to increase of frequency of a system. A ,.: wido variable so the change will be left unifoimly throughout the

•

r

,

:~,t

;~

•

••

. J'rI" Assistant Professor in E&EE, B.I.E.T,Davangere.

115 POWER SYSTEM PLANNING

QUESTIONS BANK

o

1) 2) 3) 4) 5)

Explain system adequacy and security of power system reliability. Explain reliability evaluation and calcuiationso. _o_ Explain basic methods to evaluate generation reliability. Explain quality of supply for power system planning. Explain the types of power disturbances and specify the equipments that are used to reduce the problems encountertm. 6) Explain theterms (i) Flexible systems (ii) System adequacy, and (iii) System security. 7) Describe the two methods of reliability assessment. 8) Write a descriptive note on CEA's reliability planning criteria, 9) Describe different types of disturbances and the devices used to suppress the disturbance. 1-0) Explain the various methods of load management. 11) What do you mean by state ..estimation? Explain with the block diagram the function of 0

0

0

_~-

--

•
,

0

II ,

state estimation. 12) Explain with the block diagram the functions of power system simulator. 13) Explain the reliability planning in power system.

"

Questions are collected from previous year Q.P, & Model Q.P.

,.

._

OJ:

"

ANILKUMAR KM.•Assistant ProfessorinE&EE, B.I.E.T, Davanzere.

l

lOEE761

Power System Planning

POWER SYSTEM PLANNING

Subject Code: 10EE761 No. of Lecture Hrs. / Week: 04 Total No. of Lecture Hrs. 52

r, I

25

IA Marks: 25 Exam Hours: 03

Exam Marks: 100 PART -A

f

UNIT -1

Introduction of power planning, National and regional planning, structure 0 ~ower I . tools, electricity regulation, Load furecasting, forecasting techniques, system, p annmg . 8 Hours modeling.

UNIT -2 & 3 Generation planning, Integrated power generation, co-generation / captive power, po:ver pooling and power trading, transmission & distnbution planning, power system econonucs, power sector finance,financial planning, private participation, rural electrification investment, concept of rational tariffs. 10 Hours

UNIT -4 Computer aided planning: Wheeling, environmental effects, technological impacts, insulation co-ordination, reactive compensation.

green

house effect, 8 Hours

PART -B

UNIT -5 & 6 Power supply reliability, reliability planning, system management, load prediction, reactive power balance, online operation planning, load power flow studies, state estimation, computerized management. Power system simulator. Hours lO

UNIT -7 & 8 Optimal Power system expansion planning, formulation of least cost optimization problem incorporating the capital, operating and maintenance cost of candidate plants of different types (thermal hydro nuclear non conventional etc), Optimization techniques for solution by programming. 16 Hours

TEXT BOOK: 1. Electrical Power System Planning, A.S.Pabla, MaCmillan India Ltd, 1998

J

Dept. ofEEE, SJBIT Page I

Power System Planning

10EE761

• The codes and standards that guide the integration of solar PV are focused on simplifying installations and prescnbe grid interconnection requirements that cause minimal interaction with the grid. When solar PV becomes a significant overall source of generation in the power system, some of the present interconnection requirements likely will be counterproductive.

National and Regional Planning: 1. All issues relating to planning and 2.

3.

.1

5.

fi.

development of Transmission System in the country are dealt in the Power System Wing of CEA. This includes evolving long term and short term transmission plans. The network expansion plans are optimized base on network simulation studies and techno economic analysis. This also involves formulation of specific schemes, evolving a phased implementation plan in consultation with the Central and State transmission utilities and assistance in the process of investment approval for the Central sector schemes, issues pertaining to development of National. Power Grid in the country and issues relating to trans-country power transfer. Transmission planning studies are being conducted to identify evacuation system from generation projects and to strengthen the transmission system in various regions. The studies for long-term perspective plans' are also being carried out on All India basis for establishing inter regional connectivity aimed towards formation of the National Power System. . The National Power System is being evolved to facilitate free flow of power across regional boundaries, to meet the short fall of deficit regions. from a surplus region as well as for evacuation of power from project(s) located in QI\e region to the beneficiaries located in other region(s).

'::>'niciure of Power System: Generating statkm 11 ltV

_Stspdown~ 22QkV/33kV

::::-

.. I

" Dept. ofEEE,

SJBIT

Page 5

Power System Planning

IOEE761

l. An essential component of power systems is the three-phase ac generator known as synchronous generator or alternator. 2. The source of the mechanical power, commonly known as the prime mover, may be hydraulic turbines, steam turbines whose energy comes from the burning ••of coal, gas and nuclear fuel, gas turbines, or occasionally internal combustion engines burning oil 3. The transformer transfers power with very high efficiency from one level of voltage to another level The power transferred to the secondary is almost the same as the primary, except for losses in the transfurmer. 4. An overhead transmission network transfers electric power from generating units to the distnbution system which ultimatelv supplies the load. 5. High voltage transmission lines are terminated in substations, which are called .: highvoltage substations, receiving substations, or primary substations. /; . The distribution system connects the distribution substations to the consumers' servicentrance equipment. The primary distnbution lines from 4 to 34.5 kV and supply the load in a well-defined geographical area. Industrial loads are composite loads, and induction motors form a high proportion of these loads. These composite loads are functions of voltage and frequency and fonn a . major part of the system load . . Planning

Tools:

I. Planning engineer's pnmary requirement is to give power supply to consumers m a reliable manner at a minimum cost with due flexibility for future expansion. 2. The criteria and constraints in planning an energy system are reliability, environmental economics, electricity pricing, financial constraints, society impacts. 3. reliability, environmental, economic and financial constraints can be quantified. Social

effects are evaluated qualitatively. 4. The system must be optimal over a period of time from day of operation to the lifetime. S. Various computer programs are availabIe and are used for fast screening of alternative plans with respect to technical, environmental and economic constraints. The available tools for power system planning can be split into:

•

Simulation tools: these simulate the behavior of the system under certain conditions and calculate relevant indices. Examples are load flow models, short circuit models, stability models, etc.

•

Optimization tools: these minimize or maximize an objective function by choosing adequate values fur decision variables. Examples are optimum power, least cost expansion planning, generation expansion planning, etc.

•

Scenario tools: this is a method of viewing the future in a quantitative fashion. All possible outcomes are investigated. The sort of decision or assumptions which might be made by a utility developing such a scenario might be: should we computerize automate the management of power system after certain date.

Dept. ofEEE, SJBIT

Page 6

Power System Planning

10EE761

Least Cost Utility Planning: There are two fimdarnental problems inherent in traditional planning. The first is that demand forecasting and investment planning are treated as sequential steps in planning, rather than as interdependent aspects of the planning process. The second problem is that planning efforts are inadequately directed at the main constraints facing the sector, namely the serious shortage of resources. 1. Demand forecasts are little more than extrapolations of past trends of consumption, no attempt is made to understand neither the extent of unrnet demand nor the extent to which the prices influence the demand growth, Greater attention should be paid to end use efficiency, plant rehabilitation, loss reduction program, etc. 2. Least cost planning (LCUP) is least cost utility planning strategy to provide reliable electrical services at lowest overall cost with a mix of supply side and demand side . options. 3. The LCUP uses various options like end use efficiency, load management, transmission and distnbution options, alternative tariff options, etc. 4. This planning process can yield enon11OUSbenefits to consumers and society because it affords acquisition of resources' that meet consumer energy service needs that are low in cost, environmentally friendly. S. LCUP as a planning and regulatory process can greatly reduce the uncertainty and risks faced by utilities. The logic for least cist planning is shown in the figure below:

Options (plans) Regulations

Least Cost Planning Process

_

..

-

~>

Attributes:

-

6. For an investment to be least cost, the lifetime costs are considered. These include capital costs, interest on capital, fuel cost and operation and maintenance costs.

Dept. ofEEE, SJBIT

Page 7

IOEE761

Power System Planning

.. simulation

social and environmental factors

resource mixes

1----+ analysis

monitor

Fig: flowchart for least cost planning Electricity Regulation: THE ELECTRICITY REGULATORY •

•

COMMISSIONS ACT, 1956

Act to provide for the establishment of a Central Electricity Regulatory Commission and state Electricity Regulatory Commissions, rationalization of electricity tariff; transparent policies regarding subsidies, prormtion of efficient and environmentally benign policies and matters connected therewith or incidental there to. Be it enacted by Parliament in the Forty-ninth Year of the republic of India as follows:

STATEMENT OF OBJECTS AND REASONS •

•

India's power sector is beset by problems that impede its capacity to respond to the rapidly growing demand for energy brought about by economic hberalisation. Despite the stated desire for reform and the initial measures that have been implemented, senous problems persist. As the problems of the Power Sector deepen, reform becomes increasingly difficult underscoring the need to act decisively and without delay. It is essential that the Government exit implement significant reforms by focussing on the fimdamental issues

Dept. ofEEE, SJBIT

Page 8

Power System Planning

lOEE761

facing the power sector, namely the lack of rational retail taritfs, the high level of crosssubsidies, poor planningand operation, inadequate capacity, the neglect of the consumer, the limited involvement of private sector skills and resources and the absence of an independent regulatory authority. •

Considering the pararoount importance of restructure power sector, Government of India organised two Conferences of Chie Ministers to discuss the whole gamut of issues in the power sector and the outcome of these meetings was the adoption of the Common Minimum National Action Plan for Power (CMNPP).

•

The CMNPP recognised that the gap between demand and supply of power is widening . and acknowledged that the financial position of State Electricity Boards is fast deteriorating and' the future development in the power sector cannot be sustained without viable State Electricity Boards and improvement of their operational performance.

i.

II

The CMNPP identified creation of regulatory Commission as a step in this direction and specifically provided for establishment of the Central Electricity Regulatory Commission (CERC) and State Electricity Regulatory commissions (SERCs). After the finalisation of the, national agenda contained in CMNPP, the Ministry of Power assigned the task of studying the restructuring needs of the regulatory system to Administrative Staff College of India "(ASCI), Hyderabad. The ASCI report strongly recommended the creation of independent Electricity Regulatory Corrmissions both at the Centre and the States.

•

To grve effect to the aforesaid proposals, the Electricity Regulatory Commissions Bill. 1997 was introduced in the Lok Sabha on 14th August, 1997, However it could not be passed due to the dissolution of the Eleventh Lok Sabha.

•

This has resulted in delay in establishing the Regulatory Commissions leading to confusion and misgivings in various sections about the commitment of the Government to the reforms and restructuring of the power sector. Needless to say, this has also slowed down the flow of public and private investment in power sector.

•

..

Since it was considered necessary to ensure the speedy establishment of the Regulatory Commissions and as Parliament was not in session, the President promulgated the Electricity Regulatory Commissions Ordinance, 1998 on 25th day of April, 1998 .

• The salient features of the -said Ordinance are as follows: (a) It provides for the establishment of a Central Electricity Regulatory Commission at the Central level and State Electricity Commissions at the State levels-, (b) The main functions of CERC are: -

Dept. ofEEE, SJBIT

Page 9

Power System Planning

1OEE761

(i) To regulate the tariff of generating comparues owned or controlled by the Central Government; (ii) To regulate inter-State transmission including tariff of the transmission utilities; (iii) To regulate inter-State sale of power; (iv) To aid and advise the Central Government in the fomrulation of tariff policy. (c) The main fimctions of the SERC, to start with, shall be: (i) To determine the tariff for electricity, wholesale, bulk, grid and retail; (ii) To determine the tariff payable for use of the transmission facilities; (iii) To regulate power purchase the procurement process of the transmission utilities; and (iv) Subsequently, as and when each State Government notifies, other regulatory fimctions could also be assigned to SERCS. .lso aims at improving the financial health of the State Electricity Boards (SEBS) which are loosing heavily on account of irrational tariffs and lack of budgetary support from the State Goverrunents as a result of which, the SEBs have become incapable of even proper maintenance, leave alone purposive investment. Further, the lack of creditworthiness of SEBs has been a deterrent in attracting investment both from the public and private sectors. Hence, it is made mandatory for State Commissions to fix tariff in a manner that none of the consumers or class of consumers shall be charged less than fifty per cent. of the average cost of supply, it enables the State Govemments to exercise the option of providing subsidies to weaker sections on condition that the state Goverrunents through a subsidy compensate the SEBS.

(I;

•

As regards the agriculture sector, it provides that if the State Commission considers it necessary it may allow the consumers in the agricultural sector to be charged less than fifty per cent, fora maximum period of three years from the date of commencement of the Ordinance.

•

It also empowers the State Goverrunent to reduce the tariff further but in that case it shall compensate the SEBs or its successor utility, the different between the tariff fixed by the State Commission and the tariff proposed by the State Goverrunent by providing budgetary allocations.Therefore, it enables the State Goverrunents to fix any tariff for agriculture and other sectors provided it gives subsidy to State Electricity Boards to meet the loss.

Forecasting Techniques: Load forecasting is vitally important for the electric industry in the deregulated economy. It has many applications including energy purchasing and generation, load switching, contract evaluation, and infrastructure development. A large variety of mathematical methods have been developed for load forecasting. In this chapter we discuss various approaches to load forecasting.

Dept. ofEEE, SJBIT

Page 10

..

Power System Planning

... ,.

I OEE76 I

Forecasting Methods • Over the last few decades a mnnber of forecasting methods have been developed. Two of the thods, so-called end-use and econometric approach are broadly used fur medjum- and long-term forecasting. Avariety of methods, which include the so-called similar day approach, various regression models, time series, neural networks, expert systems.fuzzy logic, and statistical learning algorithms, are used for short-term forecasting. • The development, improve:rrents, and investigation of the appropriate mathematical tools will lead to the development of more accurate load forecasting techniques. Statistical approaches usually require a mathematical model that represents load as fimction of different factors such as time, weather, and customer class. • The two important categories of such mathematical models are: additive models and muhiplicative models. They differ in whether the forecast load is the sum (additive) of a number of components or the product (multiplicative) of a munber of factors. For example, Chen et al. [4] presented an additive model that takes the form of predicting load as the fimction offour components: L = Ln + L w + Ls + Lr, where L is the total load, Ln represents the ''nonna!'' part of the load,which is a set of standardized load shapes for each "type" of day that has been identified as occurring throughout th~ year, L w represents the weather sensitive part of the load, Ls is a special event component that create a substantial deviation from the usual load pattern, and Lr is a completely random term, the noise. • A multiplicative model may be of the form L = Ln . Fw . Fs . Fr, where Ln is the normal (base) load and the correction factors Fw, Fs, and Fr are positive numbers that can increase or decrease the overall load. These corrections are based .on current weather (Fw), special events (Fs), and random fluctuation (Fr). Factors such as electricity pricing (Fp) and load growth (Fg) can also be included. Rahman [29] presented a' mlebased forecast using a multiplicative model. Weather variables and the base load associated with the weather measures were included in the model. Forecasting Modeling Depends on 1. Degree of Accuracy Required 2. 2 Cost of Producing Forecasts 3. 3 Forecast Horizon 4. 4 Degree of Complexity Required 5. 5 Available Data Classification of Estimation Methods 1. Time Series Methods 2. Causal Methods 3. Judgemental Methods Time Series Methods: Use historical data as a basis, Underlying patterns are fairly stable. 1. Autoregressive Moving Average (ARMA) Dept. ofEEE, SJBIT

Page II

Power System Planning

1OEE761

2. Exponential Smoothing 3. Extrapolation 4. Linear Prediction 5. Trend Estimation 6. Growth Curve 7. Box-Jenkins Approach Causal Methods Belief that some other time senes can be useful. Assumption that it is possible to identify the underlying factors

1. Regression Analysis 2. Linear Regression . 3. Non-Linear Regression 4. Econometrics

Dept. ofEEE, SJBIT

Page 12

Power System Planning

10EE761 UNIT 2&3

Generation Planning The electric utility planning process begins with the electricity load-demand forecast. The demand fur electricity initiates actions by utilities to add generation, transmission, or distribution capacity. Because of the long lead time required to construct new facilities, decisions are often to be made 2 to 10 years in advance. A load forecast was developed for the Kingdom and the results are presented in the following sections covering the study period 2008 to 2023. Load forecasts are developed for all SEC operating areas. TI1emethodology and the basis of development of demand forecast are highlighted below: • Multiple regression analysis is used to forecast the Energy for the KSA. • Independent variables are chosen .to be the population and the Gross Domestic Product (GDP) . • The dependent variable is the Energy forecast for KSA. •. The data for the historical and the forecasted GDP has been obtained from the Ministry of Planning. The forecast for the total sold energy for the Kingdom was obtained using the regression model. The total sold energy was then divided between the four operating areas using historical value of percentage energy sales for each operating areas. This gives the. total sold energy forecast for each of the operating areas. Peak Demand is calculated using the. equation Forecasted Peak Demand in Region= Forecasted Energy in RegioDl8760*Load Factor. Co-Generation!

Captive Power

Captive power plants are associated with specific industrial complexes, and their output is almost entirely consumed by that industrial plant. Another term that may sometimes be synonymous is 'cogeneration' in which the power plant produces multiple forms of energy (e.g., electric power and steam), and where both are raw-materials for a related industrial process. Probably the most classic example is that of a paper mill. Boilers produce steam The steam passes through a turbine that spins a generator to produce electricity. Exhaust steam from the turbine is then used as a source of heat to dry freshly-made paper befure is is finally condensed into water and returned to the boiler. The boiler itself burns the bark that itself cannot be used to make paper and would otherwise be a waste material. In addition, the process of making pulp produces a chemical waste called ''black liquor' that can also be burned as a fuel in a boiler. Captive power plants don't necessarily have to be islands that are disconnected from 'the grid'. In fact, it is often the case that the demand of the industrial process exceeds the capacity of the captive plant, and power must be taken from the grid to make up the difference. Also, there must be some provision to 'bootstrap' the integrated process into operation - often this means relying Dept. ofEEE, SJBIT

Page 13

lOEE761

Power System Planning

on grid power to start-up the plant following an outage. And it is possible that there are times when the captive plant will produce more power than can be consumed in the industrial process, and rather than throttle back the excess is sold to the grid. TYPES OF COGENERATION SYSTEMS 1. Steam Turbine Cogeneration System Steam turbines are one of the most versatile and oldest prime mover technologies still in general production Power generation using steam turbines has been in use for about 100 years, when they replaced reciprocating steam engines due to their higher efficiencies and lower costs. The capacity of steam turbines can range from 50 kW to several hundred MWs for large utility power plants. Steam turbines are widely used for combined heat and power (CHP) applications. 2. Back Pressure Steam Turbine A back pressure steam turbine is the simplest configuration. Steam exits the turbine at a pressure higher or at least equal to the atmospheric pressure, which depends on the needs of the thermal load. This is why the term back- pressure is used. It is also possible to extract steam from intermediate stages of the steam turbine, at a pressure and temperature appropriate for the thermal load. After the exit from the turbine, the steam is fed to the load, where it releases heat and is condensed.

Fig. Back Pressure Steam Turbine 3. Extraction Condensing Steam Turbine In such a system, steam for the thermal load is obtained by extraction from one or more intermediate stages at the appropriate pressure and temperature. The remaining steam is exhausted to the pressure of the condenser, which can be as low as 0.05 bar with a corresponding condensing temperature of about 33°C. It is rather improbable that such low temperature heat finds useful applications. Consequently, it is rejected to the environment. In comparison to the back - pressure system, the condensing type turbine has a higher capital cost and, in general, a lower total efficiency. However, to a certain extent, it can control the electrical power independent of the thermal load by proper regulation of the steam flow rate through the turbine. 4. Gas Turbine Cogeneration System

Dept. ofEEE, SJBIT

Page 14

".

Power System Planning

...

10EE761

Gas turbine systems operate on the thermodynamic cycle known as the Brayton cycle. In a Brayton cycle, atmospheric air is compressed, heated, and then expanded, with the excess of power produced by the turbine or expander over that consumed by the compressor used for power generation. Gas turbine cogeneration systems can produce all or a part of the energy requirement of the site, and the energy released at high temperature in the exhaust stack can be recovered fur various heating and cooling applications (see Fig 4 below). Though natural gas is most commonly used, other fuels such as light fuel oil or diesel can also be employed. The typical range of gas turbines varies from a fraction of a MW to around 100 MW .

Figure 4. Open Cycle Gas Turblne Cogeneration Air

5. Closed-cycle gas turbine cogeneration: systems In the closed-cycle system, the working fluid (usually helium or air) circulates in a closed circuit. It is heated in a heat exchanger before entering the turbine, and it is cooled down after the exit of the turbine releasing useful heat. Thus, the working fluid remains clean and it does not cause corrosion or erosion. As shown in Fig.5 below.

Dept. ofEEE, SJBIT

Page 15

10EE761

Power System Planning

...

FiuUre 5: Closed Cycle Gas Turbine Co~eneration system

6. Reciprocating Engine Cogeneration System Reciprocating engines are well suited to a variety of distnbuted generation applications, industrial, commercial, and institutional facilities for power generation and CHP. Reciprocating engines start quickly, follow load well, have good part-load efficiencies, and generally have high reliabilities. In many cases, multiple reciprocating engine units further increase overall plant capacity and availability. Reciprocating engines have higher electrical efficiencies than gas turbines of comparable size, and thus lower fuel-related operating costs.

Le,Eng

Power Pooling: Power pooling is used to balance electrical load over a larger network (electrical grid) than a single utility. It is a mechanism for interchange of power between two and more utilities which Dept. ofEEE, SJBIT

Page 16

Power System Planning

provide

or

interchange between

lOEE761

generate electricity agreement

which

For

exchange

is signed

by

of

power

them,

but

between signing up

two an

utilities interchange

each pair of utilities within a system can be a difficult task where several

are interconnected.

Thus, it is more advantageous

that all join. That agreement

provides

established

there

is an

agreement large utilities

to form a power pool with a single agreement

terms and conditions for pool members and is

generally rmre complex than a bilateral agreement. In one model, the power pool, fonned by the utilities, has a control dispatch office from where the pool is administered. All the tasks regarding interchange of power and the settlement of disputes are assigned to the pool administrator. The formation of power pools provide the following potential advantages: 1. decrease in operating costs 2. saving in reverse capacity requirements

3. help from pool in unit commitment 4. minimization of costs of maintenance scheduling 5. more reliable operation The formation of a power pool is associated with a number of problems and constraints. These include:

1. pool agreement may be very complex 2. costs associated with establishing central dispatch office and the needed cornmmication and computational facilities

3. the opposition of pool members to grve up their rights to engage in independent transactions outside the pooL

4. the complexity towards dealing with regulatory authorities, if pool operates in more than one state. 5. the effort by each member of the pool to maximize its savings. Power pooling is very important for extending energy control over a large area served by multip le utilities Power Trading

In economic terms, electricity (both power and energy) is a commodity capable of being bought, sold and traded. An electricity

market is a system fur effecting purchases, through bids to buy;

sales, through offers to sell; and short-term trades, generally in the form of financial or obligation swaps. Bids and offers use supply and demand principles to set the price. Long-term trades are contracts

similar to power

purchase

agreements and

generally considered

private

bi-lateral

transactions between counterparties. Wholesale transactions (bids and offers) in electricity are typically cleared and settled by the market operator or a special-purpose independent entity charged exclusively with that fimction. Market operators do not clear trades but often require knowledge of the trade in order to maintain

Dept. ofEEE, SJBIT

Page 17

10EE761

Power System Planning

generation and load balance. The corrnnodities within an electric market generally consist of two types: power and energy. Power is the metered net electrical transfer rate at any given moment and is measured in megawatts (MW). Energy is electricity that flows through a metered point for a given period and is measured in megawatt hours (MWh). Markets for energy-related corrnnodities trade net generation output for a number of intervals usually in increments of 5, 15 and 60 minutes. Markets for power-related commodities required and managed by (and paid for by) market operators to ensure reliability, are considered ancillary services and include such names as spinning reserve, non-spinning reserve, operating reserves, responsive reserve, regulation up, regulation down, and installed capacity. In addition, for most major operators, electricity derivatives such as

there are markets for transmission congestion and ..

electricity futures arid options,

which are

actively traded.

These

markets developed as a result of the restructuring of electric power systems around the world. This process has often gone on in parallel with the restructuring of natural gas markets.

Transmission and Distribution Planning: Electricity distnbution is the final stage

m the delivery of electricity to

end" users .. A

distnbution system's network carries electricity from the transmission system and delivers it to consumers. Typically, the network would include medium-voltage (2kV to 34.SkV) power lines, substations and pole-mounted transformers, low-voltage (less than 1 kV) distnbution wiring such as a Service Drop and sometimes meters. •

The modem distribution system begins as the primary circuit leaves the sub-station and ends as the secondary service enters the customer's meter socket by way of a service drop. Distnbution circuits serve many customers.

•

The voltage used is appropriate for the shorter distance and varies from 2,300 to about 35,000 volts depending on utility standard practice, distance, and load to be served. Distribution circuits are fed from a transformer located in an electrical substation, where the voltage is reduced from the high values used for power transmission.

•

Conductors for distnbution may be carried on overhead pole lines, or in densely populated areas, buried underground

•

. Urban and suburban distnbution is done with three-phase systems to serve both residential, corrmercial, and industrial loads. Distnbution in rural areas may be only single-phase if it is not economical to install three-phase power for relatively few and small customers.

Dept. ofEEE, SJBIT

Page 18

Power System Planning

lOEE761

•

Only large consumers are fed directly from distnbution voltages; most utility customers are connected to a transfurmer, which reduces the distnbution voltage to the relatively low voltage used by lighting and interior wiring systems.

•

The transformer may be pole-mounted or set on the ground in a protective enclosure. In rural areas a pole-mount transformer may serve only one customer, but in more buih-up areas multipIe customers may be connected.

•

In very dense city areas, a secondary network may be formed with many transformers feeding into a common bus at the utilization voltage. Each customer has a service drop connection and a meter fur billing.

,. •

A ground connection to local earth is normally provided for the customer's system as well as for the equipment owned by the utility. The purpose of connecting the customer's system to ground is to limit the voltage that may develop if high voltage conductors full down onto lower-voltage conductors which are usually mounted lower to the ground, or if a failure occurs within a distnbution transformer .

.;,

If all conductive objects are bonded to the same earth grounding system, the risk of electric shock is minimized. However, multiple connections between the utility ground and customer ground can lead to stray voltage problems; customer piping, swirrnning pools or other equipment may develop objectionable voltages. These problems may be difficult to resolve since they often originate from places other than the customer's prenuses.

Distribution network configurations ...................•............•.•.••..................•...............••.•....

•

Distnbution networks are typically of two types, radial or interconnected.

•

A radial network leaves the station and passes through the network area with no normal connection to any other supply. This is typical of long rural lines with isolated load areas. An interconnected network is generally found in more urban areas and will have multiple connections to other points of supply.

•

These points of connection are normally open but allow various configurations by the operating utility by closing and opening switches. Operation of these switches may be by remote control from a control center or by a lineman, The benefit of the interconnected

'I

model is that in the event of a fault or required maintenance a small area of network can be isolated and the remainder kept on supply. •

Within these networks there may be a mix of overhead line construction utilizing traditional utility poles and wires and, increasingly, underground construction with cables

Dept. ofEEE, SJBIT

Page 19

Power System Planning

10EE761

and indoor or cabinet substations. However, underground distribution is significantly more expensive than overhead construction •

In part to reduce this cost, underground power lines are sometimes co-located with other utility lines in what are called corrnnon utility ducts. Distribution feeders emanating from a substation are generally controlled by a circuit breaker which will open when a fault is detected. Automatic circuit reclosers may be installed to further segregate the feeder thus

....

minimizing the impact of faults. •

Long feeders experience voltage drop requiring capacitors or vohage regulators to be

..

installed.

Cl.sractcrisrics

of the supply given to customers are generally mandated by contract between the

supplier and customer. Variables of the supply include: •

AC or DC - Virtually all public electricity supplies are AC today. Users of large amounts of DC power such as some electric railways, telephone exchanges and industrial processes such _,,,aluminium smelting usually either operate their own or have adjacent dedicated generating equipment, or use rectifiers to derive DC from the public AC supply. Nominal voltage, and tolerance (for example, +/- 5 per cent) Frequency, commonly 50 or 60 Hz, 16.7 Hz and 25 Hz for some railways and, in a few older industrial and mining locations, 25 Hz.

•

Phase configuration (single-phase, polyphase including two-phase and three-phase)

•

Maximum demand (some energy providers measure as the largest mean power delivered within a 15 or 30 minute period during a billing period)

•

Load factor, expressed as a ratio of average load to peak load over a period of time. Load factor indicates the degree of effective utilization of equipment (and capital investment) of distribution line or system

•

Power factor of connected load

•

Earthing systems - TI, 1N-S, TN-C-S or 1N-C

•

Prospective short circuit current

•

Maximim

level and frequency of occurrence of transients

Power System Economics: •

Power is the rate of flow of energy. Similarly, generating capacity, the ability to produce power is itself a flow. A megawatt (MW) of capacity is worth little if it lasts only a minute just as a MW of power delivered for only a minute is worth little.

Dept. ofEEE, SJBIT

Page 20

Power System Planning

1OEE76 1

But a MW of power or capacity that flows fur a year is quite valuable. The price of both power and energy can be measured in $IMWh, and since capacity is a flow like power and measured in MW, like power, it is priced like power, in $1MWh. • Many find this confusing, but an examination of screening curves shows that this is traditional (as well as necessary). :) Since fixed costs are mainly the cost of capacity they are measured in $IMWh and can be added to variable costs to find total cost in $1MWh. When generation cost data are presented, capacity cost is usually stated in $IkW. • TIlls is the cost of the flow of capacity produced by a generator over its lifetime, so the true (but unstated) units are $IkW -lifetime. TIlls cost provides useful information but only for the purpose of finding fixed costs that can be expressed in $IMWh. No other useful economic computation can be performed with the "overnight" cost of capacity given in $IkW because they cannot be compared. with other costs until "Ievelized." While the U.S. •

·~ r

•

Department of Energy sometimes computes these economically useful (levelized) fixed' costs, it never publishes them Instead it combines them with variable costs and reports total levelized energy costs.This is the result of a widespread lack of understanding of the nature of capacity costs. Confusion over units causes too many different units to be used, and this requires unnecessary and sometimes impossibIe conversions.

Private Paticpation: •

Private participation in 1991 to hasten the increase in generating capacity and to improve the system efficiency as well. However, although several plants are under construction, till early 1999, eneration had commenced at private plants totalling less than 2,000 MW.

•

In contrast, some state undertakings have completed their projects even earlier than scheduled.Independent power producers (JPPs) claim that their progress has been hindered by problems such as litigation, fmancial arrangements, and obtaining clearances and fuel supply agreements. On the other hand, the State Electricity Boards have been burdened by power purchase agreements (PPAs) that favour the IPPs with such clauses as availability payment irrespective of plant utilization, tariffs retlecting high capital costs and returns on equity, etc.

•

The process of invitingprivate participation in the power sector and the problems experienced seem to have spurred on the restructuring of the power sector, includingthe formation of Central and State Electricity Regulatory Commissions.

•

However, some important problems have not been addressed. Additions to the generation capacity without corresponding improvement of the transmission and distribution facilities are likely to further undermine the system efficiency.

Dept. ofEEE, SJBIT

Page 21

10EE761

Power System Planning

•

What is more, issues like the reduction of "commercial losses" appear to have been ignored.Most importantly, investment in infrastructure has been a state responsibility because the intrinsically long gestation coupled with the relatively low returns from serving all categories of consumers have rendered such projects commercially unprofitable. Whether or not private participation can take on such tasks is to be seen.

Rural Electrification Investment: •

Rural Electrification Corporation Limited (REC) is a leading public Infrastructure

..

Finance Company in India's power sector. it

The company finances and promotes rural electrification projects across India, operating through a network of 13 Project Offices and 5 Zonal Offices, headquartered in New Delhi. The company provides loans to Central/ State Sector Power Utilities, State Electricity Boards, Rural Electric Cooperatives, NGOs and Private Power Developers.

•

REC is a N avratna Company fimctioning under the purview of the Ministry of Power Government of India. The company' is listed on both National Stock Exchange of India and Bombay Stock Exchange.

•

The company is primarily engaged ill providing finance for rural electrification projects across India and provides loans to Central/ State Sector Power Utilities, State Electricity Boards, Rural Electric Cooperatives, NGOs and Private Power Developers.

•

The company sanctions loan as a sole lender or co-lender or in consortium with or without the status of lead financer. It also provides consultancy, project monitoring and financial/ technical appraisal support for projects, also in the role of nodal agency for Government

of

India

schemes

or

projects.

REC

finances

all types

of Power

Generation projects including Thermal, Hyde], Renewable Energy, etc. without limit on size or location. •

The company aim; to mcrease presence

ill

emergmg areas like de-centralised distnbuted

generation (DDG) projects, and new and renewable energy sources to reach remote and difficult terrains not connected by power grid network. •

In Transmission & Distnbution (T&D), REC is primarily engaged ill ascertaining financial requirements of power utilities in the country in the T&D sector along with appraising T&D schemes for financing.

•

REC has financed T&D schemes for system improvement, intensive electrification, pump-set energisation and APDRP Programme. The company is also actively involved in physical as well as financial monitoring ofT&D schemes.

Dept. ofEEE, SJBIT

Page 22

Power System Planning

•

10EE761

REC also offers loan products for financingRenewable Energy projects. The company has tied up a line of credit for EUR 100 rnn(approximately{ 6000 rnn) with KfW under Indo-German Development Cooperation at concessional rates of interest.

;j

fur financingrenewable energy power projects

Eligible projects include Solar, Wind, Small Hydro, Biomass Power, and Cogeneration Power & Hybrid Projects .

.~ Wheeling: In electric

power

transmission, wheeling is

the

transportation

of

electric

power

(rregawatts or rregavolt-aroperes) over transmission lines.[l]

•

Electric

power

networks

networks. Transmission

are lines move

divided

into

electric

transmission power

and

distnbution

between generating

fucilitiesand substations, usually in or near population centers. From substations, power is sent to users over a distnbution network. A transmission line might move power over a few miles or hundreds of miles.

*

An entity that generates power does not have to own power transmission lines: only a connection to the network or grid. The entity then pays the owner of the transmission line based on how much power is being moved and how congested the line is.

•

Some power generating entities join a group which has shared ownership of transmission lines. These groups may include investor-owned combination of these.

•

utilities, government agencies, or a

Since prices to move power are based on congestion m transmission line networks, utilities try to charge customers more to use power during peak usage (demand) periods. This is accomplished by installing time-of-use meters to recover wheeling costs .

•

Dept. ofEEE, SJBIT

Page 23

1OEE761

Power System Planning

UNIT 4:

Computer aided Planning: With the increasing complexity of electrical power systems, the need for accm-ate tools for their design, planning and operation become a necessity. Investigations are made on the appropriate design tools for analyzing complicated energy system configurations under different contingencies in order to cope with the challenges. Education and training using these tools requires familiarization with software and hardware employed in this process. Studies shows that the new

delivery modes using the, fi.J11advantage

of digital computers

in a multi-media

environment will nnprove the efficiency of instruction., and understanding of complex problems.

Environmental impact: •

The environmental impact of electricity generation is' significant because 1110dem society uses

large amounts of electrical power.

This power

is normally generated at power

plants that convert -some other kind of energy into electrical power. Each system has advantages and disadvantages, but many of them pose environmental concerns. •

The amount of water usage is often of great concem for electricity generating systems as populations

increase and droughts become

a concern.

Still, according

to the U.S.

Geological Survey, thermoelectric power generation accounts for only 3.3 percent of net freshwater consumption with over 80 percent going to irrigation. Likely future trends in water consumption are covered here. General numbers for fresh water usage of different power sources are shown below. •

Steam-cycle plants (nuclear, coal, NG, solar thermal) require a great deal of water for cooling, to remove the heat at the steam condensors. The amount of water needed relative to plant output will be reduced with increasing boiler temperatures. Coal- and gas- fired boilers can produce high steam terrperatures and so are more efficient, and require less cooling water relative to output. Nuclear boilers are limited in steam temperature by material constraints, and solar is limited by concentration of the energy source.

•

Thermal cycle plants near the ocean have the option of using seawater. Such a site will not have cooling towers and will be much less limited by environmental concerns of the discharge

temperature

since

dumping

heat

will have

very

little effect on water

temperatures, This will also not deplete the water available for other uses. Nuclear power in Japan for instance, uses no cooling towers at all because all plants are located on the coast. If dry cooling systems are used, significant water from the water table will not be

Dept. ofEEE, SJBIT

Page 24

.... ..

Power System Planning

I OEE76 I

used. Other, more novel, cooling solutions exist, such as sewage cooling at the Palo Verde Nuclear Generating Station. •

Most electricity today is generated by burning fossil fuels and producing steam which is then used to drive a steam turbine that, in tum, drives an electrical generator. Such systems allow electricity to be generated where it is needed, since fossil fuels can readily be transported. They also take advantage of a large infrastructure designed to support consumer automobiles.

·~

•

The world's supply of fossil fuels is large, but finite. Exhaustion of low-cost fossil fuels will have significant consequences

,.

for energy. sources as \\_'ell as for the manufacture

of plastics and many other things. Various estimates have been calculated for exactly when it will be exhausted (see Peak oil). New sources of fossil fuels keep being discovered, although the rate of discovery is slowing while the difficulty of extraction simultaneously increases. •

Nuclear power plants do not bum fossil fuels and so do not directly emit carbon dioxide; because of the high energy yield of nuclear fuels, the carbon dioxide emitted during mining, enrichment, fabrication and transport of fuel is .small when compared with the carbon dioxide emitted by fossil fuels of similar energy yield.

;)

A large nuclear power plant may reject waste heat to a natural body of water; this can

result in undesirab Ie increase of the water temperature with adverse effect on aquatic life.

Green House Effect: The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re- radiation is back towards the surface and the lower atmosphere, it results in an elevation of the average surface temperature above what it would be in the absence of the gases. Solar radiation at the frequencies of visible lightlargely passes through the atmosphere to warm the planetary surface, which then emits this energy at the lower frequencies of infrared thermal radiation. Infrared radiation is absorbed by greenhouse gases, which in turn re-radiate much of the energy to the surface and lower atmosphere. The mechanism is named after the effect of solar radiation passing through glass and warming a greenhouse, but the way it retains heat is fundamentally different as a greenhouse works by reducing airflow, isolating the warm air inside the structure so that heat is not lost by convection.

Dept. ofEEE,

SJBIT

Page 25

Power System Planning

Insulation •

lOEE761

Co-ordination:

The term Insulation Co-ordination was originally introduced to arrange the insulation levels of the several components in the transmission system in such a manner that an insulation failure, if it did occur, would be confined to the place on the system where it would result in the least damage, be the least expensive to repair, and cause the least disturbance to the continuity of the supply. The present usage of the term is broader.

•

Insulation co-ordination now comprises the selection of the electric strength of equipment

...

in relation to the voltages which can appear on the system for which the equipment is intended. The overall aim is to reduce to an economically and operationally acceptable level the cost and disturbance caused by insulation failure and resulting system outages. •

To keep interruptions to a minimum, the insulation of the various parts of the system must be so graded that flashovers only occur at intended points. With increasing system voltage, the need to reduce the amount of insulation in the system, by proper coordination of the insulating levels. become more critical.

Reactive compensation: •

•

•

•

•

Except in a very few special situations, electrical energy is generated, transmitted, distnbuted, and utilized as alternating current (AC). However,alternating current has several distinct disadvantages. One of these is the necessity of reactive power that needs to be supplied along with active power. Reactive power can be leading or lagging.While it is the active power that contnbutes to the energy consumed, or transmitted, reactive power does not contribute to the energy. Reactive power is an inherent part of the "total power." Reactive power is either generated or consumed in ahnost every component of the system, generation, transmission, and distnbution and eventually by the loads. The impedance of a branch of a circuit in an AC system consists of two components, resistance and reactance. Reactance can be either inductive or capacitive, which contnbute to reactive power in the circuit.Most of the loads are inductive, and must be supplied with lagging reactive power. It is economical to supply this reactive power closer to the load in the distnbution systemReactive power compensation in power systems can be either shunt or series.

Dept. ofEEE, SJBIT

Page 26

..

Power System Planning

10EE761

Slut Capadors: Shunt capacitors are employed at substation level for the following reasons:

•

·~

,.

Redicrg power bsses

Compensating the load lagging power factor with the bus connected shunt capacitor bank improves the power factor and reduces current flow .through ...the transmission lines, transformers, generators, etc. This will reduce power losses (I2R losses) in this equipment.

•

lnreased lifuatbn of equprren

Shunt compensation with capacitor banks reduces kVA loading of lines, transformers, and . generators, which means with compensation:' they can be used for delivering more power without overloading the equipment. Reactive power compensation in a power system is of two types-shunt and series. Shunt. compensation can be installed near the load, in a distnbution substation, along the distnbution feeder, or in a transmission substation. • Volage regubtbn The main reason that shunt capacitors are installed at substations is to control the voltage within required levels. Load varies <;lver.the day, with very low load from midnight toearly morning and peak values occurring the evening between 4 PM and 7 PM. Shape of the load curve also varies from weekday to weekend, with weekend load typically low.

'm

't

Shrt Reactse PowerCorrpensatbn

Since most loads are inductive and consume lagging reactive power, the compensation required is usually supplied by leading reactive power. Shoot compensation of reactive power can be employed either at load level, substation level, or at transmission level • It can be capacitive (leading) or inductive (lagging) reactive power, although in most cases compensation is capacitive. The most common form of leading reactive power compensation is by connecting shunt capacitors to the line. • As the load varies, voltage at the substation bus and at the load bus varies. Since the load power factor is always lagging, a shunt connected capacitor bank at the substation can raise voltage when the load is high. The shoot capacitor banks can be permanently connected to the bus (fixed capacitor bank) or can be switched as needed. Switching can be based on titne, if load variation is predictable, or can be based on voltage, power factor, or line current.

,

Dept. ofEEE, SJBIT

Page 27

lOEE761

Power System Planning

UNIT 5&6 Power Supply Reliability: • The term reliability is broad in meaning. In general, reliability designates the ability of a system to perform its assigned fimction, where past experience helps to form advance estimates of future performance. • Reliability can be measured through the mathematical concept of probability by identifying the probability of successful performance with the degree of reliability. Generally, a device or system is said to perform satisfactorily if it does not fail during the time of service. On the other hand, a broad range of devices are expected to undergo failures, be repaired and then returned to service during their entire useful life.

• In this case a more appropriate measure of reliability is the availability of the device, which is defined as follows: • The indices used in reliability evaluation are probabilistic and, consequently, they do not provide exact predictions. TIley state averages of past events and chances of future ones by means of most frequent values and long-run averages. 111is infonmtion should be complemented with other economic and policy considerations for decision-making in planning, design and operation. The fimction of an electric power system is to provide electricity to its customers efficiently and with a reasonable assurance of continuity and quality. • The task of achieving economic' efficiency is assigned to system operators or competitive markets, depending on the type of industry structure adopted. On the other hand, the quality of the service is evaluated by the extent to which the supply of electricity is available to customers at a usable voltage and frequency. TIle reliability of power supply is, therefore, related to the probability of providing customers with continuous service and with a voltage and frequency within prescnbed ranges around the nominal values. Load management: • Load management, also known as demand side management (DSM), is the process of balancing the supply of electricity on the network with the electrical load by adjusting or controlling the load rather than the power station output. • 111is can be achieved by direct intervention of the utility in real time, by the use of frequency sensitive relays triggering circuit breakers (ripple control), by time clocks, or by using special tariffs to influence consumer behavior. • Load management allows utilities to reduce demand for electricity during peak usage times, which can, in turn, reduce costs by eliminating the need for peaking power plants. In addition, peaking power plants also often require hours to bring on-line, presenting challenges should a plant go off-line unexpectedly,

Dept. ofEEE, SJBIT

Page 28

Power System Planning

•

10EE761

Load management can also help reduce harmful emissions, smce peaking plants or backup generators are often dirtier and less efficient than base load power plants. New load-management technologies are constantly under development both by private industry and public entities.

Load Prediction:

....

Electric load forecasting is the process used to forecast fiiture' electric load, given historical load and weather information and current and forecasted weather information. In the past :few decades, several models have been developed. to. forecast .electric . load more accurately. Load forecasting can be divided into three major categories: ~ Long-term electric load forecasting, used to supply electric utility company . management with prediction of future needs for expansion, equipment purchases, or staff hiring • Medium-term forecasting, used for the purpose of scheduling. fuel supplies and unit maintenance . . . • Short-term forecasting, used to supply necessary information for the system . managerrent of day-to-day operations and unit commitment.

Reactive Power balance: The balance for the reactive power

m a who le- or a part of a system 1$ the next: LQE+QI=LQF+QH, where: LQE is the amount of the reactive power from the power plants QI is the balance of the imported reactive power flows (incoming is the positive) LQF is the amount of the substations reactive power consrnnptions Q H is the amount of the system elements reactive power consrnnptions (wires, cables, transformers, reactors, static compensators, etc.). The reactive power flows from the capacitors and overexcited generators called reactive power production, the under excited generators and inductances reactive power called reactive power consrnnption. The reactive power is positive, if the current is delaying to the voltage, while the active power is positive compared to the power flows on an arbitrary system element S=P+jQ. These principles considers to the high/middle voltage level systems, but there is no reason to not to use in micro/smart grid systems as well.

,

Online power flow studies: In power

engineering, the power-flow

study,

also

known as load- flow study, is an

important tool involvingnumerical analysis applied to a power

system

A power- flow study

usually uses simplified notation such as a one-line diagram and per-unit system, and focuses on various fonns of AC power (i.e.: voltages, voltage angles, real power and reactive power). It analyzes

the

power

systems

in normal

steady-state

operation.

A

number

of

software

implementations of power- flow studies exist. Dept. ofEEE, SJBIT

Page 29

10EE761

Power System Planning

•

Many

software

circuit fault

implementations perform

analysis,

stability

studies

other

(transient

types

of

analysis, such

& steady-state),

unit

as short-

corrnnitment

and economic dispatch. In particular, some programs use linear programming to find the optimal power flow, the conditions which give the lowest cost per kilowatt hour delivered. •

Power-flow or load-flow studies are important for planning future expansion of power systems as well as in determining the best operation of existing systems. The principal information obtained from the power-flow study is the magnitude and phase angle of the voltage at each bus, and the real and reactive power flowing in each line.

•

Commercial power systems are usually too large to allow for hand solution of the power flow. Special purpose network analyzers were built between 1929 and the early 1960s to provide laboratory models of power systems; large-scale digital computers replaced the analog methods.

•

Newton-Raphson

method is the most widely accepted

load flow solution algorithm

However LU factorization remains a computationally challenging task to meet the realtime needs of the power system •

The application of very fast multifrontal direct linear solvers for solving the linear system sub-problem of power system real-time load flow analysis by utilizing the state-of-the-art algorithms for ordering and preprocessing.

•

Additionally the optimized

unsyrrnuetric rilultifrontal method

Intel Math

Kernel

multifrontal algorithms

for

Library

BLAS

for

has been

unsymmetric matrices

LU

factorization

used.

Two

and

highly

state-of-the-art

namely UMFPACK

VS.2.0

and

sequential MUMPS 4.8.3 ("Multifrontal Massively Parallel Solver'') are customized for the AC power system Newton-Raphson •

based load flow analysis.

The multifrontal solvers are compared

against the state-of-the-art

sparse

Gaussian

Elimination based HSL sparse solver MA48. This study evaluates the performance of above muhifrontal solvers in terms of number of factors, computational time, number of floating-point operations

and memory, in the context of load flow solution on nine

systems including very large real power systems. •

The resuhs of the performance evaluation are reported. The proposed method achieves significant reduction in computational time.

Dept. ofEEE, SJBIT

Page 30

•

Power System Planning

10EE761

State Estimation: State estimators allow the calculation of these variables of interest with high confidence despite measurements that are corrupted by noise measurements that may be missing or grossly Inaccurate. Objectives: •

·...

To provide a view of real-time power system conditions

• . Real-time data primarily come from SCADA smooth,

SE supplements SCADA data: filter, fill,

• .To provide a consistent representation for power system security analysis • On-line dispatcher power flow 'J Contingency Analysis • •

Load Frequency Control To provide diagnostics for modeling & maintenance

Computerized

management:

Research shows that personal computers (PC) are not being actively used during the vast .majority of the time that they are kept on. It is estimated that an average PC is in use 4 hours each work day and idle for another 5.5 hours. It's also estimated that some 30-40 percent of the US's work PCs are left running at night and on weekends. Office equipment is the fastest growing electricity load ill the commercial sector. Computer systems are believed to account for 10 percent or more of commercial electricity consumption already. Since computer systems generate waste heat, they also increase the amount of electricity necessary to cool office spaces. For the Medical Center, we estimate the savings from PC power management to be hundreds of thousands of dollars annually, even without factoring in increased office cooling costs. Considerable savings are also possible from easing wear-and-tear on the computers themselves. Power System Simulator: Power system simulation models are a class of computer simulation programs that focus on the

,

operation of electrical power systems. These computer programs are used in a wide range of planning and operational situations including: l. Long-term generation and transmission expansion planning 2. Short-term operational simulations

3. Market analysis (e.g. price forecasting)

Dept. ofEEE, SJBIT

Page 31

Power System Planning

These

program;

typically

lOEE76 1

make

use

of mathematical

optimization teclmiques

such linear

prograrmning, quadratic prograrmning, and mixed integer programming. Key elements of power system; that are modeled include: 1. Load flow (power flow study) 2. Short circuit 3. Transient stability

"'.

4. Optimal dispatch of generating units (unit cormnitment) 5. Transmission (optimal power flow)

•

Dept. ofEEE, SJBIT

Page 32

Power System Planning

1OEE76 1 UNIT 7&8:

Optimal Power System Expansion Planning: Dptirnization Techniques:

. ~..

, .

In everyday life, all of us are confronted with some decision makings. Normally, we try to decide or the best. If someone is to buy a corrnnodity, he or she tries to buy the best quality, yet with the east cost. These types of decision makings are categorized as optimization problems in which the aim is to find the optimum solutions; where the optimum may be either the least or the most. Most of the operational and planning problems consist of the fullowing three major steps • Definition • Modeling • Solution algorithm Decision variables are the independent variables; the decision maker has to determine their optimum values and based on those, other variables (dependent) can be determined. For instance, in an optimum generation scheduling problem, the active power generations of power plants may be the decision variables. The dependent variables can be the total fuel consumption, system losses, etc. which can be calculated upon determining the decision variables. In a capacitor allocation problem, the locations and the sizing of the capacitor banks are the decision variables, whereas the dependent variables may be bus voltages, system losses, etc. Mathematical Algorithms.

•

,

A mathematical optnruzation technique formulates the problem m a mathematical representation; as given by (2.2) through (2.4) .. Provided the objective function and/or the constraints are nonlinear, the resulting problem is designated as Non Linear optimization Problem (NLP). A special case of NLP is quadratic programming in which the objective function ;0; a quadratic function of x. If both the objective functions and the constraints are linear functions of X, the problem is designated as a Linear Programming (LP) problem Other categories may also be identified based on the nature of the variables. For instance, if x is of integer type, the problem is denoted by Integer Programming (IP). Mixed types such as MILP(Mixed Integer Linear Programming) may also exist in which while the variables may be both real and integer, the problem is also of LP type. For mathematical based formulations, some algorithms have, so fur, been developed; based on them some commercial software have also been generated. In the following subsections, we briefly review these algorithms. We should, however, note that generally speaking, a mathematical algorithm may suffer from numerical problems and may be quite complex in implementation. However, its convergence may be guaranteed but finding the global optimum solution may only be guaranteed for some types such as LP. There is no definite and fixed classification of mathematical algorithms. Here, we are not going to discuss them in details. Instead, we are going to introduce some topics which are of more interest in this book and may be applicable to power system planning issues. 1 Some topics, such as game theory, which are of more interest for other power system issues (such as market analysis of power ystems), are not addressed here.

Dept. ofEEE, SJBIT

Page 33

Power System Planning

IOEE76I

Calculus Method: These types of methods are the traditional way of seeking optirrnnn points. These are applicable to continuous and differentiable functions of both objective and constraints terms. They make use of differential calculus in locating the optimum points. Based on the basic differential calculus developed for finding the optirrnnn points of C(x) , the method of Lagrange Multipliers has been developed in finding the optimum points; where equality constraints may also apply. If inequality constraints (2.4) are also applicable, still the basic method may be used; however, the so called Kulm-Tucker conditions should be observed. The solution is not so straightforward in that case.

....

Linear Programming (LP) Method: As already noted, LP is an optimization method in which both the objective function and the constraints are linear functions of the decision variables. This type of problem was first recs'-clzed in the 1930s by the economists in developing methods for the optimal allocation of resources. Noting the fact that • Any LP problem can be stated as a minimization problem; due to the fact that, as already described, maximizing C(x) is equivalent to minimizing (-C(x». The problem can be stated in a form known as canonical Then, a solution known as the simplex method, first devised in 1940s, , \-'1" used to solve the problem Using the simplex method normally requires a large amount of computer storage and time. The so called revised simplex method is a revised method in which less computational time and storage space are required. Still another topic of interest in LP problems is the duality theory. In fact, associated with every LP problem, a so called dual -roblem may be fonnulated. In many cases, the solution of an LP problem may be more easily obtained from the dual problem If the LP problem has a special structure, a so called decomposition principle may be employed to solve the problem in which less computer storage ,is required. '

Non Linear Programming (NLP) Method: We noted earlier that if the objective function and/or the constraints are nonlinear functions of the decision variables, the resulting optimization problem is called NLP. Before proceeding further on NLP problems, we should note that most practical problems are of constrained type in which some constraint functions should be satisfied. As for constrained problems, however, some algorithms work on the principle of transforming the problem into a unconstrained case, we initially review some existing algorithms on solving unconstrained problems. The solution methods for unconstrained problems may be generally classified as direct search (or nongradient) methods and descent (or gradient) methods. The fonner methods do not use the partial derivatives of the objective function and are suitable for simple problems involving a relatively small number of variables. The latter methods require the evaluations of the first and possibly, the higher order derivatives of the objective function. As a result, these methods are generally more efficient than the direct methods. All the unconstrained optimization methods are iterative in nature and start from an initial trial solution; moving stepwise in a sequential manner towards the optimum solution. The gradient methods have received more attention in power system literature. For instance, in the so called steepest descent method; widely used in power system literature, the gradient vector is used to calculate the optimum step length along the search direction so that the algorithm efficiency is maxirnized.

Dept. ofEEE, SJBIT

Page 34

•

..

Power System Planning

_"

•

,

10EE761

Let us come back to the constrained case. Two types of methods, namely, direct and indirect methods apply. In the former methods, the constraints are handled in an explicit manner, while in most of the latter methods; the constrained problem is converted into a sequence of unconstrained problems and solved through available algorithms. As an example of the direct methods, in the so called constraint approximation method, the objective fimction and the constraints are linearized about some point. The resulting approximated LP problem is solved using LP techniques. The resulting solution is then used to construct a new LP problem The process is continued until a convergence criterion is satisfied. As an example of the indirect methods, the so called penalty fimction method, works on the principle of converting the problem into an unconstrained type. It is, in tum, classified as interior and exterior penalty function methods. In the former, the sequence of unconstrained minima lie in the feasible region while in the latter, they lie in the infeasible region. In both, they move towards the desired.

"Jpamic Programming (DP) Method: Dynamic Programming is a widely used technique in power system studies. It is, in fact, a mathematical technique used for muhistage decision problems; originally developed in 1950s. A multistage decision problem is a problem in which optimal decisions have to be made over some stages. The stages may be different times, different spaces, different levels, etc. The important point is that the output of each stage is the input to the next serial stage. The overall objective fimction is to be optimized over all stages. It is normally a fimction of the decision variables (xi) of all stages. The important fact is that one cannot start from optimizing the first stage; moving forward toward the final stage; as there may be some correlations between the stages, too. To make the problem clear, let us express a power system example. Suppose we are going to minimize the generation cost of a power system over a 24-h period. Some information is as follows . • There are four generation units available; each of which may be either off or on (so that various combinatio ns are possible, such as, 1111, 1101, 1001" 00 11, ... ). • The unit efficiencies are different; so that if the system load is low and say, two units can meet the load, we should use the higher efficient units to supply the load. • The load varies throughout the 24-h period; changing at each hour (stage). The multistage decision problem is, in fact, deciding on the units to be on at each stage so that the overall generation cost over the 24-h period is minimized. We note that if no other constraint was imposed, we should optimize our problem at each. stage and sum it over all stages. In other words, 24 single stage optimization problems2 have to be solved to find the final solution. Suppose that the final solution looks like Fig. 2.5 in which the unit combinations are shown at each stage. As shown, unit 1 is on at hours 1 and 2, off at hour 3, and on again at hour 4. Now what happens if a constraint is imposed expressing the fact that if unit 1 is turned off, it cannot be turned on unless a 5-h period is elapsed. Integer Programming Method: In the algorithms discussed so fur, each of the decision variables may take any real value. What happens if a decision variable is limited to take only an integer value? For instance, if the decision variable is the number of generation units, taking a real value is meaningless. The optimization algorithms developed for this class of problems are classified as IP methods. If all decision variables are of integer type, the problem is addressed as IP problem If some decision variables are of integer type while some others are of non-integer type, the problem is known as Dept. ofEEE, SJBIT

Page 35

Power System Planning

IOEE76 I

mixed integer programming problem Moreover, based on the nature of the original problem, both integer linear programming and integer nonlinear programming methods have been developed. As a resuh, in power system literature, some terms such as MILP have appeared. 2.3.2 Heuristic Algorithms Most mathematical based algorithms can guarantee reaching an optimal solution; while do not necessarily guarantee reaching a global optimum Global optimality may be only reached, checked or guaranteed for simple cases. On the other hand, many practical optimization problems do not full in strict forms and assumptions of mathematical based algorithms. Moreover, if the problem is highly complex, we may not readily be able to solve them, at all, through mathematical algorithms. Besides, finding global optimum is of interest, as finding a local one would be a major drawback. Heuristic algorithms are devised to tackle the above mentioned points. They, normally, can solve the combinatorial problems, sometimes very complex, yet in a reasonable time. However, they seek good solutions, without being able to guarantee the optimality, or even how close the solutions are to the optimal point.

....

•

Dept. ofEEE, SJBIT

Page 36

Power System planning

10EE761

Assignment Questions

UNIT I

1. Explain Lease Cost Planning with flowchart 2. Descnbe the two techniques of load forecasting in power system 3. Discuss the different planning tools. 4. What do you mean by planning process? Explain step by step procedme for strategic planning. 5. Explain national and regional planning. 6. Explain forecast modeling. 7. Explain the different components of power system 8. Explain the electricity regulation act 1956.

UNIT 2&3 1. Explain the strategy for transmission expansion in power system 2. What are the basic processes of co-generation? Explain. 3. What is the need for private participation in generation planning? How can it improve the power situation in India?

•

4. Discuss in brief the basic: tariff making philosophy. 5. Explain the benefit of cogeneration. 6. What are the objectives of sound pricing? Explain. 7. Discuss the factors to be considered for dispatchability in power system planning studies. 8. Write a note on rural electrification investment. 9. With the help of block diagram, explain distnbuted power generation planning. List plan options, uncertainties and attnbutes. 10. Write a note on distnbution planning. II. Discuss in brief rational tariff. UNIT 4

,

1. What are the source of absorption and generation of reactive power in transmission and distnbution lines? Compare advantages and disadvantages of any 4 compensating equipments. 2. Explain the methods of post combustion cleanup process to reduce gaseous pollutions. 3. Explain computer aided planning with block diagram 4. Write a note on greenhouse effect of power generation. Department of EEE, SJBIT

Page 1

1OEE761

Power System planning 5. Discuss wheeling in power system and list the typical objectives in wheeling. 6. Explain the effect of power generation on environment. 7. Explain insulation coordination with a neat sketch. 8. What are the technological impacts from power generation? 9. Write a note on reactive compensation.

UNIT 5&6

1. Define system reliability and explain reliability planning criteria. 2. 3. 4. 5. 6.

With the help of schematic diagram, explain load management technique. Explain reactive power balance in power system With the help of block diagram, explain computerized management of power system Explain power system simulator with a neat sketch. Explain in brief the following real time operations: a. State estimation.

b. AGe c. Economic load dispatch d. Stability. 7. What is load prediction? 8. Write a note on online power flow studies 9. With the help of a schematic diagram, explain state estimation.

UNIT 7&8

1. Develop mathematical objective function of power system expansion planning. 2. What are the constraints observed during optimization process of power

system

expansion planning? 3. Explain least cost optimization problem 4. Explain in brief two optimization techniques. 5. Explain least cost optimization problem for thermal plants 6. Explain least cost optimization problem for hydro plants 7. Explain least cost optimization problem for nuclear plants

•

8. Explain least cost optimization problem for non-conventional plants.

Department of EEE, SJBIT

Page 2

Power System planning

10EE761 VTU QUESTION

BANK

UNIT 1

1. Explain Lease Cost Planning with flowchart.

[Dec 201311an 2014]

2. Descnbe the two techniques of load forecasting in power system 3. Discuss the different planning tools.

[Dec 201311an 2014] [Dec 201311an 2014]

UNIT 2&3

1. With the help of block diagram, explain distnbuted power generation planning. List plan options, uncertainties and attnbutes. [Dec 201311an 2014] 2. What is co-generation? Descnbe the two techniques ofcogeneration.[Dec 201311an 2014] ~. Write a note on distnbution planning. [Dec 201311an 2014] 4. Discuss in brief rational tariff. [Dec 20 1311an2014] 5. What is the need for private participation in generation planning? How can it improve the power situation in India? [Dec 201311an 2014] UNIT 4

1. Discuss wheeling in power system and list the typical objectives in wheeling. [Dec 201311an 2014] 2. Explain the effect of power generation on environment. [Dec 201311an 2014] 3. What are the source of absorption and generation of reactive power in transmission and distribution lines? Compare advantages and disadvantages of any 4 compensating equipments. [Dec 201311an 2014] UNIT 5&6

,

1. Define system reliability and explain reliability planning criteria.

[Dec 201311an 2014]

2. Explain in brief the following real time operations: s. State estimation. b. AGC c. Economic load dispatch d. Stability.

[Dec 20 1311an2014]

Department of EEE, SJBIT

Page 1

lOEE761

Power System planning

3. With the help of schematic diagram, explain load management technique. [Dec 20l3/Jan 2014] 4. Explain reactive power balance in power system [Dec 20l3/Jan 2014] 5. With the help of block diagram, explain computerized management of power system [Dec 2013/Jan 2014]

UNIT 7&8

1. Develop mathematical objective function of power system expansion planning: . [Dec 2013/Jan 2. What are the constraints observed during optimization process of power [Dec 2013/Jall expansion planning? [Dec 20l3/Jan 3. Explain least cost optimization problem [Dec 2013/Jan 4. Explain in brief two optimization techniques.

Department of EEE, SJBfT

2014] system 2014] 2014] 2014]

Page 2

Power System planning

10EE761 Solution to VTU Question Bank

UNIT 1 I. Explain Lease Cost Planning with flowchart.

[Dec 2013/Jan 2014]

Least Cost Utility Planning:

....

There are two fimdamental problems inherent in traditional planning. The first is that demand forecasting and investment planning are treated as sequential steps in planning, rather than as interdependent aspects of the planning process. The second problem is that planning efforts are inadequately directed at the main constraints facing the sector, namely the serious shortage of resources. 1. Demand forecasts are little more than extrapolations of past trends of consumption, no attempt is made to understand neither the extent of unmet demand nor the extent to which the prices influence the demand growth. Greater attention should be paid to end use efficiency, plant rehabilitation, loss reduction program, etc. 2. Least cost planning (LCUP) is least cost utility planning strategy to provide reliable electrical services at lowest overall cost with a mix of supply side and demand side options. 3. The LCUP uses various options like end use efficiency, load management, transmission and distnbution options, alternative tariff options, etc. 4. This planning process can yield enormous benefits to consumers and society because it affords acquisition of resources that meet consumer energy service needs that are low in cost, environmentally fiiendly. 5. LCUP as a planning and regulatory process can greatly reduce the uncertainty and risks faced by utilities. The logic for least cist planning is shown in the figure below:

Op tions

(plans) Regula tions

Least Cost Planning Process

...

-

>Attributes:

, 6. For an investment to be least cost, the lifetime costs are considered. These include capital costs, interest on capital, fuel cost and operation and maintenance costs.

Department ofEEE, SJBIT

Page 1

10EE761

Power System planning

simulation

social and environmental factors

resource mixes

1----+'analysis

monitor

Fig: flowchart for least cost planning

2.

Descnbe

Forecasting

the two techniques

of load forecasting

in power system

[Dec 20 13/Jan 2014]

Techniques:

Load forecasting is vitally important for the electric industry in the deregulated economy. It has many applications including energy purchasing and generation, load switching, contract evaluation, and infrastructure development. A large variety of matherratical methods have been developed for load forecasting. In this chapter we discuss various approaches to load forecasting.

Forecasting Methods • Over the last few decades a number of forecasting methods have been developed. Two of the thods, so-called end-use and econometric approach are broadly used for medium- and long-term forecasting. Avariety of methods, which include the so-called similar day approach, various regression models, time series, neural networks, expert systems,fuzzy logic, and statistical learning algorithms, are used for short-term forecasting. • The development, improvements, and investigation of the appropriate mathematical tools will lead to the development of more accurate load forecasting techniques. Statistical Department of EEE, SJBIT

Page 2

...

•

Power System planning

•

10EE761

approaches usually require a mathematical model that represents load as fi.mction of different factors such as time, weather, and customer class. • The two important categories of such mathematical models are: additive models and multiplicative models. They differ in whether the forecast load is the sum (additive) of a mnnber of components or the product (multiplicative) of a number of factors. For example, Chen et al. [4] presented an additive model that takes the form of predicting load as the fimction offour components: L = Ln + L w + Ls + Lr, where L is the total load, Ln represents the "normal" part of the load,which is a set of standardized load shapes for each "type" of day that has been identified as occurring throughout the year, Lw represents the weather sensitive part of the load, Ls is a special event component that create a substantial deviation from the usual load pattern, and Lr is a completely random . term, the noise. ~ A multiplicative model may be of the form L = Ln . Fw . Fs . Fr, where Ln is the normal (base) load and the correction factors Fw, Fs, and Fr are positive· numbers that can increase or decrease the overall load. These corrections are based on current weather (Flv), special events (Fs), and random fluctuation (Fr). Factors such as electricity pricing (Fp) and load growth (Fg) can also be included. Rahman [29] presented a rulebased forecast using a multiplicative model. Weather variables and the base load associated with the weather measures were included in the modeL .

3. Discuss the different planning tools.

[Dec 2013/Jan 2014]

Planning Tools: 1. Planning engineer's primary requirement is to give power supply to consumers in a reliable manner at a minimum cost with due flexibility for future expansion. 2. The criteria and constraints in planning an energy system are reliability, environmental economics, electricity pricing, financial constraints, society impacts. 3. reliability, environmental, economic and financial constraints can be quantified. Social effects are evaluated qualitatively. 4. The system must be optimal over a period of time from day of operation to the lifetime.

S. Various computer programs are available and are used for fast screening ofaltemative plans with respect to technical, environmental. and economic constraints.

,

The available tools for power system planning can be split into:

•

Simulation tools: these simulate the behavior of the system under certain conditions and calculate relevant indices. Examp les are load flow models, short circuit models, stability models, etc.

•

Optimization tools: these minimize or rraxrrmze an objective fimction by choosing adequate values for decision variables. Examples are optimum power, least cost expansion planning, generation expansion planning, etc.

Department of E EE, SJBIT

Page 3

Power System planning

10EE761

e. MAIN DISCONNECT To insure the uhimate in safety for the City of Gallup fire personnel, all new or rewired electric services shall have a single disconnect point on the exterior part of the building so that the fire department can de-energize the building if necessary in case of fire. The Developer shall provide the size of the main disconnect on the design submitted.

4. Discuss in brief rational tariff. •

,

.,

•

[Dec 20l3/Jan 2014]

Power is the rate of flow of energy. Similarly, generating capacity, the ability to produce power is itself a flow. A megawatt (MW) of capacity is worth little if it lasts only a minute just as a MW of power delivered for only a minute is worth little. But a MW of power or capacity that flows for a year is quite valuable. The price of both power and energy can be measured in $/MWh, and since capacity is a flow like power and measured in MW, like power, it is priced like power, in $/MWh. Many find this confusing, but an examination of screening curves shows that this is traditional (as well as necessary). Since fixed costs are mainly the cost of capacity they are measured in $IMWh and can be added to variable costs to find. total cost in $lMWh. When generation cost data are presented, capacity cost is usually stated in $/kW . This is the cost of the flow of capacity produced by a generator over its lifetime, so the true (but unstated) units are $/kW -lifetime. This cost provides useful information but only for the purpose of finding fixed costs that can be expressed in $/MWh. No other useful economic computation can be performed with the "overnight" cost of capacity given in $/kW because they cannot be compared with other costs until "levelized." While the U.S. Department of Energy sometimes computes these economically useful (levelized) fixed costs, it never publishes them Instead it combines them with variable costs and reports total levelized energy costs.This is the result of a widespread lack of understanding of the nature of capacity costs. Confusion over units causes too many different units to be used, and this requires unnecessary and sometimes impossible conversions.

,

5. What is the need for private participation in generation planning? How can it improve the power situation in India? [Dec 2013/Jan 2014] Private Paticpation: • Private participation in 1991 to hasten the increase in generating capacity and to improve the system efficiency as well However, although several plants are under construction, till early 1999, eneration had commenced at private plants totalling less than 2,000 MW. •

In contrast, some state undertakings have completed their projects even earlier than scheduled.Independent power producers (IPPs) claim that their progress has been hindered by

Department of EEE, SJBIT

Page 7

10EE761

Power System planning

problems

such as litigation, fmancial arrangements,

agreements. purchase

and obtaining clearances

and fuel supply

On the other hand, the State Electricity Boards have been burdened by power

agreements

(PPAs)

that favour the IPPs with such clauses as availability payment

irrespective of plant utilization, tariffs reflecting high capital costs and returns on equity, etc.

•

The process of inviting private participation in the seem to have spurred on the restructuring

power sector and the problems experienced

of the power sector, including the formation of Central

and State Electricity Regulatory Commissions. •

However, capacity

some important

problems

without corresponding

have not been addressed.

improvement

Additions to the generation

of the transmission and distribution facilities are

likely to further undermine the system efficiency .. •

What is more, issues like the reduction of "commercial losses" appear to have been ignored.Most importantly, investment in infrastructure

has been a state responsibility because the intrinsically

long gestation coupled with the relatively low returns from serving all categories

of consumers

have rendered such projects commercially unprofitable. Whether or not private participation

can

take on such tasks is to be seen.

UNIT 4 1. Discuss wheeling in power system and list the typical objectives in wheeling. [Dec 2013/Jan 2014] Wheeling: •

In electric power transmission, wheeling is the transportation (megawatts or megavolt-amperes) over transmission lines.[I]

•

Electric

power

networks are divided into networks. Transmission lines move electric

transmission power

of

electric

and

power

distnbution

between generating

facilitiesand substations, usually in or near population centers. From substations, power is sent to users over a distnbution network. A transmission line might move power over a few miles or hundreds of miles.

•

An entity that generates power does not have to own power transmission lines: only a connection to the network or grid. The entity then pays the owner of the transmission line based on how much power is being moved and how congested the line is.

Department of EEE, SJBIT

Page 8

Power System planning

•

10EE761

Some power generating entities join a group which has shared ownership of transmission lines. These groups may include investor-owned

utilities, government agencies, or a

combination of these. •

Since prices to move power are based on congestion in transmission line networks, utilities try to charge customers more to use power during peak usage (demand) periods.

This is accomplished by installing time-of-use meters to recover wheeling costs.

2. Explain the effect of power generation on environment. Environmental

[Dec 2013/Jan 2014]

impact:

The environmental impact of electricity generation is significant because uses

large 'amounts of electrical power.

This power

modem society

is normally generated at power

plants that convert some other kind of energy into electrical power. Each system has advantages and disadvantages, but many of them pose environmental concerns. The amount of water usage is often of great concern for electricity generating systems as populations increase' and droughts

become

a concern.

Still, according to the U.S.

Geological Survey, thermoelectric power generation accounts for only 3.3 percent of net freshwater consumption with over 80 percent going to irrigation. Likely future trends in water consumption are covered here. General numbers for fresh water usage of different power sources are shown below. •

Steam-cycle plants (nuclear, coal, NG, solar thermal) require a great deal of water for cooling, to remove the heat at the steam condensors. The amount of water needed relative to plant output will be reduced with increasing boiler temperatures. Coal- and gas-fired boilers can produce high steam temperatures and so are more efficient, and require less cooling water relative to output. Nuclear boilers are limited in steam temperature by material constraints, and solar is limited by concentration of the energy source.

•

Thermal cycle plants near the ocean have the option of using seawater. Such a site will not have cooling towers and will be much less limited by environmental concerns of the discharge

'i

temperature

since

dumping heat

will have

very

little effect on water

temperatures. This will also not deplete the water available for other uses. Nuclear power in Japan for instance, uses no cooling towers at all because all plants are located on the coast. If dry cooling systems are used, significant water from the water table will not be used. Other, more novel, cooling solutions exist, such as sewage cooling at the Palo Verde Nuclear Generating Station. •

Most electricity today is generated by burning fossil fuels and producing steam which is then used to drive a steam turbine that, in tum, drives an electrical generator. Such

Department of EEE, SJBIT

Page 9

10EE761

Power System planning

systems allow electricity to be generated where it is needed, since fossil fuels can readily be transported.

They also take advantage of a large infrastructure designed to support

consumer automobiles. •

The world's supply of fossil fuels is large, but finite. Exhaustion of low-cost fossil fuels will have significant consequences for energy sources as well as for the manufacture of plastics and many other things. Various estimates have been calculated for exactly when it will be exhausted (see Peak discovered,

oil). New

sources of fossil fuels keep being

although the rate of discovery is slowing while the difficulty of extraction

simultaneously increases.

3. What are the source of absorption and generation of reactive power in transmission and distnbution

lines? Compare

advantages

and

equipments.

disadvantages

of any 4 compensating [Dec 20l3/Jan 2014]

leactive compensation: •

•

•

•

•

Except in a very few special situations, electrical energy is generated, transmitted, distnbuted, and utilized as alternating current (AC) .. However.alternating current has several distinct disadvantages. One of these is the necessity of reactive power that needs to be supplied along with active power. Reactive power can be leading or lagging.While it is the' .active power that contnbutes . to the energy consumed, or transmitted, reactive power does not contnbute to the energy. Reactive power is an inherent part of the "total power." Reactive power is either generated or consumed in almost every component of the system, generation, transmission, and distnbution and eventually by the loads. The impedance of a branch of a circuit in an AC system consists of two components, resistance and reactance. Reactance can be either inductive or capacitive, which contnbute to reactive power in the circuit.Most of the loads are inductive, and must be supplied with lagging reactive power. It is economical to supply this reactive power closer to the load in the distrIbution systemReactive power compensation in power systems can be either shunt or series.

Shurt Capadors: Shoot capacitors are employed at substation level for

•

fullowing reasons:

Reducilg power bsses

Department of EEE, SJBIT

Page 10

,

Power System planning

10EE761

the load lagging power factor with the bus connected shunt capacitor bank improves the power factor and reduces. current flow through the transmission lines, transformers, generators, etc. This will reduce power losses (l2R losses) in this equipment. Compensating

• lnreased uiizaton of equprren Shunt compensation with capacitor banks reduces kVA loading of lines, transformers, and generators, which means with compensation they can be used for delivering more power without overloading the equipment. Reactive power compensation in a power system is of two types-shoot and series. Shunt compensation can be installed near the load, in a distnbution substation, along the distnbution reeder, or in a transmission substation. • Vo~ regulrtim The main reason that shunt capacitors are installed at substations is to control the voltage within required levels. Load varies over the day, with very low load from midnight toearly morning and peak values occurring in the evening between 4 PM and 7 PM. Shape of the load curve also varies from weekday to weekend, with weekend load typically low. • Slut Reactse Power Corrpersaton Since most ·loads are inductive· and consume lagging reactive power, the compensation required is usually supplied by leading reactive power. Shunt compensation of reactive power .can. be .employed either at load level, substation level, or at transmission level • It can be capacitive (leading) or inductive (lagging) reactive power, although in most cases compensation is capacitive. The most common form of leading reactive power compensation is by connecting shunt capacitors to the line. • As the load varies, voltage at the substation bus and at the load bus varies. Since the .load power factor is always lagging, a shunt connected capacitor bank at the substation . can raise voltage when the load is high. The shunt capacitor banks can be permanently . connected to the bus (fixed capacitor bank) or can be switched as needed. Switching can be based on time, if load variation is predictable, or can be based on voltage, power factor, or line current.

UNIT 5&6 1. Define system reliability and explain reliability planning criteria.

[Dec 20l3/Jan 2014]

Power Supply Reliability: • The term reliability is broad in meaning. In general, reliability designates the ability of a system to perform its assigned fimction, where past experience helps to form advance estimates of future performance. • Reliability can be measured through the mathematical concept of probability by identifying the probability of successful performance with the degree of reliability. Generally, a device or system is said to perform satisfactorily if it does not mil Department of EEE, SJBIT

Page 11

Power System planning

10EE761

during the time of service. On the other hand, a broad range of devices are expected to undergo failures, be repaired and then returned to service during their entire useful life. • In this case a more appropriate measure of reliability is the availability of the device, which is defined as follows: • The indices used in reliability evaluation are probabilistic and, consequently, they do not provide exact predictions. They state averages of past events and chances of future ones by means of most frequent values and long-run averages. This information should be complemented with other economic and policy considerations for decision-making in planning, design and operation. The function of an electric power system is to provide electricity to its customers efficiently and with a reasonable assurance of continuity and quality. • The task of achieving economic efficiency is assigned to system operators or competitive markets, depending on the type of industry structure adopted. On the other hand, the quality of the service is evaluated by the extent to which the supply of electricity is available to customers at a usable voltage and frequency. The reliability of power supply is, therefore, related to the probability of providing customers with continuous service and with a voltage and frequency within prescnbed ranges around the nominal. values. 2. Explain in brief the following real time operations:

[Dec 2013/Jan 2014]

a. State estimation: State estimators allow the calculation: of these variables of interest with high confidence despite measurements that are corrupted by noise measurements that may be missing or grossly Inaccurate. Objectives: •

To provide a view of real-time power.system conditions

•

Real-time data primarily come from SCADA SE supplements SCADA data: fiher, fill,

..

smooth. •

To provide a consistent representation for power system security analysis

•

On-line dispatcher power flow

•

Contingency Analysis

• •

Load Frequency Control To provide diagnostics for modeling & maintenance

•

b. AGe: In an electric power system, Automatic generation control (AGC) is a system for adjusting the power output of multiple generators at different power plants, in response to changes in the load. Since a power grid requires that generation and load Department of EEE, 5JBfT

Page 12

Power System planning

10EE761

c10sely balance moment by moment, frequent adjustments to the output of generators are necessary. The balance can be judged by measuring the system frequency; if it is increasing, more power is being generated than used, and all the machines in the system are accelerating. If the system frequency is decreasing, more 10ad is on the system than the instantaneous generation can provide, and all generators are slowing down.

c. Economic load dispatch: Economic dispatch is the short-term determination of the optimal output of a number of electricity generation facilities, to meet the system load, at the lowest possible cost, subject to transmission and operational constraints. The Economic Dispatch Problem is solved by specialised computer software which should honour the operational and system constraints of the availabIe resources and corresponding transmission capabilities. The main idea is that in order to serve 10ad at minimum total cost, the set of generators with the lowest marginal costs must be used first, with the marginal cost of the final generator needed to meet load setting the .system marginal cost. This is the cost of delivering one additional MW of energy onto the system The historic methodology for economic dispatch was deve10ped to manage fossil fuel burning power plants, relying on calculations involving the input/output characteristics of power stations. d. Stability: TIle stability of a system refers to the ability of a system to return back to its steady state when subjected to, a disturbance. As mentioned before, power is generated by synchronous generators that operate in synchronism' with the rest of the system A generator is synchronized with frequency, voltage and phase sequence. We as the ability of the power system to synchronism Usually power system State, Transient and Dynamic Stability.

a bus when both of them have same can thus define the power system stability return to steady state without losing stability IS categorized into Steady

3. With the help of schematic diagram, explain load management technique. [Dec 2013/Jan 2014] Load management: • Load management, also known as demand side management (DSM), is the process of balancing the supply of electricity on the network with the electrical 10ad by adjusting or controlling the load rather than the power station output. • This can be achieved by direct intervention of the utility in real time, by the use of frequency sensitive relays triggering circuit breakers (ripple control), by time clocks, or by using special tam to influence consumer behavior. • Load management allows utilities to reduce demand for electricity during peak usage times, which can, in turn, reduce costs by eliminating the need for peaking power plants. Department of EEE, SJB!T

Page 13

Power System planning

•

In addition, peaking power plants challenges should a plant go off-line Load management can also help backup generators are often dirtier load-management technologies are industry and public entities.

10EE761 also often require hours to bring on-line, presenting unexpectedly. reduce harmful emissions, since peaking plants or and less efficient than base load power plants. New constantly under development both by private

4. Explain reactive power balance in power system [Dec 20l3/Jan 2014] Large flows of reactive power have been observed in parts of the network with a large penetration of wind power. -The transfer of reactive power leads to the following problems:Occupation of active power transfer capacityThermal lossesVoltage differencesOccupation of dynamic compensation reservesDecrease in vohage stability margin -The installation of reactors, capacitors, SCs, SVCs or STATCOMs in the transmission ystem is expensive -Only little knowledge of the actual reactive power flows in the distribution systems.

5. With the help of block diagram, explain computerized management of power system. [Dec 2013/Jan 2014]

Computerized management: Research shows that personal computers (PC) are not being actively used during the vast majority of the time that they are kept on. It is estimated that an average PC is in use 4 hours each work day and idle for another 5.5 hours. It's also estimated that some 30-40 percent of the US's work PCs are left nmning at night and on weekends. Office equipment is the fastest growing electricity load m the commercial sector. Computer systems are believed to account for 10 percent or more of commercial electricity consumption already. Since computer systems generate waste heat, they also increase the amount of electricity necessary to cool office spaces. For the Medical Center, we estimate the savings from PC power management to be hundreds of thousands of dollars annually, even without factoring in increased office cooling costs. Considerable savings are also possible from easing wear-and-tear on the computers themselves.

Department of EEE, SJBIT

Page 14

•

•

Power System planning

lOEE761 UNIT 7&8

1. Develop mathematical objective function of power system expansion planning. [Dec 2013/Jan 2014] A mathematical optimization technique formulates the problem in a mathematical representation; as given by (2.2) through (2.4). Provided the objective fimction and/or the constraints are nonlinear, the resulting problem is designated as Non Linear optimization Problem (NLP). A special case of NLP is quadratic programming in which the objective fimction is a quadratic fimction of x. If both the objective fimctions and the constraints are linear fimctions of X, the problem is designated as a Linear Programming (LP) problem Other categories may also be identified based on the nature of the variables. For instance, if x is of integer type, the problem is denoted by Integer Programming (IP). Mixed types such as MILP(Mixed Integer Linear Progrannning) may also exist in which while the variables may be both real and integer, the problem is also of LP type. For mathematical based formulations, some algorithms have, so fur, been developed; based on them some commercial software have also been generated. In the following subsections, we briefly review these algorithms. We should, however, note that generally speaking, a mathematical algorithm may suffer from numerical problems and may be quite complex in implementation.· However, its convergence may be guaranteed but finding the global optimum solution may only be guaranteed for some types such as LP. There is no definite and fixed classification of mathematical algorithms. Here, we are not going to discuss them in details. Instead, we are going to introduce some topics which are of more interest in this book and may be applicable to power system planning issues.l Some topics, such as game theory, which are .of more interest for other power system issues (such as market analysis of power ystems); are not addressed here. 2. What are the constraints expansion planning? Constraints

observed

during optimization process of power system [Dec 2013/Jan 2014]

The constraints to be observed during the optimization process are as follows: •

Generation capacity: the capacity sum of newly installed and existing generating units are more than or equal to the load demand plus reserve in each year within planning period.

•

Reliability: the reliability index LOLP is used to evaluate adequacy of generating units. LOLP index of critical period in year t and

•

The presence of hydro power plants: this constraint expresses the maximum energy obtained from a hydro power plant in the different periods of the planning horizon at different climatic conditions.

•

Fuel constraint: maximum fuel supply of different fuel types of thermal plants.

•

Emission constraint: maximum production rate of pollution.

Department of EEE, SJBIT

Page 15

Power System planning

1OEE76 1

3. Explain in brief two optimization techniques. [Dec 20l3/Jan 2014] Energy consumption is rapidly increased in development countries, which effects global climate change and global and regional energy management. Among the various kinds of energy carriers, electricity has a special role in helping to attain social and economic development. The problem of power system planning may be classified as generation expansion planning (GEP), transmission expansion planning (TEP), and distribution expansion planning (DEP). This decomposition is normally performed to make the very highly complex combined problem possible. Generation Expansion Planning (GEP) is considered one of major parts of power system planning issues. The aim of GEP is to ';k the most economical generation expansion scheme achieving an acceptable reliability level according to the forecast of demand increase in a certain period of time. The feasibility of the generation structure, the cost of primary energy resources and fuel for the scheme, and the reliability indices of electricity supply, make generation planning

•

a very complicated optimization mathematically. Some of these restrictions have been applied in GEP in the recent literature WASP-IV is powerful software developed by International Atomic Energy Agency (IAEA) in which a dynamic programming approach is employed to find an overall optimal required generation capacity for the network so that an index, such as LOLP, is minimized.

4.

Explain least cost optimization problem

[Dec 20l3/Jan 2014]

Optimization Techniques: In everyday life, all of us are confronted with some decision makings. Normally, we try to decide or the best. If someone is to buy a commodity, he or she tries to buy the best quality, yet with the east cost. These types of decision makings are categorized as optimization problems in which the aim. is to find the optimum solutions; where the optimum may be either the least or the most. Most of the operational and planning problems consist of the following three major steps • Definition • Modeling • Solution algorithm Decision variables are the independent variables; the decision maker has to determine their optimum values and based on those, other variables (dependent) can be determined. For instance, in an optimum generation scheduling problem, the active power generations of power plants may be the decision variables. The dependent variables can be the total fuel consumption, system losses, etc. which can be calculated upon determining the decision variables. In a capacitor allocation problem, the locations and the sizing of the capacitor banks are the decision variables, whereas the dependent variables may be bus voltages, system losses, etc. Mathematical Algorithms. Department of EEE, SJ8IT

Page 16

•