Report On Workshop: Submitted By

REPORT ON WORKSHOP

SUBMITTED BY

NAME

: V.KRISHNAN

COURSE

: ELECTRICAL TRANSIENT AND ANALYSIS PROGRAM

TRAINING PERIOD

: 08.12.2018 to 08.01.2019

DATE OF SUBMISSION : 21.12.2018

Power system studies on ETAP (Electrical Transient and Analysis Program) Modules available in ETAP: 1. Load flow analysis 2. Short circuit studies 3. Motor acceleration studies 4. Harmonic studies 5. Transient stability 6. Relay coordination 7. Arc flash studies 8. Optimal power flow 9. Unbalanced loadflow 10. DC Load flow 11. DC Short Circuit 12. Ground Grid Design 13. Cable Ampacity 14. Cable Puling 15. etc 16.

1. Load flow analysis : Objective of the load flow analysis is to determine the following things o Component loading or circuit loading Steady state bus voltage Real, Apparent, Reactive power flow Modelling of Transformer tap position System loss Generator / excited voltage set points Performance under emergency condition (Contingency Analysis) Steady State Stability Limit 2. Standards:o 1. IEEE - 399 : Recommended Practice for Industrial and Commercial • Power Systems Analysis o 2. IEC 60034 : Rotating Electric Machines o 3. IEC 60076 : Transformers

60038 60050 60502 60909 61363

3.Ferranti Effect: During light load / No load conditions in Long/ Very Long, HV / EHV line, Vr > Vs due to shunt capacitance. This is called Ferranti effect. It is more pronounced with increase frequency. In DC there is no Ferranti effect since there is no Capacitive reactance effect. Receiving end voltage will be higher than the sending end voltage at no load condition and low load condition in EHV/HV lines and long transmission lines. Types of Transmission lines:1. Short transmission line ( below 80 km ) 2. Medium transmission line ( 80 – 160 km ) 3. Long transmission line ( above 160 km ) • •

When the distance between the conductor and ground is low then the shunt capacitance will be high ( Hill areas ) Transposition is required in long transmission line to reduce the unbalance in line parameters

4. Surge Impedance Loading: Surge Impedance Loading is a very essential parameter when it comes to the study of power systems as it is used in the prediction of maximum loading capacity of transmission lines. Define surge Impedance Loading 5.

Simulation for SIL:

a)

Ferranti Effect

Plot kW, kVAR As per above simulation in Sending end voltage is greater than receiving end voltage Bus 1 voltage = 400 kV Bus 2 voltage = 427 kV Transmission parameters, Z = 0.1 + 0.4j and Y = 3.6 x 10^-6

b) At SIL

Voltage at sending end and receiving end will be same at SIL. (Here SIL is calculated with R=0 and simulation R = 30 ohm hence the drop in voltage due to R. Repeat the simulation with very small R value) In this case surge impedance load is connected to bus 2 as per calculation, Now voltage at the receiving end is controlled. 𝐿

Zs = √𝐶 𝑍

𝑅+𝑗𝑋

Which is derived from SIL = √𝑌 = √𝐺+𝑗𝐵

Shunt Conductance (G)is negligible in T.L Therefore substitute the line parameters then we get Surge impedance Zs= 333.33 ohm

Interns of power S = V2 / Zs = 4002 / 333.33 = 480 MVA So in above simulation 480 MVA static load is connected in bus 2 and the receiving end voltage is controlled Vs = 400kV , Vr = 366.3 kV ( results obtained from simulation)

Prepare manual calculation for Ferranti effect (Reactive power generated and Consumed)

Identify the right shunt reactor value to reduce the Vr during no load

6. Types of Buses:1. Swing bus 2. PV bus ( Voltage control bus ) 3. PQ bus ( load bus )

Bus

Known

Unknown

Slack

Voltage, Angle , PD, QD

PG , QG

PV

PG, Voltage , PD, QD

QG , Angle

PQ

PD, QD, PG, QG

Voltage and Angle

7. Types of Loads:Varies types of loads are there, ZIP load is called constant Impedance load, constant current load, constant power load. 1. Constant Impedance load (Ex: Heater, Any R L C loads) 2. Constant Current Load (Ex: Any power electronic device, Mobile charger) 3. Constant Power Load (Ex: Motors) Refer the book Voltage stability by Cutsum a)Power consumption formula for the ZIP load:

𝑽 𝟐

𝑽

𝐕𝟎

𝐕𝟎

P= P0[𝒂 ( ) + 𝒃 ( ) + 𝒄]

where P = Real power, Q= Reactive power ,

𝐕

𝟐

𝐕

Q= Q0[𝐚 (𝐕𝟎) + 𝐛 (𝐕𝟎) + 𝐜]

a – impedance, b – current, c – power

8. Simulation:Name plate tab of the Lumped load screenshot is given below. In Load type property for o constant power load – 100 % has to set on constant KVA o constant impedance load – 100 % on constant Z o constant current load – Model type –>Polynomial Ratings- p1 = 0 (impedance), p2 = 1 ( current) , p3 = 0 (power) a)Lumped load screenshot:

9. Example for ZIP load: o 25 MW constant current load from voltage source with V = 0.95pu and calculate the power consumption on the load o As per the manual calculation using the above formula for power consumption on ZIP load o P = 23.75 MW (Validate with manual calculation using formula) o and simulation results for the same problem also given below, as per simulation real power consumption (P) on load is P = 23.8 MW (Plot it in kW so that results are more accurate) o

10. Simulation: a)

Simulation for power consumption on Constant current load

Solve all three questions Solve a question with combination on all type of loads and simulate to validate. 11. Tap changer: The purpose of a tap changer is to regulate the output voltage of a bus. It does this by altering the number of turns in HV winding and thereby changing the turns ratio of the transformer. Two types of tap changer are there. 1. On Load Tap Changer 2. Deenergised Tap Changer o Tap changers are always installed in HV side of the transformer because in HV side current will be low so that arc is reduced while changing the tap o HV side of the transformer has more winding so it has enough space to provide more number of taps. 1. on Load Tap Changer: OLTC is used for changing the tap of the transformer while it is connected to load. Modelling of OLTC:Formula for modelling the no of steps of OLTC Steps of OLTC =

Max−min step

+ 1

Where, Max = maximum range of the OLTC Min = minimum range of the OLTC Steps = Range of the taps (default values = 1.25, 2.25) Upper band and lower band =

1.25 2

= ±0.625

Simulation:Simulation performed for modelling OLTC of Transformer for the following condition •

choose the tap ratio to maintain the 11kv voltage within ±5 % tolerance for the system shown in simulation when the 110 kv grid voltage fluctuates from -17.5 % to 12.5 % and load changes from 10MW to 38 MW ( lumped load is 100% constant power load )

Taps has to be designed in a way that for the following maximum and minimum conditions the 11kv bus voltage fluctuations has to be within ±5 % Conditions:Grid voltage = 112.5% , 11 kv bus voltage = +5 % , Load = 38 MW (pf??) Grid voltage = 82.55% , 11 kv bus voltage = -5 % , Load = 38 Grid voltage = 112.5% , 11 kv bus voltage = +5 % , Load = 10 Grid voltage = 82.5% , 11 kv bus voltage = +5 % , Load = 10

From above conditions Max range of OLTC = 7.5 Min range of OLTC = -12.5 Steps = 1.25

Formula for modelling the no of steps of OLTC Steps of OLTC =

Max−min step

+ 1

Values are substituted in the above formula. No of steps = 17 a)Tap setting of transformer :

a) After providing taps to transformer simulation done for above four conditions

Display the tap position •

From simulation results 11kv bus voltage is maintained for ±5% tolerance by providing taps to transformer as modelled

tap changer: It is used for providing taps for the transformer when it is not connected to load. Percentage of the tap can be given in fixed tap row as per shown in the screenshot a) off load tap changer setting

Power factor correction:Because of change in grid voltage, bus voltage the power of grid may change. To maintain the power factor capacitor banks has to be connected parallel to the loads. Formulas for power factor correction:1. 2. 3. 4. 5. 6.

P = I2 R P =√3VIcosɸ Q = I2 X Q = √3VIsinɸ S = I2 Z S = √3VI

7. S= √P 2 + Q2 P

8. cosɸ = S

Example:•

Find out grid power factor for the given system. What is the capacitor rating required to boost the grid power factor to 0.95 when the load of 38 MW, 0.8 PF load is connected to bus 2... Validate the results with manual calculation

a) Power factor correction simulation

b) Reactive power flow from grid and Reactive power compensated by capacitor bank

•

• • •

•

Grid PF is found from simulation 𝑐𝑜𝑠ɸ = 0.74 Pf to be maintained 𝑐𝑜𝑠ɸ(𝑛𝑒𝑤) = 0.95 Capacitor bank value calculated = 17.14 Mvar From PF correction formula From simulation b) we can find out the reactive power demand of the load 22.8 Mvar is compensated by the capacitor bank (17.14 Mvar) and the reactive power flow from grid is also reduced from 27.5 to 9.3 Mvar because the required reactive power to maintain Pf at 0.95 is compensated by capacitor bank. Hence power factor correction at grid to 0.95 is done

Contingency Analysis: (Kindly note contingency and configuration are different) Contingency Analysis is a major activity in power system planning and operation. In general an outage of one transmission line or transformer may lead to over loads in other branches and/or sudden system voltage rise or drop. Contingency analysis is used to calculate violations. Example: Contingency analysis is done for the following Single line diagram a) Single Line Diagram

2.5MVA transformer is ONAN only (3.125 should be 2.5) 6.6/0.433 Display the transformer Impedance, Load rating etc

b) Conditions: Peak Generation Normal Generation Minimum Generation Peak load Normal load Minimum load

90% - is it Voltage or Power? 100% 110% 90% - is it Voltage or Power 70% 20%

c) Cases:

case 1 case 2 case 3 case 4

Service In

Service Out

Xmer 4, Xmer 2 , Xmer 3 Xmer 1, Xmer 3 , Xmer 4 Xmer 1, Xmer 2 , Xmer 3 Xmer 1, Xmer 2 , Xmer 4

Xmer 1 Xmer 2 Xmer 4 Xmer 3

Procedure and screenshot for applying the conditions and cases in Etap:a) Loading and Generation categories:Project – settings - loading category, generation category

b) Configuration for 4 cases:Configuration manager – New – case 1, case 2 , case 3 , case 4

•

In configuration manager cases can be created and In each case CBs also can be close and open c) Study case: New study case – Generation peak, Load Peak ( Pg, Pd )

d) Edit study case: a) Loading tab

• •

b) Alert tab:-

Edit study case – loading tab – loading and generation category is assigned as peak Alert tab - For all the equipments Critical, Marginal values can be given in percentage. If the bus voltage is going beyond the critical or marginal limits alert will be shown while running simulation.

e) Scenario wizard:

• •

•

For each study case new scenario has to be created and renamed as Pg Pd scenario Then for each configuration status of each study case, Output report name has to be changed then only for corresponding study case and configurations reports will be generated After selecting Scenario , Study case , Configuration we have to Run the simulation by clicking Run button

f) Study wizard:

o In study wizard all the scenario has to be added by clicking add button then after adding all the scenarios we have to run the simulation g) Load flow analyzer:

o In load flow analyzer all the study reports are shown here we can see for what is the cases simulation has been done. o Report type: General information, Bus results, Loads, Sources, Branch results can be viewed in report type tab. o All those reports can be exported in excel by clicking export.

Simulation reports:a) General:

b) Bus:

c) Branch

d)Load

e) Source

• •

various scenario is done for various scenario and configuration, results of Branch, Bus , Load , Source also obtained From the results obtained we can observe that Xmer 1 , Xmer 2 is over loaded for all the cases and categories so adding another Xmer in Bus 2 , Bus 8 or Increasing the capacity of the Xmer 1,2 shall be suggested as per results obtained from contingency analysis. Write your conclusions and recommendation based on the various scenario Present your results in much better way (Graphs instead of tables etc)

Short Circuit Analysis

Topics covered in Short circuit analysis:- (Write similarly for Load flow studies as well) 1. Short circuit and it’ effect 2. Types of faults 3. Types of unbalance 4. Value of fault current at different location (Explanation with example) 5. Objective of Short circuit studies 6. Standard for Short circuit studies 7. Limitations of IEC 60909 8. Assumptions in IEC 60909 9. Symmetrical components for Generator, Transformer, Transmission line 10. Grounding a) Effect due to Un grounding b) Purpose of Grounding c) Types of Grounding 11. Significance of X/R ratio 12. C-factor ETAP Practice Modelling in ETAP a) Simulation Questions 1,2,3 b) Inference from the result by using plot and data options

Short Circuit and its Effect:-

A short circuit is simply a low resistance connection between the two conductors supplying electrical power to any circuit. This results in excessive current flow in the power source through the ‘short,’ and may even cause the power source to be destroyed Effects:When a short circuit occurs, the current in the system increases to an abnormally high value while the system voltage decreases to a low value. 1. The heavy current due to short-circuit causes excessive heating which may result in fire or explosion. Sometimes short-circuit takes the form of an arc and causes considerable damage to the system. For example, an arc on a transmission line not cleared quickly will burn the conductor severely causing it to break, resulting in a long time interruption of the line. 2. The low voltage created by the fault has a very harmful effect on the service rendered by the power system. If the voltage remains low for even a few seconds, the consumer’s motors may be shut down and generators on the power system may become unstable. 3. Affects sensitive equipments operation. 4. Weakening the insulation. 5. For every 10 degree Celsius increase more than equipment insulation rated temperature its life will be reduced by 50 % Causes of fault:1. 2. 3. 4. 5. 6. 7. 8. Types of Faults:1. Symmetrical fault 2. Unsymmetrical fault

Symmetrical fault:-

Insulation failure Switching over voltage Lightning Overload Equipment damage Tree branches/ Birds Wind / Ice loading Environment / chemical pollution

➢ Line to line to line fault ( L-L-L) ➢ Line to line to line to ground fault ( L-L-L-G) • •

Severity of the fault is very high – 90 % Probability of fault occurrence is 2 %

Unsymmetrical fault:➢ Line to ground fault ( L-G) ➢ Line to line fault ( L-L) ➢ Line to line to ground fault ( L-L-G) •

•

•

(I could not get what you mean)Probability of occurrence 1. Line to ground fault ( L-G) – 85 % 2. Line to line fault ( L-L) – 8% 3. Line to line to ground fault ( L-L-G) – 5% Severity of the fault 1. Line to ground fault – 10 % (No, SLG fault is also severe in solidly earthed system) Single phase fault is greater than three phase fault when fault is near to the solid grounded Generator/Transformer and auto transformer

Value of the fault current at different location:• •

Example:-

If the fault is near to source then the fault current will be high because of low impedance between fault and source If the fault is away from the source then the fault current will be low because of higher impedance

• •

In this simulation bus 2,3,4 is faulted Fault current at bus 2 is higher than the fault current at bus 4

(Explain what fault you have created, What results are plotted) Objectives of short circuit studies:1. To find Short time withstand capacity of the equipment. 2. Circuit Breaker selection based on As- symmetrical fault current. 3. Information for relay setting. 4. Withstand capacity of the insulation. 5. Analysis of network behaviour during short circuit. 6. Cable selection based on Short circuit current.

Standards for short circuit analysis:1. IEC – 60909 – For short circuit analysis steady state studies 2. IEC – 61363 – For transient state studies

3. ANSI C57

- Short circuit analysis for 60 Hz systems

Assumptions in IEC – 60909: (Extract from the standard,) 1. 2. 3. 4. 5. 6.

Three phase fault current occurs simultaneously Type of fault is same for the entire Short circuit duration. No change in network parameters during short circuit Arc path resistance is negligible. Transformers shunt elements are neglected. Positive, negative, zero sequence shunt capacitance is neglected on high impedance transmission line. 7. For low impedance transmission line only zero sequence shunt capacitance is considered. 8. All the faults are considered as bolted fault ( fault path impedance is zero). 9. Non rotating loads are neglected. Limitation of IEC – 60909:1. 2. 3. 4.

It can be used up to 550 KV only. It can be used for both 50 Hz and 60 Hz. For laboratory and instrument testing IEC-60909 is not applicable. It cannot be used in shipping and aircraft applications

Sequence components:For analysis purpose un-symmetrical components shall be changed into symmetrical components after mathematical calculations or analysis again symmetrical components can be changed into un-symmetrical components. 1. Zero sequence components 2. Positive sequence components 3. Negative sequence components Un symmetrical components in terms of symmetrical components Va = Va0 + Va1 +Va2 Va = Vb0 + Vb1 +Vb2 Vc = Vc0 + Vc1 +Vc2

Symmetrical components of Generator:-

• • •

• •

Negative sequence reactance and positive sequence reactance are greater than zero sequence reactance Va1 = Ea1 - Ia1 Za1 Va2 = - Ia2 Za2 Va0 = - Ia0 ( Zao 3 Zn ) X0 < X2 < Xd”

Symmetrical components of Transformer:• • •

•

In Transformer positive, negative, zero sequence impedance are same Z0 = Z1 = Z2 But Zero sequence impedance of the transformer value is depends upon winding configuration If the transformer winding is 1. Star delta Z0= 0 2. Delta star Z0 = Z1 or Z2 Positive , Negative sequence impedance will be same Z 1 = Z2 Z0 is 90% to 110% of Z1 as per IEC 60076

Symmetrical components of Transmission line model:• •

In transmission line positive and negative sequence components are equal Zero sequence reactance will be 3 times of positive sequence reactance 1. Z0 = Zs +2 Zm 2. X0 = 3X1 3. X1 = X2

Fault current formula:-

𝟑 𝐄𝐚𝟏

1. L-G Fault current If = 𝒁𝟏+𝒁𝟐+𝒁𝟎+𝟑𝒁𝒏+𝒁𝒇 √𝟑 𝐄𝐚𝟏

2. L-L fault current

If = 𝒁𝟏+𝒁𝟐

3. L-L-G Fault current

If = 𝒁𝟏+𝒁𝟐 𝑰𝑰 (𝒁𝒐+𝟑𝒁𝒏)

4. Three phase fault current If =

𝟑 𝐄𝐚𝟏

𝐄𝐚𝟏 𝒁𝟏+𝒁𝒇

Where Ea1 – Positive sequence supply voltage Z0 , Z1 , Z2 , - Zero, positive, Negative sequence Impedance Zn - Neutral Impedance Zf - Fault path impedance ( As per IEC 60909 Fault path impedance is negligible )

Types of Grounding:- (Refer V K Metha & Earthing Practices 1 and Earth Practices II by Dr K Rajamani) 1. Equipment Grounding:Non conducting metal part is connected to ground. Equipment grounding is used to protect the equipment and personnel. 2. System Grounding:Neutral of the system is connected to ground. It is used to protect the system. There are various types of system grounding. 1. Solid grounding 2. Resistance grounding 3. Reactance grounding 4. Resonance grounding 5. Ungrounded System C-Factor:- (Extract the table given in IEC 60909) It is source voltage correction factor as per IEC 60909 minimum and values are given below C max= 1.1 C min = 1.0

maximum

a)C-Max:

b)C-Min:

X/R for Peak Current:•

Method A – Using the uniform ratio X/R in calculating the peak current

•

Method B – Using the X/R ratio at the short circuit location in calculating the peak current

•

Method C – Using equivalent frequency in calculating the peak current

C) ANSI

•

As per ANSI C37 standard pre-fault voltage can be fixed as shown in screenshot.

X/R Ratio:• • • • •

It is the ratio of reactance and resistance. For any system reactance will be greater than the resistance If resistance is greater than the reactance then there will be more loss So the X/R ratio has to be more than 1 If the reactance value is very high then reactive drop will be high so the value has to be optimum. As per IEC 62271 for 50 Hz system X/R = 14 (Relate with time constant and Power factor, IEC 62271) 60 Hz system X/R = 17

Transformer impedance tolerance:• •

For the short circuit studies impedance tolerance is important factor. Negative impedance tolerance of the equipment will be used for short circuit studies because in negative tolerance impedance value will be low so the current will be high so it should be considered for short circuit studies. If % of Z <= 10 then tolerance will be ±10 % of Z > 10 then tolerance will be ±7.5

Example:-

For the given system three phase and single phase fault current at bus 3has to be find out. a)SLD-1 for Short circuit studies

Grid Parameters: Rated KC= 33kV X/R = 14 KAsc = 40

Transformer Parameters: Voltage = 33/11 KV Base MVA = 25 Impedance = 10 % Z tolerance = ±10

X/R = 20 (typical value taken) Grounding = Solid grounding Manual calculation:- (Prepare in an excel sheet and attach) If the fault is at bus 3, all the equipments impedance has to be calculated which is connected till bus 3 Generator Impedance Per unit value can be calculated from following formulas. •

MVAsc = √𝟑 𝑲𝑽 𝑿 𝑲𝑨𝒔𝒄 Where MVAsc – Short circuit power KV - Rated voltage KAsc – Short circuit capacity per second

•

Zp.u =

𝐙𝐬 𝐚𝐜𝐭𝐮𝐚𝐥 𝐙𝐬 𝐛𝐚𝐬𝐞

Where Zp.u = Source Impedance per unit Zs.base = Base Impedance Zs.acutal = Actual Impedance ` •

Zs.base =

𝐊𝐕𝐛𝟐 𝐌𝐕𝐀𝐛

Where KVb - Base voltage MVAb = Base power (MVA) •

X/R = 14 so X= 14 R

•

Z= √𝑹𝟐 + 𝑿𝟐

Transformer Impedance shall be calculated by given formulas. %𝐙

•

Zp.u =

•

Zold = Zp.u - 10% of Zp.u

•

ZT.Pu = Zpu.old X (𝑲𝑽𝒃.𝒏𝒆𝒘) X ( 𝑴𝑽𝑨 𝒃.𝒐𝒍𝒅 )

𝟏𝟎𝟎

𝑲𝑽𝒃.𝒐𝒍𝒅 𝟐

𝑴𝑽𝑨 𝒃.𝒏𝒆𝒘

For Transmission Line Impedance shall be calculated by given formulas. •

Zp.u =

𝐙𝐬 𝐚𝐜𝐭𝐮𝐚𝐥 𝐙𝐬 𝐛𝐚𝐬𝐞

•

Zs.base =

𝐊𝐕𝐛𝟐 𝐌𝐕𝐀𝐛

Fault current calculation. 𝟑 𝐄𝐚𝟏

1. L-G Fault current If = 𝒁𝟏+𝒁𝟐+𝒁𝟎+𝟑𝒁𝒏+𝒁𝒇 𝐄𝐚𝟏

2. Three phase fault current If = 𝒁𝟏+𝒁𝒇 3. Actual fault current If.actual = If.p.u X Ibase Simulation of short circuit analysis: •

Simulation as per IEC 60609

a) Single phase fault current

b) Three phase fault current

Display the results at right place (19.05kV & 6.34kV at same bus???)

C) Manual and Simulation results are compared: Note: Manually calculated values has to be multiplied by Cmax = 1.1 Three phase fault current(KA)

Bus 3

Single phase fault current ( KA)

Simulation

Manual

Simulation

Manual

1.52

1.38

0.952

0.86

Formula for manual calculation: 𝑽𝒎

1. Iss = |𝒁|√𝟐 ( Steady state current ) 2. Vrms =

𝐕𝐦𝐚𝐱 √𝟐

𝑽𝒎

3. Isym = Iss = |𝒁|√𝟐 (Initial Symmetrical RMS fault current ) ( Irms) 4. IAsym = √𝑰𝒕𝒓𝟐 + 𝑰𝒔𝒚𝒎𝟐 ( Initial As-symmetrical fault current ) 5. Imm.rms = 2 Ip ( maximum momentry RMS fault current ) = 2 √𝟐 Isym 6. Ip = Peak current = Irms =

𝐈𝐦𝐚𝐱 √𝟐

7. Im.rms = √𝟑 𝑿 𝑰𝒔𝒚𝒎 ( momentry RMS fault current ) 8. Idc.rms = √𝟐 X Isym Where Vm = Maximum voltage Itr = Transient Current, |𝒁| =Magnitude of Impedance •

The entire fault currents can be obtained from simulation also. Simulation results given below

Simulation: (Where IEC 61363 is used, Why) • •

Simulation has to be run for IEC 61363 Select IEC 61363 plot graphs

a)IEC 61363 Plot selection: Discuss three cases Grid with Infinite X/R Grid with X/R = 14 Physical Generator

b) Percent of DC component fault current:

C) A.C component fault current:-

•

By clicking on line -> data - > values can be obtained

d) Top envelop of fault current:

e) DC component fault current:

f)Total fault current:-

Report for simulation:-

• •

All the values which are calculated manual shall be compared with simulation report. As-symmetrical is used for selecting circuit breakers rating.

Three Phase fault on NO load Operating Generator:• • • • • • •

During transient period transient reactance will be lower than sub transient reactance. And sub transient reactance will be lower than steady state reactance Xd” < Xd’ < Xd So that Transient fault current will be higher than the sub transient and steady state fault current If” > If ‘ > If Induction machine fault current will decrease to steady state on 2 to 4 cycles Synchronous machine fault current will decrease to steady state on 6 to 8 cycles

Write your understanding and conclusions

1. Harmonic Analysis: Objective: • •

•

The presence of harmonics in electrical systems means that current and voltage are distorted and deviate from sinusoidal waveforms. In power systems, harmonics are defined as positive integer multiples of the fundamental frequency. Thus, the third order harmonic is the third multiple of the fundamental frequency. There are two types of harmonics. 1. Current Harmonics. 2. Voltage Harmonics.

Current Harmonics: •

•

Current harmonics are caused by non-linear loads. When a non-linear load, such as a rectifier is connected to the system, it draws a current that is not necessarily sinusoidal. The current waveform can become quite complex, depending on the type of load and its interaction with other components of the system.

Voltage harmonics: •

•

Voltage harmonics are mostly caused by current harmonics. The voltage provided by the voltage source will be distorted by current harmonics due to source impedance. If the source impedance of the voltage source is small, current harmonics will cause only small voltage harmonics. It is typically the case that voltage harmonics are indeed small compared to current harmonics.

Sources Of Harmonics: •

Switched Mode Power supply.

•

Uninterrupted Power Supply.

•

Soft Starter.

•

Electronic Ballast.

•

Arc Furnace.

•

Discharge Lamps

•

Rectifier.

Effects of Harmonics: • • • •

The possibility of amplification of some harmonics as a result of serial and parallel resonance. Performance reduction in generation, transport and energy usage systems. The aging of the grid insulation components and as a consequence, energy reduction. Malfunctioning of the system or some of its components.

• • • •

False tripping of branch circuit breakers. Metering errors. Lower system power factor, resulting in penalties on monthly utility bills. Increased internal energy losses in connected equipment, causing component failure and shortened life span.

Need for Harmonic analysis: Harmonic studies are performed to determine harmonic distortion levels and filtering requirements within a facility and to determine if harmonic voltages and currents are at acceptable levels. Harmonic studies has to be done for the following conditions. • • •

Harmonic loads are 30 to 50% of total load. Wherever voltage sensitive devices are available. Harmonics studies has to be done for all the industry.

Total Harmonic Distortion: Total harmonic distortion, or THD, is the summation of all harmonic components of the voltage or current waveform compared against the fundamental component of the voltage or current wave.

Individual harmonic distortion: Individual harmonic distortion is the ratio between the RMS value of the individual harmonic and the RMS value of the fundamental. %IHD =

𝐈𝐧

In =

I1

𝐈𝟏

n

Where In = Harmonic current, I1 = Fundamental current , n = Harmonics

Harmonic Limits: •

As per the IEEE 519 standard, there are limits for voltage and current harmonics.

•

Voltage harmonic limits are mentioned in the following table 1.

•

Current harmonic limits are mentioned in the following table 2.

Table:

S.No

Voltage Rating

% IHD

% THD

1

Up To 1KV

5

8

2

1KV < V <69 KV

3

5

3

69KV
1.5

2.1

4

Above 161 KV

1

1.5

Power Factor: There are three types of power factor. •

Displacement Power Factor.

•

Distortion Power Factor.

•

True Power Factor.

Displacement Power Factor: • •

The displacement power factor is the power factor due to the phase shift between voltage and current at the fundamental line frequency. Displacement power factor = Cos (ɸ)

Distortion Power Factor: •

Distortion power factor is caused by the presence of harmonics in the current waveform.

•

Distortion P.F =

•

Distortion power factor should always less.

𝟏 √𝟏+𝐓𝐇𝐃𝟐

True Power Factor: • •

True power factor is defined as the product of Displacement power factor and Distortion power factor. True power factor = Displacement power factor x Distortion power factor

Total Demand Distortion(TDD): √∑n h=1 Ih2

TDD = Load Current

K-Rated Transformer: K-factor transformers are designed to reduce the heating effects of harmonic currents created by loads. • •

The K-factor rating is an index of the transformer's ability to withstand harmonic content while operating within the temperature limits of its insulating system. K-factor is a weighting of the harmonic load currents according to their effects on transformer heating, as derived from ANSI/IEEE C57.110. A K-factor of 1.0 indicates a linear load (no harmonics). The higher the K-factor, the greater the harmonic heating effects.

Harmonic Sequence: •

Harmonic sequence refers to the phasor rotation of the harmonic voltages and currents with respect to the fundamental waveform.

•

Harmonics are grouped into positive , negative and zero, sequence components.

•

Positive sequence harmonics (harmonic numbers 1, 4, 7, 10, 13, etc.) produce magnetic fields and currents, rotating in the same direction as the fundamental frequency.

•

Negative sequence harmonics (harmonic numbers 2, 5, 8, 11, 14, etc.) develop magnetic fields and currents that rotate in a direction opposite to the fundamental frequency set.

•

Zero sequence harmonics (harmonic numbers 3, 9, 15, 21, etc.) do not develop usable torque, but produce additional losses in the machine. Zero sequence harmonics are those harmonics which doesn’t rotate at all because they’re in phase with each other.

Harmonics Injected By Pulse: •

Pulse converter is used to reduce the harmonics. The higher the pulse, harmonics level will be reduced. np± 1 (where P- no of pulses )

•

When the pulses are high then the Harmonics will be less

Mitigation of Harmonics: There are two ways to mitigate the harmonics. 1. Passive Filter 2. Active Filter

Passive Filter: Passive or Line harmonic filters are also known as harmonic trap filters and are used to eliminate or control more dominant lower order harmonics specifically 5th, 7th, 11th and 13th. •

It can be either used as a standalone part integral to a large nonlinear load (such as a 6-pulse drive) or can be used for a multiple small single phase nonlinear loads by connecting it to a switch board.

•

LHF is comprised of a passive L-C circuit (and also frequently resistor R for damping) which is tuned to a specific harmonic frequency which needs to be mitigated (for example, 5th, 7th, 11th, 13th etc).

•

Their operation relies on the “resonance phenomenon” which occurs due to variations in frequency in inductors and capacitors.

Active Filter:

•

Active filters are now relatively common in industrial applications for both harmonic mitigation and reactive power compensation (i.e., electronic power factor correction).

•

Unlike passive L-C filters, active filters do not present potential resonance to the network and are unaffected to changes in source impedance.

•

Shunt-connected active filters (i.e. parallel with the nonlinear load) are the common configuration of the active filter.

•

The active filter is comprised of the IGBT bridge and DC bus architecture similar to that seen in AC PWM drives. The DC bus is used as an energy storage unit.

•

The active filter measures the “distortion current” wave shape by filtering out the fundamental current from the nonlinear load current waveform, which then fed to the controller to generate the corresponding IGBT firing patterns to replicate and amplify the “distortion current” and generate the “compensation current”, which is injected into the load in anti-phase (i.e. 180° displayed) to compensate for the harmonic current.

•

When rated correctly in terms of “harmonic compensation current”, the active filter provides the nonlinear load with the harmonic current it needs to function while the source provides only the fundamental current.

•

Active filters are complex and expensive products. Also, careful commissioning of active filter is very important to obtain optimum performance, although “self tuning” models are now available.

•

However, active filters do offer good performance in the reduction of harmonics and the control of power factor. Their use should be examined on a project-by-project basis, depending on the application criteria.

Manual Calculation for Modeling Harmonic filters: 𝐊𝐕 𝟐

Xbank perphase = 𝐌𝐕𝐀𝐫 Xbank = XL - Xc nXL =

𝐗𝐜 𝐧

XL = Lѡ

( At resonance condition )

Where ѡ = 2ᴨF L=

𝐗𝐋 𝟐ᴨ𝐅

Xc = n2 XL 𝟏

Xc = 𝐜ѡ 𝟏

C= 𝟐ᴨ𝐟𝐗𝐋

Example: a) Harmonics analysis for the given SLD: • Load flow analysis has been done and screenshot given below

b) Harmonics in Load:

•

•

In harmonic analysis Loads which are connected to the bus has to inject harmonics to bus for that Loads-> harmonics tab -> select the source from library That is 6 pulse device so 5th and 7th order harmonics will be injected by load

•

Formula for Harmonics order by no of pulse= np±1

c) Edit study case: • For which Bus THD value has to be found out will be selected in edit study case.

d) Harmonic analysis and % of THD: • Run Harmonic load flow

• • •

Total THD value is also obtained from simulations. For reducing the THD level. Harmonics filter has to be connected in load So appropriate Harmonic filter has to be modelled.

e) Harmonic filter:

• • • • •

To size the Harmonic filter Parameter tab – Size filter Harmonic order – 5 ( for 6 pulse) Harmonic current = 151.5 A (at PCC of Bus 2 Obtained from load flow analysis of SLD ) Existing Pf = 0.82 , Desired Pf = .95 Size filter and substitute

•

In parameter tab -> Rated KV =

•

Q factor = 40 ((XL1/RL1) for inductor L1.)

Max Kv √3

f) Harmonic analysis after connecting filters:

• • • • •

After addition of Harmonic filter. % of THD is reduced. THD = 16.06 % before adding filters THD = 3.69 % after addition of filter THD = 5 % ( For 11kv system as per IEEE 519 ) Now for 11 kv system % of THD as per IEEE 519 standard

g) Harmonic analysis plot:

•

From graph it can be observed that 5 th order harmonics at Bus 13 is reduced.

h) Harmonic analysis report:

• •

Harmonics of the Bus 2 and Bus 13 are obtained from Harmonic report. Hence the harmonic level at bus 13 is reduced by adding the Harmonic filter as designed.

Equipment Parameters for Each studies:

Not visible. Send the excel sheet Equipments

General

Load flow Analysis

Short circuit Analysis

Harmonic Studies

Bus

ID, Tag number, Standard , conductor typle

Nominal voltage, Condition , Connection

Nominal voltage, Condition , Connection

Nominal voltage, Condition , Connection

2 winding transformer

Id, Tag number , Service,Standard

Primary, secondary voltage, base MVA , % impedance, class , type, X/R value , Tap setting value , Grounding, phase shift

Primary, secondary voltage, base MVA , % impedance, class , type, X/R value , Tap setting value , Grounding, positive , zero sequence impedance, Impedance tolerance

Primary, secondary voltage, base MVA , % impedance, class , type, X/R value , Tap setting value , Grounding, positive , zero sequence impedance, Impedance tolerance, Harmonics

Bus duct

Id, Tag number , Service,Standard

Type and material ( cu,al).

Type and material ( cu,al).

Type and material ( cu,al).

Cable

Id, Tag number , Service

Cable type, insultation type , no of cores, type of Cable type, insultation type , no of cores, type of Cable type, insultation type , no of cores, type of concutor, voltage rating, no of runs, length, concutor, voltage rating, no of runs, length, Impedance ( concutor, voltage rating, no of runs, length, positive positive , zero sequence Impedance ( R, R, X, L , Y) , zero sequence Impedance ( R, X, L , Y), X, L , Y),

Transmission Line

Id, Tag number , Service

conductor type ( al, cu) , length , ground wire type, R, X values per km, configuration type , spacing , transposed

conductor type ( al, cu) , length , ground wire type, R, X values per km, configuration type , spacing , transposed ,Postive, negative , zero sequence impedance

conductor type ( al, cu) , length , ground wire type, R, X values per km, configuration type , spacing , transposed ,Postive, negative , zero sequence impedance

Reactor current Limiting

Id, Tag number , Service

voltage, current rating , connection, impedance

voltage, current rating , connection, impedance ,zero sequence , positive sequence impedance

voltage, current rating , connection, impedance ,zero sequence , positive sequence impedance

Impedance

Id, Tag number , Service

Rating

Rating,zero sequence , positive sequence impedance

Rating,zero sequence , positive sequence impedance

Power Grid

Id, Tag number , Service

Mode of operation ( configuration ), Rated voltage , X/R ratio

Mode of operation ( configuration ), Rated voltage , X/R ratio, MVAsc, Kasc, positive, negative, zero sequence impedance, balanced or un balanced

Mode of operation ( configuration ), Rated voltage , X/R ratio, MVAsc, Kasc, positive, negative, zero sequence impedance, balanced or un balanced ,Harminics library

Generator

Id, Tag number , Service

Mode of operation ( configuration ), Rated voltage , X/R ratio, power factor , MVA, MW , grounding type, Qmin , Qmax

Mode of operation ( configuration ), Rated voltage Mode of operation ( configuration ), Rated voltage , , X/R ratio, power factor , MVA, MW , grounding X/R ratio, power factor , MVA, MW , grounding type, zero sequence , negative sequence, type, zero sequence , negative sequence, transient transient reactance Xd" , Xd"/R reactance Xd" , Xd"/R, Harminics library

Induction Machine

Id, Tag number , Service

Rated Kv, Full load current (FLA ), Power factor, HP , Speed , Slip , No of poles , locked rotor current , PF

Rated Kv, Full load current (FLA ), Power factor, HP , Speed , Slip , No of poles , locked rotor current , PF, Zero sequence , negative sequence impedance , Transient reactence

Rated Kv, Full load current (FLA ), Power factor, HP , Speed , Slip , No of poles , locked rotor current , PF, Zero sequence , negative sequence impedance , Transient reactence, Harmonics

Sytnchronous Machine

Id, Tag number , Service

Rated Kv, Full load current (FLA ), Power factor, HP , Speed , Slip , No of poles , locked rotor current , PF

Rated Kv, Full load current (FLA ), Power factor, HP , Speed , Slip , No of poles , locked rotor current , PF, Zero sequence , negative sequence impedance , Transient reactence

Rated Kv, Full load current (FLA ), Power factor, HP , Speed , Slip , No of poles , locked rotor current , PF, Zero sequence , negative sequence impedance , Transient reactence, Harmonics

Lumped load

Id, Tag number , Service

Reted Voltage , Power, PF, Constant current , Impedance, Power load ,

Reted Voltage , Power, PF, Constant current , Impedance, Power load , LRC

Static Load

Id, Tag number , Service

Reted Voltage , Power, PF

Capacitor

Id, Tag number , Service

HV Circuit Breaker

Id, Tag number , Service,Standard

Id, Tag number , Service,Standard, status, Rated voltage, rated currert

Id, Tag number , Service,Standard, status, Rated voltage, rated currert , Short circuit current

LV Circuit Breaker

Id, Tag number , Service,Standard

Id, Tag number , Service,Standard, status, Rated voltage, rated currert

Id, Tag number , Service,Standard, status, Rated voltage, rated currert , Short circuit current, Trip device

Reted Voltage , Power, PF, Harmonics