Gas Turbine Manual

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328.1 MW COMBINED CYCLE GAS TURBINE MODULE

OPERATION MANUAL

KAWAS SIMULATOR CENTER KAWAS GAS POWER PROJECT NATIONAL THERMAL POWER CORPORATION LTD.

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EXECUTIVE DIRECTOR’S ADDRESS

Economic liberalisation, Power Sector reforms and challenges from power multinationals have awaken the Public Sector Giants having Navaratna status. Power has brought a sea change in the quality of living of the Indian population. However, with the increase of demand for Power from all sectors, the need of the hour is to opt for increase in Power Supply either by capacity addition or by capacity utilisation of our existing power stations. In the competitive environment, to keep edge over others and to maintain record performance, Power Giant NTPC has geared up to meet new challenges. Human Resource Development is the key of success for any industry. NTPC firmly believes that power plant engineers are to be trained regularly through high technology tools like Real Time Simulator which provides comprehensive training covering whole spectrum of normal and abnormal operations in a power plant. In this line, 328.1 MW Real Time Replica Simulator at Kawas is providing cost and time effective training to operation engineers of all NTPC Gas Power Projects and other power utilities from India & abroad since 1993. To augment systematic hands on training, the Kawas Simulator Centre has brought out this first revised Operation Manual edition in CD – FORMAT after carefully revising and adding a new topic on “Efficiency aspects of CCPP” and incorporating the feedback received from time to time. I hope that the revised edition will serve the need of the practising power engineers to run Gas Power Stations more efficiently and economically. However suggestions & comments for further improvement of this manual are welcome and will be appreciated. I believe that sincere efforts put by the Simulator staff and all faculty members from Kawas (O & M) Department to bring out this Operation Manual in CD - Format shall go a long way to help operation engineers to operate power station efficiently leading to better capacity utilisation and optimum Generation Cost. I wish all success to Kawas Simulator in its drive for creating a pool of talented power plant operators.

(L. V. RAO) EXECUTIVE DIRECTOR NTPC - WESTERN REGION

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COMBINED CYCLE GAS TURBINE MODULE – 328.1 MW STACK – 109 ºC

STACK – 109 ºC

PRE-HEATER

PRE-HEATER FEED WATER TANK

ECONOMIZER

H

EVAPO

R S G

SUPER HEATER

SUPER HEATER

ECONOMIZER

ECONOMIZER

B EVAPO

213 DEG, 7.6 BAR, 40 T/H

SUPER HEATER

520 DEG, 70 BAR, 171 T/H

BYPASS

HP GAS TURBINE

GAS FUEL LIQ FUEL

SUPER HEATER

STARTING DEVICE

CEX PUMPS

BYPASS GENERATOR

LP

COMPRESSOR

COMBUSTION CHAMBER

EVAPO

AIR GENERATOR

AIR

GENERATOR

GEN. X-FORMER

H R S G

EVAPO

HP

A

11.5 KV

COOLING TOWER

ECONOMIZER

CONDENSER HOTWELL

COMPRESSOR STARTING DEVICE

GAS TURBINE

COMBUSTION CHAMBER

LIQ FUEL

220 KV TRANSFER BUS

X

X 200 KV MAIN BUS-1

ULTIMATE PLANT CAPACITY STARTING DEVICE COMPRESSOR COMBUSTOR GAS TURBINE WASTE HEAT RECOVERY BOILER HP STEAM TURBINE LP STEAM TURBINE CONDENSER COOLING TOWER OUTGOING FEEDERS

X 200 KV MAIN BUS-2

328.1 MW + 328.1 MW 1000 KW CRANKING MOTOR. 17 STAGES, AXIAL FLOW TYPE CANNULAR TYPE, 14 PORTS, 2 IGNITERS 3 STAGE IMPULSE TYPE DOUBLE DRUM, NON-FIRING, FORCED CIRCULATION TYPE 13 STAGE, SINGLE FLOW 5 STAGE, DOUBLE FLOW 2 PASSES, STEAM IN SHELLS, WATER IN TUBES NATURAL DRAFT TYPE NAVSARI, HALDARVA, VAV, ICHHAPORE.

11.5 KV GEN. X-FORMER

CIRCULATING WATER

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INDEX NO. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

CHAPTERS Simulator – A Training Tool Introduction to Gas Turbine – GT Plant Kawas Package Power Plant Compressor Section Combustion Section Turbine Section Starting System Lubrication System GT Cooling Water System Cooling & Sealing air System Ventilation & Heating System Hydraulic Supply System & IGV Trip Oil System Gas Fuel System Liquid Fuel System Atomising air System Fire Protection System GT Operation GT Control System Speedtronic System GT Performance & Trouble Shooting Efficiency Aspects Of Gas Turbine

PAGE NO. 07 to 09 10 to 16 17 to 20 21 to 32 33 to 37 38 to 43 44 to 49 50 to 54 55 to 57 58 to 61 62 to 63 64 to 68 69 to 72 73 to 77 78 to 87 88 to 91 92 to 94 95 to 112 113 to 127 128 to 137 138 to 143 144 to 162

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(1) SIMULATOR –A TRAINING TOOL Introduction Kawas Gas Power Plant is composed of two combined cycle modules supplied by M/s GEC Alsthom – France. Each modules consists of two Gas Turbine Generators 106 MW each), two waste heat recovery boilers (CMIBelgium make) and one Steam Turbine Generator 116.1 MW. The Simulator is designed to reproduce real time behaviour of one module for following operating conditions: (1) Each Gas Turbine operating in opens cycle or combined cycle in base or droop mode. (2) Steam Turbine and Boilers operating in constant or sliding pressure mode. (3) Cold or hot start up, normal of emergency shutdown, steady or varying Load operation. (4) Automatic Control system, logics, protection and interlock systems. Basically Simulator consist of 1. Replica control panel consisting of Centralog CRT, Keyboard to function as Trainee Station. 2. The instructor Station with Simulator Computers. 3. Centralog Control Computers. The trainee station consists of a single Centralog, based on same hardware as used for reference plant. It consist of • • • • •

One 25” alarm colour CRT, Four 19” Colour CRT, Four Operator Keyboards, Three Log Printers Two Colour Hard Copiers.

These peripherals are controlled by a single distributed VME bus architecture using same components as in reference plant and consist of: CDS: CVS: UGG: CCC-S: CCC-M: CDS:

One data server for management of data traffic on network, Data storage and control of printers. Five operator station for mimic display, control and monitoring of process. Cluster head connected with Simulator computers for communication management. SUN-work station connected with Network to perform system start up shut down modification etc. Engineer workstation with 19” colour CRT and key board for creation and modification Mimics. One data server for management of data traffic on network, Data storage and control of printers.

The instructor station basically comprises of two 32-bit HEWLETT PACKARD Computers (HP 9000,834 CH) based on RISC processor technology and having UNIX operating system. Additionally two 19” Colour CRTs

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have been provided through which instructor can initiate, control & supervise a Training session. The instructor Station and trainee Station are connected through a high data link

Instructional features Simulator provides some very distinct and versatile tools in hands of instructor using which he can impart highly useful and flexible training. The instructor implements following training features from instructor console. INITIALIZATIOIN: - In Simulator, the plant conditions can be created to start a training session from different situations such as black start up condition, plant at 30 %, 45%, 60% or 100% Load condition. These various previously stored conditions facilitate to maintain the continuity of training without any time wastage. Such 20 pre-memorised initial conditions are provided. The instructor has the option to read, write or remove at any time a preselected initial condition. SNAP SHOP: - This facility is provided to create 10 additional initial conditions by taking snap shop of current process and C&I status TIME SCALING: - Simulator can operate in four different time scales. Real time, slow time ½, slow time1/10 and fast time. Simulator normally operates in real time mode. Slow time mode gives better grasping of fast transient phenomena. Fast time accelerates some sluggish processes to four times. FREEZE: - This mode interrupts the simulator and process parameters are frozen in current status. On removal, the simulation resumes. This feature allows instructor to explain during operation by temporarily freezing the process. BACKTRACK: - The status of process parameters is continuously memorised every minute and record is maintained for past 60 minutes which can be accessed as starting point. REMOTE FUNCTIONS: - The remote function allows instructor to perform any manual action on the field devices like opening / closing of a manual valve etc. which are not normally possible from central control room. There is a provision of 100 remote functions. MALFUNCTION: - The Simulation is designed to simulate 250 Malfunctions in process models. Such malfunction is of digital or analog type, the severity of the malfunction is specified by the instructor. CRY WOLF: - The instructor can spuriously modify any parameter value presented to trainee so as to test his ability to distinguish about the falseness of a value from other related data. CURVES: - Simulated process variables can be displayed as curves on a CRT. From menu, the instructor can modify, cancel or define up to 100 variables for which he wants to visualize the evolution in time. SOFTWARE ARCHITECTURE: The Simulator software is split in to four main blocks. • Simulation environment • The process Model • The C&I Model (Logic & regulation) • The CENTRALOG Control & supervision.

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The Simulator environment software provides services like configuration of system hardware, management of simulation sessions, and tools for development of C&I Models etc. The process model software does the basic math modelling of plant based on physical laws. It is built from elementary models such as valves, heater, pump, drum etc. which are connected together to correspond with actual process to be simulated. The process models have adjustable parameters such as volume, mass, heat exchange coefficient etc., so that models can be adapted to a given requirement. Process models are written in FORTRAN 77 language. The C&I models simulate the algorithms involved in control loops & logic circuits. The C&I models are written in GRAFSTEP and FORTRAN-77 language. The control and supervision software has same functional characteristics as the CENTRALOG system used to supervise the actual power plant.

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(2) INTRODUCTION TO GAS TURBINE GAS TURBINE PLANT Introduction The gas turbine is a common form of heat engine working with a series of processes consisting of compression of air taken from atmosphere, increase of working medium temperature by constant pressure ignition of fuel in combustion chamber, expansion of SI and IC engines in working medium and combustion, but it is like steam turbine in its aspect of the steady flow of the working medium. It was in 1939, Brown Beaver developed the first industrial duty gas turbine. The out put being 4000 KW with open cycle efficiency of 18%. The development in the science of aerodynamics and metallurgy significantly contributed to increased compression and expansion efficiency in the recent years. At Kawas, the GE-Alsthom make Gas Turbine (Model 9E) has an operating efficiency of 31% and 49% in open cycle and combined cycle mode respectively when natural gas is used as fuel. Today gas turbine unit sizes with output above 250 MW at ISO conditions have been designed and developed. Thus the advances in metallurgical technology have brought with a good competitive edge over conventional steam cycle power plant. Kawas Gas Turbine Plant: The modern gas turbine plants are commonly available in package form with few functional sub assemblies. The 9E model GEC-Alsthom package consists of • Control compartment • Accessory compartment • Turbine compartment • Inlet exhaust system • Load package • Generator excitation compartment • CO2 fire protection unit Each station component is a factory assembled pretested assembly & is housed in all weather & acoustic proof enclosure

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COMBINED CYCLE: Combine cycle power plant integrates two power conversion cycle-Brayton cycle (Gas turbine) and Rankine cycle (Steam turbine) with the principal objective of increasing overall plant efficiency. BRAYTON CYCLE Gas turbine plants operate on this cycle in which air is compressed (process 1-2, in P-V diagram of figure-1B). This compressed air is heated in the combustor by burning fuel, where plant of compressed air is used for combustion (process 2-3) and the flue gases produced are allowed to expand in the turbine (process 3-4), which is coupled with the generator. In modern gas turbines the temp. of the exhaust gases is in the range of 500 °C to 550 ° C RANKINE CYCLE: The conversion of heat energy to mechanical energy with the aid of steam is based on this thermodynamic cycle. In its simplest form the cycle works as follows: • The initial stage of working fluid is water (point 3 of figure 2), which at a certain temperature is pressurised by a pump (process 3-4) and fed to the boiler • In the boiler the pressurised water is heated at constant pressure (process 4-5-6-1) • Superheated steam (generated at point-1) is expanded in the turbine (process1-2), which is coupled with generator. Modern steam power plants have steam temperature in the range of 500°C to 550 °C at the inlet of the turbine.

COMBINING TWO CYCLES TO IMPROVE EFFICIENCY We have seen in the above two cycles that exhaust is at temperature of 500-550 °C and in Rankine cycle heat is required to generate steam at the temperature of 500-550 °C. Therefore gas turbine exhaust heat can be recovered using a waste heat recovery boiler to run a steam turbine on Rankine cycle. If efficiency of gas turbine cycle (when natural gas is used as fuel) is 31% and the efficiency of Rankine cycle is 35%, then over all efficiency comes to 49%. Conventional fossil fuel fired boiler of the steam power plant is replaced with a heat recovery steam generator (HRSG). Exhaust gas from the gas turbine is led to the HRSG where heat in exhaust gas is utilised to produce steam at desired parameters as required by the steam turbine.

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Figure-1A

Figure-1B

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ADVANTAGES OF GAS TURBINE PLANT Some of the advantages are quite obvious, such as fast operation, minimum site investment. • • • • • •

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Low installation cost owing to standardization, factory assembly and test. This makes the installation of the station easy and keeps the cost per installed kilowatt low because the package power station is quickly ready to be put in operation. Site implementation includes one simple and robust structure to get unit alignment. Transport: Package concept makes easier shipping, handling, because of its robustness. Low standby cost: fast start up and shut down reduce conventional stand by cost. The power requirements to keep the plant in standby condition are significantly lower than those for other types of prime movers. Maximum application flexibility: The package plant may be operated either in parallel with existing plants or as a completely isolated station. These units have been used, widely for base, peaking and even emergency service. The station can be equipped with remote control for starting, synchronizing & loading. Control reliability: the microcomputer based control, with an integrated temperature system (ITS) provides accurate control, quick protection and complete sequential start up & shut down & operation. Maintenance Cost is comparatively low.

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(3) KAWAS PACKAGE POWER PLANT BRIEF DESCRIPTION OF THE PACKAGE POWER PLANT

The basic functional sub assemblies of Kawas GT package plant are: • Control compartment The control compartment contains the equipment needed to provide control indication and protection functions. Arrangement can be made for manual operation or for remote unattended operation. The control compartment is located at local control room and includes the turbine control panel, generator control panel, batteries and battery charger. • Accessory compartment The accessory compartment, contains the mechanical and control elements necessary to allow the gas turbine to be a self, contained operational station. The major components located in the accessory compartment are the lubricating oil system and reservoir, lube oil cooler, starting means, accessory gear fuel system, turbine gauge panel, hydraulic system and atomising air system, water system, cranking motor exhaust frame blowers (88TK1, 88 TK-2.) • Turbine compartment The gas turbine has a 17 stage axial compressor. The compressor rotor consists of individual discs for each stage, and is connected by through bolts to the forward and aft stub shafts. The turbine rotor consists of three stages, with one wheel for each bucket stage. The turbine rotor wheels are assembled by through bolts similar to the compressor, and with two spacers, one between the first and second stage wheels, and the other between the second and the third stage wheels. The entire stator stages utilize precision cast, segmented nozzles, with the 2nd and 3rd stage segments supported from the stationary shrouds. This arrangement removes the hot gas path from direct contact with the turbine shell. The turbine rotor stages also have precision cast, long shank buckets (air foils on the compressor wheels are called blades, those on turbine wheels are called buckets) and this feature effectively shields the wheel rims and bucket dovetails from the high temperature of the main gas steam. The gas turbine unit and shells are split and flanged horizontally for convenience of disassembly. Compressor discharge air is contained by the discharge casing, combustion wrapper, and turbine shell. The 14 combustion liners are mounted completely inside the combustion wrapper, which eliminates the need for combustion cans. • Inlet and exhaust system The inlet arrangement includes inlet air filters, silencing, ducting and trash screens to protect the compressor from debris. The inlet arrangements generally comes out from the back of the inlet air house, over the control and accessory compartments, and down to the inlet plenum, which is mounted on the turbine base. The exhaust arrangement includes the ducting, silencing, and necessary expansion joints. The exhaust gases exit from the side to exhaust plenum, which is mounted separately on its own base, and are directed straight out to the exhaust arrangement. • Load package The load package consists of an air-cooled, synchronous generator and associated equipment. The generator also has roof-mounted terminals for out going leads. An air-cooled open ventilation of generator and associated equipments can be used in the load compartment

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• Fire protection unit The fire protection system consisting of on base piping, detectors etc. capable of distributing a fire extinguishing agent (CO2, or Halon) in all the compartments of the gas turbine and local control room. The bulk of fire extinguishing agent stage unit is located near gas turbine with one main CO2 skid. OPERATION The package plant has been designed to provide maximum operational flexibility and simplicity. The actual operating sequence can be best understood by considering the four basic operating modes: Stand By, Start, Run and Shutdown. •

Stand by During stand by, each component must be maintained in a state, which allows for immediate start up operation if needed. All the station components that are affected by low temperature or moisture are fully protected during stand by. The lubricating oil and the control compartment are maintained at a minimum temperature. The batteries are kept fully charged and heated. Turbine compartment is also maintained hot.

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Starting the unit Start-up can be ordered either remote or from the control compartment. (LCR)

1. 2. 3. 4. 5.

The starting sequence is given below: The starting system consists of an induction motor and torque converter coupled to the accessory gear. The staring system is energized and connected to the turbine up to the value from which Turbine becomes self-sustaining. At about 12% normal speed, fuel is injected and ignited. To avoid thermal shocks in hot parts of turbine, the unit is accelerated under acceleration mode after a short Warm-up period. When the turbine becomes self-sustaining, the gas turbine speeding up continues, but the starting system (Cranking motor) is automatically made off at 60% speed.

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Running The operator at either the local or remote station has the option of holding the station at spinning reserve, or loading to a point, or running under maximum load exhaust temperature control. The load can be varied manually over the entire load range.

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Shut down Upon initiation of a normal shut down signal, either locally or remotely, the following events occur: 1. 2. 3. 4.

The generator load is gradually reduced to zero. The generator breaker is opened. The fuel supply is reduced & then is shut off. The gas turbine coasting down to rest.

The starting system components also provide slow speed rotation of the turbine for cool down purposes after shut down. A crank and restart can be initiated at any time below 10% speed & can also be started above 95% speed.

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GAS TURBINE EQUIPMENT DATA SUMMARY •

COMPRESSOR SECTION Number of compressor stages Compressor type Casing split Inlet guide vanes

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TURBINE SECTION Number of turbine stages Casing splits Nozzles

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Three (3) Horizontal Fixed area

COMBUSTION SECTION Type Fuel nozzles Spark plugs Flame detectors

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Seventeen (17) Axial flow, heavy duty Horizontal flange Modulated

Fourteen (14) multiple combustors, reverse flow design One (1) per combustion chamber i.e. (one for gas & one for liquid) Two-(2) electrode type, spring-injected self-retracting. Four (4),ultra-violet type

BEARING ASSEMBLIES Quantity Three (3) Lubrication Pressure lubrication No.1 bearing assembly Active and inactive thrust and journal, all contained in (Located in inlet casing assembly) one assembly Journal Elliptical Active thrust Tilting pad, self-equalizing Inactive thrust Tapered land No.2 bearing assembly (Located in the Elliptical journal compressor discharge casing) No.3 bearing assembly (Located in the Journal, tilting pad exhaust frame) STARTING SYSTEM Starting device Torque converter Fuel pump Gas stop ratio & control valve

Electrical starting motor 1 MW drive Hydraulic with adjustor drive Accessory gear-driven, Continuous out put screw type pump Electro hydraulic servo-control

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LUBRICATION SYSTEM Lubricant MOT capacityMain tube pump Emergency lube pump Auxiliary lube pump Heat exchanger (s) Type Quantity Filter (s) Type Quantity Cartridge type

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Auxiliary hydraulic supply pump

Full flow with transfer valve Two (Duplex) Five-micron filtration pleated paper.

Accessory gear-driven, variable positive displacement, axial piston Driven by electric motor (88HQ), with accumulators- 2 nos.

COOLING WATER SYSTEM Pumps Water cooling modules

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Oil heat to fresh water Two in parallel

HYDRAULIC SUPPLY SYSTEM Main hydraulic supply pump

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Petroleum base 3,300 gallons (aprox.) i.e.12,540 litres (aprox.) Shaft driven. D.C. motor driven vertical submerged, centrifugal type (88QE) A.C. motor driven, vertical submerged, centrifugal (88QA)

Two water pumps located on lube oil tank inside the accessory compartment. 15 nos. fans and finned tube radiators

CONTROL SYSTEM SPEEDTRONIC MARK IV control system

Note: -Two additional cooling water pumps and associated finned tube radiators are provided for each gas turbine generator cooling.

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(4) COMPRESSOR SECTION •

GENERAL Description: The axial-flow compressor section consists of the compressor rotor and the casing. Included within the compressor casing are inlet guide vanes, the 17 stages of rotor and stator blading, and the exit guide vanes. In the compressor, air is confined to the space between the rotor and stator blading where it is compressed in stages by a series of alternate rotating (rotor) and stationary (stator) airfoil-shaped blades. The rotor blades supply the force needed to compress the air in each stage and the stator blades guide the air so that it enters in the following rotor stage at the proper angle. The compressed air exits through the compressor-discharge casing to the combustion chambers. Air is extracted from the compressor for turbine bearing cooling sealing, and for pulsation control during start-up (to avoid surging). Since minimum clearance between rotor and stator provides best performance in a compressor, parts have to be assembled very accurately.

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COMPRESSOR ROTOR DESCRIPTION

The compressor rotor is an assembly of 15 individual wheels; two stub shafts, each with an integral wheel, tie bolts, and the compressor rotor blades. Each wheel and the wheel portion of each stub shafts have slots broached around its periphery. The rotor blades and spacers are inserted into these slots and are held in axial position by staking at each end of the slot. The wheel and stubshafts are assembled to each other with mating rabbets for concentricity control and are held together with tie bolts. Selective positioning of the wheels is made during assembly to reduce balance correction. After assembly, the rotor is dynamically balanced to a fine limit. The forward stub shaft is machined to provide the forward and aft thrust faces and the journal for the No.1 bearing, as well as the sealing surfaces for the No.1 bearing oil seals and the compressor low pressure air seal. •

COMPRESSOR STATOR General The stator (Casing) area of the compressor section is composed of four major sub-assemblies: 1. Inlet casing 2. Forward compressor casing 3. Aft compressor casing 4. Compressor discharge casing These sections, in conjunction with the turbine shell, constitute the outer wall of gas path annuls and forms the structural backbone of the unit. The casing bone is maintained at close tolerances with respect to the rotor blade tips for maximum aerodynamic efficiency.

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Inlet casing The inlet casing is located at forward end of the gas turbine. Its prime function is to direct the air uniformly from the inlet plenum into the compressor. The inlet casing also supports the bearing no.1 assembly/ thrust bearing. Variable inlet guide vanes are located at the aft end of the inlet casing. Forward compressor casing The forward compressor casing contains the 1st through 4th compressor stages. One end of the forward support plate is bolted and doweled to this casing’s forward flange, and the other end is bolted and doweled to the turbine base. It is equipped with two large integral casing trunnions, which are used to lift the gas turbine when it is separated from its base. Aft compressor casing The aft compressor casing contains the 5th through 10th compressor stages. Extraction ports in the casing permit removal of 5th stage and 11th stage compressor air. The 5th stage air is used for cooling and sealing functions, and the 11th stage extraction is used for bleeding air to the exhaust plenum during start up and shutdown for pulsation control

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Compressor discharge casing This casing contains the 11th to 17th compressor stages, two rows of exit guide vanes, and the discharge diffuser. The functions of the compressor discharge casing are to support the stator blading, to provide the inner and outer sidewalls of the diffuser and to join the compressor and turbine stators. This casing also provides inner support for the No.2 bearing assembly and seal with the first stage turbine nozzle assembly via the support ring. The compressor discharge casing consist of two cylinders one being a continuation of the compressor casing and the other being an inner cylinder that surrounds the compressor rotor. Radial struts connect the two cylinders. The supporting structure for the No.2 bearing assembly is contained within the inner cylinder. A diffuser is formed by the tapered annulus between the outer and inner cylinders of the discharge casing. • BLADING The compressor rotor blades are airfoil shaped and are designed to compress air efficiently at high blade tip velocities. The forged blades are attached to their wheels by axial dovetail connections. The dovetail is accurately machined to maintain each blade in the desired location on the wheel. The compressor stator blades are also forged airfoils. Stage 1 to 8 is mounted by axial dovetails in to blade ring segments. The blade ring segments are inserted into circumferential grooves in the casing and are held in place with locking keys. Stage 9 through the exit guide vanes is mounted on individual rectangular bases that are inserted directly into circumferential grooves in the casing.

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COMPRESSOR AIR EXTRACTION General During operation of the gas turbine, air is extracted from various stages of the axial flow compressor to: 1. Cool the turbine parts subject to high operating temperature. 2. Seal the turbine bearings. 3. Provide an operating air supply for air operated valves. 4. Air bleeds off to avoid pulsation. 5. For pulse Jet-cleaning system. 6. Fuel nozzle atomising air. 5th stage air Air is extracted from the compressor 5th stage and is externally piped from connections in the upper and lower half of the casing for cooling and sealing of all rotor bearings. 11th stage Air Air from the compressor 11th stage is bled only during unit start-up and shut down for pulsation control. The compressor bleed valves are closed during unit operation. 17th stage Air Air extracted from the compressor 17th stage flows radially inward between the stage 16 and 17 wheels, to the rotor bore, and then aft to the turbine where it is used for cooling the turbine 1st and 2nd stage buckets and rotor wheel spaces. Compressor discharge air Air extracted from compressor discharge is used for liquid fuel atomising air, stage 1 nozzle vane and retaining ring cooling, stage 2 nozzle cooling, pulse & for Pulse Jet cleaning system. Variable inlet guide vanes Variable inlet guide vanes are located at the aft end of the inlet casing. The position of these vanes has an effect on the quantity of compressor airflow. Movement of these guide vans is accomplished by the inlet guide vane control ring that turns individual pinion gears attached to the end of each vane. The control ring is positioned by a hydraulic actuator and linkage arm assembly.

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(5) COMBUSTION SECTION GENERAL Description The combustion system is of the reverse flow type with 14 combustion chambers arranged around the periphery of the compressor discharge casing. This system also includes fuel nozzles, spark plug ignition system, flame detectors, and crossfire tubes. Hot gases, generated from burning in combustion chambers, are used to drive the turbine. High-pressure air from the compressor discharge is directed around the transition pieces and into the combustion chambers inlets. This air enters the combustion zone through metering holes for proper fuel combustion and through slots to cool the combustion liner. Fuel is supplied to each combustion chamber through a nozzle designed to disperse and mix the fuel with the proper amount of combustion air Orientation of the combustion around the periphery of the compressor is shown on figure CS1.Combustion chambers are numbered counter-clockwise when viewed looking down-stream and starting from the top of the machine. Spark plug and flame detectors locations are also shown. COMBUSTION WRAPPER, COMBUSTION CHAMBERS AND CROSSFIRE TUBES Combustion Wrapper Combustion wrapper forms a plenum in which the compressor discharge air flow is directed to the combustion chambers. Its secondary purpose is to act as a support for the combustion chamber assemblies. In turn, wrappers are supported by the compressor discharge casing and the turbine shell. Combustion chambers: Discharge air from the axial flow compressor flows into each combustion flow sleeve from the combustion wrapper as shown in figure CS-2. The air flows up-stream along the outside of the combustion liner reaction zone through the nozzle swirl tip, through metering holes in both the cap and liner and through combustion holes in the forward half on the liner. The hot combustion gases from the reaction zone pass through a thermal soaking zone and then into dilution zone where additional air is mixed with the combustion gases. Metering holes in the dilution zone allow the correct amount of air to enter and cool the gases to the desired temperature. Along the length of the combustion liner and in the liner cap, there are openings whose function is to provide a film of air for cooling the wall of the liner and the cap as shown in figure CS-2. Transition pieces direct the hot gases from the liners to the turbine nozzles. All fourteen combustion liners, flow sleeves and transition pieces are identical. Crossfire tubes: All fourteen combustion chambers are interconnected by means of crossfire tubes. These tubes enable flame from the fired chambers to propagate to the unfired chambers.

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SPARK PLUG AND FLAME DETECTORS Spark plug: Combustion is initiated by means of the discharge from two high-voltage, retractable-electrode spark plugs installed in adjacent combustion chambers (No.12 and 13) These spring-injected and pressureretractable plugs receive their energy from ignition transformers. At the time of firing, spark at one or both plugs ignites the gases in a chamber. The remaining chambers are ignited by crossfire through the tubes that interconnect the reaction zones of the remaining chambers. As rotor speed increases, chamber pressure causes the spark plugs to retract and the electrodes are removed from the combustion zone. Flame Detectors: During the start up sequence, it is quite essential that an indication of flame or no-flame to be transmitted to the control system. For this reason, a flame monitoring system is used consisting of four sensors which are installed on four combustion chambers No.4, 5 and 10, 11 and an electronic amplifier which is mounted in the turbine control panel. The ultraviolet flame sensor consists of a flame sensor containing a gas filled detector. The gas within this flame sensor detector is sensitive to the presence of ultraviolet radiation, which is emitted by a hydrocarbon flame. D. C. voltage, supplied by the amplifier, is impressed across the detector terminals. If flame is present, the ionisation of the gas in the detector allows conduction in the circuit, which activates the electronics to give an output voltage defining flame. Conversely, the absence of flame will not generate any voltage defining “no flame’’. After the establishment of flame, if voltage is re-established to the sensors defining the loss (or lack) of flame a signal is sent to a relay panel in the turbine electronic control circuitry where auxiliary relays in the turbine firing trip circuit which shutdown the turbine. The FAILURE TO FIRE or LOSS OF FLAME is also indicated on the annunciator. If the loss of flame is sensed by only one flame detector sensor, the control circuitry will cause an annunciation only of this condition. If more than two sensors are not showing flame then only turbine trips.

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(6) TURBINE SECTION General The three-stage turbine section is the area in which the energy in the hot pressurized gas produced by compressor and combustion sections is converted into mechanical energy. The MS 9E major turbine section components include: the turbine rotor, turbine shell, exhaust frame, exhaust diffuser, nozzles and diaphragms, buckets & shrouds, and No.3 (aft) bearing assembly, spacers. TURBINE ROTOR Structure The turbine rotor assembly consists of a forward wheel shaft, the first, second and third stage turbine wheels and buckets, two turbine wheel spacers, and the aft turbine wheel shaft. Concentricity control is achieved with mating rabbets on the turbine wheels, spacers and wheel shafts. The turbine rotor is held together by twelve (12) through bolts. Selective positioning of rotor members is performed during assembly to minimize balance corrections during dynamic balance of the assembled rotor. The forward wheel shaft extends from the first stage turbine wheel to the aft flange of the compressor rotor assembly. The journal for the No.2 bearing is a part of this wheel shaft. The aft wheel shaft connects the third stage turbine wheel to the load coupling. The wheel shaft includes the No.3 bearing journal. Spacers between the first and second stage turbine wheels and between the second and third stage turbine wheels provide axial separation of the individual wheels. The spacer faces include radial slots for cooling air passages. Labyrinth packings are provided in second and third stage diaphragms with mat with the corresponding sealing lands of the spacers. Buckets The turbine bucket length increases from the first to the third stage. The first and second stage buckets are cooled by internal airflow. Air is introduced in to each bucket through a plenum at the base of the bucket dovetail. The air flows outward through a series of radial cooling holes and exits in to the gas path at the bucket tips. The holes are spaced and sized to obtain cooling of the airfoil, with minimum compressor extraction air. The third stage buckets are not air-cooled. The second and third stage buckets have tip shrouds with interlock buckets to provide vibration damping, and are mounted with seal teeth that reduce the tip leakage flow. The three stages of turbine buckets are attached to their wheels by straight, axial entry, multiple tangs dovetail that fit into machined cutouts in the rims of the turbine wheels. The bucket vanes are connected to their dovetails by means of shanks. These shanks locate the bucket-to-wheel attachment at a significant distance from the hot gases, which reduces the temperature at the dovetail. The turbine rotor assembly is arranged so that the buckets can be replaced without unstacking the wheels, spacers, and wheel shaft assemblies. Buckets are selectively positioned such that they can be replaced without having to rebalance the wheel assembly.

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Turbine rotor cooling The turbine rotor is cooled by means of a positive flow or relatively cool (relative to hot gas path air) airextracted from the compressor. Air extracted through the rotor, ahead of the compressor 17th stage, is used for cooling the 1st and 2nd stage buckets and the 2nd stage aft and 3rd stage forward rotor wheel spaces. This air also maintains temp of the turbine wheels, turbine spacers, and wheel shaft at approximately compressor discharge temperature to assure low steady state thermal gradients thus ensuring long wheel life. The 1st stage forward wheel space is cooled by air that passes through the high-pressure packing seal at the aft end of the compressor rotor. The 1st stage aft and 2nd stage forward wheel spaces are cooled by compressor discharge air that passes through the stage 1 shrouds and then radially inward through the stage 2nd nozzle vanes. Cooling air that exits from the exhaust frame cooling circuit cools the 3rd aft wheel space. TURBINE STATOR Structure The turbine shell and the exhaust frame constitute the major portion of the MS 9E gas turbine stator structure. The turbine nozzles, shrouds, No. 3 bearing and turbine exhaust diffuser are internally supported from these components. Turbine Shell The turbine shell controls the axial and radial position of the shrouds and nozzles, and thus controls turbine clearances and the location of the nozzles relative to the turbine buckets. This positioning is critical to gas turbine performance. In addition, eddy current probe holes, nozzle deflection holes and bore scope holes are provided for inspection of buckets and nozzles. The turbine shell is cooled by motor driven external air blower, which is piped in to the exhaust frame plenum. Part of this cooling air passes through a series of axial holes and exits into the turbine compartment before venting. Nozzles In the turbine section there are three stages of stationary nozzles. Because of the high-pressure drop across these nozzles, there are seals at both the inside and outside diameters to prevent loss of system energy by leakage. The first stage nozzle is made up of 18 cast nozzle segments, each with two vanes, and is cooled with compressor discharge air. A core plug is inserted in each vane to improve cooling effectiveness. The segments are contained by a horizontally split retaining ring which remains centered in the shell and allows for radial growth resulting from changes in temperature. The second stage nozzle is also cooled with compressor discharge air. A core plug is inserted in each vane to improve cooling effectiveness. The nozzle is made up of 16 cast segments, each with three vanes. The nozzle segments are held in circumferential position by radial pins from the shell into axial slot in the nozzle outer sidewall. The third stage nozzle consists of 16 cast segments, each with four vanes. It is held in the turbine shrouds in a manner identical to that used in second stage nozzles.

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Diaphragms Attached to the inside diameters of both the second and third stage nozzle segments are the nozzle diaphragms. These diaphragms prevent air leakage past the inner sidewall of the nozzles and the turbine rotor. The high/low labyrinth-type seal teeth are machined into the inside diameter of the diaphragm. They mate with opposing sealing glands on the turbine rotor. Minimal radial clearance between stationary parts (diaphragm and nozzle) and the moving rotor are essential for maintaining low inter stage leakage. This results in higher turbine efficiency. Shrouds The turbine bucket tips run directly under stationary annular curved segments called turbine shrouds. Primary function of shroud is to provide a cylindrical surface for minimizing bucket tip clearance leakage. The turbine shrouds secondary function is to provide a high thermal resistance between the hot gases and the comparatively cool shell. By accomplishing this function, the shell-cooling load is drastically reduced, the shell diameter is controlled, the shell roundness is maintained and the important turbine clearances are assured. The shroud segments are maintained in the circumferential position by radial pins from the shell. Interconnecting tongues and grooves seals joints between shroud segments. Exhaust frame The exhaust frame is bolted to the aft flange of the turbine shell. Structurally, the frame consists of an outer and an inner cylinder interconnected by the radial struts. The No.3 bearing is supported from the inner cylinder.

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(7) STARTING SYSTEM General and simplified schematic Before the gas turbine can be fired and started, it must be rotated or cranked by the accessory equipment. This is done by an induction motor, operating through torque converter to provide cranking torque and speed required by the turbine for start-up. The starting system consists of an induction motor and torque converter coupled to the accessory gear. A motor driven torque adjustor drive, which is an integral part of the converter system, provides the means for adjusting torque output within specified ranges. Also control of the torque converter is achieved via an integrally mounted unloading solenoid valve 20 TU-1 and a hydraulically operated dump valve. Refer figure SS-1. After the shut down order, when the decreasing speed reaches below 100 rpm, then torque converter motor sets torque adjustor to the minimum torque and a turning gear motor starts. Turning gear speed is 110 rpm (3.3 %) PART 20 TU-1 23 CR-1 23 CR-2 23 CR-3 26 CR-1 33 TC-1 33 TM-5 33 TM-6 88 CR-1 88 TG-1 88 TM-1 96 TM-1

NOMENCLATURE Torque converter unloading (drain) solenoid valve Heater in cranking motor Cranking motor, high temperature Limit switch torque converter filling valve Torque adjustor- limit switch/low torque limit Torque adjustor-limit switch/high limit Cranking motor Turning gear motor Torque adjustor-drive motor Position transmitter

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FUNCTIONAL DESCRIPTION Start-up function description In the normal starting sequence, fluid is admitted into the torque converter hydraulic circuit from the lubrication system by the integral 20 TU-1 valve. The torque convertor angle is kept at 66 degree to provide maximum torque during the start up from zero speed. After few seconds the starting motor 88 CR is energized. Breakaway is achieved and the turbine starts to rotate & turbine speed increases to 10 % speed when the speed relay 14 HM picks up. At this point when the torque convertor angle is reduced to 50% and 1 minute purging cycle starts. After completion of 1 minute purging timer, the solenoid 20 TU is de-energised & oil supply to torque convertor is stopped, which results into decrease of shaft speed to firing speed (12 %). During this, the torque convertor angle comes down to its firing angle (15 degree). When shaft reaches the firing speed, the stop valves open and allows the start up fuel to flow into the combustion chamber for firing. If within one minute, any 2/4 flame scanner senses the flame, then warm up timer (1 minute) starts. Otherwise turbine coast down. During this 1 minute warm up cycle, constant fuel is maintained to minimise the thermal shock during start up. When turbine reaches the firing speed, solenoid 20 TU is energised. After 5 second of flame sensing, the torque convertor angle is increased to maximum to cater for the acceleration cycle which i9s started immediately after completion of 1 minute warm up timer. Readjustment of the converter geometry (torque adjustment) at the end of warm-up allows the torque converter to assist in accelerating the unit up to self-sustaining speed. This speed, (about 60% of normal speed), the torque converter hydraulic circuit is drained, by de-energizing solenoid valve 20 TU-1. At the same time cranking motor 88 CR is de-energized, which effects disconnection. A crank and restart can be initiated at any time below 14 HM speed. Various switches provide torque adjustment range limits. These are TM-5 and TM–6, to limit the torque in case of malfunction of the system. Shut-down The shutdown order is given and the turbine speed slows down at about 3.3% speed, when 14 HP drops & the turning motor 88 TG starts. Solenoid valve 20 TU-1 is energized and the torque is adjusted to 34% allowing to turn the turbine at a speed 100 rpm for cool down purpose after shut down. This cool down sequence lasts at least 14 hours. It must be manually stopped to bring turbine to standstill position. Turning The turbine is at standstill & all circuits are ready for turning. The operator turns the operation selector switch 43 of the turbine control panel to position TURNING “then gives a”START “order. The starting motor 88 CR starts and 20 TU-1 energized. When the speed reaches about 4%, motor 88CR is stopped. The speed decreases a little and at about 3.3% speed, turning motor 88 TG starts. Re-adjustment of the converter geometry (torque adjustment) will allow a turning speed of about 100 rpm. Turning will last at least 14 hours. It must be manually stopped. 88 TM-1 is the motor that operates the vanes in torque adjustor device. The position transmitter 96 TM-1 indicates the position of the buckets on the wheels of the torque converter. TORQUE CONVERTER AND STARTING DRIVE COMPONENTS The starting motor drives the torque converter input through a flexible coupling. The torque converter output is coupled to the accessory gear and provides the required torque multiplication for the starting motor to drive the turbine. The main parts of torque converter are the impeller driven by the input shaft, the turbine wheel, which drives the output shaft, and the stator, which directs fluid from the impeller to the turbine at the correct angle to produce the required output torque.

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The function of the accessory gear in this system is to drive a number of the control components as well as to provide the connection between the starting motor and gas turbine compressor. It is permanently coupled to turbine compressor shaft by a flexible coupling. ACCESSORY DRIVE General The accessory drive gear, located at the compressor end of the gas turbine, is a gear assembly coupled directly through a flexible coupling to the turbine rotor. Its function is to drive each gas turbine accessory at its proper speed. In addition, it contains the system main lube oil pumps and the turbine over speed bolt mechanism. Contained within the gear casing are the gear trains, which provide the proper gear reductions to drive the accessory devices at the required speed, with the correct torque value. Accessories driven by the gear include: the main lube oil pump, the main hydraulic supply pump, the liquid fuel pump, and the main atomising air compressor. Lubrication of the gear is from the turbine’s pressurized bearing header oil supply. A high-pressure turbine over speed trip (capable of mechanically dumping the oil in the trip circuit) is mounted on the exterior casing of the gear. This device can shut the turbine down when the speed exceeds the design speed. The over speed bolt which actuates the trip upon over speed is installed in the main shaft. DESCRIPTION For ease of maintenance and inspection, the gear casing is split at the horizontal plane into an upper and lower section. Interconnected shafts are arranged in a parallel axis in the lower casing. Three of the shafts are located on the same horizontal plane as the casing joint. The gear consists of four parallel axis, interconnected shafts arranged in a casing, which provides mounting pads for the various driven accessories. With the exception of the lube oil pump and hydraulic supply pump shaft, all the shaft centre lines are located on the horizontal joint of the accessory drive casing. The gear casing is made of cast iron and split at he horizontal joint to facilitate assembly. The lower casing has a closed bottom with openings for lube oil pump suction and discharge lines and casing drain line. All of the shafts are connected together by single helical gears, which are shrunk to the shaft after the teeth are cut. It is possible, in some instances to remove individual gear, which may have been damaged in service, and to replace them with new gear. This operation, however, should be performed at the factory so that the required precision may be maintained. All the shafts located on the horizontal joint are contained in babbit-lined steel-backed journal bearings with integral thrust faces which are split on the horizontal joint of the casing. The thrust faces of the bearings maintain the shafts in their proper axial location and the necessary thrust clearance is preset at the factory. The shafts which are not on the horizontal joint are contained in babbit-lined, steel backed, non-split bushings with integral thrust faces. Their thrust clearance is likewise preset at the factory. The main lubricating oil pump is located on the inboard wall of the lower half casing of the accessory drive gear.

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(8) LUBRICATION SYSTEM DESCRIPTION AND SIMPLIFIED SCHEMATIC The lubricating requirements for the gas turbine power plant are furnished by a common forced-feed lubrication system. This lubrication system, complete with tank pumps, coolers, filters, valves and various control and protection devices, furnishes normal lubrication and absorption of heat load of the bearing of gas turbine. Lubricating fluid is circulated to the three main turbine bearing, generator bearings, and to the turbine accessory gears and fuel pumps. Also lubricating fluid is supplied to the starting means torque converter for use as hydraulic fluid as well as for lubrication. Additionally, a portion of the pressurized fluid is diverted and filtered again for use by hydraulic control device as control fluid. The lubrication system including all major components shown in figure LS-1 Major system components include: • Lube reservoir in the accessory base; • Main lube oil pump (shaft driven from the accessory gear) • Auxiliary lube oil pump and emergency lube oil pump • Pressure relief valve VR-1 in the main discharge • Lube oil heat exchangers • Lube oil filters • Bearing header pressure regulator VPR-2 Lube fluid temperatures are indicated on the thermometers, which may be located in the bearing header, bearing drains, or the oil tank. Lubricating fluid for the main, auxiliary and emergency pumps are supplied from reservoir, while lubricating fluid used for control oil supplied from the bearing header. This lubricant must be regulated to the proper, predetermined pressure to meet the requirements of the main bearings and the accessory lube oil system, as well as the hydraulic control and trip circuits. Regulating devices are shown on the lube oil System Schematic diagram LS-1. All lubricating fluid is filtered and cooled before being piped to the bearing header. The reservoir for the lubricating system is the 3300 Gallon (i.e.12540 Litres) tank, which is fabricated as an integral part of accessory base. Lubricating fluid is pumped from the reservoir by the main shaft driven pump (part of accessory gear) or auxiliary or emergency pumps at a pressure of 25 psi (g) (i.e.1.75 bar) to the bearing header, the accessory gear and the hydraulic supply system. After lubricating the bearing, the lubricant flows back through various drain lines to the lube reservoir. All lubricant pumped from the lube reservoir to the bearing header flows through the lube fluid heat exchanger(s) to remove excess heat and then through the cartridge type filters providing five-micron filtration. The dual heat exchangers are connected in parallel. Filtration of all lube oil is accomplished by a 5 micron, pleated paper filter, installed in the lube oil system just after the lube oil heat exchanger. Two (dual) filters are used with a transfer valve installed between the filters to direct oil flow through either filter and into the lube oil headier. The dual filters have removable resin-impregnated paper pleated filter elements and a differential pressure gauge, which indicates when the filter element should be changed. Differential pressure switch 63 QQ-1 will cause an alarm if differential pressure across the oil filters becomes too high. Lubricant from the turbine bearing No.1 assembly is piped through an internal drain line to the lube oil tank. Drain from the other turbine and generator-bearing assemblies are piped to a surge tank and then to an externally routed drain header that interconnects the accessory base, turbine base and generator base. The lube fluid drain

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flows forward through this common drain header to the lube reservoir. The main oil reservoir receives sealing air also, which flow into three bearing seals & then into the reservoir. A lube oil level gauge and alarm system, composed of a hermetically sealed, float arm-operated device, is mounted to the side of the lube oil reservoir above the maximum expected level of the lube supply. The float mechanism operates a dial gauge and two devices switches 71 QH and 71 QL. The switches are connected into the alarm circuit of the turbine panel scope and sound an audible alarm if the liquid level rises above, or fall below a predetermined level. A lubricant drain connection is located on the side of the accessory base to drain the lube reservoir. For the accessory coupling, lubricating oil is filtered through a dual filter system with a transfer valve. This system provides a 0.5-micron filtration. During standby periods, the lubricating fluid is maintained at a viscosity proper for turbine start-up by heaters installed in the lube reservoir. Temperature switches sense reservoir fluid temperature, and control the heaters to maintain fluid temperature to achieve allowable viscosity. Another temperature switch senses reservoir temperature, and will not permit the turbine to be started if the fluid temperature droops below the viscosity required for start-up. PART 23 QT-1,-2 26 QA-1 26 QL-1 26 QN-1 26 QT-1A 26 QT-1B 63 QA-1 63 QL 63 QQ-1 63 QT-2A 63 QT-2B 71 QH-1 71 QL-1 88 QA 88 QE VPR-2 VR-1 LT-TH-1 LT BT ID LT B ID LT B 2D LT B ID LT B 3D LT-G 1D LT-G2D

NOMECLATURE Immersion heater. Lube oil tank. Lube oil header high temperature alarm. Temperature switch. Lube oil tank temperature. Low temperature switch Lube oil tank temperature. Normal temperature switch. Lube oil header high temperature trip temperature switch. Low lube oil pressure, Auxiliary pump start pressure switch. Low lube oil pressure, Emergency pump start pressure switch. Main lube oil filter differential pressure alarm. Low lube oil pressure trip. Pressure switch (On the generator). High lube oil level. Alarm. Low lube oil level. Alarm. Auxiliary lube oil pumps motor. Emergency lube oil pumps motor. Bearing header pressure regulator valve. Main lube pump pressure relief valve. Lube oil system turbine header thermocouple. Lube system temperature turbine no.1 thrust bearing drain. Lube system temperature- turbine bearing no.1 (sump) drain. Lube system temperature- turbine bearing no.2 (sump) drain. Lube system temp. Turbine bearing no.1 (sump) drain. Lube system temp. Turbine bearing no.3 (sump) drain. Lube oil system temp. Generator bearing no.4. Lube oil system temp. Generator bearing no.5.

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LUBRICATING OIL PUMPS Lubrication to the bearing header is supplied by three lube oil pumps 1 The main lube supply pump is positive displacement type pump mounted in and driven by the accessory gear. 2 The auxiliary lube supply is a submerged centrifugal pimp driven by an A.C. motor. 3 The emergency lube supply pump is a submerged centrifugal pump driven by a D.C. Motor. Main lube pump The main lube pump is built in to the inboard wall of the lower half casing of the accessory gear. A splind quill shaft drives it from the lower driver gear. A backpressure valve to maintain system pressure limits the out put pressure to the lubrication system. Auxiliary Lube Pump Auxiliary Lube Pump is a submerged centrifugal type pump driven by an AC motor It provides lubricant pressure during start-up and shutdown of the gas turbine when the main pump cannot supply sufficient pressure for safe operation. Operation of this pump is as follows: The auxiliary lube pump is started by a lube oil pressure low alarm switch (63 QA-1). This causes the auxiliary pump to run under low lube oil pressure conditions, as is the case during start-up or shutdown of the gas turbine when the main pump, driven by the accessory drive device, does not supply sufficient pressure. At turbine startup, the AC pump start automatically when the master control switch on the turbine control panel is turned to the START position. The auxiliary pump continues to operate until the turbine reaches approximately 95 percent of operational speed. At this point, the shaft-driven, main lube pump supplies the auxiliary lube pump shutdown and system pressure. During the turbine starting sequence, the pump starts when the start signal is given. The control circuit is through the normally closed contacts of pressure switch 63 QA-1. The pump will run until the turbine operating speed is reached (operating speed relay 14 HS pick up), even though the lube oil header is at rated pressure and the pressure switch (63 QA-1) contacts have opened. When the turbine is on the shutdown sequence, this pressure switch will signal for the auxiliary pump to start running when the lube oil header pressure falls to the point at which the contacts of the switch are set to close. Emergency Lube pump The emergency lube pump is a DC motor-driven pump, of submerged centrifugal type. This pump supplies lube oil to the main bearing header during an emergency shutdown in the event the auxiliary pump has been forced out of service because of loss of AC power, or for other reasons. It operates as follows: This pump is started automatically by the action of pressure switch 63 QL whenever the lube oil pressure in the main bearing header fails below the pressure switch setting. When the auxiliary lube oil pump is started, the emergency pump will be stopped by a pressure switch (63 QL) after the header pressure exceeds the setting switch. Should the auxiliary pump fail during the shut-down sequence, because of an AC power failure or any other cause, the emergency lube oil pump will be started automatically by the action of low lube oil pressure switch 63 QL and continue to run until the turbine shaft comes to rest. Test valve for low lube oil pressure. Auxiliary pump start.

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A gauge mounted test valve is also used to provide the means of checking the automatic operation of the auxiliary lube oil pump and pressure switch 63 QA-1, while the unit is operating normally on the lube pump. The test valve is installed in the piping after the switch and it is normally closed holding the lube oil system pressure on the switch. When a test is performed, the test valve should be opened gradually to lower the lube oil system pressure in switch piping. This oil pressure is indicated on a gauge connected into the pressure line. The gauge provides a means of checking the pressure point at which the switch operates and starts the pump, when the oil pressure falls to the setting of switch 63 QA-1. Test valve for low lube oil pressure, Emergency start. A test valve, mounted on the gauge cabinet, provides the means of checking automatic start-up of the emergency lube oil pump and pressure switch 63 QL. This can be done while the unit is operating normally on the main lube oil pump. The test valve is normally closed and maintains lubricating system pressure on the switch. When a test is performed, the test valve have should be opened gradually to lower lubricating system pressure in the piping in which switch is mounted. (Refer to the pressure gauge to determine the effect of this action). It provides the means of checking the pressure points at which the switch operate to start the pump. A low lubricating fluid pressure indication should occur before the pump is started. Upon closing the test valve, lube pressure is returned to normal and the pump should stop as a result of the restoration on the 63 QL switch. PRESSURE, TEMPERATURE REGULATION AND PROTECTION DEVICES

Pressure regulation Two regulating valves are used to control lubrication system pressure. A back-pressure relief valve VR-1, limits the positive displacement main pump discharge header pressure and relieves excess fluid to the lube reservoir. The lube pressure in the bearing header is maintained at approximately 25 psi (g) (i.e.1.75 bar) by the diaphragm operated regulating valve VPR-2. This valve has orifices which permits 80% flow. The diaphragm valve is operated by sensing fluid pressure in the bearing header. Pressure and temperature protective devices A pressure switch that opens after a decrease of line pressure to a specified value and trips the unit detects the condition of low lubricating fluid pressure. Pressure switches 63 QT-2A and 63 QT-2B are installed in the lubricant feed piping gives an alarm if the lubricant pressure drops to an unacceptable level. Similarly temperature switches 26 QA-1, 26QT-1A & 26 QT-1B are installed in the lubricating fluid header piping and cause an alarm to sound and tripping of unit, should the temperature of the lubricant to the bearings exceed a preset limit. The setting of switches is such that an alarm is actuated by 26 QA-1, before the turbine is tripped by temperature switches 26 QT-1A, &26 QT-1B. Provisions are made for checking lube flow to the main turbine and generator bearing by means of oil sight, thermocouples, and thermometers. In addition, thermometers are provided to indicate temperature in the lube bearing reservoir header.

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(9) GT COOLING WATER SYSTEM General The cooling water system is a pressurised closed system designed to accommodate the heat dissipation requirements of the lubrication system, the atomising air system and the turbine support legs. An aqueous solution of ethylene glycol is used in the system; therefore, it is capable of performing its function throughout the year if the ambient temperature is not too high. During frost the cooling system must be filled with an aqueous solution of ethylene glycol. Cooling water system consists of the cooling cells, the pumps, miscellaneous valve and certain control and protection devices. PART 26 WH-1 26 WH-2 63 WL-1 63 WL-2 88 CR 88 WC-1 88 WC-2 VTR-1 VTR-2

NOMENCLATURE Cooling water temperature - Moderate (Stop cooling water fan motor) Cooling water temperature - High (Starting cooling water fan motor) Low cooling water pressure- pump for starting back up . Cranking motor Cooling water pump motor. Bearing header temperature regulating valve Atomizing air pre-cooler discharge temp. Regulating valve

FUNCTIONAL DESCREPTION The cooling water system circulates water as a cooling medium to maintain the lubricating oil temperature at acceptable levels and to cool several other turbine components. Water is circulated in parallel through the lube oil and the atomising air heat exchangers, and turbine support legs. After absorbing the heat rejected by these items, the coolant flows through the cooling equipment where it gets cooled. The coolant circulation is done by two motor-driven pumps 88 WC-1 and WC-2; one of these is a standby. These pumps are of A.C. motor driven centrifugal type pumps. If pump 88 WC-1 is in service and if its outlet pressure drops to a preset level on the manostat 63 WL-1 located at its outlet, the motor-pump 88 WC-2 receives a starting order. It operates in the same way for 88WC-2. If manostat 63 WL-2 registers a pressure drop, the pressure reaches its set value; the motor-pump 88 WC-1 receives a starting order. If the standby pump is running and still pressure drops to the preset level of a manostat located at the outlet of the motor-pumps assembly, an alarm appears. The coolant circuit for the lube oil and atomising air heat exchangers have a temperature actuated 3- way valve (VTR-1 and VTR-2, respectively) installed in the coolant inlet line to the heat exchangers. This type valve, which control coolant flow to the heat exchanger, has a manually operated device, which can override the thermal element. The manual override should be used only when the valves thermal element is faulty, but machine operation is required. Atomising air compressor inlet and lube oil feed header temperature are sensed by the bulb associated with the each valve which controls the flow of coolant through the heat exchanger and maintains the air and lube oil temperatures at predetermined values. The valves automatically control flow of the medium (coolant) passing through them to the heat exchangers by responding to temperature changes affecting the bulb.

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The bulb contains a thermal-sensitive liquid, which vaporizes when heated. Pressure generated in the bulb is transmitted through the capillary tube to the bellows, which positions the valve disc to control the flow of coolant through heat exchangers. The valve is closed during turbine start-up, and will start to open as the sensed fluid temperature approaches the control setting. Valve VRT-2 in the coolant line to the atomising air heat exchanger has a small bypass orifice drilled in valve body to assure that the cooler is “flooded” at all times. At the inlet of each cooling water circuit (lube oil heat exchangers circuit, atomising air heat exchanger circuit and turbine support legs circuit), an orifice allows water flow rate calibration to the circuit concerned. The cooling water system is equipped with thermostats: • 26 WH-2: High temperature cooling water thermostat, it starts the cooling water fan motor. • 26 WH-1: Moderate temperature cooling water thermostat, it stops the cooling water fan motor once the water temperature has dropped to the wanted level. Shut- off valves Shut off valves are provided in the piping so that the water side of the lube oil heat exchangers may be isolated from the water system for maintenance. Valves are not installed in the piping leading to the atomising air heat exchanger due to the severe consequences of inadvertently shutting off coolant flow to this component.

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(10) COOLING AND SEALING AIR SYSTEM General The cooling and sealing air system provides the necessary airflow from the gas turbine compressor to other parts of the gas turbine rotor and stator to prevent excessive temperature build-up in these parts during normal operation and sealing of the turbine bearings. Air from two centrifugal type blowers is used to cool the turbine exhaust frame. These two fans are part also the part of cooling system. Cooling and Sealing functions provided by the system are as follows: • Sealing of the turbine bearings • Cooling of internal turbine parts subjected to high temperature. • Providing an operating air supply for air operated valves. The cooling and sealing air system consists of specially designed air passages in the turbine casing, turbine nozzles and rotating wheels, piping for the compressor extraction air and associated components. Associated components used in the system include: • Turbine exhaust frame cooling blower (88 TK1/88 TK2) • Air filter (with poro-stone element) • Pressure gauge • Dirt separator FUNCTIONAL DESCRIPTION General Air extracted from the axial flow compressor is used for sealing the bearings, cooling turbine internal parts and provide a clean air for air operated control valves, as well as for avoiding pulsations of the compressor during turbine start-up and shutdown. Bearing sealing air is extracted from the fifth stage of the compressor. Internal cooling air is extracted from the compressor discharge including the internal flow of the cooling air through the turbine rotating and stationary parts. Air used in cooling of turbine external casing is ambient air supplied by motor driven blowers. The schematic flow diagram, figure CS-1, shows both the internal and external flow of cooling and sealing air. Bearing cooling and sealing. Cooling and sealing air is provided from two connections on the compressor casing at the fifth stage and is piped to each of the three turbine bearings. Orifices in the airlines to the turbine bearing limit the flow of air and the pressure to the proper value. The centrifugal dirt separator located in the fifth stage-piping removes any particles of dirt or foreign matter that might be harmful to the bearings. The pressurized air-cools and seals the bearing by containing any lubrication fluid within the bearing housing that otherwise might pass to the mechanical seals. Air is directed to both of each bearing housing for providing a pressure barrier to the lubricating fluid. After performing this function, the air is vented via the oil drain passage from the bearings No.1 and NO.3 while air from the bearing No. 2is vented to atmosphere.

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Exhaust frame and turbine shell cooling Two electric motor-driven, centrifugal blowers (88 TK-1 and 88 TK-2) are mounted external to the turbine for cooling of the exhaust frame and turbine shell. An inlet screen is provided with each blower and the discharge of each passes through a back-draft damper (check valve), VCK7-1 or VCK7-2 before entering openings in the exhaust frame’s outer sidewall cavity. The cooling airflow splits, with part of the air passing along and cooling the turbine shell and the other portion flowing through the exhaust frame strut passages. The airflow through the struts divides, with a portion directed through passages to cool the third-stage turbine aft wheel space and the remainder flowing in to the load shaft tunnel where it discharges through a duct to atmosphere. See figure CS-1. Air for cooling the exhaust frame and turbine shell is normally provided by two blowers operating simultaneously in parallel. Each blower has a pressure switch, 63 TK-1 or 63 TK-2, to sense blower discharge pressure. If one of the blowers should fail, the loss of blower discharge pressure will cause contacts of the respective 63 TK pressure switch to close and an alarm will be annunciate. The turbine will continue to run with the other blower providing cooling air at a reduced flow rate. If both blowers fail, the turbine will be shut down in a normal shut down sequence. Note: If one blower fails, it should be repaired or replaced as soon as possible to avoid the possibility of shutting down the turbine by failure of the remaining blower. Pulsation Protection The pressure, speed and flow characteristics of the gas turbine compressor are such that air must be extracted from the 11th stage and vented to the atmosphere to prevent pulsation of the compressor during the acceleration period of the turbine starting sequence and during deceleration of the turbine at shutdown. Pneumatically operated 11th stage air extraction valves, controlled by a three-way solenoid valve, are used to accomplish the pulsation function. Eleventh stage air is extracted from the compressor at four flanged connections on the compressor casing. Each of these connections is piped through a normally open, piston operated, butterfly or vee-ball type valve, VA -1,2,-3 and –4 to the turbine exhaust plenum. Limit switches 33 CB-1, -2,-3 and –4 are mounted on the valves to give an indication of valve position. See figure CS-1. Compressor discharge air controlled by solenoid valve 20 CB is used to close the compressor bleed valves. Air from 11th stage compressor discharge is piped to a porous air filter, which removes dirt and water from the compressor discharge air, by means of a continuous blow down orifice before the air enters solenoid valve 20 CB. From the solenoid valve, the air is piped to the piston housing of the four-extraction valve. During turbine start-up 20 CB is de-energized and 11th stage extraction valves open allowing 11th stage air to be discharged in to the exhaust plenum thereby eliminating the possibility of the compressor pulsation. Limit switches 33 CB-1 through CB–4 on the valve provide permissive logic in the starting sequence and ensure that the extraction valves are fully opened before the turbine is fired & turbine accelerates to full speed. When the generator circuit breaker close, 20 CB solenoid valve is energized to close the extraction valves and allow normal running operation of the turbine. When a turbine shutdown signal is initiated and the generator circuit breaker is opened, 20 CB is de-energized and 11th stage air is again discharged into the exhaust plenum to prevent compressor pulsation during the turbine deceleration period. CAUTION: Under no circumstances, attempts should be made to start the turbine if all four-extraction valves are not fully opened. Serious damage to the gas turbine may occur if all the valves are not opened during accelerating and decelerating cycle of the turbine.

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Pressurized air supply Compressor discharge air is also used as a source of air for operating various air- operated valves in other system. Air for this purpose is taken at the discharge of the compressor and is then piped to the various air valves. WATER WASH PROVISIONS During water washing of the compressor, it is important to keep water out of the components that are actuated by compressor discharge air and out of the turbine’s bearing. To prevent water from entering these components and the bearings, isolation valves are provided in each compressor discharge extraction line and in the sealing lines in bearings No.1, No.2, No.3. After water wash, the isolation valves must be opened to allow normal operation of the turbine. PART 20 CB-1 33 CB-1 to 4 63 TK-1 63 TK-2 88 TK-1 88 TK-2 96 CD VA 2- to 41 VCK7-1 VCK7-2

NOMENCLATURE Compressor bleed solenoid 3-way valve. 11th stage compressor bleed valve limit switch Turbine exhaust frame cooling air pressure switch Turbine exhaust frame cooling fan motor Compressor discharge pressure transmitter 11th stage compressor bleed valve. Turbine shell cooling air blower check-valve.

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(11) VENTILATION AND HEATING SYSTEM GENERAL Both heating and ventilating capabilities have been incorporated in the turbine and accessory components (enclosures), by utilizing thermally insulated side panels and roofs. The heaters given in this installation provide humidity control for both areas and are mounted on the forward bulkhead. The three compartments, accessory, turbine and load shaft are, independently ventilated as shown in figure VH-1. Gravity operated dampers are used in the system to automatically provide an enclosure when the protection system is activated. The gravity closing dampers are normally held open by the pressure- operated latches, which must be manually reset after damper release. When the extinguishing agent is discharged, pressure on the latch forces a piston against a spring, moving a locking lever, which releases the latch allowing the damper to close. In the text that follows, the location of the latches are defined, as is the component on which they are mounted. Wall mounted air conditioner maintain the acceptable temperature of the control compartment. FUNCTIONAL DESCRIPTION Accessory compartment and turbine compartment Cooling air for the compartments is brought in through ventilation opening located in the sidewalls of accessory compartment. Pressure operated damper releases are activated to close dampers when the fire extinguishing system for the turbine is activated. After circulating through the compartment, the heated air is exhausted by a centrifugal vent fan driven by an AC motor 88BT located on the turbine compartment roof. The fan, enclosed in a box type casing, has a vertical-up air intake with a horizontal discharge through a normally open emergency shut-off damper attached to the side discharge. Protection for the turbine compartment area is provided by a high temperature thermostat alarm switch 26 BT-1. This device gives an alarm when the area temperature exceeds a preset temperature limit. Load Coupling Compartment The load coupling is contained in its own enclosure and situated between the exhaust plenum and the generator. This separate compartment has its own roof section, side panels, and an access door. Cooling air for the compartment is brought in through two-ventilation opening located just above the base Hot air, after circulating through the compartment, vents upward and is exhaust through a centrifugal vent fan driven by AC motor 88 VG located on the load compartment roof. The fan is controlled by thermostat 26 VG-2 which senses high compartment temperature & trips fan and discharges the extinguishing agent. Thermostat 26 VG-1 is a high temperature alarm, which indicates fan failure. PART 26 BT-1 26 VG-1 26 VG-2 88 VG 88 BT

NOMENCLATURE Turbine compartment high temperature-alarm Load compartment high temperature- alarm Load coupling compartment-ventilating thermostat. Ventilation fan motor (load coupling compartment) Turbine compartment ventilation air fan motor

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(12) HYDRAULIC SUPPLY SYSTEM AND I.G.V. HYDRAULIC SUPPLY SYSTEM The main hydraulic supply system utilizes turbine lube oil to supply the high-pressure fluid for operating fuel control valves, or other devices. A typical main hydraulic supply system is shown schematically in figure HS-1. The hydraulic supply system regulates a supply pressure of approximately 1500 psi suitable to modulate oil fuel control valves. The system filters the oil for servo valves use, and includes accumulators to provide transient flow and to prevent hydraulic pressure spikes to devices, to protect the turbine if hydraulic pressure becomes inadequate to support essential control functions. In units, where continuous turbine operation is essential, hydraulic filters with a transfer valve and an auxiliary hydraulic pump are included in the system. A signal from hydraulic pressure switch 63HQ-1 activates the auxiliary hydraulic pump when the system pressure drops below the control panel value. PART 63 HF-1 63 HF-2 63 HQ-1 88 HQ AH1-1 FH2-1 FH2-2 PH 1 PH 2 VAB 1 VAB 2 VCK 3-1 VCK 3-2 VM 4 VPR 3-1 VR 21 VR 22

NOMENCLATURE Hydraulic filter differential Low hydraulic supply pressure, auxiliary hydraulic pump startpressure switch Auxiliary hydraulic supply pump motor Control oil hydraulic accumulator (two nos.) Hydraulic supply filters. Main hydraulic supply pump. Auxiliary hydraulic supply pump. Hydraulic system air bleeds valves. Hydraulic system air bleed valve (aux.) Hydraulic pump check valve for main pump. Hydraulic pump check valve for auxiliary pump. Hydraulic filter transfer valve. Compensator- hydraulic supply pump (in pump) Main hydraulic supply pump pressure relief valve. Auxiliary hydraulic pumps pressure relief valve

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MAJOR DIVICES AND FUNCTIONAL DESCRIPTION Main Pump The primary source of high-pressure oil is an accessory gear driven pressure compensated piston pump. The pump’s pressure compensator is designated VPR 3-1. Auxiliary pump A motor driven fixed displacement pump is provided as a backup to the main pumps. While the main pump is at low speed, during the normal starting sequence, the auxiliary pump runs until the 14 HS speed sensor indicates minimum-governing speed is reached. Any time the main pump fails to maintain adequate pressure, as sensed by 63 HQ-1 pressure switches, the auxiliary pump is started. When this pump is initiated by the 63 HQ-1 pressure switch, it will continue to run until shut down manually. Dual filter and transfer valve A 0.5-micron dual filter assembly complete with fill valve, and transfer valve is provided on continuous duty units to maintain clean oil for servo valve use. When the dual filters are supplied, following procedure should be followed for filter change over. • Open the star bleed valve on the unused filter. • Open the fill valve • When oil with air comes out of the air bleed, operate the transfer valve. • Close the fill valve. • When no air is found in oil coming from the air bleed, close the bleed valve. Delta Pressure gauges A differential pressure gauge is provided on each filter to show the amount of pressure drop through it. When one of these gauges, indicates a pressure drop of 66 psi, the filter cartridge should be changed. Relief valve Relief valve VR 22 controls the auxiliary hydraulic pump outlet pressure. In the event of failure of the main pump pressure compressor, another valve, VR 21, is provided to protect the main hydraulic pump circuit damage. Check valve. Each hydraulic pump circuit has a check valve downstream of its relief valve to keep the hydraulic lines full when the turbine is under shutdown. These are designated VCK 3-1 and VCK 3-2. Air bleed In each pump circuit, ahead of the check valve, there are automatic air bleed valves VAB 1 and VAB 2. These valves close whenever oil is supplied to them at more than 150 psig. Manifold A brazed laminated hydraulic manifold provides a convenient mounting device for relief valves, the air bleed valves, and the check valves. It also includes the connecting network for these devices. Supply pressure switch Pressure switch 63 HQ-1 causes the auxiliary hydraulic pump to start if the hydraulic supply circuit pressure falls below an acceptable level. Low hydraulic supply pressure is sensed by pressure switch 63 HQ-1, which gives an alarm. Filter differential pressure gauge Differential pressure gauges located on the gauge panel indicate the hydraulic supply pressure drop across the filter of the dual filter system. When the HP filter is dirty, two manostats 63 HF-1 & 63 Hf-2 give and alarm to the CRT.

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MODULATED INLET GUIDE VANE SYSTEM General Variable compressor inlet guide vanes are installed on the turbine to provide compressor pulsation protection during start-up and shut- down and also to be used during operation under partial load conditions. The variable inlet guide vane actuator is a hydraulically actuated assembly having a closed feedback loop to control the guide vanes angle. The vanes are automatically positioned within their operating range in response either to the control system exhaust temperature limits for normal loaded operation, or to the control system protection limit during the start-up and shutdown sequences. Inlet guide vanes are modulated in order to maintain various stresses, pressure and flows within required limits. Their corrected speed control system is a portion of their control system, to accomplish this function. Guide vane actuation The modulated inlet guide vane actuating system includes the following components: Servo valves 90 TV-1, Position sensors (LVTD) 96 TV-1 and 96 TV-2, Solenoid valve 20 TV and hydraulic pump valve VH-3. These are shown on the piping diagram here after. When the trip oil OLT is pressurized, the dump valve VH-3 is operated. Actuation of the dump valve allows hydraulic oil to flow through servo valve 90 TV. Control of 90 TV will port hydraulic oil through the dump valve to operate the variable inlet guide vane actuator. For normal shutdown, inlet guide vane actuation is the reverse of the start-up sequence. The compressor bleed valves will open when the generator breaker is opened. The inlet guide vanes will ramp to the full closed position as a function or temperature corrected speed. In the event of a turbine trip, the 11th stage bleed valves will open and the inlet guide vanes will ramp to the closed position as a function of temperature corrected speed. PART 90 TV-1 96 TV-1 96 TV-2 FH 6-1 HM 3-1 VH 3-1

NOMENCLATURE Turbine inlet guides vane (I.G.V.) servo valve Turbine inlet guide vane L.V.D.T. Servo- hydraulic supply filter for I.G.V. assembly Variable inlet guide vane system. I.G.V. dump valve hydraulically operated.

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(13) TRIP OIL SYSTEM General The gas turbine protection consists of a number of primary and secondary systems, several of which operate at normal start-up and shutdown. The other protections are strictly for abnormal and emergency operating conditions requiring shutdown of the turbine. The hydraulic trip oil is the primary protection interface between the turbine control protection system circuits (SPEEDTRONIC control system) and the component, which admit or shut off fuel and regulate IGV position. The system contains devices, which are electrically operated through turbine control panel by SPEEDTRONIC signals as well as some totally mechanical devices that operate directly in the turbine components totally independent of the turbine control panel. The trip oil system and its components are shown schematically in figure TO-1. FUNCTIONAL DESCRIPTION General Low-pressure oil taken from the turbine’s lube fluid system is used in the trip oil system. Lube fluid is passed through a piping orifice to become the trip oil (OLT). The orifice is located in the pipe running from the bearing header supply to the trip oil system. This orifice is sized to limit the flow of lube fluid into the trip oil system and ensure an adequate capacity for all tripping device operations without causing a starvation of the lube oil system when the trip oil system is activated. The devices that cause a turbine shutdown through the trip system do so by dumping fluid pressure from the system either directly or indirectly through electro hydraulic dump valves, 20FL-1 or 20 FG-1. When oil in the trip oil line is dumped, fuel stop valves close by spring return action. When the turbine is started, the dump valves are energized to reset at the desired point in the starting sequence permitting high oil pressure to open the fuel stop valves and inlet guide vanes. The fuel stop valves remain open until some trip occurs or until the unit is shutdown. Orifice check valve assemblies are installed in the trip oil lines to the liquid fuel stop valves and the gas fuel stop valves to permit operation of either fuel system, while the other is tripped. Since inlet guide vane activation is also part of the trip oil system, the orifice check valve assemblies will also permit inlet guide van operation when fuel system is in its tripped state. Pressure switches 63 HG (1, 2, 3) and 63 HL (1, 2, 3) monitor trip oil pressure to the respective gas and liquid fuel system. If the pressure to the fuel system becomes too low for reliable operation, then switch coil trips the unit and cause annunciation of low trip oil pressure. 2.2 Over speed trip mechanism This totally mechanical device, located in the accessory gear, is actuated automatically by the over speed bolt when turbine speed exceeds the bolt setting. As a result, a rapid decay of trip oil pressure (OLT) occurs ultimately stopping the flow of fuel to the turbine due to closure of fuel oil stop valves. On activation, the over speed bolt assembly trips the latching trip fingers of the over speed trip mechanism. The action releases the trip valve in the mechanism and dumps the OLT trip oil system pressure to atmosphere. In turn, this causes the oil in the fuel stop valve cylinder to return to atmospheric pressure, thus allowing spring pressure to close the valve. Additional features included in the over speed trip mechanism are a limit switch (12 HA) which gives an alarm and a manual trip push rod. Once the trip is actuated, the system remains open and drains until it is reseted manually by pulling the reset rod.

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2.3 Manual emergency trip valve (VM3) A manually operated trip device is also provided to trip the unit in an emergency called the manual emergency trip valve VM3. This valve is strategically located on the top of the gauge cabinet so that the turbine can be tripped by pressing handle and dumping the hydraulic trip oil. When activated, this dumping action results in the closing of the fuel gas and/or fuel oil stop valves thereby stopping all fuel flow to the turbine. SOLENOID DUMP VALVES Hydraulic Dump solenoid valve - 20 TV

Solenoid- operated, spring- return hydraulic dump valve 20 TV is used to trip the system operation by a signal from the master control and protection circuit. The valve is energized when the turbine is running. Functionally it dumps trip oil pressure to the inlet guide vane dump valve VH3. Gas fuel stop valve, solenoid valve - 20 FG Solenoid valve 20 FG is a spring biased spool valve, which, dumps trip oil pressure to drain causing the stop/ratio and gas control valves to close. 20 FG is de-energized to trip and energized to reset from the SPEED TRONIC control panel. This solenoid valve is spring biased to trip and, therefore protects the turbine during all abnormal situations as well as for loss of DC power. 20 FG is shown in its energized state on schematic view. Gas fuel dump valve – VH5 Dump valve VH5 ports the gas stop/ratio valve hydraulic actuation cylinder to drain to close stop/ratio valve (VSR) and to servo valve 90 SR hydraulic oil discharge port to permit control gas fuel stop/ratio valve. VH5 is pilot operated by trip oil. Gas fuel Dump valve –VH12 Dump valve VH12 ports the gas control valve hydraulic actuation cylinder to drain to close gas control valve (VGC) and a servo valve 65 GC hydraulic oil discharge port to permit control of gas fuel. VH12 is pilot operated by trip oil. Liquid Fuel Stop Valve, solenoid –20 FL Liquid fuel solenoid dump valve 20 FL is a spring biased spool valve, which relieves trip oil pressure causing the liquid fuel stop valve to trip shut. The dump valve is energized to run and de energized to trip from SPEED TRONIC panel. Since this dump valve is spring biased to trip, it protects the turbine during all normal situations as well as those times when loss of DC power occurs. Liquid Fuel Hydraulic Trip Valve -VH4 Trip valve VH4 ports the liquid fuel stop valve actuation cylinder to drain to close the stop valve and to highpressure oil to open it. Valve VH4 is pilot operated by trip oil. Lube oil inlet Orifice. An orifice, sized to limit lube oil flow into the trip oil system, is located in the pipe running from the bearing header supply to the trip oil system. It must ensure adequate capacity for all tripping device operation and to prevent starvation of the lube oil system, when the trip oil system is tripped. Liquid Fuel stop valve Actuation Rate Control Orifice. An orifice located in the line between valve VH4 and the liquid fuel stop valve hydraulic cylinder limits the stop valve closing rate and high-pressure oil flow. When tripped, the stop valve closes in less than 0.5 seconds.

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Variable Inlet Guide System, HM3 The modulated inlet guide vane system is activated by the action of the trip oil system using low-pressure trip oil (OLT) in conjunction with high-pressure oil (OH) from hydraulic supply. Electronic control signals activate & position the inlet guide vanes, both during normal operation and under trip condition through the action of servo valve 90 TV, hydraulic dump valve VH3, limit switch 33TV, position sensor 96 TV-1 and 96 TV-2 and hydraulic activating cylinder ACV1. During normal operation trip oil (OLT) is pressurized and dump valve is energized which allows hydraulic oil from the hydraulic supply system to flow through servo valve 90TV. The controlled or modulated position of inlet guide vane servo valve 90TV determines the flow of hydraulic oil through the servo valve and dump valve VH3 to the inlet guide vane hydraulic actuator ACV1. The hydraulic pressure applied to the actuator determines the position of the inlet guide vane control ring. In a trip condition trip oil is dumped, by action valve 20TV. This causes inlet guide vane dump valve VH3 to move to dump position by action of the spring-return feature thereby dumping actuator cylinder oil, which closes the inlet guide vanes. When the turbine is at rest, the inlet guide vane angle position is at the designed closed position. This close guide vane angle is the position established to limit the airflow through the compressor during the turbine accelerating and decelerating sequence. Operation The tripping devices, which cause shutdown through this system, do so by dumping low-pressure oil (OLT). This is done either directly or indirectly through Electro hydraulic dump valves 20 FL, 20FG or 20 TV. When oil in the trip oil line is dumped, fuel stop valves are closed by spring return action. At the proper point in the starting sequence, dump valves 20FL, 20FG and 20 TV are energized permitting oil pressure to open the fuel stop valves and inlet guide vanes. The fuel stop valve remains open until some trip action occurs or until the unit is shutdown. The tripping devices, which cause selective fuel system shutdown, do so by dumping pressure oil (OLT). Each individual fuel stop valve may be selectively closed by dumping the flow of low-pressure oil going to it. Dumping valve 20FL causes the trip relay on the liquid fuel valve to go to the trip state to permit closure of the liquid fuel stop valve by its spring return mechanism. Dumping valve 20FG causes the trip relays on the gas fuel stop/ratio valve and the gas control valve to go to the trip state, which permits their spring returned closure. The orifice in the check valve and orifice network permits independent dumping of each fuel branch of the trip oil system by its dump valve. Tripping all devices other than the individual dump valves, will result in dumping of total trip oil system, which will shut down unit. During start-up or fuel transfer, the SPEEDTRONIC panel will close the appropriate dump valve to activate the desired fuel system. Both dump valves will be closed only during fuel transfer or mixed fuel operation.

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(14) GAS FUEL SYSTEM General The gas fuel system is designed to deliver gas fuel to the turbine combustion chamber at the proper pressure and flow rates to meet all of the starting, acceleration and loading requirements of gas turbine operation. A schematic diagram of the gas fuel system is given in figure. The major components of a gas fuel system are the gas stop/ratio and gas control valves located on the accessory base. Associated with the two gas valves are the necessary inlet piping strainer, fuel vent valve, control servo valves, pressure gauges and the distribution piping to the 14 combustion fuel nozzles. The fuel gas stop ratio valve and the gas control valve, two independent valves, are located inside the gas fuel panel, of the accessory base. The gas fuel flows through the gas stoop ratio valve and then into the gas control valve on its way to the gas manifold and individual combustion chambers. The position of each valve is servo controlled by electrical signals from the gas turbine SPEEDTRONIC control system. Both the gas stop ratio valve and gas control valve are actuated by single –acting, hydraulic cylinders The following major components comprise the gas fuel system: • • • • • • • • • • •

Strainer Fuel gas supply pressure alarm switch Gas stop ratio valve VSR Gas control valve VGC Stop ratio LVDTS 96GC-1, 2 Stop ratio valve-control servo valve 90SR Gas control valve- control servo valve 65 GC Gas fuel dump valves VH5 and VH12 Gas fuel vent solenoid valve 20 VG-1 and 2 Pressure gauges Lines to the 14 combustion chambers

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PART 20 PG-1 20 PG-2 20 VG-1 20 VG-2 33 PG-1 33 PG-2 33 PG-3 33 PG-4 63 FG-3 63 PG-1 65 GC 90 SR 96 FG-2A 96 FG-2B 96 FG-2C 96 GC-1 96GC-2 96 SR-12 FA-6 FH-7 MG-1 VA 13-1 VA 13-2 VGA VGC VH-5 VH 12 VPR 44-1 VPR 44-2 VSR

NOMENCLATURE Gas fuel system purge solenoid valve Between Gas fuel (purge) vent solenoid valve Gas fuel system purge valve limit switch Gas fuel system purge valve limit switch Gas fuel flow pressure switch (transfer to liquid) Gas fuel system purge pressure switch Gas control valve (servo-valve) Stop/speed (pressure) ratio valve servo-valve Fuel gas pressure transmitter Gas control valve L.V.D.T. (Linear variable differential transmitter) Stop/speed (pressure) ratio valve L.V.D.T. Gas fuel system purge filter (atomising air) Gas fuel hydraulic supply filter Gas fuel nozzle. Gas fuel system purge valve air actuated by 20 PG Gas valve assembly Gas control valve. Gas fuel dump valve-stop ratio valve Gas fuel dump valve-gas control valve Air pressure regulator-gas fuel purge valve Fuel gas stop ratio valve

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FUNCTIONAL DESCRIPTION General The gas controls valve and the gas stop ratio valve are almost identical. But each performs separate function. The fuel gas control valve meters fuel for use by the combustion chambers. It is activated by a SPEEDTRONIC control signal to admit the proper amount of fuel required by the turbine for a given load or speed. The fuel gas stop ratio valve is a dual function valve. It serves as a stop valve to shut off fuel flow to the turbine whenever required during either normal operation or in an emergency shutdown situation. The stop ratio valve also serves as a pressure regulating valve to hold a known fuel gas pressure ahead of the gas control valve and enable the gas control fuel flow over the wide range required under turbine starting and operating conditions. Because of these dual functions the valve is sometime called a stop/speed ratio valve. Gas strainer A gas strainer is located in the gas fuel supply line ahead of the on-base fuel connection. Foreign particles that may be in the incoming fuel gas are removed by the strainer. A blow-down connection on the bottom of the strainer body provides for periodic cleaning of the strainer screen. Frequency of cleaning will depend on the quality of the fuel gas being used. The strainer should be cleaned shortly after full turbine load has been attained for the first time and after any disassembly of the gas lines. Gas stop ratio and gas control valves: The control valve regulates the required control valve area and utilizes a hydraulic cylinder controlled by an electro hydraulic servo-valve. The gas control valve provides a fuel gas metering function to the turbine in accordance with its speed and load requirements. The position of the gas control valve (hence fuel gas flow to the turbine) is linear function of a variable control voltage (FSR) generated by SPEEDTRONIC control. The control voltage generated acts to shift the electro hydraulic servo valve to admit oil to, or release it from the hydraulic cylinder to position the gas control valve so that the gas flow is given which is required for a given turbine speed and load situation. The gas control valve also provides a shut-off of the fuel gas flow when required by either normal operation or emergency conditions. A hydraulic trip relay (dumps valve) VH12 is located between the electro hydraulic servo valve 65 GC and hydraulic cylinders. The operation of this dump valve is the same as the trip relay (dump valve) VH5. The gas stop/ ratio valve is similar to the gas control valve. However, it provides a dual function. The ratio function of the stop valve provides a regulated inlet pressure for the control valve as a function of turbine speed. The SPEEDTRONIC pressure control loop generates a position signal to position the stop/ratio valve by means of a servo valve controlled hydraulic cylinder to provide required inter-valve pressure. The gas stop/ratio valve functions as a stop valve in the fuel gas system to provide a positive fuel shut off during either normal or emergency conditions. Any emergency trip or normal shutdown will trip the valve to its closed position. This is done either by dumping hydraulic oil from the valve’s hydraulic cylinder or driving the position control closed electrically. A dump valve VH-5 is operated by trip oil acting on the piston end of a spool. A hydraulic trip solenoid valve, 20 FG, is located in the trip oil line to the dump valve. When the trip oil pressure is normal and the 20 FG solenoid valve is energized to reset, the spool of the dump valve is held in a position that allows hydraulic oil to flow between the control servo valve and the hydraulic cylinder. In this position, normal control of the stop ratio valve is allowed.

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In event of a drop in trip oil below a predetermined limit, a spring in the dump valve shifts the spool to interrupt the flow part of oil between the control servo valve and the hydraulic cylinder. Hydraulic oil is dumped and the ratio valve closes, shutting off gas to the turbine.

Switches, Valves and gauges Gas pressure switches A low gas pressure alarm switch 63 FG-3 is installed in the gas piping ahead of the gas stop/ratio valve assembly. This switch initiates a gas fuel pressure low alarm when gas supply pressure drops below the setting. It also initiates a transfer to liquid fuel if gas supply pressure drops below its set point. Gas fuel vent valve Solenoid-operated valves 20 VG-1 is installed in the vent piping between the gas stop/speed ratio and gas control valve. When the turbine is shut down, any gas fuel that might accumulate in the space between the stop/speed ratio and gas control valves, vents to atmosphere through the piping. It also ensure that no gas fuel will leak past the closed control valve to collect in the combustors or exhaust 20 VG-2 between VA-13-1 & VA-13-2 Pressure Transmitter Pressure Transmitter, 96 FG, -2A, -2B, -2C are installed in the fuel system on the gas fuel discharge side of the stop-speed ratio valve, to provide the operational pressure feedback signal to the SPEEDTRONIC control system. The voltage out put signal is directly proportional to the gas fuel pressure applied to the transmitter. Pressure gauges Three pressure gauges are provided in the fuel gas piping. The upstream gauge measures the pressure of fuel gas entering the stop/speed ratio valve: the intermediate gauge measures the pressure as it leaves the valve: and the down stream gauge measures pressure of the gas control valve and flowing to the gas manifold. Gas Fuel purging system A special circuit is provide to purge the circuit to the gas fuel nozzles of the 14 combustor with compressor discharge air, from the gas manifold located upstream of the combustion system. This gas fuel purging system is actuated during fully liquid fuel operation of the unit. When the gas turbine is operating on liquid fuel, solenoid valves 20PG-1, -2 are energized and allow filtered air to actuate pneumatic valves VA13-1 and VA13-2. Being actuated, VA13-2 allows air from another feeding piping to reach the gas manifold located upstream of the combustion system. Limit switches 33PG-2 and 33PG-4 check that valves VA13-1 and 13-2 are fully opened, and if not, they will cause an alarm to be annunciated. On the contrary, during fuel system gas operation of the unit, solenoid valves 20 PG-1, -2 are de-energized, so shutting of the pneumatic actuation of VA13-1 and VA13-2. Therefore, these valves are closed and no air reaches the gas fuel manifold. Limit switches 33PG-1 and 33 PG-3 checks the VA13-1 and VA13-2 are closed. So allowing solenoid valve 20VG-2 to be de-energized and intervalve piping to be connected to atmosphere.

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(15) LIQUID FUEL SYSTEM General The liquid fuel system pumps and distributes fuel as supplied from the off base forwarding system, to the fourteen fuel nozzles of the combustion system. The fuel system filters the fuel and device the fuel flow in to 14 equal parts for distribution to the combustion chamber at the required pressure and flow rates. Controlling the position of the fuel pump bypass valve VC3 regulates the amount of fuel input to the turbine combustion system by varying the amount of bypassed fuel. The fuel system shown in the schematic diagram is comprised of the following major components plus several other control devices, switches and gauge. • • • • • • • • •

Temporary fuel oil strainer SFI Fuel oil stop valve VSI. Liquid fuel pump PFI. Fuel pump discharge relief valve VR-4 Fuel bypass valve VC-3 High-pressure fuel strainer Fuel line check valve Fuel nozzle assemblies False start drain valve VA17-1 andVA17-2 (in bottom of combustion wrapper and exhaust frame)

Control device also associated with the fuel system include the liquid fuel pressure switches 63 FL-2, Servo valve 65 FP that controls the fuel bypass valve, fuel clutch solenoid 20 CF, and permissive limit switches 33 FL1 an –2 and trip relay valve VH4 in the fuel oil stop trip control circuit. FUNCTIONAL DISCRIPTION Low Pressure fuel strainer Fuel oil at low pressure from the fuel forwarding system flows through a temporary Y- type fuel strainer stop valve prior to entering the fuel pump. The Y type strainer housing contains a filter screen removes any extraneous particulate residue left in the fuel lines after installation. The strainer screen is to be removed after initial 600 hours of operation and the strainer housing must be cleaned and flushed upon removal of the screen prior to placing the turbine into service. Clean fuel is normally supplied to the turbine system, however during this initial period the low-pressure fuel strainer prevents contaminants from entering the fuel oil stop valve and the fuel pump, thereby preventing possible damage & subsequent improper functioning of these components. Fuel oil stop valve The fuel oil stop valve is an emergency valve operated from the protection system used to shut off the supply of fuel to the turbine during normal or emergency shutdown. This stop valve is a special purpose, hydraulically operated to position (open and close) valve with a venture disc and valve seat. When the turbine is shutdown in the normal sequence, or by emergency trip or over speed trip operation, the full oil stop valve will fully closed within total 0.5 seconds elapsed time. During normal operation of the turbine the stop valve is held open by high-pressure hydraulic oil (OH) that passed through a hydraulic trip relay (dump) valve VH4. This dump valve located between the hydraulic supply and stop valve hydraulic cylinder is hydraulically operated by trip oil (OLT) from the trip oil system. When the trip oil pressure is low (as in the case of normal or emergency shutdown), the dump valve spring shifts the valve

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spool to a position which dumps high pressure hydraulic oil (OH) in the stop valve actuating cylinder to the lube oil reservoir. The closing spring in the stop valve assembly then overcomes the oil pressure and closes the valve. Fuel pump The fuel pump is positive displacement continuous output screw type pump with two sets of opposed screws. The integral shaft screws are end mounted in roller bearings that are oil lubricated. The bearings and timing gears supplied with lube oil header and are sealed off from the fuel oil pumping chamber by internal mechanical seals. The pump is driven directly from the turbine driven accessory gear; therefore, fuel pump speed is directly proportional to turbine speed. The fuel pump discharge flow at any given turbine speed is greater than the turbine combustion requirements at that speed. A pressure switch 63FL-2 in the inlet side of the fuel pump piping measures the liquid fuel pressure and deenergizes the fuel pump clutch solenoid 20CF to stop the pump if fuel pressure fails below a safe level. This protects the pump against possible damage due to cavitations when operating with a low inlet pressure. Fuel pumps Discharge Relief Valve VR-4. The fuel pump discharge relief valve, VR-4, is located in a loop between the discharge and inlet of the pump. The valve prevents the fuel oil pressure from getting high enough to rupture any lines in the event of a flow divider malfunction or freeze up. This valve is set to operate in the range of 1200-1300 psi (83-90 bars) and relieves back into inlet pipe. Fuel bypass valve High-pressure flow from the pump is modulated by the servo controlled bypass valve assembly VC3. Components of this assembly include the bypass valve body, electro hydraulic servo valve 65 FR, and the hydraulic cylinder. This bypass valve is connected between the inlet and discharge sides or of the fuel oil pump and meters the flow of fuel to the turbine by subtracting excess fuel delivered by the pump and bypassing it back to the pump inlet. Servo valve 65 FP controls the bypass valve position according to the different requirement and the sensed fuel flow. If the fuel requirement exceeds the actual oil flow, the bypass valve closes to increase the net oil flow to the turbine. The servo valve uses high-pressure hydraulic oil (OH) to actuate the hydraulic cylinder and thus position bypass valve. High Pressure strainer Fuel oil at pump discharge pressure passes through the secondary (high pressure) fuel strainer as it flows from the fuel pump to the flow divider. This full flow high-pressure filter contains three, re-cleanable basket strainer assemblies having a 105-micron screen. A three valve manual bypass arrangements is provided which allows for basket strainer removal and cleaning while the gas turbine is in operation. This strainer helps to assure that contaminants and pipe scale are retained and prevented from entering the flow divider thereby preventing from possible damage of improper operation of this component. Flow divider The flow divider equally distributes input fuel flow to the 14 combustion nozzles. The continuous flow, freewheeling flow divider consists of 14 gear pump elements in a circular arrangement having a common inlet with a single timing gear. This timing gear serves to maintain true synchronous speed of each pumping element

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with all other elements. As the fuel enters the flow divider, each pair of gear elements distributes on fourteen of the fuel flow into each of the fuel lines nozzles. The speed of the flow divider pumping elements is directly proportional to the fuel flow through the flow divider. Two magnetic pickup assemblies 77FD-1 and 77FD-2, fitted to the flow divider, produce a flow feedback signal at a frequency proportional to fuel delivered to the combustion chambers. This signal is fed to the control panel SPEEDTRONIC where it is used in the fuel control system. Check valves. There is a check valve in each line between the flow divider nozzles. The check valve is mounted in each discharge line from the divider near the input connection to each nozzle. These valves prevent fuel oil from continuing to flow when a stop signal is given resulting in a cut-off of fuel to the nozzle. These check valves are set at a pressure, which is sufficient to prevent the fuel from the forwarding system from breaking through, when stop valve is not close. Selector valve indicator A 16- position selector valve and pressure gauge assembly is located at the output of flow divider to allow monitoring of fuel oil pressure in the selected nozzle inlet line. Positions 1 through 14 select the fuel nozzles, position 15 selects the fuel pump inlet pressure, and position 16 selects the fuel pump outlet pressure. False Start Drain Valve In the event of an unsuccessful start, the accumulation combustible fuel oil is drained through false start drains valves provided at appropriate low point in the combustion area. The false start drain valve, normally open, closes as the turbine accelerates during start-up. Air pressure from the discharge of the units axial flow compressor is used to actuate this valve. During the turbine shutdown sequence, the valve opens as compressor speed drops (compressor discharge pressure is reduced). SYSTEM REQUIREMENTS Gas Turbine Liquid Fuel Recommendations General These recommendations are for the several types of liquid fuels suitable for use in the heavy-duty gas turbines with firing temperature of 1600 ºF (870 ºC) or higher. It is intended as a guide for users of these turbine for the procurement, use, and where necessary, treatment of fuels. The fuel properties specified here include both those, which could affect turbine operation and those additional properties, which the turbine user may need to specify for his installation. These latter properties are related to fuel storage, handling and local safety and environmental codes. All of the fuels covered in this shall be hydrocarbon oil, free from organic acids and free from excessive amounts of solids, fibrous or other foreign matter likely to make frequent cleaning of filters necessary. The fuels shall be stable over storage and shall be compatible with other fuels with which they could normally be mixed. Procurement of the fuel to specifications is only the first step to successful heavy-duty gas turbine operations. Further steps required are: • • • •

Prevention of contamination before, during and after delivery; Proper design of fuel storage, heating and transfer facilities; Proper management of the entire facilities with regard to maintenance procedures and schedules; Proper design and operation of any fuel treatment equipment.

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In addition to outlining the overall fuel requirements, this also defines minimum acceptable air quality standards for turbine inlet air, and water requirements for installations, which employ either steam or water injection in their cycles. These have been included since the total contaminants entering the turbine must be considered. Fuel classifications and operational Considerations Liquid fuels applicable to heavy-duty gas turbine range from petroleum, naphtha to residual fuels. Within this range, fuels vary in hydrocarbon composition, physical properties, potential pollutants and trace metal contaminant levels. Since contaminants are a most important consideration in fuel application, the liquid fuels have been divided into two basic classes: true distillates (ash-free), and ash-bearing fuels. Table given below summarizes the general types of liquid fuels in these two classes and some operational requirements in gas turbine applications. FUEL DESCREPTION True Distillates Naphtha- A light volatile fuel with a boiling range between gasoline and light distillate. The lower flash point and higher volatility considerations. Its very low viscosity may result in poor lubricity Other names Jp-4, Jet-B O-GT Gas Turbine fuel. Kerosene-A light, highly refined and slightly more volatile fuel than light distillate. Normally more expensive than No2 distillate. Other names: GT Gas Turbine Fuel No.1 burner Fuel 1-D Diesel Fuel JP-5, Jet A Range Oil Lamp oil Light Distillate- Widely available volatile fuel with good combustion characteristics, being readily atomised and clean burning. Other names 2-GT Gas Turbine Fuel No.2 Burner Fuel Diesel Oil Marine Gas Oil Domestic Fuel Diesel Fuel- Closely related to light fuel except for additional requirements, peculiar to diesel engine operation. Other names 2-D Diesel Fuel Heavy true Distillate

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Essentially ash-free petroleum with the highest boiling range. Heavy true distillate has had limited and localized availability, frequently being a refinery by-product. This fuel may require heating for handling and forwarding due to high pour point. It may also be more difficult to atomise for optimum combustion. Other names Heavy Gas Oil Navy standard Distillate Ash Bearing Fuel Crudes and Blended Residual Fuels Crudes- Crude oil from different geographical area varies widely in levels of trace metal contaminants, ash, sulfur and wax and in such physical properties as viscosity, gravity and distillation range. Most crude will have flash point below 100F (38ºC) due to highly volatile components. Some very low ash crude, typified by Indonesian and North African crude have 0 to5 ppm of vanadium requiring minimal or no inhibition. Other crude for gas turbine application range up to 100 ppm vanadium. Most crude require desalting, especially if water transportation has been used Blended Heavy Distillate- Petroleum distillate contaminated with or blended with lesser amount of residual petroleum products, but with vanadium contents of 5 ppm or less. They may have wax contents requiring heating for pumping and filtering. They may also require washing for desalting, especially if water transportation has been used. Other names 3-GT Turbine Fuel 4-D Diesel Fuel Marine Diesel Fuel Blended Residuals- Blended residuals lie between blended heavy distillates and heavy residuals. They are commonly blended to specific maximum sulfur levels to meet applicable code. Vanadium contents are in the 5ppm to 100-ppm range normally. These fuels require complete fuel treatment. Other names No.4 Burner Fuel No.5 Burner Fuel Light Residual Oil Light Furnace Oil Intermediate Bunker Fuel Heavier residual fuel Residual Fuels These are low volatility petroleum product remaining at the end at the various refining distillation processes. As such they contain nearly all of the ash forming materials present in the original crude oil plus some additional that may be introduced in processing. They usually contain high molecular weight hydrocarbons such as aspartames, which can cause storage sludging problems. Residual fuels may have been blended with low cost distillates to lower the sulfur content and/or reduce the viscosity to ensure pumpability.

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All residual fuels require heating for pumping, filtering and proper air atomisation at the fuel nozzle. Residual fuels require washing to reduce the sodium level and vanadium inhabitation by addition of a magnesium base additive. Other names: No. 6 Burner Fuels. Boiler Fuel Bunker c. fuel Marine Fuel oil LIQUID FUEL CONTROL SYSTEM General This liquid fuel control system is made up of fuel handing components and electrical control components. The fuel handing components may include: fuel supply strainer SF1, fuel oil stop valve VS1, hydraulic trip valve VH4, fuel pump PFI , fuel bypass assembly, fuel pump pressure relief valve VR4, high and low pressure fuel filters, flow divider FD1, and combined selector valve/pressure gauge assembly, check valve VCK1-1 to14, and false start drain valve VA17-1, -2, -5. The electrical control components are: fuel oil stop valves limit switches 33 FL-1, -2, liquid fuel pump bypass valve servo valve 65 FP, liquid fuel bypass valve position feedback LVDT 96FP-1, -2, flow divider speed pickups 77FD-1, -2 and SPEEDTRONIC cards SFUC, SFKK, AOAH, SSVF AND SSVG, VA-17-5.

Electrical control components Fuel oil stop valve Limit Switches 33FL-1, -2 Limit switches 33FL-1 indicate that stop valve is closed and 33 FL-2 indicates that stop valve is fully open. An alarm is enunciated if the stop valve is closed. After the start of the FIRING SEQUENCE .The control system also checks that the valve is closed at the initiation of START, 33FL-2 detects that the stop valve is full open for initiation of the fuel control system (Relay 4LF-1). Liquid Fuel Pump Bypass Valve Servo valve 65FP. This is electro-hydraulic valve that controls the position of the fuel pump bypass valve, when the turbine is under shut down or in the trip state. This servo valve is electrically positioned to fully open the bypass valve. Linear Deferential Transformer (LVDT) 96FP-1 & 2 Two linear variable differential transformers, 96FP-1 and 96FP-2 are mounted on the liquid fuel bypass valve to provide position feedback used by the SPEEDTRONIC control system. The LVDTS have special windings that require special considerations during calibration and troubleshooting. Flow Divider Magnetic Speed Pickups 77FD-1 & 2 These are non-contact magnetic pickups which give a pulse signal at a frequency proportional to flow divider speed which is proportional to fuel flow delivered to the combustion chambers. Relay Contact 4LF-1 Function The 4 Fl-1 relay contact is a required permissive for the step initialisation of the liquid fuel pump bypass valve.

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Control System The fuel oil control system consist of closed control loops using the fuel signal (VCE) and turbine speed (NHP) as command input and using fuel pumps bypass valve position (POS) and flow divider speed as feedback signals. The position of the bypass valve determines the fuel flow through the bypass valve around the fuel pump. Due to the constant displacement fuel pump, the fuel flow to the turbine at a given pump speed is the difference between the pump flow and the bypass valve flow. Flow divider speed is measure of the fuel flow through it and to the turbine fuel nozzles. The fuel oil system command receives the turbine speed signal. NHP, from SSZD card and fuel flow signal VCE, is received from the minimum valve gate. Command signals are multiplied to yield the product commands, which may be measured at the test point REF (TP2) of the CFKK card. The fuel command relationship is REF. Fuel command= (VCE-4) NHP/100. An outer feedback loop senses the flow divider speed signal by two magnetic pickup 77FD-1 and 77FD-2. The magnetic speed pickup signals IN-1 of SFUC are converted into a voltage feed back signals. OUT-1 and OUT-2 of SFUC. The larger speed signal is selected as the feedback signals (FFN). A Comparator circuit will alarm if the difference between the two feedback signals exceeds a present value. During the ignition period, if feedback signal (FFN) exceeds a preset value a trip signal will be generated by the SFUC card. The flow divider feedback signal enters a summing junction with the product command signal and the scaled result may be measured at REF (TP-2) of SFKK. Figure shows REF as a function of VCE and turbine shaft speed (NHP). The SKFF card output feed an integrator circuit in the AOAH (D) card. The gain of the integrator card is critical to turbine light up and must be correctly set. Am AOAH (A) SPEEDTRONIC card is provided to rapidly step the AOAH (D) integrator card when attempting to fire. The AOAH (D) integrator output for firing sequence is shown in figure. SPPEDTRONIC card SSVG accepts the AOAH (D) command signal and sums this signal with the bypass valve position feedback signal. An inner (faster) feedback loop senses the liquid fuel pump bypass valve position by two linear variable differential transformers, LVDTs 96FP-1 and 96FP-2, card SSVF independently processes each LVDT signal to generate voltage feedback signals (FB1, FB2). If either LVDT feedback signals fall below a preset level, the SSVF card detects the fault and annunciates on the turbine control panel. The higher of the two feedback signals is selected. This feedback signal passes through an operational amplifier on the SSVF card where the span and zero (pots) potentiometers are set to obtain the feedback relationship (POS) given on the control Specification drawing. SPEEDTRONIC card SSVG will sum the fuel reference signal (flow divider feedback signal, NHP and VCE command signals, initialisation signal) and the liquid fuel bypass valve position feedback signal, to generate a command signal to the liquid fuel bypass valve servo (65FP) Redundancy and Comparator Circuits Redundancy is applied to all primary fuel control loops. This redundancy is applied to obtain maximum reliability so far it is practical and still maintain safe protection of the gas turbine in case of malfunction. Redundancy is applied in the servo valve current loops by connecting the servo valve torque motor coil independently to the SSVG card, which detects a difference between the two feedback lines and lights the FLTC indicating lamp on the card front and alarms on the control panel annunciator. Redundancy is applied in the position feedback loop by employing separate FLTC on the fuel pump bypass valve and independent LVDT oscillator cards, SCSGS, and separate oscillator and conditioning circuits on the SSVG card. The highest voltage output of the two LVTD conditioning circuits is diode-selected and fed to the feedback amplifier on the SSFV cards. These voltage signals are monitored by comparator on the SSVG which

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will annunciate loss of either feedback signal and which will light the FAULT indicating lamp on the card front. If an LVDT failure does occur, the unit will continue to run on the other LFCT. However, the condition must be corrected as soon as possible since loss of the other LVDT would result in an open position loop, thereby supplying excessive fuel flow to the combustion system. The SSVF card also employs a comparator circuit to detect when the fuel pump bypass valve is not at all or near the zero stokes (full open) position prior to starting firing the turbine. Redundancy is also applied in the primary liquid fuel control loop. Two independent or dual magnetic pickups are applied complete with independent pulse rate-to-analog converter circuits in the panel to obtain redundant feedback signals. This redundancy permits the turbine to continue to operate and still give shutdown and tripping protection in case of an open circuit or failure of either of the redundant feedback paths. All the above fault condition will prevent turbine or would abort the start up if the fault is occurred prior to establishing a flame in the turbine. Fuel oil control sequence When the gas turbine is given a start signal at zero speed, the liquid fuel oil control system operates as per given sequence: • • • • •

The fuel stop valve is shut since 20FL (control trip oil) have not been energized to open the stop valve. The LCE (liquid fuel control voltage) fed on to the SFKK card, is held at zero. This LCE causes the SFKK card to drive the fuel oil bypass valve servo 65 FP to a position, which will move the bypass valve to the fully open position. The divider is not turning since there is no fuel flow. Therefore, the speed pick up 77 FD-1 and –2 do not give a pulse signal to the SFUC card. The output of the SFUC card is also zero, which is fed into the SFKK card. The false start drain valve VA17-1, -2 and –5 is open until compressor discharge pressure is high enough to close the valves. The liquid fuel oil control system remains in this state except for the speed signal fed into the SFKK card until the turbine reaches firing speed.

When the turbine reaches firing speed as sensed by 14 HM and after a purge period (if applicable); the liquid fuel system then behaves as follow: •

Servo valve 20 FL is energized to open the fuel stop valve. Limit switch 33 FL-2 detects valve full open position.

•

Relay 4LF-1 picks up when stop valve is open and SPEEDTRONIC card AOAH (A) generates a command to speed the liquid fuel bypass servo valve (65FP) to rapidly move the liquid fuel bypass valve from full open position to an initial position.

•

VCE, which was clamped to zero, jumps to the VCE value required by the control specifications for firing VCE. The VCE signal and turbine speed signal NHP combines in a multiplier in the SKFF card and establish the desired rate of fuel flow for the turbine. The desired firing fuel flow will be arrived at by the SKFF command being integrated by the AOAH (D) card, to ramp the liquid fuel bypass valve further closed from the initial position.

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•

As the fuel bypass valve closes, the fuel pump discharge pressure increases. When this pressure has increased to a pressure high enough to overcome the friction in the flow divider and the check valve opening pressure, the fuel will begin to flow into the combustion chambers.

•

As the fuel flows into the turbine, the speed sensors 77FD-1 and 77 FD-2 sends a signal to the SFUC card, which gives output of the fuel flow rate signal to the SFKK card. When the fuel flow rate is equal to the called –for fuel flow rate, the servo valve 65FP is moved to the null position and the bypass valve remains “stationary”.

•

During this firing part of the turbine start-up, there is a feature on the SFUC card, which monitors the fuel flow rate into the combustion chamber and if a preset flow rate is exceeded for two seconds continuously, it will trip the turbine. This feature is inhibited after flame is established and after the turbine reaches accelerating speed as detected by the 14 HA relay.

•

Another feature of the SFUC card, which indicates a fuel oil control system fault, is a comparator which will cause an alarm if there is a large deference between fuel flow rate signal coming out of the pulse rate to analog converters. This difference is caused by a number of reasons such as: grounded wires from speed sensors, faulty speed sensors, wrong gas on speed sensors, common shaft of flow divider broken, faulty pulse rate to analog converter, etc. This alarm feature cannot be inhibited & is always in operation.

•

Once flame has been established in the combustion chambers, the VCE is lowered to the warm up level. This causes the bypass valve servo valve 65FP to modulate the bypass to regulate less fuel into the turbine.

•

After completion of the warm up period, the VCE is increased to accelerate the turbine to operating speed. The fuel control system adjusts fuel to meet the VCE and speed command fuel flow. As the turbine is accelerated, the false start drain valve closes due to increased compressor discharge pressure.

•

At constant speed the fuel control system operates as a function of VCE only. The bypass valve is modulated only to regulate fuel flow based on VCE input. When the turbine is given a shutdown signal, the VCE is decreased to some minimum value and the turbine decelerates. When 14HA drops out on SVSE, the liquid fuel system goes into the trip state and stop valve closes. At he same time VCE goes to zero, bypass valve servo 65FP is electrically driven to drain hydraulic oil from the by pass valve actuator. The bypass valve is then driven open by its spring. This stops fuel flow into the turbine so that flow divider will stop turning and the pickups 77FD-1 and 77FD-2 stop sending out a pulse signal to the SFUC card. As the turbine decelerates further, the false start drain valves will open. The fuel oil control system will remain in this state until the turbine is ready to fire during the next start up.

•

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(16) ATOMIZING AIR SYSTEM General Atomising air system provides sufficient pressure in the air atomising chamber of the fuel nozzle body to maintain the ratio of atomising air pressure to compressor discharge pressure at approximately 1.2 or greater over the full operating range of the turbine. Since the output of the main atomising air compressor, driven by the accessory gear, is low at turbine firing speed, during starting, atomising air compressor provides a similar pressure ratio during the firing and warm up period of the starting cycle and during a portion of the accelerating cycle. Continuous blow down to atmosphere is also provided to clear the main gas turbine compressor of accumulated dirt. Major system components include: the main atomising air compressor, starting air compressor, atomising air heat exhanger and an air filter. FUNCTIONAL DESCRIPTION When liquid fuel oil is sprayed into the turbine combustion chambers, it forms large droplets as it leaves the fuel nozzles. The droplets will not burn completely in the chambers and may go out of the exhaust stack in this state. A low pressure atomising air system is used to provide atomising air through supplementary orifices in the fuel nozzle witch directs the air to impinge upon the fuel jet discharging from each nozzle. This stream of atomising air breaks the fuel jet up into a fine mist, permitting ignition and combustion with significantly increased efficiency and a decrease of combustion particle discharging through the exhaust into the atmosphere. It is necessary therefore, that the air atomising system is operative from the time of ignition, firing through acceleration, and through operation of the turbine. Air taken from the atomising air extraction manifold of the compressor discharge casing passes through the airto-water heat exchanger (precooler) to reduce the temperature of the air sufficiently to maintain a uniform inlet temperature to the atomising air compressor. The atomising air precooler heat exchanger, located in the turbine base under the inlet plenum, uses water from the turbine cooling medium to dissipate the heat. Compressor discharge air, now cleaned and cooled reaches the main atomising air compressor. This is a single stage, flanged mounted, centrifugal compressor driven by an inboard shaft of the turbine accessory gear. It contains a single impeller mounted on the pinion shaft of the integral input speed-increasing gearbox driven directly by the accessory gear. Out-put of the main compressor provides sufficient air for atomising and combustion when the turbine is at approximately 60 percent speed. Differential pressure switch 63AD-1, located in a bypass around the compressor, monitors the air pressure & annunciates an alarm if the pressure rise across the compressor should drop to a level inadequate for proper atomisation of the fuel. Switch 26AA-2 is an adjustable heat sensitive thermo switch provided to sound an alarm when the temperature of the air from the atomising air compressor entering the atomising air after cooler is excessive. When the atomising air reaches the temperature setting of this switch, the alarm is activated. Improper control of the temperature may be due to failure of the sensor, the after cooler or insufficient cooling water flow. Continued operation above 275F should not be permitted for any significant length of time since it may result in insuffient atomising air to provide proper combustion. Atomizing air is piped to the atomising air manifold with “pigtail” piping providing equal pressure distribution of atomising air to the individual fuel nozzles.

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When the turbine is first fired, the accessory gear is not rotating at full speed and the main atomising air compressor is not giving sufficient output for proper atomisation. During this period, the starting (booster) atomising compressor, driven by an electric motor, 88AB is in operation supplying the necessary atomising air. The starting atomising air compressor at this time has a high-pressure ratio and is discharging through the main atomising air compressor, which has a low-pressure ratio. The main atomising air compressor pressure ratio increases with increasing turbine speed and at approximate 60% speed the flow demand of the main atomising air compressor approximates the maximum flow capability of the starting atomising air compressor. The check valve in the air input line to the main compressor begins to open allowing air to be supplied to the main compressor simultaneously from both the main air line and the starting air compressor. The pressure ratio of the starting atomising air compressor decreases to one and it is shut down approximately 60% speed (14HC pickup). Now all of the air being supplied to the main compressor is directly from the precooler through the check valve bypassing the starting air compressor completely. PURGING SYSTEM Fuel oil purge When the turbine has been operating on fuel oil and a transfer to gas fuel is activated it becomes necessary to purge any remaining fuel oil from the nozzle body and prevent chocking of the nozzle. This oil is forced into the combustion by the action of both compressor discharge air (AD) and atomising air (AA) as expanded in the following text. Initially, compressor discharge air (AD) is used as purge air, passing through valves VA19-1 in the following manner. At a point in the compressor discharge piping, after the atomising air precooler, compressor discharge air is taken off in a separate piping and pressure is regulated by valve VPR 54. Regulated air is piped to the energized solenoid valve 20PL-1. This valve has been energized to open and allow the pressure-regulated air to pass through the valve and flow to the diaphragm of valve VA19-1 causing it to open. A bypass arrangement in the atomising air piping maintains the required purge pressure ratio. Compressor discharge air, taken from the piping at a point after the precooler, operates the piston of valve VA18 in the bypass arrangement to allow successive atomising air pressure to pass through the valve into piping which feeds back to the compressor discharge air line ahead of the precooler HXI. Solenoid valve 20AA is energized to open and de energized, to close, for controlling airflow to air operate valve VA18. 3.2 FUEL GAS PURGE The fuel gas manifold is connected to the gas turbine compressor discharge through two blocks valve, VA13-1 & VA13-2. During normal operation on gas fuel, both of these valves are in their normally closed position with the line between the valves vented to atmosphere through a solenoid valve 20VG-2.When a transfer to liquid fuel is completed, solenoid valve 20PG is energized and operating air is admitted to the diaphragm actuators of VA13-1 and VA13-2. This opens the block valves and allows compressor discharge air to flow through VA13-1 and VA13-2. This opens the valve and allows compressor discharge air to flow through VA13-1 and VA13-2 to fuel gas manifold. It purges the gas fuel side of the nozzle thereby protecting the nozzles from the hot combustion chambers. Solenoid valve 20VG-2 is energized simultaneously with 20 PG to prevent loss of compressor discharge purge air to the atmosphere. Two-block valves are used in this system to prevent leakage of fuel gas into the atomising airline in the event that one of the valves should fail. Limit switches 33PG,-2, -3 and –4 mounted on the block valves are used to indicate valve position. When the block valve is open and the fuel nozzle gas passages are being purged, the contacts of switches 33PG-1 and –3 open and the contacts of 33PG-2 and –4 are closed.

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WATER WASH PROVISION During water washing of the gas turbine’s compressor selection and turbine sections, it is important to keep water out of the atomising air system. To keep water out of the atomising air system, the system inlet and discharge are given with isolation valves. In addition, the system has vent valve to avoid complete throttling of the compressor and drain valves, to remove any leakage past the isolation valves or accumulated water on the water wash side of the isolation valves. Refer to the drawing for the location of these valves. During normal operation of the gas turbine, the vent and drain valves must be closed and the isolation valve must be opened. Before initiating water wash, the two isolation valves must be close to keep water out of the atomising air system. The vent valves must be opened to allow air to pass through the atomising air compressor. The low point drain valve upstream of the atomising air system inlet isolation valve and low point drain valve downstream of the discharge isolation valve must be closed. The remainder of the low point drain valves are to be open during water wash to remove any leakage through the isolation valves during water washing. It is not necessary to start atomising air compressor during water wash. Caution Running the atomising air compressor completely throttled or dead-ended may result in overheating and damage to the compressor. Running the atomising air compressor with water in the piping will result in damage to the atomising air compressor. At the end of water wash, drain the water from the atomising air piping by opening the low point drain valves. When all the water has been drained from the piping, the drain valves and vent valves must be closed and the isolation valves are opened. COMPONENT DESCRIPTION Atomising Air pre-cooler HX1: Atomizing air precooler HX1, located in the line between the compressor discharge casing connection and the atomising air filter FAS, is air-to-water type heat exchanger designed to operate at specified limits of pressure and temperature. The unit is a shell and tube type heat exchanger with a U tube bundle and an exposed fixed tube sheet. Water flow is through the tubes. The tube bundle is supported at the bonnet and by the tube sheet so that the entire tube sheet and bundle can be removed as a complete assembly for cleaning, repair or replacement. Tapped holes are provided in the face of the tube sheet for eyebolts to assist in bundle removal. Gaskets are provided for air seal. Starting (Booster) Atomizing Air Compressor-CA-2: Starting atomising air compressor CA-2 is a compact, rotary-lobe type axial-flow compressor. The meshing of two screw type rotors synchronized by timing gears provides controlled compression of the air for maximum efficiency and pulsation-free discharge. Two heavy duty, angular contact type ball bearings are used on each rotor shaft, at the discharge end, as fixed bearings to maintain discharge end clearance. The housing is a one piece casting with flanged inlet and discharge openings. The rotors are ductile iron with integral shaft. All rotors are dynamically balanced for vibration free operation. Helical timing gears are of alloy steel with hardened and ground teeth for quiet operation.

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(17) FIRE PROTECTION SYSTEM General The carbon dioxide (CO2) fire protection system supplied is designed to extinguish fires by reducing the oxygen content of the air in the compartment from an atmosphere normal of 21 percent to less than 15 percent which is insufficient concentration to support the combustion of turbine fuel or lubricating oil. System design is in accordance with the requirements of Fire Protection recommendations and recognizing the reflash potential of combustibles exposed to high temperature metal; it provides an extended discharge to maintain an extinguishing concentration for a prolonged period to minimize the likelihood of a reflash condition. Major system components include: Carbon dioxide cylinder, (in and off- base station), discharge pipes and nozzles, pilot valves, fire detectors and pressure switches. Refer to the schematic diagram where system components are shown in their respective compartments. Carbon dioxide is supplied from an of-base CO2 skid where 2 nos. CO2 storage tanks are connected to a distribution system which transfers the carbon dioxide by pipe to discharge nozzles located among other in the various compartments of the gas turbine unit. For the gas turbine itself, there are two distinctive zones: Zone 1: Turbine accessory compartment and turbine compartment Zone 2: Tunnel of bearing no. 3 Two types of discharge are used: initial discharge and extended discharge. Within a few seconds after actuation, sufficient CO2 flows from the initial discharge system into the compartment of the machine to rapidly build up extinguishing concentration. This concentration is maintained for a prolonged period of time by the gradual addition of more CO2 from the extended discharge system. WARNING: carbon dioxide, in a concentration sufficient to extinguish fire, creates an atmosphere that will not support life. It is extremely hazardous to enter the compartments after the CO2 system has been discharged. Anyone rendered unconscious by CO2 should be rescued as quickly as possible and revived immediately with artificial respiration. The extent and type of safe guards and personnel warning that may be necessary must be designed to meet the particular requirements of each situation. It is recommended that personnel be adequately trained to take the proper action in case of such emergency. FUNCTIONAL DESCRIPTION To better understand the CO2 system, a brief description of its operation and distinctive features is given in the following paragraphs. Refer to the Fire Protection System schematic Figure FP-1. Should a fire occur in one of the protected compartment of unit, the pilot valves in the off-base skid will be energized by one of the heatsensitive fire detectors, more exactly: 45 FA-1A,-1B, 45FA-2A,-2B in the accessory compartment, 45FT1A,1B,45 FT-2A-2B:45FT3A-3B in the turbine compartment and 45FT-8A,-8B,9A,-9B in the tunnel bearing NO.3 The CO2 flow rate is controlled by the size of the orifices to the discharge nozzles in each compartment for the initial and extended discharge system. The orifices for the initial discharge must permit a rapid discharge of CO2 to quickly build up an extinguishing concentration. The orifice for the extended discharge is smaller and permits a relatively slow discharge rate in order to maintain the extinguishing concentration over a prolonged period of time. By maintaining the extinguishing concentration, the likelihood of a fire reigniting is minimized.

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In the auxiliary compartment, there are 4 nozzles for the initial discharge and 2 nozzles for the extended discharge. In the gas turbine compartment, there are 6 nozzles for the initial discharge and 2 nozzles for the extended discharge. When the fire is detected and CO2 is admitted, CO2 operated latches close the shutters provided in the ventilation system in the turbine and auxiliary compartments. There is also one such a shutter, in the bearing NO.3 tunnel zone that will be closed. Note that the CO2 latches located in the ventilation path must be opened manually after a fire. These latches are provided with a limit switch preventing a gas turbine restart after fire.

PART 45 FA- 1A 45 FA- 1B 45 FA- 2A 45 FA-2B 45 FT-1A 45 FT-1B 45 FT-2A 45 FT-2B 45 FT-3A 45 FT-3B 45 FT-8A 45 FT-8B 45 FT-9A 45 FT-9B

NOMENCLATURE Accessory compartment fire detector

Turbine compartment fire detector

Bearing No.3 fire detector Load compartment fire detector

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(18) GAS TURBINE OPERATION GT START-UP PREPARATION It is assumed that the gas turbine generator set and auxiliaries are connected adequately, with all their components and circuit in good condition. Control systems are adjusted in accordance with the control specifications. Further, MCC and all devices are powered. Emergency power is available. Following prestart checks and operations are to be preformed prior to GT start-up. Oil System • Check fluid levels in lube oil tank, cooling water system etc. • Start auxiliary lube oil pump 88 QA and generator Jacking oil pump on MANUAL. Inspect the lube oil header pressure/discharge pressure, oil flow to all bearings through sight glass and jacking oil discharge pressure. • Do the same operation for emergency lube oil pump 88QE after stopping auxiliary oil pump. • Stop 88QE and put both 88QA and QE on auto. • Check for the proper line up on oil and cooling waterside of lube oil system. Seal air system • Refer the schematic diagram of cooling and sealing air circuit, check all bearing seal air valves (Ref. 1, 3, 4 and 5) are open. • Check the seal air line drain valves (Ref.2 and 11) are closed. • Check turbine exhaust frame cooling fans 88TK-1 and 88 TK-2 is on auto. Cooling Water • Check the correct position of temperature regulating valve on lube oil heat exchanger (VTR-1 ref. 14) and atomising precooler valve (VTR-2 ref.13). These valves must be in AUTO. • Select one cooling water pump on AUTO position. Fuel Gas • Check unit gas skied manual shut off valves are open. • Check low point drain valves are closed. • Check gas strainer is correct and purge valve is closed. • Check for any gas leakage in the fuel gas piping. Fire Protection System • Check Co2 fire extinguisher system is lined up and available an auto mode. • Check Halon fire fighting cylinders are connected to manifold and lined up for operation on auto mode. Manual lock pins on individual cylinders removed. Starting System • On the speedtronic panel initiate turning gear start order. The auxiliary oil pump 88QA, jacking oil pump and cranking motor 88CR-1 are started. When the shaft speed reaches 300 RPM, the cranking motor stops and turning gear motor 88TG-1 rotates the shaft about 100 rpm. • As soon as the turning gear motor is started the torque converter motor 88 TM-1 starts to drive the torque converter blades in TURNING TORQUE position (34%). • The cooling air fan (88FC) and selected cooling water pump 88 WC-1/88 WC-2 starts.

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•

Make sure that turning gear operation is smooth; there is no abnormal sound from any rotating parts.

Ventilation System • Check different GT compartment ventilation fans 88 BT etc. are available and lined up. Keep their selection on auto in GT MCC. START-UP/SHUT-DOWN SEEQUENCE AND CONTROL General The start-up control brings the gas turbine from zero speed up to operating speed safely by providing proper fuel to establish flame, to accelerate the turbine, and do it in such a manner as to minimized the low cycle fatigue of the hot gas path during the sequence. This involves proper sequencing of command signals to the accessories, starting device and fuel control system. Since a safe and successful start-up depends on proper functioning of the gas turbine equipment, it is important to verify the state of selected devices in sequence. Much of the control logic circuitry is associated not only with actuating control devices, but enabling protective circuits, and obtaining permissive conditions before proceeding. A typical start-up sequence flow diagram is given here. Speed Detectors An important part of the start-up/shut-down sequence control of the gas turbine is proper speed sensing. Turbine speed is measured by magnetic pickups and will be discussed under speed control. The following speed relays are typically used. SPEED RELAY L 14 HR Zero-speed L 14 HP L 14 HM Minimum speed L 14 HA accelerating speed L 14 HC Cranking motor stop speed L 14 HS Operating speed L 14 HY

PICKS AT 0.06 % 04 % 10 % 50 % 60 % 95 % 8.4%

DROPS AT 0.3 % 3.3 % 9.5 % 40 % 50 % 94 % 06 %

The zero speed sensor 14 HR, provides the signal that the turbine shaft has started to rotate. If the speed is below 14 HR, permissive logic is provided to initiate the cranking sequence and energize the torque converter. Pick up of the 14 HR relay initiates logic to start the turbine accessory compartment cooling and ventilating fans. Load compartment ventilating fan starts when flame is detected. During the shut down cycle, dropping of L 14HP provides the signal to start the barring motor for automatic cool down sequence of the turbine. The minimum speed sensor 14 HM indicates that the turbine has reached the minimum firing speed and initiates the purge prior to ignition. The dropout of 14 HM minimum-speed sensor provides several permissive functions in the restarting of the turbine after shut down. The acceleration speed relay 14 HA pickup indicates when the turbine has reached approximately 50% in the acceleration cycle. The high-speed sensor L 14 HS pick up indicates when the turbine is at operating speed, and that the accelerating sequence is complete. See the Inlet Guide Vane chapter for details of the modulated guide vane system. The exhaust frame blowers are also turned on when 14 HS picks up. The cranking motor shut down by speed relay, 14 HC, provides the signal to drain the torque converter and shuts down the cranking motor.

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During normal shutdown the 14 HS dropout signal provides the permissive signal to start the atomising air booster compressor on units with liquid fuel. Flame will be maintained until the speed reaches 34% speed, or the fired shut-down timer times out, whichever comes first, at that point fuel will be cut off by F.S.R. (fuel command signal) which is brought to zero. Should the turbine and generator bog down; L14HS will drop out at the under-frequency speed setting. The inlet guide vanes will close at 53 degree and the compressor bleed valves will open. Approximately one second after 14 HS drops out, the generator breaker will trip open and the digital set point will be reset to 100.3%. As the turbine accelerates, 14 HS will pick-up, and the compressor bleed valves will close. The turbine will then require a start signal before the generator is permitted to synchronize to the system again. The actual settings of the speed relays are listed in the control Specifications and are programmed in the “C” computer of the SPEEDTRONIC control panel as PROM constants. Start-up control The start-up control operates as an open loop control using preset levels of the fuel command signal ( F.S.R.). The levels are: ZERO, FIRE, WARM-UP, ACCELERATE and MAX.The control specification provides proper setting calculated for the fuel anticipated at the site. The FSR levels are set in the SPEED TRONIC start-up control. Start-up control F.S.R. signals operate through the minimum value gate to ensure that control functions can limit F.S.R. as per requirement. The fuel command signals are generated by the SPEEDTRONIC control start-up software. In addition to the three active start-up level, the software sets maximum and minimum F.S.R. and provides for manual control of F.S.R. Pressing the switches for “MANUAL CONTROL” and” F.S.R. GAS RAISE OR LOWER” allows manual adjustment of F.S.R. setting between F.S.R MIN and F.S.R. MAX. While the turbine is at rest, electronic checks are made of the accessories, and the voltage supplies. At this time, the operator display will be normal and the” SHUT-DOWN STATUS” will be displayed on the C.R.T. Activating the Master operation switch L43 from “OFF” to an operating mode will activate the ready circuit. If all protective circuits and trip latches are reseted, the “START-UP STATUS” and “READY TO START” messages will be displayed, indicating that the turbine will accept a start signal. Depressing the “START” Master Control Switch (LISTART) and “EXECUTE” will introduce the start signal to the logic sequence. The start signal energizes the Master Control and Protection circuit (the “L4” circuit) and starts the necessary auxiliary equipment. The “L4” circuit permits the cranking motor to start. As torque converter is drained. The torque converter will be filled after two seconds. Start-up status message “STARTING” will be displayed on the CRT. See point “A” on figure Start Up-1. When the turbine “breaks away” (start to rotate). The torque converter vanes are set to max torque position (65%) until the 14 HM speed is reached. From 14 HM pick-up to the end of warm up, the torque converter vanes will be set to the 50% position. The turbine speed relay L14 HM indicates that the turbine is turning at the speed required for proper purging and ignition in the combustors. Gas fire units, that have exhaust configurations, which can trap gas leakage, have a purge timer L2TV. The purge timer is set to allow about four changes of air through the unit to ensure that all combustible mixture has been purged out of the system. The setting for L2TV is normally one minute. The starting means will hold speed until L2TV (which was stared with the L14HM signal) has completed its cycle. Units which do not have

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extensive exhaust systems may not have purge timer, but rely on the starting cycle and natural draft to purge the system. The L14 HM signal or completion of the purge cycle (L2VX) enables fuel flow, ignition & sets firing level FSR and initiates the firing timer. See point”B” on figure Start Up-1. When the flame detector output signal indicates flame is established in the combustors, (L28FD), the warm-up timer L2W starts and the fuel command signal is reduced to the “WARM-UP” F.S.R. level. The warm-up time is provided to minimize the thermal stresses of the hot gas path parts during the initial part of the start-up. If flame is not established by the time the L2F timer times out, (typically 60 seconds) then unit can be given another start signal, but firing will be delayed by the L2TV timer to avoid fuel accumulation in successive attempts. This sequence occurs even on units not requiring initial L2TV purge. At the completion of the warm-up period (L2WX), the acceleration reference during start-up is a function. Five points are used to define the start-up curve. After L2W warm-up, FSR FU ramp-up to act as a back-up limiter of temperature rise. As fuel is increased, turbine begins the acceleration phase of start-up. The torque converter will remain set at max torque to the end of start-up. When the turbine over runs the starting device, the L14HC will start down the starting device. Speed relay 14HA indicates the turbine is accelerating. The start-up phase ends when complete sequence is reached (see point”D”on figure Start Up-1) i.e. L14HS is picked up. F.S.R. is controlled by the speed loop and auxiliary systems have been shut down. The start-up control software establishes the maximum allowable levels of FSR signals during start-up. As stated before, other control circuits are able to reduce and modulate FSR to perform their control functions. In the acceleration phases of the start-up, it is possible, but not normal, to reach the temperature control limits. The C.R.T. display will show which parameter is limiting or controlling F.S.R. The minimum F.S.R. limit in the MARK IV system prevents the control circuits from driving the F.S.R. below the value, which could cause flame out during a transient condition. For example, with a sudden load rejection on the turbine, the speed control system would want to drive the F.S.R. signal to zero, but the minimum F.S.R. setting establishes the minimum fuel level which prevents a flame out. Minimum F.S.R. is a function of speed composed by four linear segments and temperature corrected on shutdown and start-up. SYNCHRONIZING AND COUPLING Generator synchronization and coupling can be accomplished by automatic or manual procedure. In this paragraph, one describes only the automatic coupling sequence, with the following equipment: • • •

Automatic synchro device and software Load regulator program Voltage matching

A normal shutdown is initiated from local SPEEDTRONIC of CCR. When stop signal is given, the digital set point count down to reduce FSR and load at a normal rate until instantaneous reverse power relay operates to open the generator breaker. When this occurs, the digital set point will continue to count down to minimum for shutdown, which allows the turbine to slow down further gradually. At 95% speed auxiliary oil pump and hydraulic oil pump takes start.

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During coasting down, the booster compressors is started at 14 HS drop out to prevent exhaust smoke during shutdown, as the turbine is having motor driven atomising air booster compressors. At about 80% temp. IGV start closing to 54 degrees. During fired shutdown, the flame is there until approximately 35% speed, which reduces the stress developed on the hot gas path at the time of the fuel shut off. The shutdown sequence is controlled by ramping FSR downs at appropriate events. FSR latches on to FSR-MIN and decreases with corrected speed. When speed drops below a defined threshold, FSRD ramp blows out (about 35% speed). Fuel is shut off with flame out. Stop/ratio valves, gas flow control valve and fuel shut off valve in gas skid close automatically. Gas vent valve opens. Initiation of cooling down sequence takes place as 14 HM speed relay drops out, the generator jacking oil pump starts and the turbine gear motor starts & torque coupling vane position comes 34%. Manual controlled shutdown When unit is operating at a given load, one can shutdown GT in automatic mode as mentioned above or in manual mode. For manual shutdown, decrease the load from LCR or CCR gradually. When load is reduced to zero, open the generator breaker manually. Now initiate GT stop order & shutdown sequence will follow automatically as already mentioned above. Checks during shutdown and cool down • Check if the auxiliary lube oil pump and hydraulic lube oil pump started automatically at 95% speed. • Compare the shutdown time and the trend of vital parameters like vibration, FSR, CPD, IGV etc. with the shutdown trend curves (start-up/shutdown curves of gas turbine in new condition can be taken as an excellent reference for any problem analysis in the later stage). • Check that the generator Jacking oil pump has started at 10% speed. • The turning gear operation should continue for 48 hours after GT fired shutdown to ensure uniform rotor cooling. At any time during the period of cooling down or after cool down GT can be started. •

Special Operations

Test on “CRANK” position (without firing). - Objective The gas turbine must rotate at a steady speed, at about 500 to 600 RPM, without firing. It is driven only by means of cranking motor. This allows special checkpoint or to makes adjustment or also for troubleshooting. This mode of operation is also used during compressor water washing. -Operation Select CRANK on speedtronic panel, then “EXECUTE”, then select START & “EXECUTE”. The turbine rotates at about 500-600 rpm with out firing. On giving a stop order, the GT will come down on turning gear. Test on “FIRE” position - Objective

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This test allows easily to check combustion process and possibly to follow the slow change in turbine parameters in case of failure. This test allows to fire the gas turbine, but there is no exponential increase in the FSR signal. -Operation From speedtronic panel, select “FIRE”, then “EXECUTE”, then select START & “EXECUTE”. In this position, the unit is fired normally at the end of purge time when 14 HM speed is reached and its speed increases slowly because the acceleration is inhibited. The field breaker closes automatically as soon as 95% of the turbine full speed is achieved. The AVR keeps the voltage to approximately 10.3 kV. Keep the Synchro switch of the unit in the switchyard control room in LOCAL position to transfer synchronization controls to the Local Control room. The turbine is at full speed no load with automatic excitation; • Turn the synchronization selector switch 43 S of the generator control panel to AUTO position. The automatic synchronisation Sequence is in service. One can follow the synchronization process by looking at the synchronizing apparatus. The program gives auto orders, until the generator voltage and frequency equal with respective line voltage and frequency. When all conditions are met, the auto-system device gives the closing order to the generator breaker (52 G). When the generator breaker is closed, the load increases automatically to the SPINNING RESERVE load, about 1.7 MW (by a RAISE order of 2 seconds) and light of the generator breaker control switch 52G/CS comes on to indicate discrepancy between the position of this switch (52G/CS) and breaker status. Turn the 43 S switch to the position OFF, to stop the auto-synchro-device and turn the switch 52G/CS to switch off discrepancy light. The machine will load to the Spinning Reserve unless a load control point has been selected with the load selector switch. The unit is now ready for loading. CAUTION: Before initiating synchronization procedure, be sure that synchronization equipment functions properly, and that the phase sequence of the incoming unit corresponds to the existing line phase sequence and the potential transformers are connected correctly to proper phases. AUTOMATIC LOADING With the load regulator, one can choose 3 modes loads. • • •

Preselected load Base load. Peak load

Here only the automatic sequences are described. Preselected load The preselected load point is adjustable from “SPINNING RESERVE” to “BASE”. Select the preselected load with “PRESEL”membrance switch, then “EXECUTE”. The load increases at the slow speed until the preselected load is reached. This load will be maintained at this value.

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Base load This load is determined by turbine exhaust temperature level. The turbine will be continuously on base temperature control. Select “BASE” membrane switch then “EXECUTE” and the unit will take the load spinning reserve to base load. NOTE: This base order can be given at any time after the 14 HR picks up. Peak Load This load is determined by turbine exhaust temperature level. The turbine will be continuously in peak temperature control. Select a peak order with the load selector switch. NOTE: Peak loading is permitted during emergency power requirement situations consistent with acceptable turbine part life. After the commissioning of GT’s on Liquid fuel the peak load capability is inhibited because of excessive thermal stress on Hot Gas Path Equipments of Combustion chamber. Fast Start In this mode, the start-up logic sequence and control are similar to normal start-up. The acceleration period is also equal to that of normal start-up. (About 12 minutes to reach FSNL). Where as the loading rate from spinning reserve to base load is reduced to half i.e. 6 minutes. Owing to faster loading rate, the thermal stresses are very high in fast mode, hence it is rarely used. One fast start is equivalent to three normal start for computation of equivalent firing hours.

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GAS TURBINE START-UP GT START PERMISSIVES Gas turbine “Ready to start” indication is displayed on the speedtronic panel, if following conditions are satisfied: 1. A.C. voltage normal: To ensure power supply at MCC of auxiliaries. 2. Compressor inlet thermocouples in agreement: • Difference between suction thermocouple readings less than 13.9 o C 3. IGV Servo current normal: • Means IGV opening is 34 degrees (Starting position). 4. Gas Turbine Speed below 14 HM level. (< 10 %) 5. Lube Oil temp. Normal. (< 76° C) 6. No overspeed trip. 7. No flame detected in all 4 sensors. 8. Relief damper open: • Ventilation fans 88BT and 88VG are provided with dampers. These relief dampers should be in open condition, for start up. These dampers will close during a fire. 9. No hydraulic circuit lockout. 10. Compressor bleed off valves are open. 11. Mater protective lockout is reset (L4 in drop condition). 12. DC supply voltage (125 V) to Emergency oil pump is normal. 13. No vibration start inhibit: • There are 5 vibration pickups in GT and 3 in Generator. If any 2 sensors either on GT side or Generator side are faulty, it will not allow start up. 14. No combined cycle signal: • It means Diverter Damper should be open to atmosphere. 15. Generator breaker is not closed. 16. Gas & liquid fuel valves position servos are normal. 17. No controller failure. 18. No normal shut down command is persisting.

***********

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GT START UP SEQUENCE •

The machine is started at a speed below 10%. With the start command, following auxiliaries take start in auto: ‹ Auxiliary lube oil pump (88QA) & if the L. O. pressure is normal, then Jacking oil pump. ‹ GT cooling water pump (88WCI OR 88WC2) ‹ Turbine compartment ventilation fan 88BT.

•

The torque converter angle is set to maximum torque level of 65% by torque adjuster drive motor and start command is automatically sent to following auxiliaries: ‹ Auxiliary Hydraulic oil pump (88HQ) ‹ Cranking motor (88CR)

•

After 2 seconds of cranking motor start, the solenoid valve 20TU-1 is energized, which establishes oil flow to the torque converter.

•

Rotation of the turbine shaft with cranking motor overcomes the inertia of the shaft, which is indicated by drop of the relay 14HR at 0.3% speed. At this point, the Oil mist separator fan takes start.

•

Speed of the turbine gradually increases further. At 8.4% speed (when relay 14HT picks up), the Exhaust compartment ventilation fan 88FX takes start.

•

At 10% speed (after 14 HM picks up), a purge timer is made “ON”, the Torque Converter angle setting is adjusted to 50%. The 1-minute purge/Vent cycle drives out any traces of unburnt hydrocarbons, which might have got deposited in combustion chambers or exhaust duct. Jacking oil pump also stops at 10% speed. After completion of purge/vent cycle, the 20TU-1 solenoid gets de-energized, thus draining off the oil in the torque converter. At the same time, the torque converter angle is adjusted to 15% (fire torque level) by drive motor to hold the firing speed constant. Draining of oil causes the turbine speed to fall slightly. The speed gradually falls to reach the firing speed level of 16-18%. As soon as the firing speed is stabilized, the torque converter drain valve 20 TU-1 gets energized again and control valve is opened by a constant percentage of about 22% (firing FSR) and spark plugs are made ON for one minute (one minute firing timer). During the above one minute period, if 2 out of 4 flame detectors sense the flame, then after 2 seconds it goes to Warm up cycle and TC angle starts increasing from 15% to 65%.

•

• • •

Detection of flame triggers start command to following auxiliaries: GT cooling water fans 1 to 6, if the water temperature above 45° C. ‹ Load compartment ventilation fan 88VG.

•

Once the warm up cycle starts, the control valve opening is set to 11% (warm up FSR).

•

The torque converter angle setting remains at maximum level of 65% for rest of the acceleration cycle.

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•

At 60% speed (14 HC level), the turbine achieves the self-sustaining speed. Thus the solenoid 20TU-1 de-energizes to make the torque converter off, at the same time cranking motor is deenergized, which affects disconnection. Following auxiliaries also take start at this speed: ‹ Generator cooling water pumps (88WC3 or 88WC4 depending on the selection). ‹ Generator cooling water fans 1 to 4, if water temperature is more than 45° C.

•

At about 80% speed, the IGV opens up from 34 degrees to 54 degrees, irrespective of whether IGV temperature control is ON or OFF.

•

At 95% speed (when speed relay 14HS picks up): ‹ Turbine Exhaust- frame cooling fan 88TK-1 starts, followed by start up of second fan 88TK-2 after 10 seconds. ‹ Exhaust plenum base cooling fan 88EH starts. ‹ Auxiliary lube oil pump (88QA) stops, if lube oil pressure is not low. ‹ Auxiliary Hydraulic oil pump (88HQ) stops, if hydraulic oil pressure is not low. ‹ All four bleed valves of the Compressor close. ‹ Starting atomizing air compressor (88AB) stops, if the Unit were started on liquid fuel. ‹ Generator excitation is made on. ‹ The turbine enters Speed Control mode and speed set point (TNR) is set at 100.3%.

•

During 10% to 95% speeds, “Sequence in progress” message appears in Speedtronic. During this period, no RESTART order can be given and NO FUEL CHANGE is possible.

•

If auto synchronization is selected, matching of voltage and speed with the grid is carried out by raising or lowering the TNT @ 6% per minute. After voltage & speed matching, generator circuit breaker closes, if auto synchronization is selected.

• •

After closing of generator circuit breaker: ‹ Generator cooling water fans 4 to 9 take start, and additional 3 nos fans (10 to 12) take start in case the water temperature crosses 53° C. ‹ GT cooling water fans 7 to 9 take start, and additional three fans cut-in if the temperature crosses 57° C.

•

If no load is selected after synchronization, the Unit will come on Spinning Reserve load.

•

If the IGV temperature control is ON, then, IGV will start opening from 54 to 84 degrees at about 82 MW load. If the control is OFF, then it will start opening at about 25 MW and will be full open at about 60 MW load.

•

BASE OR PEAK LOAD REACHED “TEMPERATURE” CONTROL

•

PRESELECTED LOAD REACHED “SPEED” CONTROL ******************************************************************************

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GAS TURBINE START-UP AUTO OR REMOTE

GAS TURBINE READY TO START PERMISSIVES Any of the above “No” All “yes” NOT READY TO START

READY TO START START

START ORDER 30 SEC

AOP START

GT WATER PUMP START

AUTO VENT

SUPER PACKAGE FAN START 88 BT

LUB OIL PRESSURE

JACKING OIL PUMP START

1 -No lube Oil pressure low trip 2 -Jacking oil pressure OK 3 -Super package vent complete 4 -Jacking oil pump motor run ALL YES

A

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GT START-UP - 2 A

HYD. OIL PUMP START

CRANKING MOTOR START

TORQUE CONVERTOR AT MAX 65%

SPEED DETECTED 14 HR (0.06%)

SPEED INCREASE 14 HT (8.4%) OIL MIST SEPERATOR START SPEED INCREASE 14 HM (10%) EXHAUST COOLING FAN MOTOR START 88 FX JACKING OIL PUMP STOP

TORQUE CONVERTOR 50%

SPEED INCREASE TO VENT SPEED

TURBINE PURGING (1 min) PURGE TIMER PICK UP

SPEED DECREASES

TORQUE CONVERTOR 15%

SPEED BOGGED DOWN TO 14 MF 12% (FIRING SPEED)

FSR FIRING LEVEL (19. 8%) SPARK PLUG 1 min FLAME DETECTION 2 OUT OF 4

2 SEC

GT COOLER FAN 1-6 START

TORQUE CONVERTOR 65%

LOAD COMPT. FAN 88VG START

FSR TO WARM UP LEVEL (9.5%)

FSR & SPEED INCREASE

EXHAUST FAN 88 TK-1 START 10 SEC 88 TK-2 START

SPEED 50 % 14 HA

SPEED 60% 14 HC

CRANKING MOTOR STOP

IGV OPEN 34 Deg TO 54 Deg

B

GEN WATER PUMP START

GEN WATER FAN 1-3 START

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B

SPEED 95% 14 HS

AOP STOP

AUX HYD OIL PUMP STOP

GEN EXCITATION ON

SPEED CONTROL

COMPRESSOR BLEED VALVES CLOSE

SPEED SET POINT 100.3%

SYNCRO ON AUTO

Yes SPEED MATCHING

VOLTAGE MATCHING

GEN CIRCUIT BREAKER CLOSE

4.5 MW IF NO LOAD SELECTION

GT COOLING WATER FAN 7, 8, 9 START

SPINNING RESERVE

GEN COOLING WATER FAN 7, 8, 9

IF COOLING WATER TEMP HIGH FAN 10, 11, 12, START

IF COOLING WATER TEMP HIGH FAN 10, 11, 12, START

C

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GT START UP: 4

C

BASE FOR PEAK LOAD SELECTED

PRESELECTED LOAD SELECTED

TNR & LOAD INCREASES

TNR & CONTROL INCREASES

IF IGV CONTROL ON

IF IGV CONTROL OFF

AT 25% LOAD IGV WILL MOVE 54 Deg TO 84 Deg

AT 80% LOAD IGV WILL MOVE 54 Deg TO 84 Deg

BASE OR PEAK LOAD REACHED TEMP. CONTROL

END

PRESELECTED LOAD REACHED SPEED CONTROL

END

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GAS TURBINE NORMAL SHUTDOWN GT SHUTDOWN -1 BASE OR PEAK LOAD

STOP ORDER

TNR DECRESES

LOAD DECRESES

IF IGV CONTROL ON

IF IGV CONTROL OFF

AT 80 % LOAD IGV WILL MOVE FROM 84 Deg. TO 54 Deg

AT 25% LOAD IGV WILL MOVE FROM 84 Deg TO 54 Deg

TNR & LOAD DECREASES

REVERSE POWER DETECTOR - 4.5 MW

GEN. CIRCUIT BREAKER OPENS

FSR SET AT MIN FSR

COMPRESSOR BLEED VALVES OPEN

GT COOLER FANS 7, 8, 9 STOP

GEN. COOLER FANS 4 TO 9 STOP

FIRED COASTING DOWN

94% SPEED 14 HS

EXHAUST BASE PLENUM FAN STOP

AUX. LUB. OIL PUMP START

AUX. HYD.PUMP START

A

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GT SHUTDOWN-2

A IGV CLOSE FROM 54 TO 34 Deg.

50% SPEED 14 HC

40% SPEED 14 HA

IF GEN COOLING WATER TEMP. LOW

BLOWOUT SPEED 35% GEN. WTR. FAN 1 TO 3 STOP

GEN COOLING WTR. P/P STOP

5 Sec LOSS OF FLAME DETECTED

IF LOAD COMPT. TEMP. LOW VENTILATION FAN 88 VG STOP

14 HM SPEED 9.5%

IF GT COOLING WTR. TEMP LOW

14 HT SPEED 6%

GT COOLER FAN 1 TO 6 STOP

SUPER PACKAGE VENT 88 BT FAN STOPS

JAKING OIL PUMP START

SUPER PACKAGE VENT FAN 88 BT START

EXHAUST COOLING FAN 88FX STOP

14 HP SPEED DECREASING 3.3 %

BARRING MOTER START

EXHAUST FRAME COOLING FAN 88 TK - 1&2 STOP

TORQUE CONVERTER AT 34%

COOL DOWN TIMER 62 CD ON

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GT SHUTDOWN –3

B

14 Hrs.

COOLDOWN OFF FROM LOCAL

BARING MOTER STOP

ZERO SPEED 14 HR 0.06%

WHEEL SPACE TEMP. LOW

SUPER PACKAGE VENT FAN 88 BT STOP

AUX. LUB OIL PUMP STOP

TORQUE CONVERTOR 65%

LUB OIL MIST SEPARATOR

JAKING OIL PUMP STOP

GT COOLING WATER PUMP STOP

OFF SELECTED

TURBINE STANDBY

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(19) GAS TURBINE CONTROL SYSTEM INTRODUCTION Control system used for GAS TURBINE at KAWAS KGPP is SPEEDTRONIC MARK- 4. This system is developed by M/s. General Electric Co. USA. This is one of the most reliable control systems for heavy-duty Gas Turbines and is being used worldwide. This control system is based on the Micro Processor Technology. The main advantages over the conventional components are: • • •

Reliability Quality Monitoring capacities

Mainly there are three controller called Controller -R Controller –S Controller –T These are basically Microcomputers. There is one more Micro Computer called COMMUNICATOR-C. Controllers R, S, T, are having identical Hardware & Software. They perform the calculations, which run Gas Turbine. The main function of communicator is to check the healthiness of all the controllers. It also provides the users interface like CRT, printer and input commands. Logic Input Processing: All the field trip contacts are wired to connect input modules CIMs 1 or 2, where this signal is parallel to the three optical isolators and fed to separate digital input cards in the RST controller. Controller C feeds the values to the CRT. Field contacts which are not needed to keep turbine running are fed to CIM module 3 to 6. They are optically isolated and fed to communicator C. Logic Out put Processing Relay Driver Modules RDM performs 2 or 3 logic voting for output signal. Here failsafe Logic is implemented means “no power” will result in safe condition. Analog Input Processing In Gas turbine control system all the analog input like Linear Variable Differential, Transformer –VDT, Pressure, Vibration etc. are fed to analog input/output modules AIO 1-3. For temperature measurements TCM modules are used. There is one module each for R S T controllers and two modules for communicator C. Analog output Processing All the Analog outputs, driving the 3 coils servo are fed by all three controllers R S T. If any controller fails, remaining two will be able to drive servo. 113

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•

ROLE OF CONTROL & INSTRUMENTATION

Control and Instrumentation can be divided into three functions: -MONITORING -CONTROL -PROTECTION Monitoring This is the most visual function of control and instrumentation. The main function is to provide measurement of all the process parameters like Pressure, Position of Valves, Temperature, flow etc. It also provides alarms to the operator when it is required. Control As the name indicates, it controls the process parameters to keep the equipment under the design limits. In gas turbine we have: 1. Start up Control 2. Acceleration Control 3. Speed Control 4. Synchronisation Control 5. Load Control 6. Temperature Control Protections All the equipments have certain limitations on operating parameters; if it crosses the limit it should trip/stop to prevent any damages. Control System Gas turbine is controlled by regulating the fuel flow to the combustors. For controlling the fuel single parameter called FUEL STROKE REFERENCE-FSR is calculated in all the three controllers R S T. START UP REF. ACCE REF. SYNC REF [FSRN] LOAD REF. [FSRT] TEMP. REF.

MIN GATE

FSR

Main Governor is taking signal from the following individual controllers. • • • •

Start up controller Acceleration controller Speed / Load controller Temp. Controller

Output of all above controller are passing through MIN gate, thus whichever controller is giving minimum value will get automatically selected. Now let us see how controller works.

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Start-up and acceleration controllers: This is an open loop controller, which increases the fuel stroke reference as the turbine start-up sequence passes through pre-assigned state. Output of the controller will be enabled when master protection is set. Initially FSR is held at Zero & airflow through combustor is increased with speed. During this time torque is maintained at 50% till purge timer (60 sec.) is reset. After purge time, torque is reduced to 15% and speed reduces. When speed reaches to 12% (Typical Firing Speed) FSR is stepped up to FIRING FSR- 19.8%. This FSR value will then be brought down to warm up level FSR-9.5%. Here warm-up timer is 60 sec. After expiry of warm-up timer FSR will ramp to FSR ACCELERATION. Thus FSR will go on rising till machine reaches to FULL SPEED NO LOAD status. FULL SPEED NO LAOD FSR is 15%. Now turbine can be puton auto for synchronisation. Synchronisation FSR Control This controller is like acceleration control but slope of ramp value is made higher so that machine can quickly attain the speed as per grid frequency. After synchronisation it will come to block load of 5 MW. After synchronisation operator has to select i.e. PRESELECT, BASE, PEAK LOAD. As per selection, speed / load controller start working. Speed / Load Controller Speed/load controller is proportional controller and it changes the FSR in proportion to the difference between actual turbine speed (TNH) and reference speed (TNR). There are two types of speed/ load governor ISOCHRONOUS CONTROL DROOP CONTROL First type i.e. ISOCHRONOUS control is not suitable for generator connected to grid because it will try to maintain the frequency of the grid. We are using droop control. The difference between actual speed TNH and Ref speed TNR is multiplied by droop gain. Droop gain will determine response of the machine during grid frequency changes. Typically, 4% droop is selected with 2% dead band. In this selection grid frequency variation from 50Hz to (+1 or –1) Hz is neglected to avoid much load variation. But if grid frequency further increases, machine will start unloading and will completely unload at 50Hz + 4% = 52Hz. Under frequency protection is set at 47.5%. Normally this 4% droop is selected and set point is calibrated such that 104% set point will generate speed reference TNR which will produce a FSRN resulting in BASE LAOD at 27°C. Manual load raise/ lower is also connected to this controller to raise /lower TNR. Temperature Control System: Temperature control system is required to control the fuel flow to the gas turbine to maintain the operating temperature with in the design limitation of turbine parts. The highest temperature in gas turbine occurs in the combustion chambers. So this must be controlled through control system. It is impractical to measure the temperature of combustion chambers. From the known aero-thermodynamics of gas turbine and thermodynamic cycle calculation it is possible to determine firing temperature as a function of exhaust temperature and pressure ratio across the turbine. This pressure ratio is determined by CPD. Turbine inlet temperature can be determined by exhaust temperature and fuel consumption. Here again we have FSR available to know fuel consumption. Normally with gas fuel selection, CPD temperature reference is lower than the FSR temperature reference. But in the case of CPD transmitter failure FSR temperature reference works as reference and alarm will be generated. 115

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To measure the exhaust temperature 24 nos of thermocouples are divided in-group of 8 and fed to R S T controllers, where they are processed and too low thermocouples are rejected to get the real picture of exhaust temperature. Based on the readings actual average temperature called TTXM is calculated. So during the normal running if the temperature is within limits, FSRT will be higher then FSRN. But if temperature increases then FSRT will reduce and get selected through minimum gate & will result in lower load. Modulated IGV: Variable compressor inlet guide vanes are installed to provide compressor pulsation protection during start up & shut down and also during partial load conditions. The variable guide vane actuator is hydraulically actuated having close loop control. EXAUST TEMPERATURE CONTROL General A temperature control system is required to control the fuel flow to the gas turbine to maintain operating temperature within design limitations of turbine parts. The highest temperature in the gas turbine occurs in the combustion chambers. These products are diluted by cooling/dilution air and then they enter into the turbine through the first stage nozzle. This temperature must be limited by the control system. The temperature control system is designed to measure and control turbine exhausts temperature because it is impractical to measure temperatures directly in the combustion chambers or at the turbine inlet. This indirect control of turbine inlet temperature, called firing temperature, is made practically by utilizing known gas turbine aero and thermodynamic characteristics and biasing the exhaust temperature signal with them, since the exhaust temperature alone does not fully determine firing temperature. From thermodynamic relationships, gas turbine cycle performance calculations, and know site conditions, firing temperature can be determined as a function or exhaust temperature and pressure ratio across the turbine. The latter is determined form the measured compressor discharge pressure (C.P.D.). Firing temperature can also be determined as a function of exhaust temperature and fuel consumption, which is proportional to the fuel flow command Fuel Stroke Reference (F.S.R.). These relationships are shown on Figure TC-1. The lines of constant firing temperature is used in the control system to limit gas turbine operating temperatures, while the constant exhaust temperature limit protects the exhaust system during start-up. Exhaust temperature control hardware In our gas turbine model there are 24 Chrome / Alumel exhaust temperature thermocouples. These thermocouples are located in the exhaust plenum, mounted in an axial direction circumferentially symmetric around the output coupling, in individual radiation shields that allow the radial outward diffuser flow to pass over these 1 / 16” diameter (1.6 mm) stainless steel sheathed thermocouples at a high velocity with minimum effect from cooler walls. The signals from these individual, ungrounded detectors are sent to the SPEEDTRONIC MARK IV control panel through shielded thermocouple cables.

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Exhaust temperature control software The microcomputer contains a series of application programs written to perform the control and monitoring functions, such as digital and analog input scan. A major function is the exhaust temperature control, which consists of the following programs: • • • • •

Temperature control command. Temperature control bias calculations. Temperature reference selection. Cold junction compensation. Cold junction scans.

The temperature control software determines the cold junction compensated thermocouple reading, selects the temperature control set point value, and calculates the representative exhaust temperature value. Compares this value with the set point, and generates a command signal to the analog control system to limit exhaust temperature. Temperature control command programme The temperature control command program compares the exhaust temperature control set point with measured gas turbine exhaust temperature as obtained from thermocouples mounted in the exhaust plenum. These thermocouples are scanned and cold junctions are corrected by programs described later. These signals are accessed by SPEEDTRONIC panel controller R.S.T. as well as communicator C. The temperature control command program reads the exhaust thermocouple temperature values and sorts them from the highest to the lowest. These signals (TTXD2) are used in the combustion monitor program as well as in the Temperature control program. In the temperature control program, each value is looked at and if any reading is too low as compared to a constant, it will be rejected. The remaining ones are looked at again, and the highest and lowest are rejected. The remaining ones are averaged for the TTXC signals. The TTXC signal is then used in another part of the program. Here all the thermocouples are sorted again, highest to lowest. A median of the reading is selected (TTM1) and compared to TTXC, which will produce a calculated exhaust temperature feed back (TTXM). This calculation is based on an average, and a median is used so as to eliminate error due to bad thermocouples or readings. If any controller fails, this program will detect it and ignores the readings from the failing controller. The TTXM signal will be based on the remaining controllers’ thermocouples and an alarm will be generated. The TTXM value is used as the feed back for the exhaust temperature comparator. This calculated feedback is used because the value is not affected by extreme values that may be result of faulty instrumentation. The temperature controller program in R, S, and T compares exhaust temperature control set point (calculated in the temperature control bias program and is stored in the computer memory) TTRX to the TTXM value to determine the temperature error. The software program coverts the temperature error to a fuel strokes reference signals, FSRT. Should one of the communication links fail between one of the controllers and communicator C, the controller affected will freeze the value of TTXC at the last healthy sample and compare it with the current sample of TTXM of the controller. This prevents large changes in the feedback signals. When the link becomes healthy again there is a fixed rate of correction to prevent sudden bumps in the system. With three FSRT values most errors can be removed to give more reliable unit operation. This is true as each controller doing the same calculation for TTXC and TTXM. 117

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Temperature control bias program Gas turbine firing temperature is determined by the measured parameters of exhaust temperature and C.P.D. (compressor discharge pressure), or of exhaust temperature and fuel consumption proportional to (F.S.R.). In the computer, firing temperature is limited by a line-raised function of exhaust temperature and C.P.D. backed by a line raised function of exhaust temperature and F.S.R. (see figure TC-1). The temperature control bias program calculates the exhaust temperature control set point based on the C.P.D. data stored in computer memory and the constants from the selected temperature reference table. The program calculates another set point based on F.S.R. and the constants. The program selects the minimum of the three set points, C.P.D. bias, F.S.R bias and isothermal for the final exhaust temperature control reference. FUEL GAS CONTROL SYSTEM General Fuel gas is controlled with the fuel gas stop/ratio and control valve assembly. This assembly contains two valves and hydraulic manifold as shown in figure FG-1. Both valves are servo controlled by signal from SPEEDTRONIC control panel and actuated by single-acting hydraulic cylinder. The gas control fuel flow in response to the command voltage, FSR2. Speed stop/ratio valve regulates gas control valve inlet pressure, p2, so that the gas flow is proportional to FSR2 and turbine speed. Other system features, as discussed here are provided for reliability of operation against malfunction. The fuel gas control system contains the following components: Gas strainer, gas supply pressure switch 63 FG-3, Speed/ratio valve assembly, fuel gas pressure transducers 96FG-2A, B, C, gas fuel vent solenoid valve 20VG-1, control valve assembly, three LVDTs 96GC-1, -2 and 96SR-1, -2, two electro hydraulic servo valves 90SR and 65GC, dump valves VH5 and VH12, three pressure gauges, and SPEEDTONIC cards HSAA, NVCD. Refer to figure FG-2, where all components are shown interconnected schematically. A functional explanation of each part of subsystem is contained in subsequent paragraphs. Gas Control Valve The position of the gas control valve stem is intended to be proportional to FSR-2, which represents fuel. This is accomplished by a position feedback loop. The gas control valve stem position is sensed by the output of a linear variable differential transducer (LVDT) and is fed back to an operational amplifier. The feedback is compared to the FSR2 input signal at the summing junction. If the feedback is in error with FSR, the operational amplifier will increase the signal to the hydraulic servo valve to drive the gas control valve to meter the correct gas fuel. Actuation of the spring-loaded gas control valve is by a hydraulic cylinder controlled by the electro hydraulic servo valve. The plug in the gas control valve is contoured to provide the proper flow of gas fuel in relation to valve stroke. The gas control valve uses a skirted valve disc and venturi seat to obtain adequate pressure recovery. High-pressure recovery occurs at overall valve pressure ratios substantially less than the critical pressure ratio. The net result is that flow through the control valve is independent of pressure drop across valve. Gas flow then is function of valve inlet pressure, P2, and valve area only.

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Strainer The strainer should be periodically cleaned. The frequency of cleaning will depend upon the quality of the fuel gas used. The strainer should be cleaned shortly after full load has been attained for the first time and afterwards during assembly of fuel gas lines. Low-pressure switch, 63FG-3 Pressure switch 63 FG-3, installed on the gas/stop ratio and control valve assembly inlet pressure gauge line, initiates a Gas fuel pressure low alarm on the enunciator panel when gas supply pressure drops below its set point. This switch also initiates a transfer to liquid fuel if gas supply pressure drops below its set point. Gas supply pressure below 63FG-3 set point will cause the stop/speed ratio control valve to open fully and be out of control when operating at peak load on a minimum site ambient temperature day. Pressure guage Three pressure gauges, with hand valve are installed in the fuel gas supply line. The upstream pressure guage measures P2 pressure ahead of the gas control valve and the downstream guage measures the pressure at the exit of the gas control valve. Gas fuel vent solenoid valve 20 VG. The solenoid valve vents the volume between the stop/speed ratio valve and gas control valve when the solenoid is de-energized. When the flames are detected, the solenoid is energized and the vent valve is closed. When the flames are established, the valve will be closed and remains closed until the turbine is fired. The vent is open when the turbine is shut down because the stop/speed ratio and gas control valves have metal plugs and metal seats and therefore they are not leak tight. The vent valve insures that during the shut down period, fuel gas pressure will not build up between the stop/speed ratio and gas control valves and that no fuel gas will leak past the closed gas control valve into the combustors or exhaust.

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MODULATED INTET GUIDE VANE SYSTEM General Variable compressor inlet guide vanes (VIGV) are installed on the turbine to provide compressor pulsation protection during start-up & shut down and also to be used during operation under partial load conditions. The variable inlet guide vane actuator is a hydraulically actuated assembly having a closed feedback control loop to control the guide vanes angle. The vanes are automatically positioned within their operating range in response either to the control system exhaust temperature limits for normal loading operation or to the control system pulsation protection limits during the start-up & shutdown sequences. Guide Vanes Actuation: The Modulated inlet guide vanes actuating system includes the following components: servo valve 90 TV, position sensors (LVDT) 96TV-2, solenoid valve 20 TV and hydraulic dump valve VH3. When the inlet guide vane servo valve 20 TV is energized, its drain ports are blocked thus allowing the hydraulic oil to flow through 90TV. Control of 90TV will port hydraulic oil through the dump valve to operate the variable inlet guide van actuator (see figure MIVG-1). For normal shutdown, inlet guide vane actuation is the reverse of the start-up sequence. The compressor bleed valves will open when the generator breaker is opened. The inlet guide vanes will ramp to the fuel closed position as a function of temperature corrected speed. In the event of turbine trip, the 11th stage bleed valves will open and the inlet guide vanes will ramp to the closed position as a function corrected speed. Pulsation protection control: The inlet guide vanes are automatically positioned during a start-up and a shut down sequence to avoid gas turbine compressor pulsation limit which is expressed as a function of IGV angle and corrected speed. Shown by the broken line on figure MIGV-2. Corrected speed is a compressor design parameter that is a function of the actual running speed of the compressor and the inlet air temperature. The control system utilizes measured value of turbine speed and ambient temperature to determine the corrected speed at which the IGV will open at the minimum angle. Usually it is 53 deg. Note that the control program is set to avoid IGV operation, which would result in negative pressure at its 5th stage extraction air used for bearing seals. Exhaust temperature control For application such as a regenerative cycle or where there is a steam generator (boiler) in the gas turbine exhaust, it is desirable to maximize the exhaust temperature. The control program for such turbine includes an exhaust temperature control, which automatically holds the IGV at a minimum angle during part load operation. Figure MIGV-3 shows part of the program for the exhaust temperature control mode where the IGV is positioned to the minimum angle at the end of the start-up, when full speed is attained. A switch is provided to permit the operator to select this mode of operation. Operation During a normal start-up, the inlet guide vanes are held in the full closed position until the proper temperature corrected speed is reached, at which time, the inlet guide vanes will open to a preset value, and will remain at this position, until exhaust temperature condition asks for more opening. During full speed operation and with less than 20% load, the inlet guide vanes remain in the minimum full-open position. The compressor bleed valves will close at 14HS pick-up speed. 120

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When the IGV temperature control mode is not activated and IGV is in the simple cycle mode, the guide vanes are held at the minimum full speed angle until the simple cycle IGV exhaust temperature set point is reached. This temperature set point is programmed in the software. The IGV control temperature curve is generated by the program. The IGV exhaust temperature reference is set approximately at 700 deg. F. This reference is compared with the fuel exhaust temperature reference (TTRX). (The minimum of the two is selected for IGV control temperature reference). For application, which requires exhaust temperature control by inlet guide vanes, the guide vanes are held at the minimum at full speed until combined cycle IGV exhaust temperature set point is reached. The IGV exhaust temperature is programmed at a value slightly lower than the BASE temperature (fuel) control set point as is shown on Figure MIVG-3, with the same CPD bias in both. The heavy line traces a typical exhaust temperature pattern as the turbine out put changes. Point A is the operating point at the end of startup with IGV positioned at the minimum full speed angle. As output increases, the IGV is held at this minimum angle until IGV temperature control set point is reached (point B). Between point B and C, IGV is opened to maintain set point temperature, as output is further increased. At point C, IGV is at its full open position and upon further increase in output; the turbine will reach to its BASE temperature limit (point D). Note that Figure MIVG-3 also shows a trace of exhaust temperature for the IGV in the simple cycle mode, form point A to B to C to D, full-speed-no-load to full load respectively. The operator can activate or deactivate the IGV temperature control mode at any time via the panel sector switch. The control system will automatically reprogram the IGV to the correct position in controlled rate. Manual open/close soft switches are provided on the manual control display to allow the operator to manually position the IGV between the minimum full speed (14 HS level). The manual control has authority to command on IGV angle. When automatic control system is in normal operation, the manual control is set at full open. Fault protection The guide vane protection system will trip solenoid valve 20TV, initiate a fast normal shutdown and annuciate if there is low hydraulic supply pressure, or the LVDT feedback is different from command, or IGV position trouble is indicated. Should the inlet guide vane system be tripped under one of the above conditions, the Mark I.V. sequencing logic generates a signal, which is used in the start check circuit to prevent any attempt to restart the turbine prior to eliminating the cause for the trip.

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(20) SPEEDTRONIC PROTECTION SYSTEMS INTRODUCTION: Gas Turbine protective systems respond to the simple trip signals such as pressure switches or system relay as used for low lube oil pressure, high gas compressor discharge pressure or similar. They respond to more complex parameters such as vibration, over speed, over temperature, and loss of flame. To do this, some of these protection systems and their components operate through the master control and protection circuit in the SPEEDTRONIC system; while other totally mechanical systems operate directly on the components of the turbine. In each case there are two essentially independent paths for stopping fuel flow, making use of both the control valve (F.C.V.) and the stop valve (F.S.V.). Each protection system is designed independent of the control system to avoid the possibility of a control system failure disabling the protective devices. On machines using liquid fuel, the bypass valve is opened wide and the fuel pump clutch is tripped with master protective signal as well as the fuel stop valve. A hydraulic trip system called Trip Oil is the protection interface between the turbine control and protection system and the components of the turbine, which admit, or shut-off fuel flow. The system contains devices, which are electrically operated by SPEEDTRONIC control signals as well as some totally mechanical devices.(See fig. TM-1) Besides the tripping functions, trip oil also provides a hydraulic signal to the fuel stop valves for normal start up and shutdown sequences. On gas turbine equipped for dual (gas and oil) fuel operation, this system is used to selectively close off the system when not required. PROTECTIONS: Flame Detection and Protection System The speedtronic flame detectors perform two functions; one is in the sequential system and the other in the protective system. During a normal start-up, the flame detectors indicate when a flame has been established in the combustion chambers and allows the start-up sequence to continue. Should one flame detector indicate loss of flame, an alarm will be sounded. If three out of four flame detectors indicate a loss of flame condition, then fuel is immediately shut off. This avoids possible accumulation of an explosive mixture in the turbine and any exhaust heat recovery equipment, which may be installed. The flame detector system, used with the SPEEDTRONIC system, detects flame by sensing ultraviolet radiation. Such radiation results from the combustion of hydrocarbon fuels and is more reliably detected with visible light which varies in colour and intensity. The flame detector system consists of four independent detectors per set of inter connected combustion chambers; A flame detector channel is shown in Figure FD-1. The flame sensor is a copper cathode detector designed to detect the presence of ultraviolet radiation. The electronic package consists of a transistor copper oscillator and transformer for converting the 28 V DC to a large AC voltage to be rectified and filtered. The power supply will furnish up to +350 V DC to drive the ultraviolet detector tube. When the voltage across C2 is high enough, the comparator amplifier output will switch to positive saturation, which will cause Q1 to turn on, make FL or 28FD-2 logic “O”, indicating a flame is present. Figure FD-1 is a functional diagram only and does not show all the circuitry present in the actual circuit. 128

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The flame detector system is similar to other protective system, which is self-monitoring. For example, when the gas turbine is below 14HM, all channels must indicate “NO FLAME”. If this condition is not met, the condition is annunciated as a “FLAME DETECTOR TROUBLE” alarm, and the turbine cannot be started. After firing speed has been reached & one detector per combustion set sees flame, the starting sequence is allowed to proceed. A failure of one detector per combustion chamber group will be annunciate as “FLAME DETECTOR TROUBLE”, when complete sequence is reached, and the turbine will continue to run. Three out of four flame detectors must indicate “NO FLAME” in order to trip the turbine. (Note that a short circuited or open circuited detector tube will result in a “NO FLAME” signal.) Overspeed Protection System The SPEEDTRONIC electronic overspeed system is designed to protect the gas turbine against possible damages caused by overspeeding of the turbine shaft. Under normal operation, the speed of this shaft is under the control of the speed loop. This over speed system would not be called on except after the failure of other systems. The over speed protection consists of a primary and secondary (back-up) system for the normal control shutdown features. The primary over speed protection system is the electronic over speed system and consists of magnetic pick-ups to sense turbine speed, speed detection software and associated logic circuits. The secondary system is mechanical and consists of the over speed bolt assembly in the accessory gear shaft and the over speed trip mechanism. Both systems operate to trip close the fuel oil stop valve and the fuel gas speed ratio/valve, and subsequently, drive the F.S.R.command to zero. A composite block diagram showing all components for this mechanical over speed protection is shown in Figure OST-1A 1. Electronic over speed protection system. The Electronic over speed protection system function is performed in the computer software as shown in Figure OST –1B. The turbine speed signal (TNH) derived from the magnetic pickup sensors is compared to an over speed set point (TNKOS). When TNH exceeds the set point, the over speed trip signal (L12H) is transmitted to the master protective circuit to shut down the turbine & “ELECTRICAL OVER SPEED TRIP” message will be displayed on the C.R.T. This alarm will latch and must be reset by master reset signal L86MR. 2 Mechanical over speed protection system The mechanical over speed protection system consists of the following principal components • Over speed bolt assemblies in the accessory gear shaft • Over speed trip mechanism in the accessory gear • Position limit switch 12 HA The mechanical overspeed protection system is the back up for the electronic over speed protection system. As the back-up system, the trip speed setting is higher than the primary of electronic over speed protection system. For the most part, the mechanical over speed protection is an integral part of the gas turbine unit which will trip close the fuel stop valve(s) when the turbine speed exceeds the trip setting on the over speed bolt assembly. This trip action is totally independent of the electronic connections in the turbine control panel. Whenever these Over speed trip mechanism is actuated, an alarm will be flashed in annunciator.

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Over speed bolt assembly: An over speed bolt assembly mounted in the accessory gear shaft is used to sense the over speed of the gas turbine. It is spring loaded, eccentrically located bolt assembled in a cartridge and designed so that the spring force holds the bolt in the seated position until the trip speed is reached. When shaft speed increases, centrifugal forces acting on the bolt are balanced by the spring force within the bolt assembly and bolt remains seated. Further increase of the shaft speed causes the centrifugal force on the bolt to exceed the spring force and the bolt moves out ward in less than one shaft revolution where it contacts and trip the over speed trip mechanism. The spring force can be adjusted so that the over speed bolt will trip at a specified shaft speed only. Over speed trip mechanism: The over speed trip mechanism for turbine shaft is also mounted in the accessory gear adjacent to the over speed bolt assembly. When actuated, the over speed bolt assembly trips the latching trip finger of the over speed trip mechanism. This action releases the trip valve in the mechanism and dumps the OLT hydraulic trip system pressure to the atmospheric pressure. This, in turn causes the oil in the relay dump valve of the speed ratio/stop valve assembly to return to atmospheric pressure (in case of use of gas fuel in the gas turbine). This in turns dumps the hydraulic control oil from the SVR actuating cylinder to drain, thus closing the valve, or, in case of use of fuel oil in the gas turbine, it causes the oil in the pilot dump valve cylinder of the liquid fuel stop valve to return to atmospheric pressure, thus closing the valve. The over speed trip mechanism may tripped manually and must be reset manually. The trip button and the reset handle are mounted with the over speed trip mechanism limit switch 12 HA on the out side of the accessory gear.

Over temperature Protection General The over temperature protection system protects the gas turbine against possible damage caused by over firing. It is a back-up system, which operates only after failure of the temperature control loop. Under normal operating conditions, the exhaust temperature control system acts to control fuel flow, when the firing temperature and fuel flow can exceed control limits. Under such circumstances the over temperature protection system provides an over temperature alarm and to avoid further temperature increase, it starts unloading the gas turbine and thus avoids the tripping. If the temperature increases further, the gas turbine gets tripped. Over temperature trip and alarm set point are determined from the temperature control set point derived by the exhaust temperature control software, see figure OTP-1. Also refer to the exhaust temperature control section.

Over temperature protection software Over temperature alarm (L30 TXA): The representative value of the exhaust temperature thermocouples (TTXM) is compared with alarm and trip temperature set point. EXHAUST TEMPERATURE HIGH alarm message will be displayed when the exhaust temperature (TTXM) exceeds the temperature control reference (TTRX) plus the alarm margin 130

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(TTKOT3) programmed as an EEPROM constant in the software. The alarm will automatically reset, if the temperature decreases below the set point. Over temperature trip (L86TXT): An over temperature trip can occur, if the exhaust temperature (TTXM) exceeds the temperature control reference (TTRX) plus the trip margin (TTKOT2), or if it exceeds the isothermal trip set point (TTKOT1). The over temperature trip will latch and EXHAUST OVER TEMPERATURE TRIP message will be displayed. The turbine will be tripped through the master protection circuit. The trip function will be latched in and the master reset signal L86MR1 must be true to reset and unlatch the trip. Vibration protection The vibration protection system of a gas turbine unit is composed of several independent vibration channels. Each channel detects excessive vibration by means of a pickup mounted on bearing housing of the gas turbine and driven load. If a predetermined vibration level is exceeded, the vibration protection system trips the turbine and annunciation is flashed. Each channel includes one vibration pickup (velocity type) and the SPEEDTRONIC amplifier circuit. The vibration detector generates a relatively low voltage by the relative motion of a permanent magnet suspended in a coil and therefore no excitation is necessary. A two pair shielded cable is used to connect the detector to the analog I/O module (I/O means inputs/outputs). The pick up signal from the analog I/O module is input to the computer software, where it is compared with the alarm and trip levels programmed as EEPROM constants. When the vibration amplitude reaches the programmed trip set point, the channel will trigger a trip signal; the circuit will latch, and display a HIGH VIBRATION TRIP message. Removal of the latches trip condition can be accomplished only by depressing the master reset button (RESET signal L86MR1), when vibration is not excessive. When the VIBRATION TRANSDUCER FAULT message is displayed, and machine operation is not interrupted; either an open or short condition in circuit may be the cause. This message indicates that maintenance or replacement is required. For each set of two adjacent sensors, a comparison is made between the two channels, and if the difference exceeds a present value, an alarm will be annunciated. By using the display keyboard and C.R.T. display, it is possible to monitor vibration levels of each channel while the turbine is running, without interrupting operation.

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GAS TURBINE EMERGENCY TRIPPINGS 01. EXHAUST TEMP. VERY HIGH 615 ºC OR TEMP. >TTRX +22.5 02. MANNUAL EMERGENCY TRIPPING (FROM LCR) 03. CCR EMERGENCY TRIPPING. 04. FIRE PROTECTION (TURBINE) 05. VERY HIGH VIBRATION 25.0 mm/sec. 06. CONTROL SYSTEM FAILURE 07. OVERSPEED (I) ELECTRICAL AT 110% (II) MECHANICAL AT 112% 08. IGV TROUBLE AND NOT OPERATING SPEED 09. STARTING DEVICE BOGGDOWN AND NOT OPERATING SPEED 10. FLAME PROTECTION MIN TWO FLAME 11. EXHAUST SPREAD PROTECTION 12. STARTUP FUEL FLOW VERY HIGH. LVDT FEEDBACK IS 28.6% AND NO FLAME. 13. FIRE PROTECTION FROM GENERATOR. 14. CRANKING MOTOR MCC TROUBLE AND NOT IN ACCELERATION MODE (TEMP.OF MOTOR WDG IS 133 DEG C). 15. DURING STARTUP WITH NO FLAME AND DC LUBE OIL UNDER VOLTAGE AND SERVO CHECK FAIL. 16. LUBE OIL PRESSURE V.LOW 0.55 BAR (FROM BOTH SWITCHES) 17. LUBE OIL PR.VERY LOW FROM ONE SWITCH AND PR.LOW ALARM ALSO PERSISTING. 18. LUBE OIL TEMP.V. HIGH FROM BOTH SWITCHES (SETTING 80 DEG C) 19. LUBE OIL TEMP. VERY HIGH FROM ONE SWITCH & LUBE OIL HIGH ALARM PERSISTING. 20. SHUT OFF VALVE CLOSING 21. EMERGENCY TRIP FROM BACK UP DESK 22. FINAL SCRUBER LEVEL % HIGH. 23. HRSG TRIP WITH DIVERTER FAULT 132

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24. FUEL GAS TEMP. VERY LOW (<10 DEG.) NORMAL SHUT DOWN • GENERATOR BREAKER NOT CLOSED AND LOAD COUPLING TEMP. 375 ºC. • VIBRATION DETECTOR FAULT OR DISABLED • GENERATOR BREAKER TROUBLE AT FIRING • TORQUE CONVERTOR TROUBLE SOLENOID VALVE DRAINED • GAS PR.HIGH AND PURGE SOLENOID NOT ENERGISED WITH FLAME OK. • GENERATOR TROUBLE AT FIRING SPEED • GENERATOR / EXCITOR LIQUID LEVEL VERY HIGH. • EXCESSIVE DROP ACROSS THE FILTER ELEMENTS (2000 Pa) • JACKING OIL TROUBLE • LCR STOP COMMAND • ATOMISING AIR TEMP. VERY HIGH>135 ºC PARTIAL LOAD OPERATION 1. GENERATOR BREAKER CLOSED AND EXHAUST FRAME COOLING PRESSURE LOW 2. GENERATOR BREAKER CLOSED AND LOAD COUPLING OVER TEMP. >370 ºC (EXHAUST OVER TEMPERATURE ALARM.)

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(21) GAS TURBINE PERFORMANCE & TROUBLE SHOOTING GAS TURBINE PERFORMANCE Introduction: The performance of gas turbine is directly influenced by external factors like atmospheric pressure, humidity, ambient temperature and internal factor mainly compressor performance. Through environment factors are beyond the control of operation, it is interesting to understand the response of GT under different atmospheric conditions as given below: Ambient temperature When inlet air density decreases at higher ambient temperature, compressor mass flow decreases although volumetric flow remains constant. Due to reduce airflow to combustor, gas turbine fuel flow also reduces to limit the gas turbine exhaust temperature. Consequently, GT output reduces as there is lesser mass medium to expand across gas turbine and GT efficiency also decreases. Atmospheric pressure Air density increases with rise in pressure, thereby compressor supplying more mass flow to combustors; consequently GT fuel control system allows more fuel flow to maintain exhaust temp and therefore turbine out put increases. But efficiency and exhaust temperature are not affected. Relative humidity Relative humidity of air has very small influence on GT performance. However, in rainy season, increased humidity causes larger DP loss across the suction filter and consequently there is an appreciable drop in compressor discharge flow. This leads to reduced GT out put and efficiency. Compressor Performance Gas turbine performance may decline as a result of deposits on compressor during operation. A decline in performance is indicated by gradual loos of Power out put and an increase in fuel consumption. Many of the problems are direct result of dirt or fouling in axial flow compressor. Fouled compressors result in reduced airflow, lower compressor efficiency and lower compressor ratio. The two methods available for compressor cleaning are carbo blasting (online dry cleaning) and compressor wet washing (off line cleaning). Depending on the nature of compressor fouling, one of the above two cleaning method is used. COMPRESSOR WASHING Introduction: The inlet air to compressor may contain dirt, dust, hydrocarbon fumes, salt etc. A large portion of these things can be arrested by inlet air filtration. The dry contaminates that pass through filters can be removed by online abrasive or nutshell cleaning. Wet contaminants such as hydrocarbons cannot be removed effectively by nutshelling and therefore, compressor must be washed with water-detergent solution according to OFFLINE washing procedure. Compressor-Water Wash Sequence 01. Pressure the washing skid and raise wash water temp.85 ºC 02. Ensure difference between the wheel space and wash water temp. < 67 ºC 03. Divert false start drains and exhaust plenum drain to effluent tank. 138

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04. 05. 06. 07. 08. 09. 10. 11. 12. 13. 14.

Close bearing seal air valves and open seal air drain valves. Start GT on crank mode. Do wetting of compressor for 5 minutes with wash pump. Do compressor detergent washing for 10 mts. by running detergent pump and wash pump. Do rinsing of compressor with plain water for 10 mts. Isolate washing skid Stop GT and soak for 20 mts. Do compressor-drying operating at crank speed for 20 mts. Open bearing seal air valves close drain valves. Divert false start drains & plenum drain to sludge tank. Start GT and operate at FSNL for at least 5 mts. With 24 hrs wash

Vibration: Through speedtronic system provides the temperature of vibration parameter and protection of gas turbine, periodic measurements with special instruments are to be done to judge the exact mechanical condition of the machine. The maximum overall vibration velocity should never exceed 25mm /sec.

The following table gives the analysis for high machine vibration. CAUSE AMPLITUDE Lack of balance Proportional to lack of balance: greater in the radial direction Buck lush and bluck-ness

FREQUENCY Once the rotation speed 1 x rpm

PHASE Once the reference mark

OBSERVATION The most usual cause of vibration

Twice the rotation speed

Usually, with unbalancing and misalignments

Misalignments of couplings or bearings, deformation of shafts Faulty bearings

Great in the axial direction (the half or more) of the radial vibration Unstable measure speed

Once, twice or three times the rotation speed

Two reference marks Single, double or triple ref. mark Irregular

Faulty bearing is next to the maximum vibration point.

Journal eccentricity

Generally speed at high

Gear or mechanical drive faults

Measure speed at feable load

Electrical failure Aerodynamic or hydraulic Strength

Very high: several times the rotation speed Once the rotation speed Very high: depends on the tooth number Once the rpm or once at twice synchronous frequency Once the rpm or the blade number multiplied by rpm

Only one reference mark Irregular

One or two

Check for axial vibration, if there is no misalignment, the rotor must be balanced.

Gear vibrations disappear when slowing down. Unbalancing of pump or ventilator. The phenomenon ceases when current is switched off. Rare: Only in case of resonance.

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TROUBLE SHOOTING OF GAS TURBINE SR MALFUNCTION PROBABLE CAUSE NO. 01 Lube oil tank level High lube oil tank level or high some liquid coming in the tank 02 Lube oil tank level Level low or level switch low 71QL-1 may be defective 03 Lube oil pressure low Lube oil system leakage of pump/pressure switch trouble or filter clogged. 04

Emergency lube oil Failure of main and pump running auxiliary lube oil pumps, or filter clogged

05

Lube oil header Lube oil temperature above temperature high 165ºF

06

Lube oil pressure trip

07

Lube oil pressure has fallen below trip (63 QT-2A, 2B & 63QA pressure switches disconnected.) Lube oil temperature Lube oil inlet temperature high trip above 80 ºC or 2 out of 3 temperature switches disconnected (26QT-1A, 1B and 26QA).

RECOMMENDED ACTION Investigate and restore normal level. Stop the unit if some other fluid (water or liquid fuel) is mixed with lube oil Refill to normal level if level is lower & attend the level switch Ensure aux lube oil pump is running, Repair leak or check for proper operation of pressure switch or changeover lube oil filter Do not stop DC pump immediately. Check for leaks and pump malfunction, Check for correct pressure switch operation. Check for the proper operation of cooling water fans, coolers check temperature regulating valve VTR-1 and temp. switch 26QA-1 Find out the correct cause before restarting the unit. Check for proper operation of pressure regulating valve VPR-2. Check for the operation of cooling water valve VTR-1, check temp. switch, or liquid fuel is mixed with lube oil.

Note: Similar to the malfunctions listed above. It can happen with hydraulic trip oil system due to similar nature of defects. Thus, it can be remedied accordingly by the operation.

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08 09

10 11 12

13 14 15

16 17

Gas fuel hydraulic trip Low trip oil pressure or 2 pressure low out of 3 trip oil pressure switches disconnected. Gas scrubber Condensate level very condensate level trip high in the gas scrubber high and unit trips when running with the gas fuel. Gas ratio valve LVDT is disconnected; position servo trouble valve is not closed when GT is not running. Gas control valve Gas control valve position servo trouble. feedback abnormal. Start-up, excessive Shut off valve not reseted fuel flow trip. during GT start-up or unit gas skid not properly lined up. This will cause excessive opening of gas control valve. Main fuel pump Leakage detected on the leakage trip. main fuel pump and unit trip. Turbine air inlet drop. High differential pressure detected at turbine inlet. HRSG Turbine trip. HRSG diverter damper has failed to close in 40 sec. time on protection closing order. Starting device trip Failure of cranking motor to start. Normal shutdown Electric trouble on protective lockout. generator with normal shutdown for unit.

18

Torque converter drain valve trouble

19

Cool down trouble

20

The shaft does not break away. Torque converter guide valve transducer trouble. IGV position servo

21 22

Check control oil piping turbine might have been tripped manually. If any hydraulic oil leakage, get it attended. Check condensate level in scrubber, Check level indicator 71 GHH. Check the calibration of both LVDTs servo valve. Check both LVDTs of the servo valve. Do calibration if required. Check unit gas skid line up and reset shut off valve during start-up before purge time is over.

Check the status of fuel pump. check the proper operation of the level switch 71FP-2. Check the proper operation of air inlet system (filters, compressed air system) Check the damper close limit switches and transmitter.

Check cranking motor and breaker, Identify and repair the fault. Determine the electrical trouble with matrix in protection panel. The unit should not be operated until the problems are found and corrected. Torque converter drain Check the proper operation of the drain valve is not actuated in the valve, check the limit switch. same time as the solenoid valve (20TU-1). Turning gear sequence is Check the AC power supply on the unit. stopped. Check the turbine gear. Unit can not reach its Check the starting means also check the normal speed start-up FSR. Guide vane transducer Check the transducer and verify the damaged or disconnected adjustment. Do not restart before this.

Loss of feed back

Check LVDT and logic circuit. 141

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23

trouble Atomising air temp. High

24

Chamber flame out during shutdown.

25

Loss of flame trip.

26

Failure to ignite

27

Combustion trouble

28

Flame detector trouble

29

Exhaust Temp. High

30

High exhaust temperature spread trip. Exhaust overtemperature trip.

31

32 33

Exhaust thermocouples open trip. Turbine incomplete sequence

34

Fire zone 2

35

Fire zone 1

36

Fire (Generator)

Temperature high at atomising compressor output. GT flame extinguished before normal flame out speed during shutdown. At least 3 out of 4 flame detectors sense no flame in combustion chambers. During GT start up, failure to fire in one minute period Faulty thermocouples or uneven distribution of fuel-to-fuel nozzles. One of the UV detectors sensing flame before GT firing. Exhaust gas temp. is excessive. Uneven distribution of fuel to the fuel nozzle. Temperature control system has not limited the exhaust temperature with in the limits. Excessive number of thermocouples not connected. Failure of unit to reach complete sequence. Fire detected in bearing no. 3 Fire detected in the turbine and accessory compartment. Fire detected inside the generator.

Check the operation of temp. Control valve VRT-2 and temp. Switch 26AA-1. Check fuel supply, fuel control and fuel nozzle. Check flame detector. Check the UV flame detector, check control valve any damages fire tubes. Check the spark plugs, clean if required. Check fuel supply ignition power supply and flame detectors. Analyse the data trends. At earliest shutdown, check thermocouples. Check for plugged nozzles. Check that flame detector quartz windows are clean. Repair or replace if necessary Check the thermocouples, if the thermocouples are ok, Check the temp. control loop and fuel control system. Analyse data for trends. Check fuel nozzles for plugging. Perform bore scope or combustion inspection if necessary. Check the temperature control loop and fuel control system. Check and reconnect the thermocouples. Check the combustion in combustion chamber. Check equipment, which is causing the problem in normal sequence: Starting motor, torque converter, fuel control, and acceleration loop. Check for the causes of the trip, hot air or fuel or oil leaks or short circuit. Check for hot air or fuel or oil leaks or short circuit. Check for the causes of trip like short circuit.

NOTE: RESTARTING AFTER THE OPERATION CO2 SYSTEM, IT REQUIRES THAT THE CO2 SYSTEM IS RESETED, INCLUDING ALL DOORS, DAMPERS &CO2 RELEASE MECHANISM (APPPLICABLE TO ABOVE LAST THREE CASES)

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37

Failure to synchronise

38

Generator protection trip Failure to start

39

40

FSR GAS not at maximum limit.

41

Master protective start up lockout

42

Control system self check trip.

43

Load compartment temperature high.

44

Generator stator temp. is very high communication link inoperative

45 46

Fire Zone-1

47

Water wash inhibits wheel space temperature high. Fire Zone-2

48 49

Communication link MSP –R 232 failure

Generator breaker does not close within certain expected time. Electrical trouble with emergency shutdown. The master protective signal “L4” has not been set within 30 seconds of start signal has tripped the unit twice or if the unit is operating in remove, flame was not established after two tries at establishing flame. Manual FSR has not been reset to a position where it will not interfere with automatic FSR control. Three microcomputers R, S, T are in disagreement for master protective logic “4X”. Microcomputer R, S, T selfchecking programme has uncovered a fault or HCMA card failed. A high temperature defected in load compartment. Magnetic core temp. (140ºC) Automatic shutdown occurs. Communication between controller and communicator failed Fire detector or turbine and accessory compartment in trouble Water washing inhibited because of high wheel space temperature Fire detector in load compartment and bearing no.3 in trouble The communication between speedtronic panel and room is faulty

Investigate the synchronising systems. Check the stability of turbine speed control. Determine which protection has operated, from the generator panel. Check all signals going L4 logic signal and determine the cause of lack of flame establishment.

Raise the manual FSR control to maximum from L.C.R. Determine which computer is in disagreement with other two. Check which condition is not authorising start up. Investigate the problem; check HCMA card status”OK” lights. Check for proper operation of fan 88 VG. Check that load compartment is open. Check the cooling system & the temp. detector set point Check for the power supply of and ; check the serial link between the two computers Check the fire detectors and their electrical circuit Wait for wheel space temperature to all below 48ºC before starting water washing Check the detector and correct it. Before starting maintain inhibit fire protection Operate the unit locally.

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(22) INTRODUCTION TO CCPP EFFICIENCY ASPECTS Gas turbine technology can be used in variety of configuration for electricity generation.

Conventional applications are • Simple cycle operation. • Combined cycle operation. • Co-generation. Electric utility companies use gas turbine predominantly in simple cycle and combined cycle applications. Industrial Company uses them as co-generation power plants. Advantages of gas turbine in contrast to steam turbine are: 1) 2) 3) 4)

Standardization and Modularization. Due to modular approach they are relatively easy and faster to install. Fast to start. Low capital cost.

Benefits of low capital costs were initially offset by higher operating costs when compared with other installed capacities. Therefore earlier gas turbine was strictly for peak load operation. Improvements in efficiency and reliability and application of combined cycle operation have added economic benefits to the gas turbine based power plants. Combined cycle approach for generation of electricity had been a concept for long time. This approach envisages combination of two thermodynamic cycles. This combination is basically aimed at efficient generation of electricity. In combined cycle heat rejected by first cycle is used as a heat source for the second cycle. Combination of cycles, which were thought, is 1. Combination of two Rankine cycles. 2. Combination of Brayton Cycle and Rankine Cycle. First option could not be put to use, as two suitable working fluids could not be found. Second option could not be put to use for long time, due to technological constraints in development of gas turbines suitable for combined cycle purpose. Now with technological advancement made in metallurgy, manufacturing processes, aerodynamics and due to commercial viability created due to availability of two suitable working fluids, combined cycle plants are reality. These plants utilize liquid and gaseous fuels.

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Thermodynamic approach to Gas Turbine The working of Gas Turbine is based on Brayton Cycle. A typical Brayton cycle consists of two reversible isobars and two reversible adiabatic.

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Cycle Efficiency of Brayton Cycle is given below r −1

P Thermal Efficiency = η = 1-1/ ( 2 ) r P1 Where p 2 /p 1 = Pressure Ratio. γ = Adiabatic Constant.

So ideally, Thermal Efficiency of a Brayton Cycle is dependent on Pressure ratio of the cycle. But for all practical reasons thermal efficiency will depend on •

Pressure Ratio.

•

Turbine Inlet Temperature.

•

Compressor Inlet temperature.

•

Efficiency of Compressor and Turbine.

Effect of Pressure Ratio In ideal case, efficiency continuously increases with increase in Pressure ratio. However as pressure ratio changes, Specific out put also changes. So when pressure ratio increases, beyond certain pressure ratio, Specific out put starts decreasing and at one point Specific out put becomes zero and efficiency becomes maximum (i.e. Carnot cycle efficiency). In Actual case as pressure ratio increases, the specific work produced by turbine increases more rapidly than the specific work that compressor consumes. The result is increase in Shaft specific work output and increases in efficiency. As pressure ratio further increases, the temperature rise across the compressor also increases and now the work consumed by compressor increases more rapidly than work produced by turbine so the net output decreases and at certain point it becomes zero when work out put from turbine will be totally consumed by compressor. At this point efficiency is maximum as heat added in turbine will be minimum.

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149

Thus for any fixed turbine inlet temperature, there exist a particular Pressure ratio beyond which net work out put from the turbine will start decreasing and with increase in turbine inlet temperature this particular pressure ratio also increases.

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Effect of Turbine Inlet Temperature on Efficiency As the Turbine inlet temperature increases the thermal efficiency of the cycle increases. In ideal case there will not be any effect on efficiency as we increases the turbine inlet temperature but practically as turbine inlet temperature increases, the deviation of turbine expansion from ideal process decreases (turbine efficiency increases ) and overall efficiency of the cycle increases. However in actual gas turbines, these temperatures cannot be increased indefinitely because of temperature limitations of the materials. From this, it is quite understandable why gas turbine manufacturers continue to focus on improving hot gas path metallurgy and cooling methods to increase the allowable turbine inlet temperature and there by increases the cycle efficiency.

Effect of Compressor Inlet Temperature on Efficiency As the compressor inlet temperature decreases the compressor out let temperature also decreases and to achieve the same turbine inlet temperature, more amount of heat is required to be added in combustor. But the reduction in compressor work is more significant than extra heat input. So the cycle efficiency increases.

Effect of Compressor & Turbine efficiency on cycle efficiency As compressor and turbine efficiency falls the cycle efficiency also falls because as efficiency falls the temperature of working fluids unduly increases and which causes increase in compressor work. From the graph it is seen that as turbine and compressor efficiency decreases cycle efficiency decreases. For lower turbine and compressor efficiency we cannot go for higher pressure ratio because as pressure ratio increases cycle efficiency decreases and may become zero. A change of 1% in turbine and compressor efficiency can result in 3 to 5% change in cycle efficiency.

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With single pressure level boiler, the choice is very limited since the super heater, evaporator and economizer have to be placed in descending fluid temperature along the gas path. In multi pressure level unit this general order is maintained, but various sections may be interchanged so that nearly parallel relation between the temperature gradients can be achieved. In single pressure boiler there is limited amount of heat that can be extracted, because the exhaust gas temperature cannot be reduced below the saturation temperature. However with multi pressure system the recoverable heat range can be extended by extracting heat at various levels, as the saturation temperature are lower at each successive pressure.

Number of Steam Pressure Cycles The general philosophy of the WHRB is to exchange heat from the gas to the fluid at the highest temperature difference available. This can best be accomplished by making gas and the fluid temperature gradients as nearly parallel to each other as possible. From the graph it is clear that steam turbine out put is maximum at an optimum steam pressure. At this working pressure of the boiler sufficient heat is available in out going gases. In conventional boilers this heat is used for heating the air going to combustion zone. Combined cycle boiler has no such requirement and so the residual heat in out going gases is used to raise the steam of low pressure. However each successive pressure level adds to the plant cost and complexity, which make them uneconomical for most combined cycle application. Due to this reason dual pressure WHRB’s are commonly used, particularly in combined cycle plats. Dual pressure WHRB’s are basically two WHRB’s utilizing the same gas stream. Splitting the HP economizer in two sections and moving the cooler section to the downstream of LP evaporator can provide for more efficient utilization of the heat source. Table shows the effect of no. pressure cycles on Gross efficiency. Single pressure Dual pressure Triple pressure

Gas Turbine 160.2 MW 160.2 MW 159.0 MW

Steam Turbine 67.1 MW 82.9 MW 92.1 MW

Gross. Efficiency 51.3 53.3 55.1

Thus for any fixed turbine inlet temperature there a particular pressure ratio beyond which net work out put from the turbine will start decreasing and with increases in turbine inlet temperature. This particular pressure ratio also increases. It can be seen that an efficiency gain of 2 % is achievable when we go from single pressure cycle to dual pressure cycle. Also an efficiency gain of 1.8% is achievable when we go from dual pressure to triple pressure cycle.

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DESIGN CONDITIONS Ambient Temperature

27°C

Atmosphere Pressure

1.013 bar

Relative Humidity

60 %

Fuel

Natural Gas

Power Factor

0.8

Frequency

50 Hz

Gas Turbine Inlet duct Pressure drop

100 mm of WC

Gas Turbine Exhaust duct Pressure drop

127 mm of WC

Condenser Vaccuum

92 mbar

Condenser inlet cooling water temp.

32°C

Gas Turbine Load

106 MW

Steam Turbine Load

116.1 MW

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EFFECT OF VARYING CONDITIONS ON GT PERFORMANCE SL.NO. 1

2

3

4

5

6

7

CONDITIONS Ambient Air Pressure Increase Decrease Ambient Air Temperature Increase Decrease Specific Humidity Increase Decrease Inlet Pressure Drop Increase Decrease Exhaust Pressure Drop Increase Decrease Compressor Speed Increase Decrease Water Injection Increase Decrease

OUTPUT

HEAT RATE

Increase Decrease

No effect No effect

Decrease Increase

Increase Decrease

Decrease Increase

Increase Decrease

Decrease Increase

Increase Decrease

Decrease Increase

Increase Decrease

Increase Decrease

Decrease Increase

Increase Decrease

Increase Decrease

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POWER REQUIRED BY COMPRESSOR Power required by Compressor is defined by:Net Output Work Ratio = ---------------Turbine Work

=

(T3 – T4) – (T2 – T1) ------------------------T3 – T4

For Frame 9E Gas Turbine: T1 = 27°C T2 = 350°C T3 = 1104°C T4 = 545°C Work Ratio

=

Turbine Work =

236 ------ = 0.422 = 559

Net Output ---------------- = Turbine Work

106 -------Tw

106 --------- = 251 MW 0.422

Compressor Work = 251 – 106 = 145 MW 154

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EFFECT OF AMBIENT TEMPERATURE Ambient temperature

Output

Heat Rate

Exhaust Temp.

Increases Decreases

Decreases Increases

Increases Decreases

Increases Decreases

Reasons: At higher ambient temperature: a) Compressor work increases & Rate of increase is high. b) Heat supplied decreases & Rate of decrease is less C) Efficiency decreases & Heat Rate increases. At higher temp, air density decreases and compressor supplies, in spite of its constant volume flow, a smaller mass into the combustor. As air is the energy transporting means of gas turbine, its reduction results directly in a corresponding decrease of output. Once heated to base load temp., this reduced mass flow takes on a smaller volume, which by passing through the turbine, causes a smaller resistance leading to smaller back pressure at the compressor discharge. Since the hot gases enter the turbine with lower pressure, they can only become less expanded and their temperature drop will be less important. In consequence, the exhaust temperature rises and more waste heat is blown into the atmosphere, which means efficiency decreases. For every 5.6 °C rise in temp. Output decreases by 3.75% & H.R. increases by 1.0%. EFFECT OF AMBIENT PRESSURE Ambient pressure

Output

Heat Rate

Exh.Temp.

Increases Decreases

Increases Decreases

No Effect No Effect

No Effect No Effect

Reasons: (1) With increasing pressure, air density increases and the compressor supplies a greater mass flow. Hence output increases. For every 0.01 kg/cm2 increase in ambient pressure, power output increases by 0.6%. (2)

Efficiency: With increase in atmosphere pressure, Compressor discharge pressure increases, but the stack pressure also increases. Hence, the pressure head in the turbine does not change. Hence, exhaust temperature remains same. So the efficiency does not change. 155

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EFFECT OF PRESSURE DROP IN INLET DUCT Cause: (1) Line losses (2) Dirty Air filters (3) Pressure drop in the silencer Effect Output

Heat Rate

Exh.Temp.

Decreases

Increases

Increases

Reason: (1)

Absolute inlet pressure decreases, hence air density decreases, hence output decreases.

(2)

CPD decreases, but pressure at stack remains same. Also heat addition increases. The pressure drop and temp. drop decreases. Exhaust temp. and waste heat increases thereby reducing efficiency.

ALLOWABLE: 8.78 mbar inlet pressure drop. TREND: At every increase of 10 mbar inlet

Output -1.5%

Heat +0.5%

EFFECT OF PRESSURE DROP IN OUTLET DUCT Cause: (1) Line losses in duct. (2) Pressure drop in silencer Effect Output Heat Rate Decreases

Increases

Exh. Temp. +1.2° C

Exh.Temp. Increases

Reason: The pressure at exhaust increases causing pressure & temp. differential to decrease. CPD remains same. Exhaust temperature & waste heat increases, decreasing net Mass flow, hence output will reduce. But compared to inlet pressure drop, reduction will be less. ALLOWABLE: 12.5 mbar ADDITION PRESSURE DROP EFFECTS: At every increase of

Output

Heat

Exh. Temp.

10 mbar

-0.45

+0.45

+1.2° C 156

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GAS TURBINE COMPRESSOR CLEANING The basic thermodynamic cycle on which the working of our gas turbine is based on is Brayton cycle in which the air after being compressor is ignited in combustion chamber which gives the motive power to the turbine. The power taken by compressor is being given by the gas turbine. As such any reduction in power consumption of the compressor increases the net output from the gas turbine. The gas turbine frame 9001E supplied by GEC Alsthom is rated for 106 MW at inlet air pressure & temp 1.013 bar & 27 °C, with machine speed 3000 rpm. Any variation in these operating parameters affects the output of the gas turbine. The ambient air temperature varies considerably resulting in change in inlet air density and hence mass flow through the compressor. Any change in grid frequency affects the compressor speed resulting in low compressor discharge pressure. Also the characteristics of air flow which flow through the compressor is based on the compressor blade profile which on continuous operation may change due to deposition of foreign particles resulting in lower compressor discharge pressure and high compressor discharge temperature.

In above Brayton Cycle isentropic expansion is shown by straight line T1 - T2 ’, but due to friction & other unavoidable losses, the actual process takes the curve T1 - T2 .

η =

Isentropic..increase..in..enthalpy Actual..incrase..in..enthalpy

η =

or η =

Cp(T2 '-T1 ) h2'-h1 = Cp(T2 - T1) h2 - h1 (T2 '-T1 ) (T2 - T1 )

---------------(1) 157

158

Here T1 = Ambient air temperature T2 = Actual Compressor Discharge air temperature T2 ’ = Isentropic Compressor Discharge temperature For Isentropic Compression r −1 T2' P2 r = ( ) ------------------(2) P1 T1 Where P2 = Compressor Discharge Pressure P1 = Inlet air Pressure to Compressor Cp γ = (for air γ = 1.4) CV Compressor Discharge Pressure and the Compressor Discharge air temperature are known from equation (1) & (2), the isentropic efficiency of the Compressor can be found out. r −1

P2 r ) P1 (T2 '-T1 ) Hence η = (T2 - T1 ) T2 ’ = T1 × (

Here T2 ’, T1 & T2 are known quantities Decline in performance is indicated by a gradual loss of GT power output and an increase in fuel consumption. Many of the problems are a direct result of dirty or fouled axial-flow compressor. Fouled compressor result in reduced air flow, lower compressor efficiency and lower compressor pressure ratio. These combined parameters deteriorate compressor performance. There are different types of compressor fouling. The type and rate of fouling depend on the environment in which the gas turbine operates and the type of inlet air filtration mechanism, if any. Among the most comman types of contaminants are: 1. Dirt or soil 2. Sea shell 3. Coal 4. Insect 5. Salt 6. Oil Salt, asides from being a contaminant, also causes corrosion of blades & duct, and subsequent ingestion of rust and scale. Oil increases the ability of contaminants to stick to compressor passages and airfoils.

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METHOD OF DETECTION

Visual Inspection Visually inspecting the compressor early stages blades, if there is any dust or filmy deposit, it can be wiped or scraped out immediately before these deposit causes compressor fouling which is sufficient to affect compressor performance. Performance Monitoring The second method for detecting a fouled compressor is performance monitoring. It involves obtaining gas turbine data on a routine basis for calculating performance of the compressor. Shown below is the case for GT-1A compressor cleaning. The parameters were taken in the morning to nullify the effect of the variations in the ambient conditions. BEFORE COMPRESSOR CLEANING

SET-1

FREQ.

Cpd (bar)

50.19

10.71

T1 °C 16.30

T2 °C 339.0

T2 ’ °C 296.59

T1 °C 23.25

T2 °C 342.0

T2 ’ °C 303.55

η

COMPRESSOR

86.85

AFTER COMPRESSOR CLEANING

SET- 2

FREQ.

Cpd (bar)

49.59

10.29

η

COMPRESSOR

87.89

Where: Cpd is Compressor Discharge Pressure η COMPRESSOR is Compressor efficiency The average compressor efficiency prior to cleaning was 86.85% which after cleaning increases to 87.89%. The increase in compressor efficiency means less work on the compressor. Hence for the same total output of the Gas Turbine, less power will be consumed by the compressor resulting in increased net power output. Comparing the two sets of reading one can find that the grid frequency is less in the second case & so is the compressor discharge pressure. The ambient temperature has increased from 16.3 °C to 23.25 °C. But in spite of these conditions (which lead to decrease in compressor efficiency) the compressor efficiency increases which can only be attributed to the improved flow through the clean compressor.

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DEFINITIONS P.L.F. %

Actual generation in MU X 100 Generation Capacity during the period

Generator on bar Availability factor %

Period for Gen. synchronized with grid X 100 Reference time during the period

Machine availability factor %

Machine availability period for Gen. X 100 Reference time

Specific Gas Consumption

Gas consumed per unit of generation SMC KWH

Specific Naptha Consumption Heat Rate Efficiency Loading Factor %

Naptha consumed per unit of gen. Litre KWH Energy consumed per unit of generation Kcal = SMC X Kcal KWH KWH SMC Output = KWH = KJ/S X 3600 S = 860 Input Kcal 4.186 KJ H.R. Plant load factor X 100 Gen. On bar availability factor

Pinch Point

Difference of gas temp. at evaporator outlet and drum saturated steam temperature

Approach temperature

Difference of drum saturated steam temperature and water temperature at economizer outlet

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R. D. CHAUHAN SR. MANAGER (SIMULATOR) NTPC-KAWAS E-MAIL: [email protected] E-MAIL: [email protected]

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