KWU Text Governing

7/31/2019 KWU Text Governing

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KWU TURBINE

GOVERNING SYSTEM

NOTE


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TURBINE GOVERNING SYSTEM

In order to maintain the synchronous speed under changing load/steam conditions,the KWU turbine supplied by BHEL is equipped with electro-hydraulic governor;fully backed-up by a hydraulic governor. The measuring and processing of electricalsignal offer the advantages such as flexibility, dynamic stability and simplerepresentation of complicated functional systems. The integration of electrical andhydraulic system has the following advantages:

Exact load-frequency droop with high sensitivity. Avoids over speeding of turbine during load throw offs. Adjustment of droop in fine steps, even during on-load operation.

Elements of Governing System

The main elements of the governing system are as follows:

Remote trip solenoids (RTS). Main trip valves (Turbine trip gear). Starting and Load limit device. Speeder Gear (Hydraulic Governor). Aux. follow-up piston valves. Hydraulic amplifier. Follow-up piston valves. Electro-Hydraulic Converter (EHC). Sequence trimming device. Solenoids for load shedding relay. Test valve. Extraction valve relay. Oil shutoff valve. Hydraulic protective devices.

REMOTE TRIP SOLENOIDS (RTS)

The remote trip solenoid operated valves are two in number and form a part ofturbine protection circuit. During the normal operation of the turbine, thesesolenoids remain de-energised. In this condition, the control oil from the governingrack is free to pass through them to the main trip valves. The solenoids getsenergised whenever any electrical trip command is initiated or turbine is tripped


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manually from local or UCB. Under energised condition the down stream oil supplyafter the remote trip solenoids gets connected to drain and the upstream will be

blocked. By resetting Unit Trip Relays (UTR) from UCB, these solenoids can be reset.

REMOTE TRIP SOLENOIDS

MAIN TRIP VALVES

The main trip valves (two in numbers) are the main trip gear of the turbine protectivecircuit. All turbine tripping take place through these valves. The control oil fromremote trip solenoids is supplied to them.

TURBINE TRIP GEAR


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Under normal conditions, this oil flows into two different circuits, called as the TripOil and Auxiliary Trip Oil. The Trip Oil is supplied to the Stop Valves (of HP Turbineand IP Turbine), Auxiliary Secondary Oil circuit and Secondary Oil circuits. The

Auxiliary Trip Oil flows in a closed loop formed by main trip valves and turbinehydraulic protective devices (Over Speed trip device, Low Vacuum trip device and

Thrust Bearing trip device).

The construction of main trip valves is such that when aux. trip oil pressure isadequate, it holds the valves' spools in open condition against the spring force.

Whenever control oil pressure drops or any of the hydraulic protective devices areactuated, the main trip valves are tripped. Under tripped condition, trip oil pressureis drained rapidly through the main valves; closing turbine stop and control valves.

STARTING AND LOAD LIMIT DEVICE

The starting and load limit device is used for resetting the turbine after tripping, foropening the stop valves and releasing the control valves for opening. The startingdevice consists of a pilot valve that can be operated either manually by means of ahand wheel or by means of a motor from remote. It has got port connections with thecontrol oil, start-up oil and auxiliary start-up oil circuits. The starting device canmechanically act upon the hydraulic governor bellows by means of a lever and link

arrangement.

Before start-up, the pilot valve is brought to its bottom limit position by reducing thestarting device to 0% position. This causes the hydraulic governor bellows to becompressed thus blocking the build-up of secondary oil pressure. This is known ascontrol valve close position. With the valve in the bottom limit position (startingdevice = 0%) control oil flows into the auxiliary start-up circuit (to reset trip gear andprotective devices) and into the start-up oil circuit (to reset turbine stop valves). A

build-up of oil pressure in these circuits can be observed, while bringing the startingdevice to zero position. When the pilot valve i.e. the starting device position is raised,the start-up oil and auxiliary start-up oil circuits are drained. This opens the stop

valves; ESVs open at 42% and IVs open at 56% positions of the starting device.

Further raising of the starting device release hydraulic governor bellows which is inequilibrium with hydraulic governor's spring tension and primary oil pressure(turbine speed), and raises the aux. sec. oil pressure; closing the aux. follow-updrains of hydraulic governor.

SPEEDER GEAR

The speeder gear is an assembly of a bellow and a spring, the tension of which canbe adjusted manually from UCB by an electric motor or locally by a hand wheel. Thebellow compression depends upon the position of the starting device and the speedergear position, which alters the spring tension on the top of the bellow. The bellow isalso subjected to the primary oil pressure, which is the feedback signal for actualturbine speed. The zero position of speeder gear corresponds to 2800 rpm i.e.

hydraulic governor comes into action after 2800 RPM. The bellow and springassembly is rigidly linked to the sleeves of the auxiliary follow-up piston valves. Theposition of the sleeve changes with the equilibrium position of the bellow.


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SPEEDERG

EAR

STARTINGD

EVICE

ACTINGO

N

SPEEDERG

EAR


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HYDRAULIC SPEED TRANSMITTER

The hydraulic speedtransmitter runs in the MOP

bearing and operates on theprinciple of a centrifugalpump. The variation ofpressure in the discharge lineis proportional to the square

of the machine speed. Thisprimary oil pressure acts asthe control impulse for thehydraulic speed governor.

The transmitter is suppliedwith control oil via an oilreservoir. An annular groovein the speed transmitterensures that its inside isalways covered with a thinlayer of oil to maintain auniform initial pressure.Excess oil drains into the

bearing pedestal.

CURVE SHOWING TURBINE SPEED Vs PRIMARY OIL


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AUXILIARY FOLLOW-UP PISTON VALVES

Two Auxiliary Follow-up pistonsare connected in parallel and thetrip oil is supplied to themthrough orifice. The sleeves ofthese valves are attached to thespeeder gear bellow link. The

position of the sleeve determinesthe draining rate of trip oilthrough the ports. Accordinglythe trip oil pressure downstreamof these valves changes. Oildownstream of auxiliary follow-uppistons circuit is termed as

AUXILIARY SECONDARY OIL.Hence, aux. follow-up piston

valves can be said to controlauxiliary secondary oil pressure.

SEQUENCE TRIMMING DEVICE

The function of the sequence trimming device or HP/IP TRIM DEVICE is to preventany excessive HP turbine exhaust temperature due to churning. It changes responseof main and reheat control valves. When the reheat pressure is more than 32

Kg/cm2

and load less than 20% the IP turbine tends to get loaded more than HPturbine. The steam flow through HP turbine tends to fall to very minimum, causing alot of churning and excessive exhaust temperature. The trim device operates at thismoment trimming the IP turbine control valve. The control valves of HPT open moreto maintain flow of steam, reducing the HPT exhaust temperature.

It consists of a spring-loaded piston assembly, which is supported by control oilpressure from beneath, under normal conditions. The control oil is supplied via anenergised solenoid valve. When the turbine loads is less then 40 MW and hot reheat

pressure is more than 32 kg/cm2

the solenoid valve gets de-energised cutting out thecontrol oil supply to the trim device.

The trim device trips under spring pressure. The trim device is connected to thefollow-up piston valves of IP control valves by means of a lever. Upon tripping, thetrim device alters the spring tension of follow-up pistons of IP pistons control valves,draining the secondary oil. The IP control valves openings are trimmed down.

HYDRAULIC AMPLIFIER

Hydraulic Amplifier consists of a pilot valve and an amplifier piston. The position ofthe pilot valve spool depends upon the aux. secondary oil pressure. Depending uponthe pilot spool position, the control oil is admitted either to the top or the bottom ofthe amplifier piston. The other side of amplifier is connected to the drain. Themovements of the amplifier piston are transformed into rotation of a Camshaftthrough a piston rod and a lever assembly. A feedback linkage mechanism stabilisesthe system for one particular aux. secondary oil pressure.


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HYDRAULIC AMPLIFIER

1. Amplifier piston2. Follow-up piston3. Sleeve4. Shaft5. Lever6. Feedback lever7. Pilot valve8. Compression spring9. Adjusting screw

a : Control oil

b : Secondary oilb1 : Aux. Sec oilc : Return oil

SOLENOIDS FOR LOAD SHEDDING RELAY

A pair of solenoid valves has been incorporated in the IP Sec oil line on control valvesand Aux Sec. oil line, in order to prevent the turbine from reaching high speed in theevent of sudden turbine load throw-off. The control valves are operated (closed) bythe load-shedding relay when the rate of load reduction exceeds a certain value. Thesolenoid drains the IPCV secondary oil directly. Direct draining of IP Sec oil circuitcauses the reheat valves to close without any significant delay. The HP control valvesare closed due to draining of aux. secondary oil before the hydraulic amplifier, by thesecond solenoid valve. The extraction stops valves controlled by IP secondary oil

acting through extraction valves relays also get closed. After an adjustable time delay(approx. 2 seconds) the solenoid valves are re-closed and secondary oil pressurecorresponding to reduce load builds-up in the HP and IP turbine secondary oil lines.

FOLLOW-UP PISTON VALVES

The trip oil is supplied to the follow up piston valves through orifices and flows inthe secondary oil piping to control valves. The secondary oil pressure depends uponposition of sleeves of follow-up piston valves; which determines the amount ofdrainage of trip oil.

There are in all twelve follow-up piston valves. Six of them are associated withhydraulic amplifier and six of them with EHC in the governing system. The follow-uppiston valves constitute a minimum value gate for both the governors. This meansthe governor with lower reference set point, is effectively in control. This is alsotermed as HYDRAULIC MINIMUM SELECTION of governors.

The drain port openings of follow-up pistons of hydraulic amplifier depends onauxiliary secondary oil pressure, upstream of aux. follow-up pistons; and that ofelectro hydraulic converter, on the piston of pilot spool valve of the elector-hydraulicconverter (i.e. EHC output).


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FOLLOW-UP PISTON VALVES

TEST VALVE

1.

Bolt2. Hand wheel3. Spindle4. Cover5. Oil Seal6. Bushing7. O-ring8. Valve Cover9. Valve Body10. Trip Oil11. Piston sleeve12. Trip Oil13. Piston valve14. Spring plate15. Spring16. Spacer17. Bottom cover18. Trip oil19. Drain20. Trip oil21. Startup oil


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Each of the HP and IP stop valves' servomotors receives trip oil through theirassociated test valves. The test valves have got port openings for trip oil as well asstart-up oil. The test valves facilitate supply of trip oil pressure beneath theservomotor disc. (Stop valve open condition, under normal operation). For thepurpose of resetting stop valves after a tripping, start-up oil pressure is supplied tothe associated test valves, which moves their spool downwards against the springforce. In their bottom most position the trip oil pressure starts building up above thestop valve servomotor piston while the trip oil beneath the disc gets connected to

drain. When start-up oil pressure is reduced the test valve moves up draining trip oilabove the servomotor piston and building the trip oil pressure below the disc, thusopening the stop valve. A hand wheel is also provided for manual operation of test

valves.

EXTRACTION N.R.VS AND EXTRACTION VALVE RELAY

Four pair of swing-check valves are provided in the extraction lines to the feedheaters (LP Heaters No: 2,3, Deaerator and HPH No: 5) to prevent back flow ofcondensed steam into the turbine from heaters on account of high levels in theheaters. There are two NRVs provided in each of these extraction lines and is forceclosing type. Both these valves are free-swinging check type, however the first valveis equipped with an actuator. In case of flow reversals, both the valves are closed

automatically. The actuator assists the fast closing of the first valve. The mechanicaldesign of force-closed valves is such that they are brought into free-swinging position

by means of trip oil. They are open as soon as differential pressure is sufficient. Ifthe trip oil pressure falls, the spring force closes the valve when steam pressureeither falls or is lowered (reduced load).

The extraction valve relay, its changeover valve and its solenoid valve control the tripoil to each of the actuators of force closing type valves. In case of turbine trip orsudden load reduction, by energising the associated solenoid valve, draining of trip


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oil pressure through extraction valve relay assists closing movements of FCNRVs. Inboth the cases the actuator is devoid of trip oil and its spring force closes the NRV.Extraction (4) FCNRV solenoid is also energised additionally by lower differentialpressure in the extraction line.

b : Control Oil c : Return Oil

b1 : Secondary Oil x : Trip Oil

b2 : Secondary Oil x1 : Trip Oil

COLD REHEAT SWING CHECK VALVE

Two numbers of swing check valves are provided on the CRH lines from which thesteam is drawn for HPH-6. Their pilot valves via their rotary servomotor inproportion to secondary oil pressure operate the CRH NRVs. They open out fully

when main control valves open up corresponding to 5-10% of maximum turbine out-put. Only when the control valves are closed to this threshold again, the NRVsreturn into steam flow by the hydraulic actuator, so that when the steam flow ceasesin the normal direction, they are closed by the torque of rotary servomotor. Even

when the pressure of secondary oil has not built up sufficiently, NRVs can be openedup like safety valves when the upstream pressure rises above the downstream side

pressure by one bar.


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VACUUM BREAKER

The function of the vacuum breakers is to cause an increase in condenser pressureby conducting atmospheric air into the condenser together with the steam flowingfrom the LP Bypass. When the pressure in the condenser increases, the ventilationof the turbine balding is increased, which causes the turboset to slow down so thatthe running down time of the turboset and the time needed for passing throughcritical speeds are shortened.


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Electro-Hydraulic Governor (EHG)

Electro-Hydraulic Governor (EHG) works in parallel with Hydraulic governor at alltimes of requirements. Basically the Electro-Hydraulic Converter (EHC) is theconnecting element between the electrical and hydraulic parts of the turbinegoverning control system for carrying out the Electro-Hydraulic Governing of theturbine.

The Electro-Hydraulic Governor (EHG) is beneficial in

Offering the flexibility, dynamic stability, dependability, excellent operationalreliability, Low transients and steady-state speed deviations at all instances.

Maintaining exact load frequency droop with high sensitivity.Providing reliable operation at times of grid isolation conditions.Operating the turbo-generator Safely in conjunction with TSE.In KWU turbines, Electro-Hydraulic Governing has been achieved through variouselectronic / selector modules configured in four modes of controls:

Admission Control mode, Speed Control mode, Load Control mode Pressure Controlmode.

The Hydraulic governor and the EHG system have been designed such that thegovernor with lower set point takes over or assumes the system control, as suchnormally, the set point of the Hydraulic Governor must be set above that of theElectro-Hydraulic Governor when EHG is effective. In cases, when EHG fails to causeshut-off, the set point that is, affected is that of Hydraulic Governor.

In such situations the Tracking Device provides a revised set point of 5-10% abovethe EHG set point and it causes increase in small load when the control istransferred to Hydraulic-Governor. The tracking device is either switched on or off

manually but when EHG failure or turbine trip occurs, the tracking device isswitched off automatically thus tracking under faulted operation mode is preventedor prohibited. More details on tracking actions are covered in the follow-up circuitsof the speed/load control modes.

Electro Hydraulic Converter

Electro Hydraulic Converter converts the electrical signal in to the hydraulic signalsand large positioning forces are generated in control valves. The electrical signal fromgovernor control circuit operates the sleeve and pilot valve spool; this regulates thetrip fluid drain. Under steady state condition pilot is at central position; in deflectedposition, the control oil is admitted above or below the amplifier piston. The motionof the amplifier piston is transmitted via a lever to a camshaft, which actuates thesleeves of follow-up piston valves, causing secondary oil pressure to change. Thespeed, load, and pressure signals are measured and converted into conditionedsignal in electronic modules.


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1. Differnetial transformer2. Amplifier casing3. Amplifierpiston4. Piston rod5. Valve bushing6. Piston valve7. Grooved ball bearing8. Spring dics9. Compression spring10.Sleeve11.Casing support12.Moving coil system

a. control oilb. Trip Oil

Electro Hydraulic Converter

Admission Valve (spool) Controller

Admission Valve (spool) Controller also referred as the position controller is Commonfor all three modes of EHG, and it supplies the operating current for driving the

plunger coil. The Position controller loop uses a PID control mode for processingoutputs that provide the driving current signal to the plunger and regulate the oildrains of HP/IP control valves (CV); thereby it controls steam supply into theturbine.

The current in the plunger coil is increased for closing the HP /IP CV and vice versafor opening of the HP /IP Control Valve. The reference signal therefore works inreverse manner (rise in the coil current for low reference condition). By using twoNos of differential transformer (housed in EHC), feedback signal from the valve lift isderived to ensure proper stationing of plunger spool.

Whenever current through the plunger coil gets interrupted or the electrical feedbackcircuit gets faulted, the reference value of the Hydraulic controller determines the

actual valve position. Although the force to the plunger coil and to the control sleeveis, considerably smaller, but the regulating signal to the secondary auxiliary oil flowas transformed is quite large. The figure below gives various connections andmodules used in EHG.


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Actual speed (nact) Measurement:

Actual speed nact is acquired by three digital speed pickups (Hall probes) in the formof pulses /frequency. Channel-2 is utilized while other two-channel pick-up remainsredundant; electronically switching ensures no affect in channel in service and alsoa full - proof monitoring. The selected sensed speed channel signal is further dividedinto three measuring signals (f/v of 0-60 Hz, low range 0-6 Hz & full range 0-60 Hzand a quartz frequency standard) for various other applications in the EHG and

other circuits.

The difference of actual speed and time dependent speed signals (nact - nRTD) formthe input error of the Speed controller which outputs control signal (in the path asexplained in selection section) through the selection modules for driving the EHC

and finally establishing the EHG.

ACTUAL SPEED MEASUREMENT


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TURBINE PROTECTION SYSTEM

Turbine protection system performs to cover the following functions: -

a. Protection of turbine from inadmissible operating conditions.

b. In case of plant failures, protection against subsequent damages.

c. It restricts occurring failures to minimum.

Standard turbine protection system comprises the following:

Mechanical/hydraulic turbine protection. Electrical turbine protections.

BLOCK DIAGRAM OF TURBINE PROTECTION AND ATT

Mechanical Hydraulic Turbine Protection

The design of mechanical hydraul ic protecti on equipment is in accordancewith hydraulic break current principle and consists of following:


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a. Two manual trip devices (main trip valves)

b. Two speed monitors (over speed trip device)

c. One hydraulic low vacuum device

d. Two solenoid valves for trip initiation (remote solenoid valves)

As explained earlier, turbine stop and control valves are tripped to close position ifthe trip oil pressure is reduced below the minimum value. The main trip valves allowrapid draining of trip oil in case they are operated either manually or automatically

by the reduction of aux. trip oil pressure. Aux. trip oil pressure can be drainedbecause of actuation of hydraulic low vacuum trip device, over speed trip device orthrust bearing trip device. The principle of functioning of individual hydraulic tripdevices is explained in details under the chapter of Automatic Turbine TestingSystem.

Remote trip solenoids act as interfaces between mechanical hydraulic and electro-hydraulic protection equipment of turbine. Upon receiving the electrical tripcommand, the solenoids get energised and close the valves. Thus control oil supply

to main trip values is cut off leading to their closure.

Electrical Hydraulic Turbine Protection

Electrical turbine trip equipments comprise two-channel redundancy and functionon operating current principle. All electrical trip criteria act on the two remote tripsolenoid valves to energise the solenoids.

The electro-hydraulic turbine protection equipment features -

-Two solenoid operated valves for trip initiation (Remote trip solenoids).-Emergency trip contactor cabinet containing trip channels 1 and 2-Monitors with signal conditioning-One substitute channel to ensure uninterrupted transmission of eventualturbine trip signals during testing by ATT.

The remote trip solenoids (RTS) have already been described. Operation of any onechannel causes energising both solenoid-operated valves leading to turbine tripeventually. Transmitters that cause a trip in the case of any electrical tripping signalare conditioned and monitored via binary signal conditioning of the ATT system or

via the central analog/binary signal conditioning.


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TURBINE PROTECTION FOR 200MW KWU SETS


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Turbine Trip Actuation Circuits

The turbine protection system is sub divided into two parts:

a. Protective circuits for the standard turbine protection equipments or criteria.b. Protective criteria from other areas.

Standard criteria are specified by the turbine manufacturer and are responsible forfull protection of turbine under various specific conditions, which are:


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1. Manual tripping devices (Turbine trip gear local operating lever)

2. Speed monitors (over speed trip devices)

3. Thrust bearing trip device

4. Hydraulic low vacuum trip device

5. Electrical low vacuum trip device

6. Lub oil pressure protection

7. Fire protection

8. Manual turbine tripping (electrical UCB switch)

Protection criteria from other areas are as follows:

Boiler trip (MFR) Boiler drum level very high ( > + 225 mm wcl ) Main steam temperature trip ( < 480 o C ) Trip from functional group control (ATRS shut-down programme) Generator trip

Like low vacuum tripping (electrical) the low steam temperature protection alsocomprises 'Arming' and 'Disarming' features to facilitate re-start of turbine, underlow main steam temperature conditions.

Over Speed Trip Device

Two hydraulically operated over speed trips are provided to protect the turbineagainst over speeding in the event of load coincident with failure of speed governor.

OVER SPEED TRIP DEVICE

1. Bearing pedestal2. Spindle3. Spring4. Piston5. Piston body

6. Spring7. Pawl8. Over speed trip bolt9. Shaft journal10. Limit switch

c: Return Oil

u: Auxiliary Stratup Oilx: Auxiliary Trip Oil


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When the preset over speed is reached, the eccentric fly bolt activates the piston andlimit switch via a pawl. This connects the auxiliary trip oil to drain therebydepressurising it. The loss of auxiliary trip medium pressure causes the main trip

valve to drop, which in turn causes the trip oil pressure to collapse.

Low Vacuum Trip Device

In the hydraulic low vacuum trip device, a compression spring set to a specific

tension pushes downwards against diaphragm, the topside of which is subject to thevacuum. If the vacuum is too weak to counteract the spring tension, the springmoves valve 6 downwards. The pressure beneath valve is thereby dispersed and theauxiliary trip medium circuit is connected to drain. The resultant depressurisation ofthe auxiliary trip oil actuates main trip valves MAX51 AA 005 and MAX51 AA 006thereby closing all turbine valves.

The electrical tripping on low vacuum occurs through a pressure switch on thevacuum line to mechanical hydraulic low vacuum trip device also at the samecondenser pressure. When turbine is started up again, this pressure switch isinterlocked against a second pressure switch, which monitors this condition andprevents continuation of tripping initiation when condenser pressure is high.

Thrust Bearing Trip Device

The function of the thrust bearing trip is to monitor the shaft position in the bearingpedestal and, if a fault occurs, to depressurize the auxiliary trip medium and thusthe trip oil in the shortest possible time, thereby tripping the turbine.


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1. Compressionspring

2. Bearing pedestal3. Piston4. Valve body5. Turbine shaft6. Pawl7. Torsion spring8. Piston9.

Compressionspring

10.Limit switch11.Knoba: Test Oil

c: Return Oilu: Aux. Startup Oil

x: Aux. Trip Oil

The two rows of tripping cams, which are arranged on opposite sides of turbineshaft, have a specific clearance, equivalent to the permissible shaft displacement,relative to pawl of the thrust-bearing trip. If the axial displacement of the shaftexceeds the permissible limit, the cams engage pawl, which releases a piston to

depressurise the auxiliary trip oil and at the same time to actuate limit switch.

Electrical tripping of turbine is achieved by fire protection along withclosure/stoppage of total control oil supply to turbine governing system by trippingthe emergency stop valve on the control oil line. The fire protection trip is achieved

by manual Pushbutton in UCB or automatically by very low MOT level (- 150 mmbelow the normal working level 'O'). Please refer to the associated logics at the end ofthis chapter. Also fire protection-1 (automatic actuation) gets bypassed if the barringgear valve is 'not closed'.


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FIRE PROTECTION-1 CHANNEL-1


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FIRE PROTECTION-2 CHANNEL-1


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FIRE PROTECTION OIL TANK LEVEL MONITOR


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TRIP OIL

FUNCTION :To open the stop valves and generate auxiliary secondary oil

and secondary oil

SOURCE : Control oil

SUPPLY DEVICE : Main Trip Gears

AUXILIARY TRIP OIL

FUNCTION : To engage and operate the main trip valves

SOURCE : Trip oil

SUPPLY DEVICE : Main Trip Gears

AUX. SECONDARY OIL

FUNCTION : To provide the position signal for the hydraulic governor

SOURCE : Trip oil

SECONDARY OIL

FUNCTION : To provide the position signal for the control valve servomotor

SOURCE : Trip oil

PRIMARY OIL

FUNCTION : To supply speed signal to hydraulic governor


SUPPLY DEVICE : Hydraulic Speed Transmitter

START UP OIL

FUNCTION : To supply control signals for the stop valves


SUPPLY DEVICE : Starting Device

AUX. START UP OIL

FUNCTION : To reset the Hydraulic Protective devices


SUPPLY DEVICE : Starting Device

TEST OIL

FUNCTION : To test the hydraulic trip devices


SIGNAL OIL

FUNCTION : To operate LPBP valvesSOURCE

:Control oil


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KWU LMW

1. The types of governor used is Electro-hydraulicbacked up by Hydraulic governor

The types of governor used is Hydro-

mechanical

2. Governing type used is throttle governing Nozzle type governing is provided

3. Speed of the m/c is controlled right fromturning gear speed by Electro-hydraulicgovernor

Speed of the m/c is controlled by

Governor from 300-3450 rpm

4.Regulation range of Electro-hydraulicgovernor can be varied from 2.5 to 8% in steps

of 0.5% (Regulation range of hydraulic

governor is 7%)

Regulation range is 4%1%

5.Transient speed risea) When control valves are mounted near

casing is 8%

b) When control valves are mounted away

from casing as in BHEL sets is 8.5%

Transient speed rise is 6 to 7%

6. Dead band of Governing system: 0.01% Dead band of Governing system: 0.3%

7.

Closing time of servomotors

a) HP i) ESV: 0.2 Sec

ii) Control valve: 0.4 Sec

b) IP i) IV: 0.8 Sec

ii) Control valve: 0.8 Sec.

a) HP ESV: 0.35 Sec

b) IP: IV: 0.4 Sec

c) Control valve servomotor: 0.5 Sec.

8. Control oil pressure 8.0 Kg/cm2 Control oil pressure 20.0 Kg/cm2

9.Size of HP Stop valve (ESV)i) 160 mm - 2 nos

ii) zie of HP control valves 128 mm - 2 nos) (0.8

times of ESV)

iii) Size of IV valves - 320 mm (2 nos)

iv) Size of IP control valves - 256 mm (02 nos)

Size of control valves 1,2,3,4 (4 nos)

125,150,150.150 mm

Size of IV valves 320 mm (2nos)

Size of IP control valves (4nos)

10.Automatic turbine testing is provided to check

the protective devices while M/C is in

operation

Automatic testing device is not provided

to check the protective devices while

M/C is in operation

11.All Gov.elements like Main trip valve, EHC

follow up piston block etc. are kept outsideand assembled in separate cabinet

All Gov. elements like Fly weight

governor, Summation pilot, Follow pilot;

Emergency Gov. pilots are mounted in

front pedestal.

12.Trimming device provided for IP control valves

is used for controlling HP exhaust temp. in caseof following low load operation.

(HP Exhaust or CRH pressure>32 KSC and

Generator load < 20%)

There is no trimming device provided for

IP control valves


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13.In all types of starts HP control valves controlfrom 0 to 100%. IP control valves have

controlling function along with HP control

valve up to 40%, further control is done by HP

control valves.

In cold and warm start HP control valves

control from 0 to 100%. There is no control

on IP control. In case of hot start, IP

control valves control the M/C up to

30MW. Further control is by HP control

valves for HP & LP bypass system.

14.Actual over speed test is carried out by means

of separate test lever provided in Hydraulic

governor. Both over speed governor aretested together.

Actual over speed test is carried out by

means of Speeder gear after selecting

the respective governor by means ofselector of emergency governor lever.

15.Electrical pressure controller is provided to

unload the M/C in case the main steam

pressure drops by more than 10% of rated

value.

Initial steam pressure unloading (ISPUG)

hydraulic device has been provided to

unload the M/C in case main steam

pressure drops more than 10% of the

rated value.

16.Load shedding Relay is provided to control the

acceleration rate during sudden reduction in

output load.

The electrical signal is converted into

hydraulic signal by actuation of EHT.

17.Hydraulically driven Emergency shut-off valve

is provided to interrupt the supply to thegoverning rack.

No such device is provided

18. IP control valves opens after HP control valves HP control valves opens after IP controlvalves

19.

The output signal of speed controller

(electrical) is automatically matched to the

output signal of load controller from the rated

power on down to station load. The speed

controller is then in stand by mode and stands

ready to provide station load in case of load

shedding.

Such facility does not exist, as the Turbine

is not provided with Electro hydraulic

governing system.

20. Stop & control valves are provided in samecasing

Stop & control valves are mounted indifferent casing

21. Control valves are mounted away fromturbine

Control valves are integral parts of

turbine

22. Control valves movement is in horizontaldirection

Control valves movement is in vertical

direction

23. Each control valve can be tested for spindlefreeness during operation

Such facility is not available during

operation of the M/C

24. Each control valve has a separate servomotor Only one servomotor operates all HP & IPcontrol valves.


39/43

EDC-Singrauli 39

PROBLEMChange over

valve not getting

reset

OBSERVATIONChange over valve in trip

condition and control oil

pressure low

SOLUTION

On line full flow filterself cleaning by knob

rotation

RECOMMENDATION

On line full flow filter self

cleaning by regular

knob rotation

PROBLEM

Emergency

Governor operating

within operating

speed range

OBSERVATION

Unit frequently tripping in

over speed during rolling atspeed lower than 3000 rpm.

SOLUTION

Check test oil pressure.

Check proper latching of

reset unit. Check the

position and mass of the

over speed bold

RECOMMENDATION

Period testing of O/S

Governor by simulation


40/43

EDC-Singrauli 40

PROBLEMLP By pass Not

Resetting

OBSERVATION

Getting reset after bypassing

condensate pressuremechanical switch

SOLUTIONOpen the switch found

bellow found damaged.It was replaced. Normal

operation of LP BP

observed

RECOMMENDATION

Bellow changed OR If

operation requiredbefore replacement.

Ensure temperature

switch working properly.Replace bellow at the

earliest.

PROBLEMElectro Hydraulic

Converter Hunting

OBSERVATION

Calibration of EHC checked

with Calibrator and foundoscillating

SOLUTIONOpened the EHC and one leaf out of

three leaves spring of electro hydraulic

converter found damaged. Spring wasreplaced. Stabilization voltage set to

negative (-1 mV). Problem was solved.

PROBLEM

LP Bypass WaterInjection Valve Not

Closing

OBSERVATIONSignal Oil Pressure was low and

W I actuator drain line was hot

SOLUTION

Signal oil inlet was wrongly

connected with valve actuator.


41/43

EDC-Singrauli 41

PROBLEM

HP CV Oscillating

(Hunting)

OBSERVATION

HPCV & HP Secondary Oil

Pressure Hunting

SOLUTIONDamping device was opened

and ball was found missing. It was

put back, oscillation of valve

stopped.

PROBLEM

Startup Speed NotRising

OBSERVATIONStartup device and speeder

Gear liver link was broken

SOLUTION

Lever was changed,

problem was solved

RECOMMENDATION

Same problem was

repeated after about amonth. Spring setting was

set right and stroke of

starting device andspeeder gear was re-

adjusted. Problem solved

permanently.


42/43

EDC-Singrauli 42

PROBLEMHP Control Valve

Not Opening

OBSERVATION

HP Secondary oil pressure

was not building up. This waschecked in Hydraulic mode

as well as EHC modeSOLUTION

Follow up pilot blockinspection cover was

opened and one of the

three control pilot wasfound loose and fell down.

It was placed in position.

RECOMMENDATION

Pilot was tightened in

position with a small

screw and little gluesmooth operation of

HPCV

PROBLEMHP Stop valve Not

opening

OBSERVATION

Test valve was checked and

found clearance of slideand sleeve more.

SOLUTIONTest valve was

replaced. Problem

solved.

RECOMMENDATION

Quality of oil/FRF to be

maintained for nocorrosion / mechanical

pitting. Avoid frequent

operation of manualtesting devices.


43/43

PROBLEM

IP Stop Valve NotOpening

OBSERVATION

Test valve was checked and

found OK. Flow of Trip oil toSV actuator was felt, as line

was hot. SOLUTION

Actuator was opened

and a nut was foundin between piston

and disc

RECOMMENDATION

Fault at assembly shopdo not attempt to open

the Hydraulic Actuator

without the expert

guidance.

PROBLEM

CRH NRV not

openingOBSERVATION

Supply and return line was

found hot.

SOLUTION

Servomotor wasopened and servicing

was done its seal wasfound damaged. Itwas replaced.

RECOMMENDATION

Change all the gasketand seals if opened in

governing system and

control oil system.

KWU Text Governing

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