NTPC Rihand Governor

7/31/2019 NTPC Rihand Governor

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RIHAND GOVERNOR

GOVERNING SYSTEM CAN BE CONSIDERED IN

TWO PARTS

1.STEAM FLOW COMPUTING AND

2.VALVE CONTROL

THE INTERFACE BETWEEN THESE TWO

PARTS IS AN ARRANGEMENT OF HIGHWAYS

WHICH CARRY VARIOUS VALVE POSITIONING

SIGNALS.



STEAM FLOW COMPUTING

THE PRINCIPAL ITEM OF STEAM FLOWCOMPUTING PART IS THE COMPUTINGCHANNEL.THERE ARE THREE COMPUTINGCHANNEL(CC) EACH WORKING INDEPENDENTLY

OF THE OTHER TWO.

BASIC FUNCTION OF CC IS TO MEASURE THESPEED OF THE TURBINE, COMPARED THIS WITHA DEMANDED SPEED (3000RPM) AND THEN

PROCESS THE RESULTING SPEED ERROR SIGNALVIA DROOP,BIAS AND RATE OF CHANGE CIRCUITTO PROVIDE VALVE POSITION SIGNALS FORH.P.STOP, H.P.GOVERNING AND I.P.GOVERNINGVALVES.



VALVE CONTROL

EACH VALVE IS PROVIDED WITH ITS OWN

VALVE CONTROLLER WHICH FORMS THE

ELECTRICAL SECTION OF THE ELECTRO-HYDRAULIC VALVE CONTROLLING

SYSTEM.ITS PURPOSE IS TO PROVIDE A

SUITABLE DRIVE TO THE SERVO-VALVE

SO THAT THE VALVE MAY BE POSITIONEDAS DEMANDED BY THE VALVE POSITION

SIGNALS FROM THE CC.



LOW VALUE GATE: FOCAL

POINT OF COMPUTING CH.THE LOW VALUE GATE(L.V.G.) IS THE FOCAL

POINT OF THE CC MODULE THE INPUTE,TO THEL.V.G. ARE:

1. PROTECTION

2. RUN-UP GOVERNING (WIDE RANGEGOVERNING: WRG)

3. RAMP4. HP GOV. VALVE OPENING LIMIT( 0-105%)

5. SPEED STEAM (NARROW RANGE GOVERNING:NRG)

6. VACUUM PAY-OFF



WRG

• WRG Is single channel and allows its set

point to change from barring gear to near

synchronous speed.

• ATRS: -Uses WRG interface during run-

up. Run-up modules controls of turbine

from barring speed to nominal speedusing a speed reference ramp which is

modulated by ATRS.



Speed Steam: NRG

Speed of turbine is computed from rate of pulses

generated by magnetic ups mounted adjacent to a 60-

toothed wheel fitted to turbine shaft. The pulses areamplified by head amp.& then process thro’ dynamic

compensator,accle. pcb to speed measure pcb which

generate voltage proportional to diff of actual & ref.

speed 3000rpm i.e speed error. This error then amp.

by droop amp. Dead band facility holds the o/p of

droop amp.at zero over a range of speed error signal.



Speed steam ( cont.): NRG

• The o/p of droop amp. is added to speed

error reference( SER) whose o/p is the

speed steam.

• The speed error ref.( SER) is a bias applied

to the droop amp.to set the speed steam

signal at a particular turbine speed. Thevalue of SER is controlled by CCR-desk

raise/lower push button or by other sources.



Speed steam ( cont): NRG

• The speed error signal is also fed into a lowvalue gate on summer pcb. Bias &

amplification applied to speed error signal togive 10v at 103.5% speed & 0v at 106%speed( droop: 2.5%). At maximummeasurable speed which is 106.25%. the o/p

of over-speed clipping ckt. is – 10%. Whereas governor droop which is 4% can give o/pat maximum speed is – 6.25%.





Output of LVG: steam demand

signal• Valve high way : O/p of LVG is compared with o/p

of other CC. This ckt generates an o/p average of all

3 computing ch.o/p ( if within 5%). The o/p of average& voter pcb feeds the valve high way amp. as

steam demand signal to

1 Hp gov valve high way: driven by function generator

whose in/op characteristics is inverse of valvelift/flow charac.The valve lift signal is fed to all HP

gov. valve control module.



Steam demand signal

2 HP stop valve Highway: The stop valve signalfrom the run-up module is applied to one input of LVG.The o/p of average/voter is applied to otherinput. The lowest signal is fed to non-linearamplifier for all HP stop valves

3 IP gov valve highway : Its driver sums togetherthe “steam demand signal” & sequence biassignal. Accele. Signal also summed. The o/p of summing amp. Is the valve lift signal which fed toall IP gov valve control modules.



Valve control module

• The valve controller contains the necessary

averaging,L.V.D.T. drive & demodulator ckt. It has

two ch. Control & check L.V.D.T. and when themonitors detects a discrepancy between these that

exceeds a preset value , the controller will trip its

valve shut and raise an alarm.

• Its purpose is to provide suitable drive to servovalve so that the valve may be positioned as

demanded by the averaging signal of all three

computing signals.





3000 3120 324028802760

0 +120 +240-1200%

+100%

-100%

-240

+100%

-100%

DROOP 4% & DEAD BAND+/-2%

TURBINE DROOP 4% & NO DEAD BAND



+100%

0%

-10%

GOVERNOR

DROOP 4%

OVERSPEEDCLIPPING

CKT

3060 3105

3187.53060 3105

RIHAND DROOP &OVER SPEED CLIPPING

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NTPC Rihand Governor