KWU Electro Hydraulic Governing Final1

7/31/2019 KWU Electro Hydraulic Governing Final1

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KWU Electro-Hydraulic

governing

Governor is a device to control speed /loadto a set point.

Type: Hydraulic & Electro-hydraulic

Advantages & disadvantages


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ADVANTAGES OF EHC

i) Increases the life of turboset by conservative

operation with the aid of TSE

ii) Reliable operation of isolated power grid by

Automatic Switchover of the load controller tofrequency control.

iii) Precise maintenance of the rated frequency of the

power grid by means of an exact frequency load curve.

iv) Low speed deviation under all operational

conditions.

v) Support of the pressure control system


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kwu

EHC can be divided into following sub-sections:

1 Speed measurement and Speed controller

2 Load controller and Load measurement

3 Pressure controller

4 Control transfer of Speed, Load and Pressure

Controller

5 Admission /Position Controller


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2790 2940 3060 3210

RPM

output+100%

-100%

0%

Droop of kwu m/c


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What is Droop?% of frequency change ( % of RPM change)

will lead to full travel of Governing valves or

full load change.

5% droop means: 5%*50 Hz= 2.5 Hz

Will change 500MW. In terms of output totalchange should take place is 100%


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00

+100%

TURBINE DROOP 5% & NO DEAD BAND

-100%

-150 RPM +150 RPM

3000

RPM28502700 3150

+300

3300

DROOP5% & DEAD BAND +/-2%

2940 3060

2790

3210

+100%

-100%

0%


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1a Speed measurement

Hall probes are mounted around a disc (fitted

at the turbine shaft) containing 120 magnets

(60 N-pole & 60-S pole alternatively) . An

advantage of the same is that one rotation of

disc will generate 60 positive pulses & So,

by counting the pulses for one second wecan directly determine the turbo set speed in

rpm.


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1b Speed Controller

Speed Controlleris used to increase turbine speed

from barring speed to rated speed in a controlled

manner and to assist Auto synchronizer in

synchronizing the machine and taking the blockingload. After synchronization speed controller can be

used for taking load up to 100% but as a normal

practice approx. 10% of load should be taken and then

load controller should be taken into service. It is done

because during speed controller mode a small

frequency change will cause corresponding opening in

valve opening ( hence in load)


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Speed controller can be divided into sub section:

Speed set point,

Speed set point control, Dn/Dt monitoring,

Speed control Loop, No load correction.

a) Speed set point can be changed from cabinet, desk,auto Synchronizer and SGC turbine. The set point is

called nR. The set point changes at a gradient of 2160

rpm/min up to a setting 2820 rpm. After 2820rpm

speed set point changes at a gradient of 360 rpm/min

which enables accurate setting of set point in the

working range


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b) Speed Set Point control

Speed Set Point control :- The set point

fixed in the earlier section cannot be passed

to speed control loop directly as it is onlythe desired value which can be changed at a

very fast rate and it does not take care of

turbine stress margin. To incorporate theabove facilities an integration (closed loop)

is used.


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c) Dn/Dt MONITORING

A Speed controller output (hr n c) should be more

than 0.0 V (with a time delay of 10 seconds)

B E S Vs open.

C Generator circuit breaker in open condition.

D Actual speed (n a c t) < 2850 rpm.

E Speed set point (nR) more than 700 RPM for

200MW. For 500MW,set point is > 400 rpm.

F Dn/Dt < 108 rpm

M/c will bring back to soaking speed 600rpm/360rpm


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d) Speed Controller Loop:-

Speed Controller loop is PD (P) loop with a

droop of 5%. As the rated

speed of the turbine is 3000 rpm hence 5% is

150 rpm. A deviation of 150 rpm will

correspond to full opening of the control

valve (with the assumption that full openingof control valve will give full load at rated

parameters)


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e)No Load Correction

As the speed controller loop is PD (P) so an error in

the input is a must to keep the valves open for

running the at the rated speed .To avoid this error

between set point and actual value a pressuredependent correction signal is given, as the valve

opening required for running the machine at rated

speed is directly dependent on steam pressure. Hence,

for correction purpose practical reading should betaken when the machine is running at rated speed at

different pressure


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2.Load Controller

Load controller is used to maintain the load set by

the operator ( at turbine control or at CMC

console ) or automatic load dispatch Centre(optional ). Load controller is also responsible for

taking care of frequency changes and correcting the

load. The controller comes into operation only after

synchronization, before Synchronization it remainsin the follow mode .The total loop can be divided in

the following sub-sections


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2A) Load set point (PR)

2B) Load Gradient and TSE Margin Influence.

2C) Load Set Point Control (PRTD)

2D) Frequency influence.

2E) Load Limiter

2F) Actual Load Acquisition

2G) Final Control Loop

Sub-sections of Load controller


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2A)Load Set Point:-

Load Set Point:- Load set point can bechanged from cabinet, desk, SGC or CMC orfrom Auto dispatch Centre (optional).The set

point changes at a gradient of 100 MW /Minfor 200MW & 250MW/min for 500MW).The gradient remains same through out therange. The load set point indicator isavailable at desk. The range of the indicatoris 0-250 MW for 200 MW M/c & 0-600MWfor 500MW M/c.


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2B) Load gradient and TSE

influence Load gradient is an additional feature available in load

controller. The load gradient acts in parallel with TSE

margin with minimum Selector. Load gradient range is

0-25MW/ min : 200MW & 0-60MW/min (500MW).

While for TSE margin 0-30 degree K corresponds to 0-

25 MW/min 200MW, 0-60MW/min(500Mw)

Both load gradient and TSE margin have got anON/OFF switched, so if any one is desired to be taken

out of service can be switched off.


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2C) Load set point

Control(PRTD) If load gradient is off and any change in PR is made

PRTD changes by 5%

The function of PRTD is similar to the NRTD in speedcontroller The maximum rate change here is 25MW/min or 60MW in both directions

The set point controller remains in follows mode in

generator breaker is off or load controller is off or loadis less than station load& MW error>10%. Duringthis mode PRTD follows actual load without delay

STOP command is generated if TSE fault appears


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2D)Frequency Influence

Frequency influence is used to correct theload set point. The frequency influence hasgot a droop of 5%

The frequency influence can be switchedon/off from Frequency Influence module

Indicator for the correction signal is available

at desk of range +/- 100MW for 200MW M/c& +/- 200 MW for 500MW M/c.

IN all NTPC stations this has been kept off.


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2E) Load Limiter

Final Set point (addition of PRTD and PR F ) is

fed to a minimum selector with the load limiter

Load limiter will limit the actual load and it alsocan be used for fast reduction of load in emergency

cases.

PR (in turn PRTD )also should be reduced, so that

during load increase as per PRTD and not as per

load limiter


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2F) Actual Load Acquisition

/Load measurement The actual load is measured by three load

transducers which get the signal from PT and CT

and give out put 0-250MW (or 0-500MW M/c)corresponds to 4-20 mA

The middle value of the three load measurement is

use for processing

If any value drifts from the other value by more

than 5%, a selective alarm is generated


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2G)Final Controller Loop

The final loop is a PI controller Two major parts consisting of two cards ARL 12&

ARL 13specially designed for this purpose

Error signal is generated from the final set point and

actual load in ARL 12 card. It has an inbuiltfrequency influence whose responsibility is to preventthe over speeding of the turbine. Hence, thisfrequency influence acts only to reduce the out put of

the controller The output of ARL 13 card provides the integrator

part of the loop. Apart from the integrated, ARL 13has also got a filter


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Following Above (hvo)

This mode in operation during following conditions 1- Load Controller Off

2- Generator Breaker Off

3- Pact 5% and Generatorbreaker closed.

During the above condition the load controller output

tracks the speed controller output all the time with a

constant error of-150mV. This follow-mode ensure

that during above conditions, the load controller

should not come into action.


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Following Low (hvu)

This mode is present one the breaker issynchronized and speed controller is still in action.During this mode the load controller output tracksthe speed controller output with error of 150mV

load controller output can go more than speedcontroller output (hence load controller can takeover) but it cannot go 150 mV below the speedcontroller output.

load controller can be taken into service anytimewithout any delay


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3 Pressure Controller:-

3a) Initial Pressure Mode A Pressure deviation signal(difference of required pressure as per load and actualpressure ) is fed to the controller .As long the deviationis more than + 150mV (Actual> required ) the pressure

controller output remains as maximum saturation. If thedeviation fall between 0 to +150mV, the output of thepr. controller comes out from saturation & match to theoutput of final minimum selection output

As soon as the deviation becomes negative, the outputof the pressure control starts

This mode comes when runback action comes intopicture or it is selected from console


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Pressure controller

3b Limit pressure mode

The function of this mode is similar to the initialpressure mode .The only difference being that biasing

of 10Kg/Cm2 is given in this loop. Hence, all theaction start after the pressure drops by more than10Kg/Cm2.

This mode is used when m/c is in load control; a small

pressure correction signal is also applied +/- side toload set point control.

This mode should be used once the load on turbo set isstabilized.


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4 ControlTransfer:- This loop receives the signal from speed controller

(hrnc), load controller(hr PC) and pr. controller a set of Max & Min selection and then final value

selected is passed on to position /admission controller

hrnc> and pass through a maximum value

selector and the value selected is passed on to first MINvalue selection. 10.5v is added in and this valueis also fed to first Min value selector

The value selected in first Min value selector is passed

on to the second MIN value selector along with outputof pressure controller output (hr PRC) The valueselected here is passed on the position / admissioncontroller.


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5 Position/admission Controller:

Position Controller is the final control element inEHC. It receives the signal from control transfer

It receives feedback signal from Collinstransmitters.Two Collins transmitters are provided

Selection one of two is through MIN value selector(logic MAX selector)

Plunger coil supplied in EHC is an integrator type. The

balance point of the coil is 1.0V Provision to switch ON/OFF the voltage supply to

plunger coil. Switching ON /OFF can be done only ifthe output of position controller is > 100%.


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PLUNGER COIL RESPONSE

STEP INPUT OF ORDER OF 2 VOLT DC

COLLINS RESPONSE AT INPUT OF

CARD ( 1 ,2)

EHC COIL RESPONSE

HPCV RESPONSE, DELAY BY 1 SEC


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PI

controller

AND

EHC

PlungerCoil

MIN

HP sec. oil

IP sec oilAdmission

controller

EHC>

100%

PLUNGER COIL

ON/OFF PB


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Response of plunger coil/EHC

Step I/n

collins1or2

EHCcoil Volt

HPCV1

opening


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LOAD SHEDDING RELAY

LOAD shedding relay is used to support the function of

the turbine governor. A quick correction value input tothe hydraulic governor output & secondary oil pr. ofIPCV min speed building

When acceleration time constant is very small or when

governor under load or pressure control. Sudden negative jump in load is detected electrically

instantaneously by the load shedding relay

200MW: Load throw off>40% & residual load49 Hz 500 MW: Load throw off>50% & residual load49 Hz in a response time of 100mili seconds.Full load through off


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EHC: SPEED CONTROLLER


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EHC: Load controller

CONTROL TRANSFER LOGIC & ADMISSION CONT


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SUMMER

ACTUALPR SET

THROTTLE PR.

10 KSC

INITIAL PR. MODE

PI CONTR

LOAD CONT

SPEED CONT

100% -0-+100%

MAX

OVER SPEED LIMIT

105%

MIN

MINPI

CONT.

EHC

CONV

MIN

COLLINS

CONTROL TRANSFERLOGIC & ADMISSION CONT


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LOAD SHEDDING RELY SOLENOID VALVES IN OIL CI

For example :- Turbine running at 3000 rpm


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p g p

Output of speed controller at (50Kg/Cm2)=1.5V

Output of speed controller at (150Kg/Cm2)=0.8V

The pressure transmitter ranges is 0=250Kg/Cm2 = 0-10V for 4to 20mA

The correction input as given with a gain of 0.05 and the overall gain of speed controller loop is

so net gain for correction signal =0.05x22.22=1.11Hence correction input required at 50Kg Cm2 =1.5/1.11 =1.35v and correction input required at

Y=m x +C Y= Correction Signal

X = Pressure Signal ( 50 kg/cm2=2v, 150 kg/cm2=6v)

1.35=M x 2+C. .(1)

0.72=M x 6 +C. .(2)

By solving above two equation M = -0.16

C= 1.67

Gain (M) should be adjusted by potentiometer AB 099/R11 negative polarity of (M) is taken c


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CONTROL TRANSFER LOGIG


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& ADMISSION CONTROLLER

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Documents

KWU Electro Hydraulic Governing Final1