kwu electro hydraulic governing final1
TRANSCRIPT
-
7/31/2019 KWU Electro Hydraulic Governing Final1
1/41
KWU Electro-Hydraulic
governing
Governor is a device to control speed /loadto a set point.
Type: Hydraulic & Electro-hydraulic
Advantages & disadvantages
-
7/31/2019 KWU Electro Hydraulic Governing Final1
2/41
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
-
7/31/2019 KWU Electro Hydraulic Governing Final1
3/41
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
-
7/31/2019 KWU Electro Hydraulic Governing Final1
4/41
2790 2940 3060 3210
RPM
output+100%
-100%
0%
Droop of kwu m/c
-
7/31/2019 KWU Electro Hydraulic Governing Final1
5/41
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%
-
7/31/2019 KWU Electro Hydraulic Governing Final1
6/41
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%
-
7/31/2019 KWU Electro Hydraulic Governing Final1
7/41
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.
-
7/31/2019 KWU Electro Hydraulic Governing Final1
8/41
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)
-
7/31/2019 KWU Electro Hydraulic Governing Final1
9/41
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
-
7/31/2019 KWU Electro Hydraulic Governing Final1
10/41
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.
-
7/31/2019 KWU Electro Hydraulic Governing Final1
11/41
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
-
7/31/2019 KWU Electro Hydraulic Governing Final1
12/41
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)
-
7/31/2019 KWU Electro Hydraulic Governing Final1
13/41
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
-
7/31/2019 KWU Electro Hydraulic Governing Final1
14/41
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
-
7/31/2019 KWU Electro Hydraulic Governing Final1
15/41
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
-
7/31/2019 KWU Electro Hydraulic Governing Final1
16/41
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.
-
7/31/2019 KWU Electro Hydraulic Governing Final1
17/41
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.
-
7/31/2019 KWU Electro Hydraulic Governing Final1
18/41
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
-
7/31/2019 KWU Electro Hydraulic Governing Final1
19/41
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.
-
7/31/2019 KWU Electro Hydraulic Governing Final1
20/41
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
-
7/31/2019 KWU Electro Hydraulic Governing Final1
21/41
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
-
7/31/2019 KWU Electro Hydraulic Governing Final1
22/41
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
-
7/31/2019 KWU Electro Hydraulic Governing Final1
23/41
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.
-
7/31/2019 KWU Electro Hydraulic Governing Final1
24/41
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
-
7/31/2019 KWU Electro Hydraulic Governing Final1
25/41
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
-
7/31/2019 KWU Electro Hydraulic Governing Final1
26/41
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.
-
7/31/2019 KWU Electro Hydraulic Governing Final1
27/41
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.
-
7/31/2019 KWU Electro Hydraulic Governing Final1
28/41
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%.
-
7/31/2019 KWU Electro Hydraulic Governing Final1
29/41
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
-
7/31/2019 KWU Electro Hydraulic Governing Final1
30/41
PI
controller
AND
EHC
PlungerCoil
MIN
HP sec. oil
IP sec oilAdmission
controller
EHC>
100%
PLUNGER COIL
ON/OFF PB
-
7/31/2019 KWU Electro Hydraulic Governing Final1
31/41
Response of plunger coil/EHC
Step I/n
collins1or2
EHCcoil Volt
HPCV1
opening
-
7/31/2019 KWU Electro Hydraulic Governing Final1
32/41
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
-
7/31/2019 KWU Electro Hydraulic Governing Final1
33/41
-
7/31/2019 KWU Electro Hydraulic Governing Final1
34/41
EHC: SPEED CONTROLLER
-
7/31/2019 KWU Electro Hydraulic Governing Final1
35/41
EHC: Load controller
CONTROL TRANSFER LOGIC & ADMISSION CONT
-
7/31/2019 KWU Electro Hydraulic Governing Final1
36/41
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
-
7/31/2019 KWU Electro Hydraulic Governing Final1
37/41
LOAD SHEDDING RELY SOLENOID VALVES IN OIL CI
For example :- Turbine running at 3000 rpm
-
7/31/2019 KWU Electro Hydraulic Governing Final1
38/41
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
-
7/31/2019 KWU Electro Hydraulic Governing Final1
39/41
-
7/31/2019 KWU Electro Hydraulic Governing Final1
40/41
CONTROL TRANSFER LOGIG
-
7/31/2019 KWU Electro Hydraulic Governing Final1
41/41
& ADMISSION CONTROLLER
-