ELECTRO HYDRAULIC TURBINE CONTROLLER

07.03.2020

K.V.Prathapan
NTPL, Tuticorin
 TURBINE CONTROL LOOPS

100%

+
+

hrSC
SC_O/P M
hrLC A M
I
LC_O/P X N M
1 I hr
hrPC N
PC_O/P 2

MHG_O/P ASO
 SPEED CONTROLLER LOGICS:

Raise
Speed NR Speed NRTD hrSC
Reference Reference
Limiter Speed
Setter Controller
Lower

SGC Turb Actual

Speed NACT
Auto Synch.
DCS OR NR (raise)
Back Panel P.B.
GCD if Pact < stn.load

SGC Turb
Auto Synch.
Dn/dt optd
DCS OR NR (lower)
Back Panel P.B.
GCD if pact < stn.load
 dN/dt LOGIC:

Acceleration is low (<108 rpm/min)

360 rpm<Nact>2850 rpm

GCB Open OR
A
N
HPSV 1&2 Not closed D

NR > 700 rpm

dn /dt
Operated
 SPEED REFERENCE (NR) LOGICS

i) NR Tracks to (NACT + 15 rpm) if :

i) LC O/p > SC O/p by 5% &
ii) 48.5 HZ < NACT > 51.5 HZ &
iii) ‘LC ON’ Command is there.

ii) NR is automatically raised by 15 rpm after synchronization

for block loading.

iii) In case of a turbine trip, NR tracks to (NACT – 120 rpm)

to ensure speed controller output to be less than 0 %
 SPEED REFERENCE LIMITER (NRTD) LOGIC:
TSE

Speed raise
Speed lower SR NR NRTD
(Tur.Trip) Track to (Nact – 130 rpm) setter
SR
Limiter
Track to Nact + 15 rpm

Load cont. in action A Block

48.5 HZ <NACT > 51.5 HZ

N loading
D

TSE ON & Fault

TSE Margin is< 0

OR
A Stop Reference
GCB not ON N
NRTD > NACT by 36 rpm D

Speed/pwr set point block from ATRS

 SPEED CONTROLLER

Nact -1
Nact
Nact -2
& MV3
Nact -3

Nrtd PDT
hrsc
Controller O/P
Nact
Gain = 24
5% droop
 LOAD CONTROLLER

Load Reference :-
Raise Command :-
i) From DCS
ii) From Panel
iii) SGCT

Lower Command :-
i) From DCS
ii) From Panel
iii) SGCT

Both Raise and Lower commands are issued provided ‘CMC is not ON ‘

Load Reference from CMC :

A 4-20mA signal from CMC, which is limited between 50 & 550 MW at EHTC panel.
 LOAD REFERENCE (PR) LOGIC

i) PR tracks to CMC Load reference, if “CMC is ON”.

ii) On issue of a “ Load ref tracking” signal,
PR tracks to Load actual for 1sec.
iii) PR tracks to Load actual also on following conditions :-
a) Pressure controller is in action
AND b) IP mode selected.
AND c) Load actual is < 30%, i.e.180 MW

“LOAD REF TRACKING” Signal :-

It is used as a reference matching signal during transition
(High freq. Unloading ) It is activated, if :-

i) Pact. < 180 MW

AND ii) Speed, Nact. is > 3048 rpm.
AND iii) Error to load controller is < -2%.
 LOAD CONTROLLER

Push button
Raise
CRT >1
SGC Turb. &
1
PR PR
S
E PR
‘ CMC not ON’ Lower
L

& CMC ref 2

4-20 mA
Push button signal
SEL ‘2’ if CMC is on
CRT >1 Raise & Lower Command issued if CMC is not ‘ON’.
SGC Turb. ‘PR’ selects the CMC signal if CMC is ON.
Track to CMC ref.
If CMC in ON PR PR
Track to act. load

PC in action Track to actual load for 1 sec.

A Pact <180 MW
IP mode selected N A
D Nact > 3048 rpm N High frequency unloading
Load act.< 30%
Error to load D in load control mode
Controller < -2%
 LOAD REFERENCE TIME DELAYED ( PRTD) LOGICS:

i) Integration Time constant depends upon the minimum of TSE

margin signal and load gradient signal.
ii) Load gradient signal = 100% or maximum, if gradient is ‘OFF’
OR
the selected gradient value by operator if gradient is “ON”
iii) PRTD goes to ‘FAST’ integration mode on the following conditions:-
a) Fast follow
b) Load Ref. Tracking command for 0.5 sec.
c) Run-back active command

During FAST follow, it tracks to ( Actual load + PRTD – PR)- 1 %

 PRTD SIGNAL

PR LRL
INT.
PRTD
TSE Margins Time
Constant

On fast follow, Track to

( Pact +PRTD –ΣPR) - 1%
Max. run –up time
= load gradient

Fast follow
Pact< Pstn
A
GCB ON N Fast follow .
D
LC error > 5%
Controller un-stable
 LOAD REF TRACKING SIGNAL

LC input < - 2% A
Over freq Unloading Load ref Tracking signal.
N PRTD tracks PR.
in LC active
D
Pact. < 30 %

Run back Active

Stop Integrator
Press Cont. in Action
A
LP mode selected N
D
PR >PRTD
O Stop ref. Integrator.
TSE fault & ON R
Speed power set pt. Block
from ATRS
 “FAST FOLLOW” SIGNAL

During fast follow, the margins are taken to 100%

Fast Follow is initiated if :-
i) Load controller is ‘not ON’
OR ii) GCB is not ‘ON’
OR iii) Pact < Pstn & Load controller error > 5%

Error to Load controller :

M +
ΣPR I Error
N
PRMAX
PAct.
_
 SUM OF PR( ΣPR) LOGIC
i) PR = PRTD + PR△f + Pressure correction.
ii) P R△f = 0 MW if:
i) Freq. Influence is OFF
OR ii) CMC is not “ON”
OR iii) Turbine Follow Boiler (IP mode)
iii) PR△f is active provided above conditions are not there and Pact>PStn
iv) Pressure correction is active, if :-
a) Pact > PStn
AND b) LC is in action.
AND c) LP Mode is selected.
Load controller ‘ON’ & ‘OFF’
Load controller can be switched ‘ON’ or ‘OFF’ from CRT/P.B. only and only when
speed controller is active ,and speed Controller out put is more than load controller output.

***
 ΣPR LOGIC

Pressure Correction

PRTD + ΣP R
+

PRΔ f
Pressure Correction Signal 1

0% 2 Pressure
Correction

SEL-2
Freq. Inf. OFF
CMC OFF OR
IP mode Selected
 STOP REFERENCE LIMITER LOGICS:-

Stop speed/power set point:-

The signal is generated on any of the following conditions :-
i) PC in Action & LP mode selected & (PR > PRTD)
OR ii) Speed /PWR set point block from ATRS.

The above signals directly stop PRTD .

Load Gradient “ON/OFF”

Load gradient ‘ON’ by manual command provided Set point controller is
balanced.
It is made ‘OFF’ manually if set point controller is also balanced.
It is made ’OFF’ by CMC ON Signal also.
***
 ISOLATED GRID LOGICS

“ISOLATED GRID” detected on following conditions:

i ) Speed Nact > 3036 rpm.
AND ii) Error to load controller > 8.4% for 6 sec.
AND iii) Load controller is ‘ON’
AND iv) Speed controller is not in action.
AND v) Pressure controller is not in action.
It is reset either by GCB ‘OFF’
OR
Error to load controller is less that 8.4% and isolated grid reset
command is issued by the operator.
* During isolated grid condition, the Load Controller is made sluggish
by reducing the input gain from 0.51 to 0.047 and the integral action
time is increased by 10 times.
 LOAD CONTROLLER

It is a PID Controller

Logics :-
i. During PC in action, the output follows the PC output + 2%.
ii. If LC is switched off, then the output is equal to – 10%.
iii. During LC not stable, the output will track SC output – 1.5 %.
 PRESSURE CONTROLLER
Logics :-
LP Mode :- ( Limit Pressure Mode ).

LP mode can be selected manually by:-

i) CRT button .
ii) back panel P.B.
OR iii) it is selected if ‘ CMC is ON’.

IP Mode : ( Initial Pressure Mode )

IP mode can be selected manually by
i) CRT button .
ii) back panel P.B.
Or iii) it is selected if ‘ Boiler control on manual’ signal from CMC.
Or iv) by “ Turbine follow boiler” signal from CMC.
***
 PRESSURE CONTROLLER
Pressure deviation signal is received from CMC.
Also pressure actual value is received from CMC,
from which set pressure is calculated and fed to
The controller .
Actual Press

+
Set Pressure + P
-
I
-10 Kg -1
+ R
0 Kg 2
IP Mode Sel 2
Limit between 50 to 120 %

LP Mode
A LP reached.
N Alarm
ΔP is +ve
D
 CONTOLLER SELECTION LOGIC

All the three controller’s O/P are fed to the selection

logic, the controller selected acts on the turbine.

The Logic:
Speed controller, load controller O/P are fed to a
MAX selector . The O/P of MAX and the inverted
speed controller O/P are fed to a MIN1 selector ,
whose O/P along with the pressure controller O/P
are fed to another MIN2 selector . The final output of
this MIN2 gate is fed as reference (hr) to the position
controller.
 CONT. SELECTION

Limited between 10 % to 100% .

100% +A
D
SC_O/P +D

M
M
I
A
LC_O/P N
X M
1 hr
I
N
Position
2
reference
PC_O/P
 TRACKING DEVICE LOGICS:
It is made ‘ON’ by :-
i) Manual command from DCS
ii) SGCT It is made ’OFF’ by:-
 Manual command from DCS
 SLD/HSG position fault.
 EHC position F/B fault.
 Collins transmitter 1&2 deviation > 5%.
 SGCT
 Turbine Trip.
 EHTC fault.
 Speed signal 2/3 fault.

EHTC FAULT:-
All tracking device ’OFF’ commands are treated as EHTC fault conditions.
THANK YOU