The document describes the operation of an electro-hydraulic turbine controller (EHTC) which consists of speed, load, and pressure control loops. The EHTC controls the valve lift to regulate turbine speed and load based on feedback from these loops. It allows startup, synchronization, minimum load operation, and full power range operation of the turbo generator set. The document also discusses different plant operation modes of the EHTC including boiler follow, turbine follow, and coordinated control (CMC) modes. CMC mode aims to coordinate the fast response turbine with the slow response boiler to minimize pressure and load fluctuations.

1. 1
BY
Vishal Laddha

2. Electro-Hydraulic Turbine Controller
ESSENTIALLY CONSISTS OF THE
FOLLOWING CONTROL LOOPS:
1. SPEED CONTROL LOOP.
2. LOAD CONTROL LOOP.
3. PRESSURE CONTROL LOOP.
ONE OF THESE THREE LOOPS ACT
SELECTIVELY ON THE SUBORDINATE VALVE
LIFT CONTROL.
THE VALVE LIFT CONTROLLER
ACTUATES THE PLUNGER COIL OF THE
ELECTRO-HYDRAULIC CONVERTER WHICH
EHTC

3. Speed Control
REALISES THE FOLLOWING
OPERATIONS:
1. START-UP AND SHUTDOWN OF
TURBINE
2. SYNCHRONISATION OF THE
GENERATOR
3. PROVIDES A MINIMUM LOAD
OPERATION
4. OPERATION OF THE TURBO-SET IN
THE COMPLETE POWER RANGE IN
SPEED CONTROLLER

4. Load Control
LOOP REALISES THE FOLLOWING
OPERATIONS:
1. LOAD REFERENCE LIMITER
2. FREQUENCY LOAD DROOP
3. LOAD/FREQUENCY CONTROLLER
LOAD CONTROLLER

5. Pressure Control
CONTROLS THE TURBINE LOAD W.R.T.
THE MAIN STEAM PRESSURE DEVIATION
AND PREVENTS A PRESSURE DROP e.g.
DURING A QUICK LOAD INCREASE.
TWO OPERATIONAL MODES CAN BE
SELECTED:
1.INITIAL PRESSURE CONTROL.
2.LIMIT PRESSURE CONTROL.
PRESSURE CONTROLLER

6. EHTC

7.  Boiler follow mode
 Turbine follow mode
 Coordinate mode
 Manual mode
TYPES OF PLANT MODE OF OPERATION

8. CMC

9. In This Mode:
 Boiler Follows The Turbine
 The Steam Pressure is controlled by controlling
the fuel firing in the Boiler
 Boiler Master is on Auto Mode
 EHG is on Man Mode and EHG acts as Power
Controller
 EHG in Power Control means it will try to
maintain the Generator output to a fixed follow
as per the power controller set point given from
EHG console
 Main Steam pressure set point is given from
BOILER FOLLOW MODE

10. MS FLOW
PD
MS PRESSURE
PID
+ +
Boiler Demand
BOILER
Fuel Ctrl Air Ctrl
G
Turbine
LOAD
Load Set Point
MS Pr. Set point
EHG Pr
Ctrlr
Grid
BOILER FOLLOW MODE

11.  Combustion system is fully Automatic
 The Main steam pressure varies as Boiler
response is slow (energy conversion)
 EHG, acting in Power Control mode, keeps the
Power output fixed to the set value
CHARACTERISTICS BOILER FOLLOW MOD

12. In this mode:
Turbine follows the Boiler
The Final Steam pressure is controlled by the Turbine
admission valves
The Load is controlled by the Boiler. Boiler master is kept
in Manual mode
EHG is kept in Auto. Will act in Pressure control mode
TURBINE FOLLOW MODE

13. Boiler
Fuel &
Air
PR. Tx.
GRID
EHG
PI Controller
Turbine Generator
MS Pressure
Actual
Pr. Set Point
TURBINE FOLLOW MODE

14.  The Steam pressure at Turbine inlet remains
almost constant
 The load may fluctuate depending upon the
combustion in Boiler
 In case of large load fluctuation, the Turbine
stress parameters are overlooked
 Response to changes in load demand is
sluggish
CHARACTERISTICS OF TURBINE FOLLOW

15.  In turbine follow mode, the system goes through
a fast process, overlooks load, load fluctuation,
Turbine parameters
 In Boiler follow mode, the system goes through
a slow process, pressure fluctuation happens in
large amount
 CMC is answer to the above two challenges
Co-ordinated Master Control
 CMC is a Coordination control between fast
response Turbine and slow response Boiler
 It has preset values for producing Unit Load
demand keeping in mind all the primary
protection parameters in mind
 The primary aim of CMC mode is to make the
CMC MODE

16. In this mode:
 Boiler Master should be in Auto
 EHG should be on Auto and EHG in Power
control mode
 Unit load set point given from CMC console
 Fixed/sliding pressure set point given from
CMC console
Procedure for putting into CMC
For putting machine into CMC following loops
should be in auto:-
 Airflow control should be in auto (vanes and
master control).
 Furnace pressure control in auto (IGV and
CMC MODE

17. Other Conditions
 Select the LP mode (from EHTC page).
 PA header pressure control in auto.
 Both HPBP should be closed.
 Load deviation within limits (i.e. the deviation
between load SP and actual load should be less
than 12MW).
 MS pressure deviation within limits (difference
between MS set point and actual MS pressure
should not be high preferably within + 2kg/cm2).
 HPCV should be throttled (i.e. turbine should not
be running under valve wide open condition).
 Unit should be running under steady state (MW
and fuel flow are reasonably steady for about
10-15 minutes).
CMC MODE

18. Ensuring all these conditions and auto loop
status proceeding to the next step
 Put the CMC on(i.e. from the popup given on
EHTC page )
 Now put the boiler master in auto
 The selection of plant mode control will be in
manual.
 Then select the coordinate control from the
popup given on the load page (CMC page).
CMC MODE

19. Run Down
Run down is switched ON automatically
when the Process error(negative) i.e. Feed
water, Air flow etc. becomes excessive AND(&)
the controller output of the particular loop(feed
water, air flow, furnace pressure and fuel) goes
to maximum position making process
uncontrollable. Under the situation, Unit load
demand is reduced to a value as Permitted by
the Process to get over the blockage.
Increase Blocked
In this if any of the condition comes i.e. if
process error (negative) OR the controller output
goes to maximum then Incr. blocked will come
SALIENT FEATURES OF CMC MODE

20. Conditions for Run down/Inc. blocked
 Feed water flow deviation
 Airflow deviation
 Fuel flow deviation
 Furnace pressure deviation
 PA header pressure deviation
 Load control deviation
 Throttling pressure deviation
FEATURES OF CMC MODE

21. Run Up
Run up is switched ON automatically when
the Process error (positive) i.e. Feed water, Air
flow etc. becomes excessive AND (&) the
controller output of the particular loop (feed
water, air flow, furnace pressure and fuel) goes
to minimum position making process
uncontrollable. Under the situation, Unit load
demand is reduced to a value as Permitted by
the Process to get over the blockage.
Decrease Blocked
In this if any of the condition comes i.e. if
process error (positive) OR the controller output
goes to minimum then Decr. blocked will come
FEATURES OF CMC MODE

22. Conditions for Run UP/Dec. blocked
 Feed water flow deviation
 Airflow deviation
 Fuel flow deviation
 PA header pressure deviation
 Load control deviation
 Throttling pressure deviation
FEATURES OF CMC MODE

23. Runback
It is switched ON automatically in the event
of tripping of unit auxiliaries i.e. BFP, ID, FD fans
etc. and unit capability will reduce and
accordingly the unit demand will also reduce.
Conditions for Run Back
 One ID fan/ FD Fan/ PA Fan / BFP / CEP /Air
heater/CWP/BCW/ACW tripping = 100MW will
be reduced and Unit capability will be reduced to
350MW (60 % load).
 One feeder tripping=100MW will be reduced
from unit capability and accordingly the unit load
demand.
 Turbine tripping 100 percent load rejection on
turbine.
FEATURES OF CMC MODE

24.  Down Directional Blocking:
 3 element drum level control deviation < -
9.8%
 BFP scoop < 15 %
 Air flow deviation ( set value – actual value)
<- 9.8 %
 FD fan A or B blade pitch < 15%
 Furnace pressure deviation <- 9.8%

25.  Down Directional Blocking:
 ID Fan A or B hydro coupling % <15%
 Coal flow deviation <-10%
 Mill feeder rate < 15%
 Load control deviation <-20%

26.  Turbine Stress Controller ( TSC) calculates the
thermal stress developed in different
portion of turbine viz. HPT shaft, IPT shaft,
HPT casing , IPT casing, MSV and decides a
margin for load increment or decrement
depending upon instantaneous temperatures.

27.  Tm: - Mean temperature (°C)
 ti: - Inner surface temperature (°C)
 dt :- ti - tm
 It is obvious that during load increase;
mean temperature will be less than the
inner surface temperature. The opposite
will take place in case of load decrease.
 That means dt is positive for load increase
and negative for load decrease. If we plot a
curve of dt vs. tm, then the instantaneous
point can be define on it. The point must
be within the allowable limit define in the
curve.

28. Upper temp. margin
Lower temp. margin
dt
Present operating
Point (instantaneous)
(tmi , dtu)
(tmi , dtL)
(tmi , dti) tm

29.  Say, for tm being same as that for the
current point, the maximum allowable dt for
positive side is dtu and for negative side is
dtL
 Then upper temperature margin = dtu - dti
and lower temperature margin = dti - dtL .
 If these margins go down a minimum value,
TSC will restrict load increment ( for low
upper margin ) and load decrement ( for low
lower margin)
 While machine is on CMC mode, TSC
influences the load change rate looking after
turbine thermal stress.

30. PB/VPC
Tracking for
Runback /
Rundown Or
no CMC
1
2 ADD MIN MAX
CMC in
service
Gen MW
Defeat Switch
Freq.
Influence
MAX S.P. MIN S.P.
To next slide

31. From Previous slide
EHG Hold
Load Rate SP
Up/Down Dir
Block
Runback/ Rundown
Limit
MIN
1
2 2
1
Block
Grad
TSC Rate Min
Runback/Rundown Rate
Ramp
CMC demand

32. 1
2
D
Load. Dev
Steam
Pr. Dev.
ADD
PID
ADD Boiler
Master
For Changing load
For Steady State
D

33. 2
Dead Time
Delay
3
PID / P
ADD
MAX
MIN
+
-10MW
-
+10MW
2
EHG
Pr. Dev.
3 +ve Limit
-ve Limit

34. 1
2
1
2
Load Rate
Runback / Rundown
In Action
Runback in action
Runback Rate
Rundown Rate
MIN
Load Rate
SP Stn
PB/VPC
TSC Rate