Field of Invention:
The present Invention relates to governing of steam turbines and a configuration
of Triple Modular Redundant (TMR) Turbine governing system of Steam
Turbine having 6 governing valves [2 for each High pressure (HP), Intermediate
pressure (IP), and Low pressure (LP) stage] for Triple pressure Steam Turbine.
Particularly, the Invention relates to a microprocessor based electronic control
system for triple pressure steam turbine having TMR architecture. The present
Invention is implemented with state of the art technology using TMR architecture
for governing controls.
Background of Invention:
Prior Art:
In the prior art, electronic turbine-governing system is generally implemented as
microprocessor based single channel control which does the job of turbine
rolling, synchronizing to the grid and loading the turbine as per load dispatch
center requirement. This single electronic governing control system has a
complete mechanical back up governor. This means even if electronic governing
control system fails, steam turbine can be governed with the help of backup
mechanical governor.

But now a days back up mechanical governor is not offered due to the presence
of compact, self-contained actuator (direct final element control) which requires
only high-pressure control oil. Also this provides better economical advantages.
In this electronic governing system, any single failure i.e. processor, module,
signal channel or any field transmitter does not guarantee the proper functioning
of the prior electronic governing control system.
Comparison of Prior Art and Invention:
In view of this, electronic governing control system plays an important role in the
absence of back up mechanical governor as far as availability and reliability is
concerned.
Also any single failure i.e. processor, module, channel or any field transmitter,
does not affect the proper functioning of the Triple modular Redundant (TMR)
electronic governing control system. This adds to the availability of governing
system for the power plant.
Fault detection is difficult in dual redundant system as compared to the triple
redundant system by the way of mid out of three selections.
The present invention (Electronic Governing System) governs 6 control valves as
compared to 4 control valves of prior governing system.

The present invention (Governing System) governs triple stage pressure
governing i.e. HP, IP and LP stages whereas prior art governing systems govern
two pressure stages.
Objects of Invention:
It is therefore an object of the present Invention to propose a method for turbine
governing system to meet the matching-governing requirement.
Another object of the Invention is to propose a method for turbine governing
system, which gives more reliability and availability.
A further object of the Invention is to propose a method of Triple Modular
Redundancy, which is implementable in 1 out of 3 configuration to ensure safety
and reliability of the high pressure control oil based governing system.
A still further objective of the Invention is to propose a method of fault free
functioning on any single failure i.e. processor, module, channel or any field
transmitter.
A further objective of the Invention is to propose a method of governing 6 control
valves as compared to 4 control valves of prior governing system.
A further objective of the Invention is to propose a method of triple stage
pressure governing i.e. HP, IP and LP stages.
Brief description the accompanying drawings:
The illustrations accompanying this Invention are explained as below:
Fig-1: Form2000ation of Electro Hydraulic Turbine Controller (EHTC) TMR
position controller
This figure forms a position controller for governing control valve coil i.e. High-
pressure control valve (HPCV1) coil-1. As there are two coils for each control
valve and such 6 control valves are existing as shown in figure 2, there are 12

such position controllers. This figure demonstrates the flow of controlling TMR
output to field with hardware position controller.
Fig-2: Overall valve arrangement
This figure shows the stop valve and control valve combination assembly for
High-pressure stage (2.01, 2.02, 2.03, 2.04), Intermediate-pressure stage (2.05,
2.06, 2.07, 2.08) and low-pressure stage (2.09, 2.10, 2.11, 2.12) steam turbine.
Finally this invented method and product will govern steam inputs to the control
valves as shown in 2.02, 2.04, 2.06, 2.08, 2.10, and 2.12.
Fig-3: EHTC TMR Block Diagram for triple pressure steam Turbine
This figure shows block diagram of Electro-Hydraulic Turbine Controller for triple
pressure steam turbine along with controller tracking from other TMRs. This
figure also demonstrates the various controllers like speed controller, admission
controller, and pressure controller for HP, IP & LP stage and HP exhaust temp
controller along with switching circuitry. This logic is implemented in each control
island with changes as applicable in the tracking circuitry.
Fig-4: Hardware implemented position controller for control valve coil
(HPCV1 coil 1).
This figure shows Hardware implemented position controller for HPCV1 coil 1.
Such 12 position controllers for 6 control valves reside in the cubicle as shown in
FIG 5b. These position controllers govern the control valves shown in FIG2.
Fig-5: Photographs of the hardware control panels.
This figure shows suit of 5 control panels (CJJ21, CJJ22, CJJ23, CJJ24 &
CJJ25) forms the invented product which consist of:
CJJ21: EHTC TMR1 (microprocessor based)
CJJ22: EHTC TMR2 (microprocessor based)
CJJ23: EHTC TMR3 (microprocessor based)
CJJ24: EHTC INTERFACE panel (Hardware controller based)
CJJ25: EHTC MONITORING panel (microprocessor based)

Microprocessor based EHTC TMR1, EHTC TMR2 and EHTC TMR3 all are
identical & symmetrical as shown in Fig 5a. EHTC INTERFACE panel (Fig 5b)
covers the hardware controllers of various control valves as indicated in figure 4.
Microprocessor based EHTC MONITORING panel monitors various feedback,
faults and decides for TMR changeover strategies.
The invention will now be described in an exemplary embodiment as
depicted in the accompanying drawings. There can however be other
embodiments of the same invention, all of which are deemed covered by
this description.
Detailed Description of the Present Invention:
In the present invention, a method and system have been disclosed for turbine
governing system software and hardware in TMR configuration, which take care
of all possible causes of hardware failures.
The applicant has introduced High Pressure Governing System i.e. 160 Bar
Electro Hydraulic Actuator (EHA) for HP, IP & LP valves of 129 MW Triple
pressure K-N series Steam Turbines with High pressure IP&LP Bypass system.
This Invention meets the matching control requirement, which has been designed
and engineered using C&l system for 6 governing valves steam turbine in Triple
Modular Redundant (TMR) configuration. This Invention is implemented as suite
of five cubicles to reduce inter-panel cabling and ease for testing and
troubleshooting.
Processing of Electro Hydraulic Turbine Controller (EHTC) logic is done in three
independent Control Island i.e. EHTC TMR1, EHTC TMR2, and EHTC TMR3.
Each Control Island consists of a Processing Unit and associated input / output
modules. Triple analog signals for Speed, Load, HP Inlet Pressure, IP Inlet
Pressure, LP Inlet Pressure, HP exhaust Temperature from field and remote
setpoints from higher level system are acquired, multiplied and connected to
each Control Island. In each Control Island, following controllers are implemented
as shown in figure 3:
Turbine Startup and Load Limiting Equipment (TSLLE) (3.20)
Speed Controller (3.03),
Admission Controller (3.09),
HP inlet Pressure Controller (3.12),
IP inlet Pressure Controller (3.14),
LP inlet Pressure Controller (3.16) and
HP Exhaust Temperature Controller (3.18).
The above controllers are described in details as follows:
TSLLE (3.20):
TSLLE ensures safe startup and shutdown of stop and control valves as shown
in figure 3. It ensures during startup, the sequence of opening the SV (Stop
Valve) before the CV (Control Valve) and subsequently during shutdown, of
closing the CV before the SV. Different limit signals are generated from the
TSLLE for different operations. With the reaching of a limit signal, the ramp
generator is stopped until the corresponding check back is available. Only then it
does proceed to the next limit signal.
TSLLE performs the following task:
? Triggering the turbine trip system and individual trip solenoid valves of each
actuator
? Providing interlocking signals for individual actuator Controls for opening and
closing of the turbine stop valves
? Providing an analog position value for each CV for limiting the valve position.

The TSLLE corresponds in its function to a ramp generator of output signal = 0 -
102% It can function automatically as well as can be operated manually from the
control room. Functionally, it corresponds to the starting and load-limiting device
of the conventional governing system.
Speed controller (3.04):
A Speed Reference NR (3.01), Time Dependent Speed Reference NRTD (3.02)
and Speed Actual NACT (3.05) essentially forms this controller. The integrated
functions of these blocks are explained below. The NRTD (3.02) is generated
from the NR (3.01) value. The desired NR value is set remotely from the operator
workstation.
During synchronization, speed reference setter can also receive Raise or Lower
commands from Auto Synchronizer. The time constant of the speed reference
setter is increased in the synchronization range to enable precise adjustment of
speed value to match with the grid frequency.
The speed reference signal (3.01) is juxtaposed with the output from the Turbine
Stress Controller (TSC) at every instant and a NRTD (3.02) is generated
corresponding to the highest permissible rate of speed increase which is
consistent with the safe operation of the turbine. After attaining the target
reference speed the output of the time delayed speed reference is held constant.
A simulated TSC margin of 15 K is given to the NRTD (3.02) in the event of fault
in TSC. This means that the Turbo Generator (TG) set is operated in a
conservative manner till the TSC fault is removed.
The speed controller essentially compares the speed reference generated by the
time delayed speed reference circuit and the actual speed of the turbine and
accordingly provides an output for the valve lift controller. The speed controller
exhibits a steady state proportional response to form the necessary droop

characteristics. The dynamic response is improved by the addition of proportional
and differential elements.
The speed controller realizes the following operations -
? Start up and shut down of the turbine
? Synchronization of the generator
? Provides a minimum load operation
? Operation of the turbo-set in the complete power range in case admission
controller is defective
? During load shedding
? House load operation
Admission controller (3.09):
The output of the admission set point controller takes over control of the turbine
immediately after synchronization of the turbine generator with the power system.
This function allows valve lift and thereby load to be increased continuously up to
the point at which the pressure controller takes over control of the turbine.
The admission set point Ad (3.07) is set by the output of the set point adjuster.
The set point can be adjusted manually from operator workstation. The set point
adjuster also accepts automatic set point change commands from the unit
coordination control. The admission set point is displayed on the MMI in the
control room.
The Time Dependent Admission Reference Ad td (3.08) value from the
admission set point control tracks the input signal Ad, with the rate of change
governed by the admission set point rate. This admission set point rate
(admission gradient) can be adjusted from operator Workstation. The rate can be

adjusted to anywhere between zero (minimum) and maximum permitted
admission rate (approx. 10% permin).
The admission set point rate adjuster can be activated or deactivated from the
operator Workstation. When the admission set point rate adjuster is activated,
the maximum permitted admission rate becomes effective.
The output of TSC also acts on the admission set point. The TSC component
acts on the set point changes in both directions, with the upper margin acting on
valve opening speed and the lower margin on valve closing speed. If the upper
margin should become negative during valve opening, the valve output by the
admission set point controller is automatically stopped. This ensures loading and
unloading at maximum possible rate, but without exceeding maximum permitted
thermal stress limits. The effective rate of change for the admission set point is
given by the output of a MIN gate which links the TSC component and the set
admission set point rate. The output signal from the admission set point controller
is passed on to the control transfer circuit via a switch for" Admission control -
ON/OFF" (3.06).
The output of the admission set point controller (3.09) is inhibited on the following
conditions:
? When the pressure controller (3.12, 3.14, 3.16) takes over control of the
turbine during loading of turbine.
? When the TSC is faulty but TSC influence is ON.
The output from the admission set point controller (3.09) is automatically set to
zero under the following conditions:

? If the admission set point is deactivated for more than 3 s.
? After the speed controller takes over control of the turbine during shutdown.
When the speed controller (3.03) is in action, the admission set point controller
can be activated or deactivated as required from the operator workstation. The
admission set point should always be kept activated in normal operation, as
selection of the controller to take control, which is implemented by the control
transfer circuit.
The output of the admission set point control is automatically deactivated under
the following operating conditions: -
? When the generator breaker is open.
? When the load shedding detected.
Deactivation of this set point causes the speed controller to immediately take
over control of the turbine generator. This action ensures that the turbine
generator speed will be held below trip speed under all conditions. If load on
power systems picks up again within a short period (approx. 3sec), the admission
set point is automatically reactivated. As the output signal effective on
deactivation was stored, this means that the status prior to load rejection is
restored immediately. In the event that generator actual load becomes negative
due to power system load swings (generator synchronized to power system and
supplying more than 2 % reverse power) the admission set point is immediately
deactivated.
Pressure control Loops:-
The pressure controller controls the turbine with respect to the main steam
pressure deviation and prevents a pressure drop e.g. during a quick load
increase. The controller is a PI controller.

A dedicated pressure controller (3.12, 3.14, and 3.16) is provided for each of the
HP, IP & LP turbines. The pressure controller for the HP turbine (3.12)
implements two different pressure control modes (Initial & limit press control
mode). The appropriate mode can also be selected as required. The pressure
controller for the IP & LP turbine operates as an initial pressure controller only.
In the initial pressure control mode actual pressure is compared with the
pressure set point. If actual pressure falls below the set point, the turbine control
valves are throttled to bring the pressure back to the set point. Generator loads
then stabilizes at a level, which corresponds to the steam generator power
available. In the limit pressure control mode the pressure controller tolerates
small size deviations from the pressure set point. It does not take action until
pressure drops more than set amount below the set point. The controller then
throttles the turbine control valves.
HP inlet Pressure controller (3.12):
The HP pressure deviation signal comes from the unit coordination control which
becomes the input to pressure controller in the initial pressure control mode. In
the limit pressure control mode the magnitude of the limit is first subtracted from
the deviation before this is passed on to the controller. Bump-less transfer
between the two operating modes is possible at all times. After changeover from
limit pressure to initial pressure control mode the pressure controller throttles the
control valve if actual pressure was below the pressure set point on changeover.
After changeover from initial pressure to limit pressure control mode the pressure
controller opens the control valves. This causes turbine control to be taken over
by the admission set point. This will not result in any change in turbine operating
conditions as long as the admission set point was matched to actual lift before
this changeover is performed.
IP inlet Pressure controller (3.14):
The IP pressure deviation signal comes from the unit coordination control, which
becomes the input to IP inlet pressure controller. This pressure controller output

forms the maximum opening of IP control valves. If the pressure controller
saturates to upward direction then IP control valves are controlled by the desired
final controller output.
LP inlet Pressure controller (3.16):
The LP pressure deviation signal comes from the unit coordination control, which
becomes the input to LP inlet pressure controller. This pressure controller output
forms the maximum opening of LP control valves. If the pressure controller
saturates to upward direction then LP control valves are controlled by the desired
final controller output.
HP Exhaust Temperature controller (3.18):
The valve lift configurations of the main steam valves relative to the reheat valves
depends on the correlation between the steam conditions in the main steam
system and in the reheat system under various operating conditions (startup,
shutdown and load rejection). To prevent rise in HP exhaust steam temperature
under such conditions, the valve position of the Intermediate pressure control
valve (IPCV) is trimmed as compared to the HPCV. The trimming of valve
position arrangement is done by means of a HP exhaust temperature controller
(3.18) which throttles the IPCV with the overshooting of an adjustable set value.
The controller is a PI controller. Initial set value of the HP exhaust steam
temperature is kept as 460° C, which is the interpolated function of HP shaft
temperature.
As shown in figure 3 and as described above speed controller, admission
controller, and pressure controllers outputs are gated through switching circuitry
(3.17) to form the final controller output (3.19). This final controller output and
TSLLE output are selected through min gate to generate position references for
HP (2.02, 2.04), IP (2.06, 2.08), & LP (2.10, 2.12) Control Valves. The HP, IP &
LP control valves opening are limited to manual reference set from workstation.

The final position reference from each control island (TMR) is selected as 1 out
of 3 TMRs depending on the healthiness status of the individual TMRs. Normally
when all the TMR channels are healthy, TMR1 position reference outputs are
selected through dedicated hardwired switching circuits. At this time, TMR2 &
TMR3 channels are operating as follow up controllers and will be tracking the
output of TMR1. Switching of active controller takes place based on fault
monitoring of each TMR. All the control algorithms are implemented in each
processor and the interface with the Operator Workstation (OWS) is through
network.
Analog voting of TMR output is achieved through specially designed Analog
voting cards as shown in figure 4.1 to meet the interface requirement of the High
Pressure Governing System. EHTC TMR changeover is achieved through
specially designed selection cards as shown in figure 4.2 to meet the interface
requirement of the High Pressure Governing System. Also position control is
achieved through specially designed position control cards as shown in figure 4.3
to meet the interface requirement of the High Pressure Governing System. All
these specially designed cards are mounted in one of the panels of suit of five
cubicles i.e. developed product as shown in figure 5b. Hence governing
requirement of both coils of all the control valves are driven by the separate sets
of hardwired controller as shown in figure 1 and 4.
Following are the Analog design inputs from the field or external system to be
acquired in each control island as shown in figure 5a for the embodiment.
1. Speed Actual ch1
2. Speed Actual ch2
3. Speed Actual ch3
4. Load Actual ch1
5. Load Actual ch2
6. Load Actual ch3

7. HP press Actual ch1
8. HP press Actual ch2
9. HP press Actual ch3
10. HP press Deviation ch1
11. HP press Deviation ch2
12. HP press Deviation ch3
13. IP press Deviation ch1
14. IP press Deviation ch2
15. IP press Deviation ch3
16. LP press Deviation ch1
17. LP press Deviation ch2
18. LP press Deviation ch3
19. Admission Ref ch1
20. Admission Ref ch2
21. Admission Ref ch3
22. HPS mid temp ch1
23. HPS mid temp ch2
24. HPS mid temp ch3
25. HP Exhaust steam temp ch1
26. HP Exhaust steam temp ch2
27. HP Exhaust steam temp ch3
28. Turbine Stress Evaluator (TSE) Upper Margin
29. TSE lower Margin

Following are the Analog design outputs to the field via position controller to be
available from each control island as shown in figure 5a for the embodiment.
1. HPCV1 position Ref1
2. HPCV1 position Ref2
3. HPCV2 position Ref1
4. HPCV2 position Ref2
5. IPCV1 position Ref1
6. IPCV1 position Ref2
7. IPCV2 position Ref1
8. IPCV2 position Ref2
9. Low pressure control valve (LPCV1) position Ref1
10. LPCV1 position Ref2
11. LPCV2 position Ref1
12. LPCV2 position Ref2
Following are the Digital design inputs from the field or external system to be
acquired in each control island as shown in figure 5a for the embodiment.
1. TSE Release ON
2. EHA OIL Supply Ready
3. Generator Breaker ON
4. Generator Breaker OFF
5. Tie Breaker ON
6. Tie Breaker OFF
7. Load Shedding Relay (LSR) Operated
8. TSLLE Raise
9. TSLLE Lower
10. Speed Ref Raise
11. Speed Ref Lower
12. Admission Ref Raise
13. Admission Ref Lower
14. Speed/Admission Ref Blocked
15. Over speed Test ON
16.TurbineTrip to EHTC
17. Turbine Reset to EHTC
18. Speed Actual ch1 fault
19. Speed Actual ch2 fault
20. Speed Actual ch3 fault
21. Turbine follow Boiler
22. Boiler follow Turbine
23. Run Back Active
24. Remote Set point ON [From Coordinated Master Controller (CMC) or Automatic
plant Startup (APS)]
25. Remote Set point Faulty (CMC or APS)
26.EHTC TMR1 controlling
27. EHTC TMR2 controlling
28. EHTC TMR3 controlling
Following are the Digital design outputs to the changeover circuit in switching panel
to be available from each control island as shown in figure 5a for the embodiment.
1. EHTC TMR Processor Active
2. EHTC TMR Processor Disturbed

WE CLAIM
1. An electronic governing system for triple pressure steam turbine
having TMR architecture comprising of a plurality of control
islands (EHTC TMR1, EHTC TMR2, EHTC TMR3), each such
control island comprising of
- Turbine Startup and Load Limiting Equipment (TSLLE),
(3.20),
- speed controller (3.03),
- admission controller (3.09)
- HP inlet pressure controller (3.12),
- IP inlet pressure controller (3.14),
- LP inlet pressure controller (3.16) and
- HP exhaust temperature controller (3.18),
characterized in that the said governing system ensures electronic
governing of start up and shut down of turbine in a safe manner
and synchronization of the generator without support of
mechanical governors and in that the electronic governing system
can continue to function without fault even in case of a single
failure of either processor or module or channel or any field
transmitter.

2. The electronic governing system as claimed in claim 1, wherein
the speed controller (3.03) operates depending upon a speed
reference (3.01), time dependent speed reference (3.02) and
speed actual (3.05), the time dependent speed reference
(3.02) being generated from the speed reference (3.01).
3. The electronic governing system as claimed in claim 1 and
claim 2, wherein the speed controller (3.03) oversees the
operation of the turbo-set in the complete power range if
admission controller (3.09) is defective.
4. The electronic governing system as claimed in claim 1, wherein
said TSLLE (3.20) ensures opening of the stop valve (SV)
before the control valve (CV) during startup and closing the CV
before the SV during shutdown.
5. The electronic governing system as claimed in claim 1 and 4,
wherein the TSLLE (3.20) corresponds in its function to a ramp
generator, can function either automatically or manually from
control room and corresponds to the starting and load-limiting
device of conventional governing system.
6. The electronic governing system as claimed in claim 1, wherein
the admission controller (3.09) takes over control of the
turbine immediately after synchronization of the turbine
generator and allows load to be increased continuously till the
pressure controller (3.12) takes over control of the turbine.
7. The electronic governing system as claimed in claim 1, wherein
the pressure controller (3.12) controls the turbine with respect
to the main steam pressure deviation and prevents a pressure
drop during quick load increase, the said pressure controller being a
PI controller.
8. The electronic governing system as claimed in claim 1, wherein
HP exhaust temperature controller (3.18) is a PI controller and
throttles the intermediate pressure control valve (IPCV) when
an adjustable set value is overshoot, thereby trimming valve
position arrangement to prevent rise in HP exhaust steam
temperature.

An electronic governing system for triple pressure steam turbine
having TMR architecture comprising of a plurality of control islands
(EHTC TMR1, EHTC TMR2, EHTC TMR3), each such control island
comprising of
- Turbine Startup and Load Limiting Equipment (TSLLE),
(3.20),
- speed controller (3.03),
- admission controller (3.09)
- HP inlet pressure controller (3.12),
- IP inlet pressure controller (3.14),
- LP inlet pressure controller (3.16) and
- HP exhaust temperature controller (3.18),
characterized in that the said governing system ensures electronic
governing of start up and shut down of turbine in a safe manner
and synchronization of the generator without support of
mechanical governors and in that the electronic governing system
can continue to function without fault even in case of a single
failure of either processor or module or channel or any field
transmitter.