LALITPUR POWER GENERATION COMPANY LIMITED
LALITPUR SUPERTHERMAL POWER PROJECT - 3 X 660 MW
Title of Document-: COORDINATED MASTER CONTROL SCHEME
LPGCL DOC. Number-: BE-LAL-EIV-101-J-0032 Package Name-:
BHEL DOC. Number-: PE-DG-375-145-I350 TCE DOC. Number-:
TATA Consulting Engineering Ltd.
73/1, ST. Mark’s Road
Bangalore-560001, INDIA.
BHARAT HEAVY ELECTRICALS LIMITED
PROJECT ENGINEERING MANAGEMENT, NOIDA.
00 05.01.2013 AM SCS DP
REV
DATE STATUS INTLS SGN INTLS SGN INTLS SGN INTLS SGN
NO.
ISSUE
PREPARED BY CHECKED BY APPROVED BY
AUTHORISATION
DOCUMENT TITLE DOCUMENT PE-DG-375-145-I350
NUMBER
COORDINATED MASTER CONTROL
REVISION
SCHEME NUMBER
00 DATE 05.01.2013
3X660MW LALITPUR STPP SHEET 8 OF 9
WRITE – UP
The main objective of the coordinated control is to operate the turbine – generator and the
steam generator AS AN INTEGRAL UNIT. The desired generation of the boiler turbine
combination will be established either by the operator Unit Load Demand setter (Unit Master)
or by a remote Automatic load dispatch system (ADS). The desired generation signal
(Target load) will be subjected to following limits:
a) Operator set maximum generation limit (MW)
b) Operator set minimum generation limit (MW)
c) Maximum rate of change (MW per min.).
When in Load Dispatch mode, the maximum load setter will limit the load desired by load
dispatch system to permissible values as per Plant Conditions. Load rate setter shall allow
ADS, to obtain slow / fast load change rates.
When in Operator mode, the new desired load will be set manually, through Unit Master.
Desired rate of change of load shall also be set manually from the Load rate setter. In case
Unit capacity, as set by the process, is less than manually set / automatic values, the
minimum will be taken as Unit Load demand.
The desired generation demand signal is further modified with the generation error (TSE
load margin) and frequency influence, which will be adjusted manually to match the speed
regulation inherent in the turbine governor. The modified generation demand signal is then
fed to a RAMP circuit for generation of Unit Load demand. The RAMP circuit is provided with
‘up / down directional blocking’, to regulate unit load demand during process disturbance.
As the response of turbine is faster than boiler, a second order delay is included in the
turbine demand to match with boiler.
The unit load demand is fed to boiler master to generate Boiler demand i.e. Air, Feedwater &
Fuel requirement.
The Boiler demand is modified by a throttle pressure correction by means of PID control from
throttle pressure set point and the actual value derived using redundant transmitters.
In case of unit disturbance, Run down / Run back condition are generated and the unit
demand is automatically reduced to low limit as permitted by the process. When the load
shedding relay is operated, the Unit is run under house load operation.
MODES OF CONTROL
The control system envisages following modes of operation which are selectable manually:
1. COORDINATED MODE
In this mode both Boiler Master and Turbine Control are put in `Auto’ and Unit load
demand is fed to both Boiler and Turbine to compute their individual load demands.
In addition to it, Boiler is given Throttle Pressure error for fine adjustment of the
demand. When the system is in coordinated control mode, all Run-ups and Run-
downs, load rate of change, frequency error, generation error and throttle pressure
error will function automatically.
DOCUMENT TITLE DOCUMENT PE-DG-375-145-I350
NUMBER
COORDINATED MASTER CONTROL
REVISION
SCHEME NUMBER
00 DATE 05.01.2013
3X660MW LALITPUR STPP SHEET 8 OF 9
If a run back action occurs while in CMC mode, it will bring the unit, down to runback
/ rundown limits and gradients corresponding to various RUN back and RUN down
conditions, will be applied.
2. BOILER FOLLOW MODE
In this mode, the Turbine takes lead and the boiler follows. It is adopted when
Turbine Load setpoint is in local mode. The Boiler follow and Turbine follow modes
are interlocked, so as, not to be activated at the same time.
The turbine sets the MW load and the boiler controls throttle pressure as a follower.
Whenever capabilities of TG are exceeded or limited, the boiler shall follow the
turbine load.
3. TURBINE FOLLOW MODE
In this mode, the Boiler takes lead and the turbine follows. It is adopted during Run
back situation. The boiler controls MW, while the turbine maintains throttle pressure.
4. MANUAL MODE
In this mode, both the Boiler master and turbine controller are switched over to
manual and unit is controlled manually.
5. RUN DOWN / RUN BACK
‘Run down’ is switched ON automatically when the Process error i.e. Feed water
flow, Air flow, Fuel flow, Furnace pressure etc. becomes excessive and the control
element goes to maximum position making process uncontrollable. Under this
situation, Unit load demand is reduced to a value, as permitted by the process, to get
over the blockage.
Similarly, ‘Run back’ is initiated automatically in the event of tripping of unit auxiliaries
i.e. BFP, IDF etc. to match unit demand with reduced unit capability.
‘Up / Down directional blockings’ are introduced, whenever process parameters i.e.
Feed water, Air flow etc. become Higher/Lower than permitted. This is done to ‘hold’
the unit load demand, till such time the process recovers.
6. THROTTLE PRESSURE CONTROL
Fixed or Variable Pressure mode of operation can be selected from the Pressure
setter. With Fixed Pressure operation, the set point can be fixed manually while in
Variable Pressure operation, Variable Pressure set point is generated using the load
index. The actual pressure is measured by 3-redundant transmitters (located at
Turbine end, before strainers) and mean value is taken as Process value. The
pressure error is given to Boiler Master / Turbine Controls, as required by the
operation mode mentioned above.
