1. 2.CONCEPT FOR DADRI GAS STATION CONTROL SYSTEM
TELEPERM ME PROCESS CONTROL SYSTEM
Control System Configuration
The control, protection and monitoring functions for the gas turbine generator, boiler water steam cycle &
steam turbine are implemented by using the digital process control system TELEPERM ME.
Depending on the tasks involved, functions are implemented by an AS 220 EHF, AS 220 E or AS 231
2.1. AS 220 EHF Automation Sub system – Characteristics
AS 220 EHF automation subsystem uses three independent central processing units (CPU) which operate
redundantly with synchronous clock pulses and commands and perform 2–out–of-3 voting on all input and
output signals. This ensures high availability for and fault- tolerant processing of functions of the central
section. In the event of work on one central processing module, the central section continues to operate with
The central section transmits signals to the extension units in the periphery via a triple I/O bus, these units
serving as interfaces between the automation subsystem and the process. Input to the extension units is via
2–out–of-3 voter modules. The extension modules contain binary and analog input and output modules.
Signal coming from the process are input on one or two channels into different extension units as
appropriate to their priority in terms of availability and safety. The same applies to signals to the process. In
the same way, the periphery is designed with one or more channels and appropriate redundancy configured.
For special applications (control interfaces, fast sub loop controls, HAS group alarms), modules with a
dedicated processor are used which operate in 20 ms cycles and which continue their operation even on
failure of the bus subsystem to the central unit.
Selective fault localization is ensured be LED fault indications on the module front plates and output of I/C
fault alarms on a special printer.
Any defective modules are annunciated individually and can be replaced on line.
2. System power supply is via dual redundant + 24 V DC sources. All modules have plug connectors.
The system allows easy process operation and monitoring using colour monitors and process operation
2.2. AS 231 Automation Sub system – Characteristics
The AS 231 automation subsystem is a special version of subsystem AS 230 and is designed for acquisition
of a large number of messages and alarms, criteria and statuses. Input from subsystem AS220 EHF is via
local bus interface module N8 in the form of MKS message generated in subsystem AS 220 EHF.
Output is in chronological order on a PT 89 logging printer with text storage or on a monitor of the
monitoring system (OPTION).
In addition, the firmware for the AS 231 allows implementation of calculations such as those required for
the gas turbine overhaul clock with dynamic operating hours evaluation.
3. 3.VARIOUS CYCLE AT POWER STATION
Gas Turbine Central Functions
The following central functions are processed by automation subsystems AS 220 EHF and AS 231:
o Binary controls
o Gas turbine protection system
o Hardwired alarm annunciation system (HAS)
o Overhaul clock
o Closed – loop controls
o Analog data processing
A Binary Controls
The binary controls for the gas turbine include control interfaces, protective logics, break current and make
current trip circuits, sub loop controls and subgroup controls.
Documentation for these controls is provided in the form of functional diagrams.
B Control Interface with Protective Logics
The control interface functions for
o Motors and circuit breakers
o Solenoid valves
Are implemented on calculation modules 6DS1 717/719 at the I/O level with dedicated function blocks
(software) available for the type of driver concerned.
Each pair of modules can control
o 4 motors or circuit breakers or
o 4 actuators or
o 5 solenoid valves
The control interface modules receive either direct manual input commands from the local control station or
commands via the CS 275 bus from a central operation and monitoring system (Option) in the control room.
4. Protection commands and enabling signals from the protective logic and automatic commands from the sub
loop controls and the subgroup controls also act on them.
At the control interface level these commands are gated appropriately for their priority and admissibility and
control commands transmitted to the interposing relays in the switchgear. The control interface receives
position check backs from the switchgear or actuators and then monitors and processes these. The check
backs are passed on to the local control station, the operating system and to the protective logic and
functional group controls. The protective logic prevents any inadmissible operating conditions and
switching operations; it intervenes directly at the control interface. Protective logics cannot be deactivated
and are therefore effective at all times.
A distinction is made between active (commands) and passive (enabling signals) protective logic:
Active protection commands cause actuators and plant components to transfer to a safe operating status as
soon as faults in the process occur.
Passive enabling signals prevent the plant from being brought into an inadmissible state either by manual
action or by automatic control action.
Active and passive protective logics required for drivers mainly programmed on the module concerned;
very important trip criteria from the can also be switched directly to the module. In addition, higher level
protective logics for the actuators are also implemented in the central unit.
C Protective Logics
Non drive-related protective logic such as OFF commands and enabling signals for other gas turbine
systems (frequency converter, gas turbine controller, generator protection etc.) and operating mode selection
are mainly implemented in the central unit and are linked with the individual devices via the I/O level.
D Break Current and Make Current Circuit Trip Circuits
The functions of the trip circuits are implemented in the central unit (two-out-of-three logic) and on two
independent channels on the output side up to the trip solenoid valves in trip oil circuit.
o The break current trip circuit essentially comprises the flame safeguard system as approved by the
German Technical Inspection Agency (TUV) and a monitoring system for the type of fuel being burned
(fuel starvation monitoring).
The break current trip circuit in effect forms a redundant function relative to the make current trip circuit.
The break current trip circuit outputs with relay modules, installed in several extension units act on pilot
valves of fuel oil and for fuel gas for the associated trip valves. The outputs of these trip circuits certified as
fail safe by the TUV are continuously monitored by special test programs of the AS 220 EHF.
The two- Channel configuration of these break current output circuits maintains availability of the gas
turbine generator without degrading safety.
5. o The make current circuit processes all criteria for gas turbine trip including manual trip initiation,
trip commands from the gas turbine protection system, etc.
The outputs are also implemented in two channel configuration and activate solenoid valve in the trip oil
circuit which causes the two fuel stop valves to close as soon as trip oil pressure drops.
E Subloop Controls, Automatic Changeover Controls, Drive
Subloop Controls are automatic controls which causes drives and circuit breakers to be switched on or off or
which send commands to actuators or solenoid valves as a function of process parameters such as pressure,
temperature and speed.
Subloop controls can be switched on and off either by hand or by means of automatic devices such as sub
group controls. For safety reasons, some special subloop controls can not be switched off during gas turbine
operation (e.g. turbine oil supply system)
The switching status of subloop controls is monitored as a function of operating criteria; an alarm is
generated in the event of an inadmissible status.
Depending on the time characteristics required for automatic actuation or changeover, subloop controls are
implemented either in the central unit or in a calculation module within the periphery. The “auxiliary power
changeover” subloop control with critical time needs, for example, is processed calculation module with out
any signals from the central unit.
The automatic changeover controls are implemented with the same criteria. These controls serve for
automatic selection of the pump to be activated and automatic activation of a standby pump on pump failure
where more than one 100% duty pump is provided.
Actuation of drive groups (Several drives of the same type to be energized or de-energized simultaneously)
is also performed by subloop controls which transmit commands for the desired switching or operating
status to the control interfaces of the individual drives.
Such drive groups include compressor dampers, fan for bearing oil coolers, generator cooling air dampers.
F Subgroup Control for Gas Turbine Start-up and Shutdown
Fully automatic start-up of the gas turbine generator from standstill and run-up to rated speed with
synchronization and loading to the preset set point is implemented by the “OPERATION program” of the
SGC. The “SHUTDOWN program” permits controlled unloading of the gas turbine down to fuel valve trip
turning operation and ensures turbine readiness for restart.
The “OPERATION” and “SHUTDOWN” programs are implemented in logic steps to ensure low–stress
gas turbine start-up and shutdown in an optimum time as a function of time and process conditions.
Processing of the program steps is strictly sequential, issuing commands to the process and moving to the
next step on receipt of appropriate checkbacks and/or step criteria from the process.
A digital step display at the local control station or remote control station or within the operating and
monitoring system (option) allows the operator to follow the program.
6. A waiting period can be set for each step to allow the program to be clocked with configurable clock pulses.
A monitoring time can be selected for each step to define the interval during which procession to the next
step should take place. If this monitoring time is exceeded, the alarm “SGC running time exceeded” is
generated and the step condition that has not been fulfilled is printed out by the logging printer together with
date, time, step number, identifier code and clear text.
The following essential functions are implemented in the SGC control coordinator module:
· As a prerequisite for gas turbine start-up a number of “STARTING CRITERIA” have to be
fulfilled, otherwise these signals are printed out by the logging printer together with date, time,
identifier code and clear text on issue of the start command.
· In the event of forced gas turbine shutdown (trip) by hand or by the protection system, the SCG
automatically changes over to the “SHUTDOWN” program. It then remains at the step in the
“SHUTDOWN” program which corresponds to the current state of the process.
· The SGC can be switched on or off at any time, irrespective of plant operating state.
When the SGC is switched off during plant operation, the plant remains in the state in which at was
when the SGC was switched off; when the SGC is switched on again, the program goes straight to
the step in the operating program which corresponds to the current gas turbine conditions. The
same occurs when the SGC is switched off during plant shutdown.
Step sequence and program structure for the SGC are documented in functional diagrams, when manual
start-up of the gas turbine is required; these functional diagrams can be used as check lists for the -stating
sequence (operator guide).
The entire SGC program runs in the central unit with two-out-of-three coincidence logic.
G Analog Data Processing
All important process variables are read in to the central unit of AS 220 EHF automation subsystems. These
can then be used in software processing.
Analog functions: - Gas turbine protection
- Measuring point selector switches for
Turbine and generator
- Seal air temperature monitoring
- Thermostat monitoring
- Limit monitoring
- Monitoring of process via operation and monitoring system
H Gas Turbine Protection
The gas turbine protection system is provided to
- detect incipient irregularities
- to take automatic action to prevent these from escalating into
- to relieve operating personnel of the need for fast decision making
The bearing temperature protection circuit monitors the metal temperatures of the turbine, compressor,
thrust and generator bearings for pre trip alarm and trip limits.
In the event of unacceptable temperature increases up to the pre trip alarm and trip limits, this results in
- a pre trip alarm (high)
- initiation of turbine trip and a trip alarm (hihi)
trip initiation prevents serious damage to the bearing and consequential damage to the gas turbine and
The bearing housing protection circuits monitor absolute vibration velocity for the turbine, compressor and
generator bearing housing against pre trip alarm and trip limits.
Vibration velocity is a measure of quite running of the gas turbine generator unit. If the vibration velocity
increases to above the pre trip alarm and trips limits, this result in issue of
- a pre trip alarm (high)
- initiation of turbine trip and a trip alarm (hihi)
Trip initiation here likewise prevents serious damage to the gas turbine generator unit. Unacceptable
vibration can be caused, for example by unbalance or blade failure. For technological reasons, trip initiation
by the vibration protection circuit is not initiated until vibration velocity has exceeded 8 s -1.
Turbine outlet temperature protection circuits monitor the temperature of the exhaust gas downstream of the
turbine against pre trip alarm and trip limits. To drive the corrected turbine outlet temperature (OTC) to the
formula (OTC = f(TC)), the compressor inlet temperature (Tc) is required. In addition, actual turbine outlet
temperature is measured and compared with corrected turbine outlet temperature. If measured turbine outlet
temperature exceeds the corrected turbine outlet temperature, this result is an issue of
- a pretrip alarm (high)
- initiation of turbine trip and a trip alarm (hihi).
Trip initiation here once again prevents serious damage to the turbine.
8. AS220 E Automation Subsystem – Characteristics
In addition to AS 220EHF in boiler, water steam cycle, steam turbine & switchyard operation AS 220E
control system is installed.
Application and general notes for system design.
The control function associated with the automation of processes, such as open –loop control, close –loop
control calculation and monitoring, can be solved with the AS 220E automation subsystem using function
blocks and input/output modules.
When used as an autonomous system, the AS 220E subsystem processes additional functions such as:
- Process operation and monitoring
- Alarm output and logging of faults
- Configuration and documentation
The mechanical design of the AS 220E subsystem is:
- One basic unit (subrack with central unit modules and 5 locations for I / O modules)
- Up to 6 extension units (subrack with up to 14 locations for I/O modules). Up to 87 I/O modules
can be inserted.
The basic unit and the extension units are installed in one or two cabinets.
Signal exchange between the basic unit and I/O section takes place via the I/O bus.
The power supply is 24V can be applied in a redundant manner.
Functionally distributed structures can be implemented by combining several AS 220 E automation
subsystem; these structures can be locally centralized or distributed. Coupling together of automation
subsystems and to OS subsystems used for central operation and monitoring takes places via the CS 275 bus
subsystem. Hard-wire connection of the automation subsystems to the process and the switchgear is via the
input/ output modules. Hard-wire connection can also be made from the input/output modules to other
automation subsystems, to the process computer and to the equipment in the central control room.
9. The cables to the process, to the control room, the switchgear, the protective interlocking etc. are connected
via cabinet connection elements *SAE). Connection to the CS 275 bus subsystem is made via bus
converters accommodated in the cabinet power supply unit.
The mode of operation of the AS 220E automation subsystem is determined by the function blocks and the
I/O modules. Coordination functions are implemented in the central unit using function blocks, and lower
level control function at the I/O level using I/O modules. A hierarchical division of the functions is thus
provided by the hardware, and the functions of the individual levels are clearly defined.
The central unit, consisting of function blocks and basic organizational functions, constitutes the unit
coordinator, the group and subgroup control levels within the hierarchically designed control and
The function blocks stored in EPROMs are processed cyclically and/or a cyclically by the central processor
according to the user structure. These blocks (software) correspond in function to modules (hardware) of
conventional modular systems such as TELEPERM C and ISKAMATIC B. Example of such blocks:
Integrator, differentiator, controller, adder, extreme-value selector, logic blocks, command blocks, step
Using a configuring device the function block can be “linked” together to configure the automation
Further internal, basic organizational functions are stored in the automation subsystem in addition to the
function blocks and enable – unobserved by the user – the sequencing and utilization of the function blocks
and the configuring instructions.
Since the function blocks are processed sequentially, they can be used more than once without additional
extension of the hardware within the following limits:
- The maximum possible number of I/O modules
- The maximum available RAM capacity
- The maximum processing time available per basic cycle.
The input/output section, consisting of I/O modules, constitutes the link within the hierarchically designed
control and instrumentation structure.
Process – oriented functions such as
- Signal conditioning and distribution
- Analog calculation functions and binary logic
- Individual controls with bus – independent operation and monitoring as well as
10. - Monitoring and indication of faults on the I/O modules
belong to the functions of the I/O level in addition to the transfer of signals to and from the central unit.
Above all, the I/O modules provided for use in power plants enable the implementation of a process-oriented
lower automation level. High availability of the I/O level is achieved as a result of the proven
modular design of the I/O modules.
The function of the I/O level is not influenced by a fault or by an operational shut-down of the central unit
since it can operate fully autonomously.
4. Governing system
ISKAMATIC-A & B control system is installed for GT, ST & HP/LP bypass governing and control
systems. Brief description of GT governing system application is given below.
A Task of control system
Gas turbines are used for driving generators in all possible modes such as:
- Base load
- Intermediate peaking load
- Peak load or as
- Reserve generating capacity
The control system is designed to perform the following tasks:
- Start-up fuel feed forward control above 33% nominal speed up to synchronizing speed.
- Turbo generator speed control during synchronization or on load rejection.
- Load control operation within allowable loading rates
- Turbine outlet temperature control to a pre-determined allowable level
- Possibility of operation with a second fuel
- Load control is appropriate to grid conditions on “stable grid”; “islanding” in the event of grid
B Layout of Control System
11. The turbine generator control system is electro hydraulic. This design combines the advantages of electronic
hardware, adaptability, ease of implementation of complex functions, very good dynamic control
performance, etc. with the merits of hydraulics – smooth control of large actuating forces.
Where necessary the gas turbine generator may be controlled by means of the hydraulic governing system
It is recommended to keep only one of the two control system in operation at any time in order to prevent
mutual interference. The isolating valve is provided for this purpose.
Fully automatic control of the turbine generator during start-up and shutdown is performed exclusively by
mean of the electro hydraulic control system.
C Start-up with the Electro hydraulic Controller
The gas turbine generator is accelerated synchronously by means of the static frequency converter. In this
process the turbo generator is run as a “converter – fed motor”.
At approx 20% turbine generator speed the fuel stop valve is opened and the main flame lit. Above approx.
33: turbine generator speed the turbine generator is run up to nominal speed by the “start-up fuel feed
forward controller” by continuous opening of the control valve. The frequency converter runs the turbine up
to approx. 70% speed.
The speed controller takes control of the turbine generator when nominal speed has been reached.
Loading by means of the load controller is affected once the speed controller has established synchronous
speed and the turbine generator has been synchronized with the grid. The turbine generator is then run up to
target load along the desired gradient (normal of emergency) by applying a load set point from the set point
controller. The temperature controller is on standby over the entire operating range of the speed open loop
and closed loop controls and load control in order to reduce turbine generator load to an allowable level in
the event of impermissible temperature loadings.
D Electro hydraulic Converter
The electrohydraulic converter (EHC) is the interface between the electro hydraulic turbine controller and
the hydraulic section of the control system. The output signal of the “EHC valve lift controller” energizes a
permanent magnet plunger coil system which acts on the mechanically connected control sleeve. Hence the
plunger coil converts the controller electric signal into travel (lift). A change in position of the spool valve
causes a change in position of the servo piston thus alerting the drain cross-section of the follow-up piston
which then changes the secondary oil pressure. This changed oil pressure acts on the spring-loaded spool
valve in the control valve which in turn alters the valve lift via the servo piston.
The lift of the servo pistons in the electro hydraulic converter and control valve (CV) is measured by means
of a travel transducer on each and is processed as the actual lift by the “EHC lift controller” and “CV lift
12. E Electro hydraulic Controller
The gas turbine generator electrohydraulic controller (GTC) contains the control circuits for:
- Speed under start-up fuel feed forward control
- Generator load/frequency
- Limit temperature of exhaust gas
- Fuel control valves
These various control systems are completely isolated from one another by means of control transfer
A electro hydraulic controller is an analog controller made up of ISKAMATIC A and B modules.
All modules are housed is one cabinet.