The following functions are incorporated in gas turbine control system;
The functional description:
Startup Control
The startup control sets fuel commands for firing, warm-up, and acceleration limit for starting and accelerating the gas turbine to operating speed. The fuel stroke reference determined by the startup control is passed to the fuel system.
Acceleration Control
The acceleration control controls the acceleration rate of the gas turbine during the acceleration to operating speed. The acceleration control output is restricted by the minimum fuel limit to maintain flame.
Speed Control
The speed control controls the speed of the gas turbine at operating speed when the turbine is not synchronized to the power system. The speed control is restricted by the minimum fuel limit. When the turbine is synchronized, the speed control controls the load on the turbine.
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Load Control
The load control controls the load of the gas turbine to a selectable set point of spinning reserve, pre-selected, and max load set point with a base or a peak load limit based on temperature control. Load is controlled by changing the speed/load set point.
Exhaust Temperature Control
The exhaust temperature control regulates fuel in order to provide a controlled temperature increase or decrease and an upper limit for normal operation. The median value of the thermocouples sorted highest to lowest is the exhaust temperature feedback.
Inlet Guide Vane Control
The inlet guide vane (IGV) control modulates the IGV angle on a schedule of corrected speed, which is a function of the compressor inlet temperature and the gas turbine speed when the gas turbine is started up. The IGV control also modulates the IGV angle to maintain high exhaust temperature during part load. The load brings the IGV angle to open due to increasing exhaust temperature. The IGV control program depends on the operation type selected of simple cycle operation and combined cycle operation.
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Shutdown Control
At generator breaker open, the shutdown control ramps the current fuel stroke reference to the minimum fuel limit and ramps to fuel shutoff at a defined condition for the purpose to reduce the thermal fatigue duty imposed on the hot gas path parts.
Fuel Control System
The fuel stroke reference is passed to the gas and liquid fuel systems via the fuel control signal divider in accordance with the operator fuel selection of the gas and liquid fuel systems.
The gas fuel control system is composed of the gas fuel pressure control and the gas fuel flow control. The gas fuel control valve controls the gas flow, which is proportional to the fuel command.
The liquid fuel control system achieves fuel flow control by recirculating excess fuel from the discharge back to the pump suction through the bypass valve.
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Combustion Monitor
The combustion monitor detects abnormal combustion temperature patterns reflected downstream in exhaust temperature spreads.
Gas Turbine Protection
The gas turbine protection system prevents abnormal conditions, which could result in damage to the gas turbine. The critical operating parameters monitored by the protection system are temperature, speed, vibration, flame, fire, lube oil pressure and compressor operating limit. The running reliability of the gas turbine control system is also monitored. The protection system trips the gas turbine if its signal corresponds to a trip condition through the triple-redundant master controller.
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Based on the excellent functions described above, Toshiba's Gas Turbine Control System can provide the best controllability to minimize the thermal fatigue duty of the Customer's expensive hot gas path parts.
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