Development of a Control System for a Dual-Shaft Gas Turbine for Rapid Load Acceptance and Rejection

The application required large electrical load changes with very limited variations in frequency and voltage. With a dual-shaft gas turbine, nominal rating 8000 kilowatts, instantaneous loads up to 90 per cent rated were successfully accepted and rejected with frequency maintained within a one and one half per cent band. Voltage variation did not exceed four per cent. Frequency and voltage recovery were well within two seconds. The foregoing was accomplished by incorporating a control system which permitted operation of the turbine at other than normal operating conditions when auxiliary control valves were preset in anticipation of the load variation. The auxiliary control valves were air-inlet throttling valves, an inter-turbine bleed valve, and an additional fuel valve. The basic machine consisted of a 15-stage axial compressor, a two-stage, high-pressure turbine, and a two-stage power turbine. The unique requirements necessitated off-design operation and considerable extrapolation from known test data. However, it was possible to program the control-system components so that a conventional pneumatic control system was capable of maintaining speed within the prescribed band even though the applied load varied from that anticipated by as much as 12.5 per cent.