A new method of turbine governing for improved transient stability†

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Abstract
This paper postulates torque balance governing as the ideal to be sought during the fault and post-fault periods of the transient stability regime. Series resistors have a part to play during the fault and some form of bang-bang control—excitation or series capacitor switching can provide rapid damping of rotor swings after the fault. Hitherto, the possibility of the conventionally governed turbine being able to contribute to damping during these transients has been discounted due to slowness of response of the governing systems and time lags in the turbine loop pipes and reheater. New proposals are made in which advantage is taken of the trend towards location of throttle and interceptor valves on the turbine casing, thus eliminating loop-pipe delays and also of the developing high-speed unit-actuator controlled throttle valves. These developments lead to the possibility of control of main throttle and interceptor valves in unison thus eliminating the reheater delays. By means of a carefully proportioned acceleration signal, it is shown how even the time constant due to these valve-operating times may be eliminated. The result is, potentially at least, a control system in which a steam turbine can be so controlled that, within its rating limitations, it can rapidly reduce torque even to some extent during the fault period and, moreover, contribute, again within rating limitations, to controlled damping during the post-fault period

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