POWER-SYSTEM STABILIZER APPLICATION WITH LOCAL MODE CANCELLATION

This power system stabilizer application overcomes an unusual combination of constraints which would otherwise severely limit the damping influence obtainable from a conventional stabilizer system. A specific technique of modifying the stabilizer system has been applied effectively in a two unit steam power plant and its effectiveness has been verified by system tests. This modified technique would be applicable in other plants to relieve such constraints. Several of the troublesome constraints were aggravated by the rapidly fluctuating character of a large arc furnace load located nearby. Coordinated regulator-exciter-power system stabilizer action was needed, but the noisy character of the load precluded the use of frequency deviation signals for the stabilizer. The use of shaft speed signals avoided direct disturbance from the load fluctuations. However, shaft speed signals were more sensitive to a local mode oscillation between the two machines. This, in turn, promised to severely limit usable gain in the stabilizer system to avoid exciting the local mode oscillations. Yet above the Pacific Intertie mode frequency there also was a need for strong damping of regional mode oscillations of the power system. The technique of signal summing for cancelling local mode oscillations from the stabilizer input signal conveniently solved the major problem associated with the use of shaft speed signals. This permitted development of strong damping for the oscillation modes where it was needed. Other features in the stabilizer system deal with shaft torsional oscillations and with security of the excitation control system. Copyright © 1979 by The Institute of Electrical and Electronics Engineers, Inc.