| Summary: | 碩士 === 國立成功大學 === 電機工程研究所 === 81 === Series capacitor compensation of medium and long ac tra-
nsmission lines has been recognized as a powerful t ool for
opti- mum/economical use of transmission lines, and
improving system stability and power flow through the intended
routes. This tech- nique is extensively used in the western
United States and many other countries. However,the SSR
problem has been brought to general attentionin particular
in connection with the damage that occurred on the turbine-
generator shaft at Mohave Generating station in the United
States in December 1970 and October 1971. Since this
incident, several countermeasures having different concept
basis have been developed. These countermeasures have been
proposed in many forms, e.g., supplementary control signal to
the excitation system of the generator [1],and tuned series or
shunt filters [2], [3], etc., acting as damping resistors at
cer- tain oscillation frequencies. In recent years, a new
countermeasure has been invented by Narian G. Hingorani [4], [5
], known as the NGH-scheme. This is a damping scheme working on
the basis of measuring the half-cycle period of the series
capacitor voltage. If this half-cycle period exceeds a preset
period, the capacitor charges will be dissipated into a
resistor shunting this capacitor through two anti-parallel
thyristors. Therefore, the damping capability can be
increased for all subsynchronous frequencies.
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