Influence of harmonics on power distribution system protection

Abstract

The effects of nonsinusoidal voltages and currents on the performance of static underfrequency and overcurrent relays were experimentally studied. The tests were conducted such t h a t the frequency, amplitude and phase shift of individual harmonics could be adjusted in a controlled manner by employing a waveform generator with a phase-locking circuit. The relation between the harmonic currents and voltages was modelled through the power system impedances within residential distribution systems. I t was found t h a t for harmonic voltage and current amplitudes, as they occur in distribution systems, underfrequency relays and the time delay operation of overcurrent relays show a marked deterioration in their performance. The instantaneous operating characteristics of overcurrent relays, however, are hardly affected by the presence of harmonic currents. The work described has been supported by the U.S. Department of Energy.

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