SPECTRA OF FAULT-INDUCED TRANSIENTS

During the first cycle or two following a power system fault, a high-speed protective relay is expected to make a decision as to the severity or location of the fault, usually based on 60 Hz information, i.e. the phase and magnitude of 60 Hz voltage or current signals. It is precisely at this time however that the signal is badly corrupted by noise, in the form of a dc offset or frequencies above 60 Hz. It is the purpose of this paper to identify the source of various noise frequencies, especially frequencies not far above 60 Hz, so that filters at relay input stages can be optimally designed. If the upper cut-off frequency of such a filter can thus be raised with confidence that expected noise will not be below that frequency, then the relay's speed will be improved. To this end, a variety of transmission line fault situations are simulated using a well-proven digital computer program, along with a Fourier spectrum program. The results show, amongst other things, that the phase mode travelling wave dominates. Copyright © 1979 by The Institute of Electrical and Electronics Engineers, Inc.