Resonant Overvoltage Phenomena Caused by Transmission Line Faults

Resonant overvoltages in EHV transformers can be initiated by transmission line faults. A series of field tests were performed on the 151 mile long Kammer-Marysville 765 kV line in which a sequence of single line to ground faults were applied to one outside phase at 4 different locations. Fault location criteria and fault initiation procedures are presented. Oscillograms recorded the 3 phase response at both terminals of the line; one is transformer terminated, the other is open-ended. A frequency spectrum analysis of the waveforms is provided showing transient frequencies of sufficient magnitude and duration near the EHV transformer´s resonant frequency to stimulate internal winding resonant overvoltages. Digital computer studies are presented and agree with the field tests quite favorably.