Insulation characteristics of GIS under nonstandard lightning-impulse oscillations: Insulation characteristics under single-frequency oscillations with various frequencies and damping ratios

To improve GIS insulation specifications, it is important to recognize the insulation characteristics under oscillatory overvoltage waveforms occurring in the field. This paper describes investigations of insulation characteristics for single‐frequency oscillatory waveforms with various frequencies and damping ratios. It was found that minimum breakdown voltages (Vmin) rose with frequency rising under the same damping condition and Vmin rose with damping ratio rising under the same frequency condition. From an analysis of actual breakdown voltage characteristics, the probability of breakdown at a valley of oscillation rose with damping increasing. It was found that the insulation characteristics were treated all‐inclusively based on the characteristics of Vmin for rise time or damping time. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 145(3): 43–49, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10156