Insulation characteristics of GIS under nonstandard lightning impulse oscillations: Insulation characteristics under double‐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 double-frequency oscillatory waveforms with various frequencies and damping ratios. It was found that minimum breakdown voltages (Vmin) were irrelevant to frequency changes in the range of experimental conditions under the same damping conditions. On the other hand, Vmin rose with the damping ratio rising under the same frequency conditions. The insulation characteristics at a valley of oscillation were investigated using actual breakdown voltages. It was found that the insulation characteristics were treated all-inclusively based on the characteristics of Vmin for damping time. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(2): 11–19, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10245