Evaluation Method of Non-standard Lightning Impulse Waveform for Oil-filled Transformer

For rationalizing equipment insulation level which can subsequently lead to reductions in the cost of substation equipment such as GIS’s and transformers, it is necessary to reexamine insulating test voltages by investigating the method of evaluating lightning surge waveforms in terms of the equivalent standard lightning impulse waveforms. This paper discusses the evaluation method of non-standard lightning impulse waveforms, based on the insulating characteristics of the insulating models of oil-lled transformers under such non-standard waveforms. The method is applied to a few typical cases and it turns out to be that the peak values are lowered by 10 to 30 percents in conversion to the standard lightning impulse waveform.