N₂ガスの非標準雷インパルス波形に対する絶縁特性と評価法

抄録

Until recently, SF₆ gas has widely been used as the best insulating medium in substation equipment. However, SF₆ gas was specified to be a greenhouse gas at COP3 in 1997 because of its high global warming potential (GWP), alternative insulation gases to SF₆ have been looked for since long time in the past. Alternatives using the natural gases are considered to be suitable substitute but none of them show better properties for insulation as well as good environmental compatibility. Therefore, it is necessary to rationalize the equipment insulation level and reduce the test voltage of electric power apparatus as low as possible. The actual lightning surge waveform (so-called non-standard lightning impulse waveform) occurring in the actual field is different from the standard lightning impulse waveform (1.2/50μs). There are many cases what the actual lightning surge waveform has steeply rising and large decay of overvoltage, and the insulation requirements are not as severe as those of the standard lightning impulse waveform.
In this paper, we focused our research on N₂ gas as SF₆ substitute and investigated the insulation characteristics of N₂ gas for single-frequency oscillatory waveform with various frequencies from 2.7 to 20.0MHz and damping ratios. From experimental results, it might be possible to reduce the test voltage of N₂ gas insulation by evaluating the crest value of actual lightning surge waveform that was converted into an equivalent standard lightning impulse waveform.