Study on the breakdown characteristics of SF 6 gas in quasi-uniform field under impact voltage

GIS has excellent performance and is widely used in electric power system. Its delivery test usually is standard impact which is applied in examination of its insulation, but in the field test, the oscillating impulse voltage waveform is often used. So the assessment ability in SF 6 insulation of oscillating impulse voltage and the equivalent relation of two types impulse voltages is worthy of further study. Based on the standard of the IEC60060-3, we have studied the breakdown characteristics of SF 6 gas in a quasi-uniform field including volt-time characteristic, the relationship between frequency and breakdown voltage, the relationship between polarity and breakdown voltage and so on. We also compared the difference of SF 6 gas breakdown characteristics under the standard impulse voltage and the oscillating impulse voltage. The results show that under the oscillating impulse voltage, with the increasing of the frequency, the initial breakdown voltage and the 50% breakdown voltage of SF 6 gas also increase. When the discharge time is reduced to a certain time, the volt-time characteristic started to bend up, and the polarity effect of SF 6 is not obvious under any type of impulse voltage. The results of this paper provide theoretical support for the determination of the GIS field test scheme and the overall insulation strength, which is significant in pressure test of GIS.