Evaluation of breakdown characteristics of N2 gas for non-standard lightning impulse waveforms under non-uniform electric field - breakdown characteristics for single-frequency oscillation waveforms -

SF₆ gas has been widely used in electrical power equipment such as gas insulated switchgear (GIS) due to its superior insulation and interruption characteristics. However, in 1997, SF₆ gas has been designated a greenhouse gas subject to emission restrictions at COP3 (The 3rd session of the Conference Of the Parties to the United Nations Framework Convention on Climate Change). Therefore, it is important to study the possibility of using environmentally friendly gases as alternative insulation gases for practical gas-insulated apparatuses, such as GIS. In the selection of an alternative gas, it is thought that high-pressure natural gases, such as Air, N₂, and CO₂ are promising environmentally friendly candidates. The authors are focusing on N₂ gas as one of its potential alternatives. In order to use this N₂ gas for actual GIS, the insulation characteristics for actual overvoltage waveforms generated in the field (nonstandard lightning impulse waveforms; non-standard-LIWs) must be obtained. The present study, with single-frequency oscillation waveforms as a representative basis, experimentally obtained the insulation characteristics by changing the polarity, frequency, and damping rate of the applied voltage in the non-uniform electric field represented by the presence of metallic particle in the equipment. As a result, the breakdown voltage was lower for the positive polarity under the non-uniform electric field. In this polarity, the breakdown voltage was 1.06 to 1.74 higher than that by standard lightning impulse waveforms even if the frequency and damping rate were changed. These results support the rationalization of insulation for actual surge waveforms under the quasi-uniform electric field.