Evaluation of breakdown characteristics of N2 gas for non-standard lightning impulse waveforms - method for converting non-standard lightning impulse waveforms into standard lightning impulse waveforms -

SF₆ gas, an insulation medium used for gas insulated switchgear (GIS), is known for its high global warming potential, hence the search for an effective alternative from an environmental perspective. As a potential alternative, the authors are focusing on N₂ gas. To use this N₂ gas for actual GIS, the insulation characteristics for actual overvoltage waveforms generated in the field (non-standard lightning impulse waveforms) must be obtained. For this purpose, the preceding study experimentally obtained and evaluated the insulation characteristics for various non-standard lightning impulse waveforms covering the surge waveforms generated in the actual field. In the present paper, the experimental results accumulated to date were comprehensively handled to conduct a study on the evaluation method of the insulation characteristics of the N₂ gas for nonstandard lightning impulse waveforms. Consequently, similarly to the previous study using SF₆ gas, the insulation characteristics could be expressed by one characteristic line using the duration as a parameter. In addition, based on the characteristic line, a method of evaluating insulation specifications for generated waveforms was established and applied as an example to actual surge waveforms in a substation. Furthermore, it emerged that the insulation specifications could potentially be reduced by about 10% for actual surge waveforms used in the present study.