Lightning Impulse Breakdown Characteristics of High-Pressure N2 as an Alternative Insulation Gas to SF6

Recently, SF₆ has been identified as a greenhouse gas with a long atmospheric lifetime1. Therefore, recycling guidelines for SF₆ in electrical power equipment have been discussed, and the reduction of the release of SF₆ to the atmosphere has progressed2. In addition, many researchers have investigated alternative insulation gases to SF₆3-5. High-pressure N₂ gas is one of the proposed alternative gases that have no need of SF₆. Pure N₂ has a lower withstand voltage level than SF₆, but has the advantage of being not only environmentally friendly, but also low in cost and safe. The breakdown characteristics of compressed N₂ have already been discussed as part of the basic study on gas discharge in the 1930s6. However, most data on the electrical breakdown of compressed N₂ were obtained under limited experimental conditions (small electrode scale or kinds of applied voltage waveform), and are not sufficient to estimate the insulation performance.