Application Of Alternative Gases In Retro-Filling SF6 Insulated High Voltage Equipment

六氟化硫（SF6）气体由于其优异的介电强度和灭弧性能，在气体绝缘开关设备（GIS）等高压设备中得到了广泛的应用。然而，它是京都议定书中包含的六种气体之一，具有很高的全球变暖潜力。尽管SF6在高压设备中是密封的，但包括国家电网在内的公用事业公司经常因其泄漏而受到处罚。近年来，人们提出了环保气体替代高压设备中的SF6。目前的大多数研究都集中在开发充满这些替代气体的新型高压设备上。然而，这个研究项目的目的是调查用替代气体重新填充国家电网现有的SF6设备的可行性。该项目选择的有希望的候选者之一是基于氟腈的NOVEC气体。建立了一个能模拟400kv SF6充装设备典型场的试验系统。在交流、雷电冲击（LI）和开关冲击（SI）电压下，SF6替代气体或混合气体的介电强度将被表征，而SF6仅作为基准进行测试。导体与壁间的气体绝缘和隔层表面绝缘都要考虑。在一系列压力下，将研究不同百分比的混合气体。还将研究颗粒污染和水分侵入对替代气体/气体混合物性能的影响。进行局部放电测量和气体组分放电或击穿后的光谱分析。最后将部署长期承受测试，以验证所建议解决方案的长期性能。

Sulphur hexafluoride (SF6) gas has been widely used in high voltage equipment e.g. Gas Insulated Switchgear (GIS) due to its excellent dielectric strength and arc quenching property. However it is one of the six gases included in the Kyoto Protocol, with a high global warming potential. Although SF6 is sealed in the high voltage equipment, utilities including National Grid are often penalised due to its leakage. Environmentally friendly alternative gases to replace SF6 in high voltage equipment have been proposed in recent years. Most of current research focuses on developing new high voltage equipment filled with those alternative gases. The aim of this research project is, however, to investigate the feasibility of retro-filling the existing SF6 equipment owned by National Grid with alternative gases. One of the promising candidates chosen for the project is Fluoronitrile based NOVEC gas. A test system which can replicate typical fields found in 400 kV SF6 filled equipment will be established. The dielectric strength of the alternative gas or gas mixture with SF6 under AC, lightning impulse (LI) and switching impulse (SI) voltages will be characterised, whereas SF6 only will be tested as benchmark. Both conductor to wall bulk gas insulation and spacer surface insulation will be considered. Different percentages of gas mixture under a range of pressures will be studied. Effect of particle contamination and moisture ingression on the performance of the alternative gas/gas mixture will also be studied. Partial discharge measurement and spectrum analysis of gas components after discharge or breakdown will be carried out. A long term withstand test will finally be deployed to verify the long-term performance of the proposed solution.