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

六氟化硫(SF6)气体具有优异的绝缘强度和灭弧性能，广泛应用于气体绝缘开关(GIS)等高压设备中。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被密封在高压设备中，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惩罚。近年来，人们提出了在高压设备中替代SF6的环保型替代气体。目前的研究大多集中在开发充满这些替代气体的新型高压设备上。然而，这项研究项目的目的是调查用替代气体重新填充国家电网拥有的现有SF6设备的可行性。被选为该项目的有希望的候选者之一是基于氟腈的NOVEC气体。将建立一个可以复制400KVSF6填充设备中的典型电场的测试系统。交流、雷电冲击(Li)和操作冲击(SI)电压下的替代气体或与SF6的混合气体的绝缘强度将被表征，而SF6将仅作为基准进行测试。将同时考虑导体与墙壁的整体气体绝缘和隔离器表面绝缘。将研究在一定压力范围内不同比例的混合气体。还将研究颗粒污染和水分渗透对替代气体/气体混合物性能的影响。对放电或击穿后的气体成分进行局部放电测量和光谱分析。最终将部署长期经受测试，以验证提议的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.