脉冲电压下SF6气体放电极性效应研究

Very Fast Transient Overvoltages (VFTO) may result in insulation failures inside or outside Gas Insulated Switchgears (GIS), especially in higher voltage levels. In GIS, the sulfur hexafluoride (SF6) is used as the main insulation medium due to its excellent insulating properties. However, the dielectric strength of SF6 is very sensitive to field nonuniformity. Hence, in practice, the electrical breakdown strength of compressed SF6 can be greatly reduced due to local field enhancement. However, protrusions, surface roughness and presence of conducting particles can not be avoided during the process of equipment manufacturing. So the investigation about discharge characteristics in highly nonuniform electric field of SF6 has been attracted much attention..Polarity effect is one of the research hotsports about discharge characteristics in highly nonuniform electric field. Research shows that the polarity effect under nonuniform electric field appears abnormal phenomenon when the duration of applied pulse being shorter. But up to now, the research on polarity effect of SF6 discharge is rather scarce at home and abroad, and the research conclusions are not consistent. Also the understanding about the formation mechanism of polarity reversal phenomenon is not thorough, and all the work remains to be further in-depth study..Due to the rise time of VFTO’s wavefront being very short, usually within dozens of nanoseconds, the research data about the gas discharge characteristics of SF6 under nanosecond pulse can be drawn lessons by the research under VFTO. So the study on polarity effect of SF6 discharge under pulses, not only is helpful to supplement the research data about the dielectric insulation properties, enrich and perfect the theory of gas discharge under pulses, but also can provide some references for the insulation design of GIS under VFTO. So the research work has important theoretical value and practical significance.

高电压等级VFTO对全封闭组合电器（GIS）的绝缘危害较大，SF6是GIS的主要绝缘介质。当出现不均匀电场时， SF6的绝缘特性急剧下降。设备在加工过程中不可避免的存在毛刺或残留一定的金属导电微粒，使得VFTO下极不均匀场中SF6的放电特性引发关注。极性效应是极不均匀场中气体放电特性研究的热点之一。研究表明，当脉冲作用时间较短时，极性效应会出现反常现象。目前国内外关于极不均匀场下SF6放电极性效应的研究还相当匮乏，研究结论并不一致，对于极性反常现象形成机理的认识也不够透彻，均有待进一步的深入研究。因为VFTO的上升沿为纳秒量级，因此，VFTO下SF6的放电特性研究可以借鉴纳秒脉冲下的一些研究数据。综上所述，本课题不仅有助于补充脉冲电压下电介质绝缘特性的研究数据，丰富和完善气体放电理论，而且能够为VFTO下GIS的的绝缘设计提供部分参考依据，研究工作具有重要的理论价值和实际意义。

SF6因其优良的绝缘和灭弧性能，被广泛应用于电力系统各种高压设备的绝缘系统中，尤以断路器和全封闭组合电器（GIS）中使用较多。虽然以SF6气体作为绝缘介质的电气设备在设计之初基本采用均匀或稍不均匀电场结构，但设备经机械加工形成的电极表面的缺陷、装配时残留的金属导电微粒、电极的凸缘毛刺以及支撑绝缘子与电极交界面处的气隙等因素均会形成很强的电场集中。这些高场强的存在会严重威胁电气设备的正常运行，因此，研究不均匀电场下SF6气体的绝缘特性对电气设备的优化设计具有重要参考意义。.极性效应是极不均匀场中气体放电特性中的一个重要性质。本课题针对尖-板电极在不同实验条件下的放电特性进行了研究，研究结果表明，当脉冲作用时间较短（纳秒或亚纳秒量级）时，极不均匀场下的极性效应与常规电压下的极性效应相反。间隙距离、电场不均匀系数等参数均对极性效应反转的临界气压值有影响。研究结果不仅有助于补充纳秒脉冲下电介质绝缘特性的研究数据，丰富和完善纳秒脉冲下的气体放电理论，为脉冲功率装置的绝缘设计提出指导原则，而且能够为VFTO下GIS的绝缘特性提供部分参考依据，研究工作具有重要的理论价值和实际意义。