一起现场TEV引起的法兰故障

A Flange Failure Caused by Field TEV

[目的]外壳暂态地电位升高(TEV)会对工作人员的人身安全、二次设备的正常工作产生威胁,并有可能引起GIS外壳法兰间的放电。为了对某500 kV变电站在操作隔离开关时GIS外壳法兰间出现的火花放电故障进行分析,提出了一种基于传输线理论的TEV仿真计算模型,并讨论了TEV引起法兰间放电的抑制措施。[方法]为了更精确地对TEV进行模拟,采用Cassie-Mayr理论构建了改进动态电弧模型,并将VFTO产生电路与TEV计算电路相结合,将操作隔离开关所产生的VFTO直接加至GIS外壳电位计算模型中。[结果]仿真结果表明,在最严重的情况下,法兰间的最大电压差超过了法兰间绝缘隔板的沿面闪络电压,足以引起法兰间放电。减少隔离开关孤岛侧的剩余电荷、降低接地线电感都可以不同程度地降低TEV的幅值,但不能完全抑制法兰间电位差。而使用短接片进行跨接可以有效地抑制法兰间的电压差,避免由此产生的放电现象,但需要对短接片的选型进行校验,并取消原有的三相短接排以免产生环流。[结论]经现场工程改造验证,文中所得结论正确有效,对预防此类放电现象具有较大的参考意义。

[Introduction]The transient enclosure voltage(TEV)will threaten the personal safety of the staff and the normal operation of the secondary equipment,and may cause the discharge between the flanges of the GIS enclosure.In order to analyze the spark discharge fault between the flanges of the GIS enclosure when operating the disconnecting switch in a 500 kV substation,a TEV simulation calculation model based on the transmission line theory was proposed,and the suppression measures of the discharge between the flanges caused by TEV were discussed.[Method]In order to simulate the TEV more accurately,an improved dynamic arc model was constructed using the Cassie-Mayr theory,and the VFTO generation circuit was combined with the TEV calculation circuit,and the VFTO generated by disconnecting switch operation was directly added to the GIS enclosure potential calculation model.[Result]The simulation results show that,in the worst case,the maximum voltage difference between flanges exceeds the surface flashover voltage of insulating barriers between flanges,which is enough to cause discharge between flanges.Reducing the residual charge on the island side of the disconnecting switch and reducing the inductance of the grounding wire can reduce the amplitude of TEV to varying degrees,but cannot completely suppress the potential difference between the flanges.The use of shorting connectors for bridging can effectively suppress the voltage difference between the flanges and avoid the resulting discharge phenomenon,but it is necessary to verify the selection of the shorting pieces and cancel the original three-phase shorting row to avoid circulation.[Conclusion]Verified by on-site engineering transformation,the conclusions obtained in this paper are correct and effective,and have great reference significance for preventing such discharge phenomena.