800kV特高压直流穿墙套管故障分析

Fault Analysis of 800kV UHVDC Wall Entrance Bushing

±800kV云广特高压直流工程的800kV直流穿墙套管投运3年后频繁出现故障,为分析故障的原因,对3支套管进行了解体检查,发现出现不同故障的共同原因均为套管户外端与户内端连接的锁紧环螺纹磨损。磨损产生的金属粉尘附着于套管短尾端,引起介损增加,严重时造成绝缘下降,电流击穿末屏接地点形成放电。同时螺纹磨损造成户外端与户内端连接紧固力下降,表现为套管直流电阻增大。针对故障原因,对套管结构提出增加径向锁紧的定位销的改进设计和对套管预防性试验项目增加直流电阻测试的改进建议。

800 kV wall entrance bushing failures oecurr frequently in ＋800 kV Yun-Guang UHVDC power transmission system. Overhaul of 3 bushings indicates that different failures are resulted from same screw thread abrasion of locking ring connecting bushing outdoor and 0 indoor parts. Metal dust produced by abrasion attached to casing short tail causes dielectric loss increment and insulation decrease which lead to current breakdown and grounding discharge. Thread abrasion also causes indoor and outdoor bushing connection fastening force decrease which characterized by resistance increment, Improved design of positioning pin including increased radial locking on bushing structure is proposed. Action to add resistance test in bushing preventive test procedures is also suggested.