Analysis of the breakdown fault in field voltage withstand test of 500kV SF6 current transformer

Current transformer, the major primary equipment in power system, can transform a large primary current into the standard 5A or 1A current. It provides current for the measure device and the coil of relay protection, meanwhile makes the primary equipments isolate from the secondary equipments. With the development of grid, SF₆ current transformers have been widely used. Once the fault of the internal insulation support in SF₆ current transformer appears, it will threat the safe operation of power systems. In recent years, the fault accidents of current transformer have occurred form time to time. This paper introduces the fault conditions of 500kv current transformer in the area under the jurisdiction of Xiamen EHV Power Transmission and Transformation Bureau. After it be sent back to factory and disassembled, we found that many large area of paint have come off the inner surface of shell of the current transformer, and that there many blister on the inner surface of shell. Meanwhile, send the same batch transformers back to the factory and disassemble, we found that there are many problems in the production process. So this paper suggests that the production process of SF₆ current transformer should be monitored. And after it has been installed, we have to do the aging test and voltage withstand test. To prevent the same fault of 500kv current transformer occurs again, the results in this paper can give some reference and engineering application consult.