Experimental and simulation analysis of electrical breakdown for 220kV silicone rubber pre-moulded cable joints

Abstract

In recent years, an increasing number of high voltage cable joints have been installed in large cities, such as Guangzhou and Shenzhen, in the area of China Southern Power Grid. Several failures of 110kV and 220kV silicone rubber pre-molded cable joints happened, which resulted in great power loss and big risk to the power system safe operation. In order to understand the mechanism of electrical tree initiation and propagation which is believed as the main cause of insulation breakdown, several 220kV cable joints from recent failures were investigated. The samples include ones from the service, non-service, and failed joints in operation. Samples from operation and failed joints were comprehensively investigated by the techniques of morphological observation, electrical and mechanical testing, The transient voltage was computed using EMTPE in order to justify the role of system operation in these faults development. Based on detailed analysis and the calculation of cable joint's mechanical force, it is shown that too much expanding force of the stress cone is probably a major cause of electrical treeing. Possible physical damage occurs at the molecular size level in the cable joint installation with expending process. Final breakdown of the cable joints would occur with a stress of electrical and mechanical coupling.