Evolution of Grounding Failure-Insulation Failure of 10 kV Cable Joints: Prerequisites of an Explosion in Enclosed Cable Trench

An explosion accident in an enclosed cable trench caused by the discharge of 10 kV three-phase cable joints is discussed. Combined with the disassembly analysis, the fault recording data analysis, and the validation of experiment, the evolution of the cable joint fault is deduced and discussed. The results show that the trigger of the cable joint fault is the creepage discharge at the XLPE-SiR insulation interface. This results in the partial breakdown and the grounding failure of three-phase cable joints. Under the long-term floating potential and current thermal effect, the insulations are gradually ablated and decomposed into a large amount of combustible gas. Finally, the accumulated combustible gas is ignited by the arc caused by a three-phase short circuit at the moment of the reclosing operation. The analytical method and conclusions proposed in this paper can provide suggestions and guidance for the analysis of similar fault accidents in the future.