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.