Power cable fired by transient arcing below the action value of relay protection: An analysis of a medium-voltage cable joint breakdown fault

Abstract

Cable joint breakdown accidents have occurred frequently in recent years and have gradually become an important concern of the power maintenance department. The study of the fault development process of the cable joint is helpful to detect and diagnose in advance, so as to avoid the expansion of the accident. In this paper, a breakdown fault of 20 kV damp three-core cable joint was investigated. Firstly, the recorded fault waveform was analyzed, and the fault cable joint sample was disassembled. Then, the circuit simulation model was established to calculate the short-circuit resistance, which aimed to reveal the dynamic characteristics of the short-circuit resistance of the composite interface for the damp joint. Finally, the effect of moisture on the electric field distortion of the interface and the thermal ablation damage effect of the transient short-circuit current on the copper mesh were discussed by the finite element method. This paper reveals the phenomenon of transient grounding faults arising from moisture at the internal interface of cable joint, which may damage the grounding protection line of the joint and affect the sensitivity of the protective device. The method for analyzing the breakdown fault case of damp cable joint presented in this paper can provide reference and suggestions for the investigation and solution in similar cases.