Analysis of thermal ablation faults in the grounding system of a 35 kV three-core submarine cable

Currently， submarine cables in operation （hereinafter referred to as “submarine cables”） commonly use insulated or semi-conductive polyethylene sheaths to isolate the three-phase metal sheaths， preventing complete cancellation of the induced voltage between the phases. As a result， significant sheath circulating currents can develop in the sheath when it is directly grounded at both ends. The thermal effects of these large circulating currents lead to frequent thermal ablation faults at the grounding connection of the metal sheath. Therefore， it is crucial to study the mechanism behind such fault. Using a real-life example of a thermal ablation fault at the metal sheath grounding connection of a submarine cable， the typical characteristics of the fault were analyzed through a disassembly inspection of the fault sample. Electromagnetic transient simulation software and finite element simulation software were used to analyze the temperature field distribution at the contact surface under different contact states between the submarine cable’s metal sheath and the grounding conductor. The simulation results largely replicated the actual fault characteristics， validating the fault mechanism of thermal ablation at the grounding connection of the submarine cable’s metal sheath. This research lays the foundation for the development of anomaly warning technologies for submarine cable grounding systems.