Interfacial breakdown characteristics of XLPE/EPDM double-layer for DC cable terminations with different treatment conditions

To investigate how the presence of interface state impacts the DC breakdown at the interface at the terminations of a submarine DC cable, the cross-linked polyethylene (XLPE) and ethylene-propylene-diene terpolymer (EPDM) double-layer samples with two different interface states of direct contact and coating normal silicone oil were prepared. Various temperatures and pressures were controlled to simulate the actual operating environment. The effects of pressure and temperature on the DC Interfacial breakdown characteristics were analysed. The characteristics of interface charge accumulation and dissipation were studied with different polar voltages stressing. The effects of silicone oil on the interface charge characteristics were discussed by vertical preloading and interface breakdown tests. Results show that the breakdown voltage of the interface coated with silicone oil is much higher than that of the interface without silicone oil. After coating silicone oil, the trap energy level and trap density of the interface decrease, the interface accumulated charge density decreases, and the interface residual charge decays faster. In addition, when the polarity of the residual charge at the interface aligns with that of the needle electrode in terms of consistency, the interface breakdown voltage increases, and vice versa. This paper provides a theoretical basis and innovative insights for the subsequent selection and improvement of silicone fluids to enhance interfacial breakdown performance.