Unraveling Low-Frequency Polarization Dynamics in RIP Under Polarity Reversal: The Critical Roles of Temperature-Dependent Relaxation and Interfacial Traps

When high-voltage DC equipment is subjected to polarity-reversing voltage, the insulation performance of its internal insulation material, epoxy resin-impregnated paper (RIP), is significantly affected by low-frequency polarization. To clarify the underlying mechanisms, this study analyzes the impact of the relationship between low-frequency dielectric relaxation time and polarity-reversing time on the dynamic changes of space charges at different temperatures based on the pulsed electro-acoustic (PEA) method. Furthermore, the influence of traps at the epoxy resin (EP)/RIP interface on interfacial charge accumulation is considered. By improving the existing bipolar carrier transport model, the dynamic characteristics of interfacial space charges in RIP under different polarity-reversing times are explored. The results show that at 313K, due to the low-frequency dielectric relaxation time constant exceeding 60s, the charge distribution is not significantly affected by the reversal time; At 333K and 353K, the reduction in dielectric relaxation time leads to a decrease in interfacial charge density and maximum field strength, with the peak field strength shifting towards the epoxy layer; At 373K, influenced by space charge dissipation and enhanced relaxation effect, the electrode surface charges and the maximum field strength in the epoxy layer initially decrease and then increase with increasing reversal time. The simulation results more explicitly characterize the interfacial polarization process between EP and RIP, and together with the experimental results, elucidate the mechanism of low-frequency polarization on the dynamic characteristics of space charges in RIP under polarity-reversing voltage. The research results may provide a theoretical basis and reference for the insulation design and optimization of high-voltage DC equipment.