Cryogenic Electrical Tree Characteristics of Epoxy Resin for HTS Power Equipment Under DC/Impulse Superimposed Voltage

Epoxy resin (EP) for current lead insulation in superconducting equipment offers advantages such as low costs, high chemical stability, and excellent electrical and insulation properties. However, during operation, the combined effects of complex voltage and a wide temperature range from room temperature to 77 K can easily induce partial discharge, leading to insulation faults and posing a threat to the safety and stability of the power system. In this work, we conducted electrical tree tests on bisphenol F EP to investigate the influence of environmental temperature, voltage forms, impulse frequency, and other factors on the inception and growth characteristics of electrical tree. The results indicate that low temperature can effectively inhibit the inception and growth of electrical tree in EP. Continuous dc voltage application affects traps, making superimposed voltage more likely to promote electrical tree growth than a single impulse voltage at 300 K. The impulse voltage component dominates in the superimposed voltage, and its polarity significantly affects electrical tree characteristics, though the mechanisms differ. Additionally, the form of voltage superposition influences electrical tree characteristics. The promotion effect of heteropolar superposition voltage on electrical tree is slightly lower than that of homopolar superposition voltage, but the influence is not as obvious as that of positive and negative polarity.