Breakdown characteristic differences and environment-matched detection of multilayer polymer insulation structures

Abstract

This paper investigates the breakdown characteristics and environment-matched detection of multilayer ethylene vinyl acetate (EVA) and polytetrafluoroethylene (PTFE) insulation structures for live-line protective equipment. Different from conventional material breakdown tests under a single medium, this work focuses on whether the test medium can represent the actual service environment of a flexible multilayer stack. One- to ten-layer specimens were tested under AC and DC voltages in air and KI50X insulating oil using 20 mm copper sphere-sphere electrodes at a voltage ramp rate of 1 kV/s. The results show a strong medium effect: oil-immersed structures exhibit much higher breakdown voltages, whereas air-exposed structures reach a lower saturation level after approximately five layers. For EVA, the DC oil result approached the 80 kV system limit near five layers, while the corresponding air value was only about 20 kV. For PTFE, the oil result reached the same limit at fewer layers, but the air result still showed a much lower plateau. Additional EVA tests with interlayer Vaseline gel indicate that soft filling can modify the breakdown level and dispersion by changing the interlayer gap condition. These results support an environment-matched detection principle: oil breakdown data should not be directly used to qualify air-exposed insulation. The proposed interpretation links layer-number optimization, service medium, and interfacial defect diagnosis for multilayer live-line insulation.