Experimental investigations on breakdown in cable insulation

Abstract

High voltage cables are used worldwide to transmit electric power in special cases such as underground and underwater, where the overhead lines can’t be used. Polymeric cable insulation is most commonly used for high voltage applications due to its several advantages like maintenance free when compared to oil impregnated paper. As well known, insulation is the very important concern in high voltage system. Once insulation breakdown occurs, the entire electrical system may get collapsed. So, it is necessary to understand the behaviour of insulation under different stress conditions. Several research papers explained about insulation failure that occurs due to electrical and thermal stress. But in actual practice, the high voltage cable is subjected to both electrical and thermal stress simultaneously. So, the authors have performed a series of experiments by applying both thermal and electrical stress simultaneously in power cable. The various thermal stresses are created in power cable by injecting different load current and conducted breakdown test at the controlled outer temperature of 30 °C. The different temperatures that are produced by load currents in the insulation are analyzed. These test methods are used to investigate the dependency of breakdown voltage under different thermal conditions. The distributions of breakdown voltages under different stress were studied by using Weibull distribution.