The use of superconducting power cables is one of the promising ways for handling large volumes of electric power efficiently in the future. It is necessary to study the behavior of electrical insulation at cryogenic temperature to evaluate the long-term reliability of superconducting cables. At cryogenic temperature, there are many practical studies on electrical insulation characteristics of fluids such as liquid nitrogen or liquid helium and composite insulating systems, but few studies on solids enabling a high-voltage design. This paper describes the electrical breakdown and space charge of ethylene-propylene rubber (EPR) samples with fillers for the DC electrical insulation system at cryogenic temperatures. The results show that the breakdown strength at cryogenic temperature is much higher than that at room temperature. This may be attributed to less carrier injection from the electrode.
