極低温領域におけるエチレンプロピレンゴムの短絡トリー現象と空間電荷の注入

抄録

We are now long developing the extruded EPR insulated DC superconducting cable. Since polymeric insulators often fail due to treeing breakdown, it is imperative to study the treeing resistivity of EPR to evaluate long term reliability as a cable insulator. In this paper, we have studied dc short-circuit treeing resistivity of EPR both at liquid nitrogen temperature and at room temperature to elucidate space charge behaviors in this insulator at cryogenic temperature. The results show that the short-circuit tree initiation voltage at cryogenic temperature is much higher than that at room temperature. This may be attributed to less carrier injection from electrode and higher electric strength of EPR at cryogenic temperature. Space charge measurement was carried out using pulsed electroacoustic method. At room temperature, negative space charge is injected from the cathode, but at cryogenic temperature the injection is very limited. For dc electrical insulation, space charge is less problematic at cryogenic temperature than at room temperature.