English Abstract
Deterioration Characteristics of Rubber Insulation Materials Subjected to Electrical Stress under Water Immersion.
Naofumi Chiwata,
Research & Development Center Engineering & Development Group,CHitachi Cable,CLtd.,Ibaraki, Japan. 
Nippon Gomu Kyokaishi,(2003),76(4),129-133  General Review in Japanese.

EP(Ethylene Propylene) Rubbers are usable for various power cables, cable splices and terminations, as they have a high degree of electrical properties ( breakdown voltage, volume resistivity, tracking resistance and so on) under ambient condition. But these products used for underground power distribution under water immersion or high humidity, in rare case
,Cfall into breakdown in a few years . Therefore good electrical properties are also necessary to these insulating materials under the latter condition for very long term. 
  This paper introduces accelerated test method and gives the results obtained by the method for deterioration characteristics of insulating materials subjected to electrical stress under water immersion. Test results indicate that volume resistivities and relative permitivities of EP rubber deteriorate in short term depending on its formula. Since the selected materials show long lifetimes even subjected to high temperature and high electric field , they are available for developments of power cables and their related things as stable insulators under severe circumstances.

ethylene propylene rubber
,Cdeterioration,Cimpressing voltage,C water immersion,Cvolume resistivity