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The spreading use of polymer insulating materials in environments such as space and nuclear power stations increases the concern about the reliability of electrical insulation in these environments due to radiation and atmospheric pressure effects on the surface breakdown of polymers. This paper describes the effects of atmospheric pressure and gamma-ray irradiation on the discharge characteristics. The experiment was carried out by applying dc pulse voltage under a decreased pressure. Polyphenylene Oxide which was irradiated in air up to 100kGy and 1MGy with dose rate of 10kGy/h using a Co gamma-source has been used as the test sample. The total dose of gamma-ray irradiation effects on the discharge quantity have been studied. The changes of discharge quantity is discussed with decreasing the atmospheric pressure in the range from 100kPa to 0.1kPa and the frequency of applied pulse voltage in the range from 100Hz to 200Hz. The results show that discharge quantity increased with increasing the total dose of gamma-ray irradiation, and decreased with decreasing the atmospheric pressure. It is found that discharge quantity increased with increasing the frequency of applied pulse voltage. We found the dielectric breakdown is easy to occur with increasing total dose of gamma-ray irradiation, and the dielectric breakdown is hard to be allowed under decreased pressure.

Effects of Atmospheric Pressure on Insulation Breakdown of Gamma-ray Irradiated Polyphenylene Oxide