Space charge measurement in EVA film at cryogenic through room temperature region

Space charge effect on DC breakdown strength of ethylene vinyl-acetate copolymer (EVA) was studied in the region of cryogenic to ambient temperatures. The direct space charge measurement by pulsed electroacoustic method showed no space charge at 180K, however, significant amount of positive charge was seen at 290 K. This positive charge would enhance the cathode field and reduce the DC breakdown stress. The "peak ratio" was defined in order to assess the field enhancement at cathode. The "ratio" showed almost the same temperature dependence as the breakdown strength, suggesting that the relaxation and enhancement of the cathode field by space charges significantly effects the breakdown characteristics.