Factors of hetero space charge generation in XLPE under dc electric field of 20 kV/mm

This report deals with the mechanism of space charge accumulation in cross-linked polyethylene (XLPE) under de electric field. Space charge was measured by the pulsed-electroacoustic method with applying de stress of 20 kV/mm. A large amount of hetero space charge accumulated in fresh XLPE samples. Factors influencing the space charge accumulation were analyzed in regard to cross-linking by-products and antioxidant. No space charge was seen when the fresh sample was degassed to remove cross-linking by-products. Introducing acetophenone, one of the crosslinking by-products, in a degassed sample produces no space charge, suggesting that acetophenone itself could not be the direct factor of space charge formation. However, heating this sample up to 150 degrees C results in formation of hetero space charges as in virgin samples. Hence, it is concluded that hetero space charges may be formed when impurities, such as an antioxidant, dissociate thermally with the help of acetophenone and that the dissociated products are attracted toward both electrodes under a de field to form the hetero space charges. (C) 1999 Scripta Technica, Electr Eng Jpn, 129(2): 13-21, 1999.