階段状直流昇圧過程における低密度ポリエチレン中の空間電荷蓄積および伝導電流の変化

抄録

This paper presents an experimental study on temporal change of conduction current and space charge accumulation in a low density polyethylene (LDPE) under stepwisely increasing DC voltage. Steady currents under various applied fields from 0.1 to 1.9 MV/cm are simultaneously measured with the observation of space charge distributions in a 150-µm-thick LDPE between semiconductive (SC) rubber (anode) and evaporated-Al (cathode) system or evaporated-Al (anode) and evaporated-Al (cathode) system. It is known the relationship between the conduction current and applied voltage for solid dielectrics is classified in two models, ohmic-model (electrode limited model) and space-charge-limited current (SCLC) model (bulk-limited model). In general, the conduction model for solid dielectrics shifts from ohmic-model to SCLC-model with the increase in voltage. We confirm that the current characteristic of LDPE with Al(+)/Al(-) shifts from ohmic to SCLC at the critical applied field of 0.6 MV/cm. The current characteristics of LDPE with SC(+)/Al(-) under low applied fields below 0.4 MV/cm well agree with SCLC model because positive space charges injected from the SC anode are distributed in the bulk of LDPE. On the other hand, the current characteristics under higher applied fields indicate that the conduction mechanism is based on ohmic-model though a large number of positive space charges are accumulated in LDPE. The reason will be discussed on the bases of the simultaneous measurements of the external currents and the space charge distributions.