SPACE-CHARGE DISTRIBUTION IN LOW-DENSITY POLYETHYLENE WITH CHARGE-INJECTION SUPPRESSION LAYERS

Space charges formed in low-density polyethylene (LDPE), to which high voltage is applied, are usually composed of injected homocharges from electrodes and ionized heterocharges from bulk impurities. In this paper, the heterocharges in LDPE were discriminated from homocharges using charge-injection suppression layers. Recent advanced techniques have made it possible to observe directly the space charge distributed in dielectrics. However, it is difficult to study the characteristics of charge injection from electrodes and ionization of impurities individually as the two processes may interfere with each other and become inseparable. Therefore, a layer that suppresses the charge injection from electrodes was used to discriminate between injected and ionized charges. To observe the space-charge distributions, the pulsed electroacoustic (PEA) method, one of the advanced techniques, was employed. In LDPE with suppression layers on both surfaces, hetero-space charges, which are attributed to ionization of impurities, were observed. On the other hand, in LDPE without the suppression layers, small amounts of home-space charges, which are attributed to net charges from both the electrode injection and the bulk ionization, were observed. Amounts of charge supplied from electrodes were estimated by subtracting the amount of space charge in the sample with suppression layers from that in the sample without suppression layers.