The main consideration that can be derived from this paper is that space charge and current density threshold characteristics can provide a tool which can be useful for the understanding of complex phenomena like injection, trapping and transport mechanisms. Space charge and charging current measurements can provide, in fact, co-operative information on nature of involved carriers, trapping efficiency and mode, mobility, injection and transport processes, as well as on the level of electrical threshold for space charge accumulation. Differences in the trapping process of space charges are observed in LDPE and XLPE, but not as large as those detected for the conduction current. The conductivity of LDPE is, in fact, much larger than that of HDPE. These results can be explained by the larger mobility of charge carriers in LDPE, with respect to IIDPE, which results from both space-charge depolatisation characteristics and the space-charge limited current theory. On the other hand, the threshold for space charge accumulation and that for space-charge limited current mechanism, coinciding for the same material, are very close for LDPE and HDPE, but the rate at which space charge is accumulated above the threshold differs. This reveals the presence of significantly different distributions of trap levels. The two materials treated here constitute an interesting case study, since they have limit characteristics, as conduction and charge-storage capability, among PE-based polymers used in many electrical insulating applications. It may be speculated that while one cannot say, a priori, which material is better in absolute way, the analysis here reported can help in carrying out comparative evaluations referring to specific applications.
展开▼
