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Montmorillonite (MMT)/low-density polyethylene (LDPE) nanocomposites have excellent partial discharge resistance and electrical tree resistance compared with pure LDPE. However, the MMT/LDPE nanocomposites have low breakdown strength due to the poor compatibility between nano-MMT and LDPE. In order to improve the breakdown strength of the MMT/LDPE composites without changing the LDPE matrix, an MMT/SiO 2 /LDPE multielement composite was prepared by melt blending, and its breakdown strength and electrical tree resistance properties were investigated. The results show that the MMT/SiO 2 /LDPE multielement composite has excellent breakdown strength and electrical tree resistance properties compared with the MMT/LDPE composite. The reasons for the excellent insulation properties of the MMT/SiO 2 /LDPE multielement composites were analyzed by exploring the effects of MMT and SiO 2 on the microstructure and trap characteristics of LDPE.

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Space charge existed in polymer subjected DC high electrical stress has attracted more and more attention over the world. Various methods of inhibiting space charge generation and accumulation had been attempted in order to reduce insulation deterioration. In the present paper, the polyethylene/montmorillonite nanocomposites are prepared by melting intercalation process. The distribution of space charges in the nano-composite is investigated by means of pulse electric acoustic (PEA) method under different conditions. The effects of maleic anhydride grafted polyethylene (PEMA) on space charge characteristics of the composites are discussed. The test results indicate that the heterogeneous space charges in the nanocomposite near the cathode gradually decrease with PEMA content increasing. When PEMA content is 20%, the heterogeneous space charges near the cathode almost disappear at all in the nanocomposite. In short-circuiting process, the residual space charges in the nanocomposite with compatilizer obviously decrease comparing with origin LDPE. It is suggested that PEMA as a compatilizer can improve the interaction combination between LDPE and O-MMT, consequently interfacial traps reduce.

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