Recently polymer nanocomposite has been attracting much attention as an emerging insulating material. In this paper, we measured space charge distributions for two-layered dielectric films consisting of certain combination of low-density polyethylene (LDPE) and its nanocomposite with magnesia nano-fillers during the application of dc electric field of 25 kV/mm or 100 kV/mm. Both at room temperature and 50 °C, space charge is formed at the interface of two different materials to maintain the continuity of current when the electric field is 25 kV/mm, while packet-like charge appears only in the LDPE when the electric field is 100 kV/mm. These phenomena are explained by assuming that the nano-fillers effectively suppress the increase in conductivity induced by the high electric field.
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