Polymer nanocomposites are known to exhibit superior insulation performance. As a reason for this, interactions at the filler/polymer interfaces are widely believed. To obtain information on this, the glass transition temperature (T g), complex permittivity (ε*), and conductivity (σ) were measured in various epoxy resin nanocomposites. As a result, all the parameters (T g , ε*, and σ) decrease when the filler is MgO, whereas T g decreases and ε* and σ increase when the filler is TiO 2. This fact clearly indicates that the filler exerts significant influences on various properties such as molecular motions in the host epoxy resin, and that these influences differ profoundly depending on the filler material.

This study investigates the relationship between void size and insulation lifetime due to partial discharges (PDs) in internal voids. Experimental results clearly show that the larger the void size, the shorter the insulation lifetime, which decreases the lifetime nvalue index of the voltage-time characteristics. The results also show a clear relationship between the insulation lifetime of a solid insulator having void defects and the PD energy generated in the void, which is related to the cumulative PD energy density per cycle. Therefore, we propose estimating the insulation lifetime of an insulator with voids by calculating the cumulative PD energy density per cycle.

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