Critical Agglomerate Size for Electrical Insulation Lifetime Extension of Epoxy/TiO2 Nanocomposite with a Void Defect

This study investigates the time to breakdown of epoxy/TiO2 nanocomposites with a void defect. In the tests, partial discharge (PD) is continuously monitored to clarify the degradation of the nanocomposites. In evaluating the dependence of the maximum agglomerate size and the volume fractions of the TiO2 particles, it is found that the agglomerate size, rather than the volume fractions, dominates the electrical insulation lifetime of the nanocomposites. Furthermore, the lifetime increases drastically when the agglomerate size exceeds a critical value. The continuous PD signal monitoring reveals that the lifetime extension of the nanocomposites is achieved due to delaying the electrical tree propagation in the nanocomposite, rather than extensions of the times required for the transition from the void discharges to the tree initiation.