Numerical Analysis of Surface and Internal Discharge Phenomena at the Interface of Hetero-Dielectric Composites Based on the Migration–Migration Model

Abstract

Nanocomposites have been actively studied for understanding the superior electrical characteristics and for utilizing in the electric devices of HVDC systems. Nanocomposites in electrical devices are not used unilaterally, but rather as the hetero-dielectric composites, which form an interface with other insulators. In this study, the hetero-dielectric composites comprised of nanocomposites and transformer oil were analyzed using the migration–migration model incorporating the finite element method. Until now, hetero-dielectric composites have been usually studied by using the Migration–Ohmic model, where the specific space charge behavior cannot be analyzed. Although interface conditions are significant for the transport and local accumulation of charge, the BCT models, including conditions for interface with other insulators, have not been reported. To investigate the space charge behavior of the hetero-dielectric composites, charge carriers of positive, negative ions and electrons are considered in the liquid region and electrons and holes in the nanocomposites. These hetero-dielectric composites are applied to the needle-bar electrode system to analyze the surface discharge phenomena at the interface. The BCT model was applied to the nanocomposites, and the drift dominated charge continuity model was applied to the transformer oil. These numerical results were compared with those from the previous research works validated with the experimental results. We analyzed the propagation of the streamer with an equivalent parallel current circuit and adopted the effective mobility of the electrons according to the field strength to improve the applicability of the numerical analysis model.