Electric Field Models for Liquid-Filled Insulation of Medium-Voltage AC/DC Distribution Technology

Abstract

The electric field in a liquid-filled insulation system at uniform temperature, subjected to constant dc voltage is investigated. This work emphasizes the importance of charge transport modeling by electro-hydro dynamic (EHD) equations. The EHD model is compared with the quasi-ohmic conduction (qΩ) model, often preferred for the lower computational cost, by analyzing the electric field intensity between two electrodes separated by mineral oil and impregnated paper insulation. First, the EHD model is verified by measurements available from the literature. Next, to compare the models consistently, the apparent conductivities used in the qΩ model are extrapolated by the verified EHD model, as a function of the electric field intensity. A significant deviation of the qΩ model from both the EHD model and the measurements is observed, due to the presence of space charge in the solid insulation.