Numerical Investigation of Discharge Initiation and Propagation in Insulating Oil Containing a Lossy Dielectric Material

A discharge analysis of a floating lossy dielectric material immersed in insulating oil was conducted using a fully coupled finite element method. The model incorporated both dielectric permittivity and conductivity to characterize lossy dielectric behavior, with particular attention to surface charge dynamics at the liquid–solid interface. Insulating oil is widely used in power equipment such as power transformer due to its high dielectric strength and efficient cooling capacity. However, impurities such as nonmetallic particles, primarily generated from pressboard wear, account for more than 90% of contaminants and can significantly degrade insulation performance. To date, liquid discharge analysis involving lossy dielectric materials has rarely been reported within a three-carrier system consisting of positive ions, negative ions, and electrons. The simultaneous presence of dielectric permittivity and conductivity in lossy dielectrics poses unique challenges for discharge analysis. To address this issue, we developed a numerical model based on the current continuity equation for the electric field, ensuring proper treatment of current and charge continuity across the liquid-solid interface. To validate our proposed numerical framework, a one-carrier model was first constructed to examine the internal electric field strength and surface charge density of a lossy dielectric particle compared with theoretical results. Building on this simple model, we extended the analysis to a three-carrier charge transport system to investigate the influence of lossy dielectric materials on streamer channel development. The results indicate that high conductive lossy dielectric particle facilitates charge transport, reduces the internal electric field strength, and promotes secondary discharges beneath the particle. In contrast, low-conductivity particle primarily induces surface charge accumulation, which supports streamer propagation along the interface. These findings provide new insights into streamer propagation and charge accumulation mechanisms as functions of dielectric permittivity and conductivity, offering a foundation for further studies of discharge phenomena in insulating oil.