Plasma Dynamics-Based Modeling and Analysis of Partial Discharge in Voids Inside Insulation of Power Transformer

Partial discharge (PD) modeling in voids is being studied; earlier, however, most studies considered a simplified model with many adjustable parameters. In this article, a comprehensive comparative study is being done with possible void shapes in transformer insulation using a modified drift-diffusion model with single adjustable free parameter of the electron generation rate and considering the secondary ionization process. In simulation studies, plasma-dynamics-based models are used to better understand PD activity inside voids. A drift-diffusion model is used for investigating the PD phenomena inside air-filled voids of commonly found geometries, namely, cylindrical, spherical, and ellipsoidal, bounded by different insulating materials in power transformers. The model is applicable for all void shapes and material of insulation. PD inception field, residual field, space charge density, and other electrical properties are obtained, and all the possible parameters are incorporated in the model thus improving its accuracy. In this article, the effect of void shape and insulation material on the PD activity is obtained. The inception electric field at which the discharge initiates is found to be lowest in case of spherical void resulting in easy formation of plasma discharge. This study thus uncovers the physical mechanism of PD inside insulation thus helping in maintenance and optimum design of transformer insulation.