The power transformer is the heart of the electric system and the most expensive part of the electrical utilities. Partial discharge in power transformers is among the most a crucial concern to be analyzed in the electrical power components. In this paper, a 2D finite element model of power transformer is developed to study the partial discharge defects in power transformer. Both healthy and defective conditions in power transformer have been modeled. The defective one includes different shapes of voids and crack in pressboard insulation of the transformer winding. Also bubbles and metallic particles in the oil power transformer are analysed. The power transformer is modeled and the dielectric response of the defects are carried out in the time domain. The results show that the electric field in the defective transformer is considerably high corresponding to the surrounding region showing the high electric stress in the defects. Graphs are plotted to visualize the electric field distribution.