This project studies the electric field distribution within an ideal CRDT containing an air-filled void in the epoxy insulation. Insulation is the most important part of high-voltage equipment. They are vital for isolating conductors and for their performance. The electrical field distribution in a CRDT is described by a three-dimensional field model built using SOLIDWORKS 2020. COMSOL Multiphysics 5.5 software was used to carry out the simulation based on the finite element method (FEM). The model is solved for an ideal condition as a base for further analysis. In addition, an air-filled void is introduced into the model of epoxy insulation to investigate the effect of void presence on the electric field distribution within the transformer. The distribution of the electric field is plotted on a graph, and a certain condition has been applied to the transformer, such as varying the void size and locating the void. It was observed that the electric field is 136 MV/m when the void is located near the LV winding, while it is only 0.246 MV/m when it is close to the magnetic core. It can also be seen that the electric field decreased as the size of the void increased. The findings of this study will contribute to a better understanding of the electric field response caused by the size and position of the void within the epoxy insulation, as well as the electric field stress, and may provide a path for future researchers to investigate partial discharge.