This paper presents a 2-D & 3-D FE model of 250kVA, 33/0.416 kV wound core type distribution transformer, simulated using ANSYS 17.2 software in order to evaluate the insulation system via dielectric strength under power frequency and induced withstand tests and using two types of analysis, time-harmonic analysis to simulate the dielectric tests, and electro-static analysis to calculate the capacitance matrix. The assessment is based on the maximum allowable electric field intensity. the obtained results were compared with those of the real test, and the values of electric stress were less than the maximum allowable values. also, improvements to the presented model were applied following the transformer assessment. The improvement to the transformer insulation structure was done using three suggested finite element models included reduction and changing the materials type. the results were reviewed in form of contour plots, vector plots, and curves.