Polymers are widely used as insulation materials in the electrical industry because their existing electrical and mechanical properties can be altered by adding different types of additives. Successful prediction of the service life of the insulators used in the electrical industry is important for the reliability of the system. For this purpose, insulating materials are subjected to tests according to various standards. In this study, unlike the literature, a polymeric insulator was produced by adding 3 wt.% zinc oxide (ZnO), magnetite (Fe3O4), and nickel (Ni) into the polyester. The produced samples were subjected to the inclined plane test in accordance with ASTM (American Society for Testing and Materials) D-2303 standards. In order to analyze the electric and magnetic field distributions formed on the samples during the inclined plane test, first, the current flowing on the samples during the test was measured. Following this, analyses were carried out by creating a simulation model of the samples. Studies found in the literature mainly focus on two-dimensional investigation of the electrical field distribution. This study concentrates on the three-dimensional examination of the electrical field also considering the magnetic field distribution. Results of this study showed that prior numerical analysis gives insight into information about the real-life behavior of the samples.