Insulators are the integral part of the high voltage power equipment. Several types of insulators are used in high voltage electrical power system to protect the power equipment. For the purpose of safety and better efficiency, it is necessary to keep the insulators in a healthy condition during its operation. As the insulators are always in impure form due to presence of air bubbles/other impurities inside the insulators, the local electrical breakdown so called partial discharge (PD) takes place due to the high voltage tresses. Due to this, PD occurs and property of insulators deteriorates enormously. Therefore, detection of PD is the one of the important task for electrical engineers to keep the high voltage power equipment in healthy condition. In this work, an electrical circuit model of an epoxy resin (i.e., an insulator) with a cubical void (air bubble) as an impurity is taken for realization of actual PD activity inside the insulator with the application of high voltage using MATLAB Simulink environment. In this study, the maximum amplitude of PD, partial discharge pulses at different applied voltages, and amplitude of PD with frequency is studied.