All the electrical equipment are provided with insulation material for their safe and reliable operation; hence insulation material quality contributes to the lifespan of the equipment. Partial Discharge (PD) test on solid insulation is one of the methods that determine the quality of insulation. PD activity is a physical phenomenon, in which solid insulation experiences a partial breakdown in their electrically weak regions. PD often starts from voids or cavity and lead to insulation material failure the insulating material. Better understanding of PD, helps in diagnosing insulation defects and predict flashover before they occur. Therefore, this paper investigates the impact of partial discharge as a consequence of a single cavity in solid dielectrics. The proposed algorithm is demonstrated by mathematical model and laboratory experiments. The paper evaluates the behavior of partial discharge for insulations with different thicknesses and void size. The theoretical behavior was computed using Townsend breakdown criterion along with distribution law for capacitance. An online monitoring system was used to detect partial discharge in the lab. The obtained theoretical and experimental results were compared.