Cavities in insulation systems of active high voltage (HV) equipment affect their performance, reliability and useful life periods. Cavities serve as flash points for enhanced field activity leading to ageing from partial discharge (PD) events and subsequent breakdown of the insulation material. In this paper, the impact of cavity diameter on the electric field distribution as well as on PD inception voltage are investigated in an Epoxy-resin insulation sample. A 3D adequate model of the sample with a spherical cavity was created and simulated in COMSOL for different cavity sizes and applied voltage stresses respectively. The simulation results indicate that both field distribution and the PD inception voltages are strongly influenced by cavity size as well as the applied voltage magnitude. The electric field intensity was observed to be higher in cavities with smaller diameter relative to the insulation bulk, while the inception voltage decreases with increase in the cavity diameter and vice-versa.
