Measurement and simulation of partial discharges within a spherical cavity in a solid dielectric material

For high voltage components, the measurement of partial discharge (PD) is used in the performance assessment of an insulation system. Through modelling the PD process, a better understanding of the phenomenon may be attained. In this work, a model for a spherical cavity within a homogeneous dielectric material has been developed using Finite Element Analysis (FEA) software in parallel with MATLAB programming code. The model has been used to study the effect of various applied stresses and cavity conditions on PD activity and also the electric field and temperature distributions within the cavity. The experimental measurement of PD activity within a spherical cavity has also been undertaken. The measurements were performed for different amplitudes and frequencies of the applied voltage, a range of spherical cavity sizes and temperature variation of the material. The obtained results show that PD is strongly influenced by various conditions of the cavity and applied stress. The cycle to cycle behaviour of PD events, discharge phase and magnitude distributions, numbers of PDs per cycle, total charge magnitude per cycle, mean charge magnitude and maximum charge magnitude for each experiment have been obtained and analysed. The simulation results from the PD model have been compared with the measurement results. It is found that certain model parameters are dependent on the applied stress and cavity conditions. Parameters that clearly affect PD activity can be readily identifed. These parameters include; the effective charge decay time constant, the cavity surface conductivity, the initial electron generation rate, the inception field, the extinction field and the temperature decay time constant in the cavity. The infuences of surface charge decay through conduction along the cavity wall and temperature and pressure change in the cavity on PD activity have also been studied