Numerical and Experimental Determination of PD Apparent Charges for Defective Insulation Models

The article presents the results of refining the partial discharge (PD) physico-mathematical model for gaseous voids in solid insulation in regard of calculating true and apparent charges. The model under consideration is based on replacing the distribution of charges deposited on the void walls by an equivalent spheroid. As a result, it becomes possible to formulate analytically the relation between the change of electric field strength inside the void and the charge induced in the object’s electrodes. The model is supplemented with statistical parameters, which make it possible to reproduce the recorded amplitude-phase diagrams. These parameters include the PD statistical time lag, streamer extinction electric field strength, and relaxation time of charges deposited on the void walls. The article also presents the results of apparent PD charge measurements by the electrical method on specially made solid insulation mockups. The mockups are made of caprolon with air voids simulating the insulation defects near the electrode and inside the dielectric. The model reproduces, with good accuracy, the average value of the apparent PD charge in all considered mockups. It is shown that by selecting the PD model statistical parameters, it is possible to achieve good agreement between simulated and experimental amplitude-phase diagrams, and to reproduce the measured scatter of PD apparent charge values.