Simulation of Partial Discharges Initiation in Voids in Medium Voltage Cables Insulators

This article studies the behavior of the underground electric cables for medium voltage. We are interested in the appearance conditions of partial electric discharges in the voids observed in the insulating parts of these cables. Their dimensions vary from 1 to 20 mu m. We focused on solving the Laplace equation for the electrical and the thermal constraints by the finite element method. The main objective of this study is to show that the classical Paschen curve cannot be used in this case. For this reason, we have proposed a modification of this curve which takes into account the insulating part in XLPE. We show in these cables that the partial electric discharges happen only beyond a nominal voltage of 44.2 kV. On the other hand, we conclude that the real charges at the void's wall are higher than the apparent charges and can be up to 3500 times more. The real charge values are of the order of 10(-4) to 10(-8) pC depending on the size of the void.