The behaviour of medium voltage cable terminations at artificial pollution

Terminations for medium voltage cables are mainly produced from plastic insulating materials. Under outdoor conditions electrolytic conductive layers are developed on the surface of the insulation caused by pollution and moisture. The applied operating voltage leads to a leakage current often being combined with partial discharges on the surface. The energy of these discharges results in an erosion of the surface. Following pollutants, as well as moisture, adhere to the surface. In the case of incorrect selection of the insulating material (nontracking resistant) or of unfavourable design of the termination, conductive tracking traces can occur, leading rapidly to the failure of the termination. The insulation behaviour under such conditions is proven by means of the so called salt-fog-test. The demonstration of test results of various termination designs gives a contribution to an improved interpretation, as well as an evaluation of the technical reserves.