Monitoring Results of Polyethylene Insulation Degradability from Soil Buried Power Cables

Results from a 5-year observation of 27 cables of nine underground three-phase 20 kV power lines are presented. An analysis of the evolution in time for soil / metallic screen resistance (Rms-s) the resistance between metallic screen and central conductor wire (Rms-cw) and corrosion potential (E-corr) was made. From the experimental data it was noticed that the degradation of the whole insulation for a cable is a complex process occurring in successive steps, in which the first and decisive step is the biodeterioration of external polyethylene layer. The aggressive molds were Penicillium funiculosum and Aspergillus niger, whereas Paecilomyces varioti and Trichoderma viride were the least aggressive. Both deterioration and ageing of polymeric insulation was prevented by cathodic protection against corrosion of the cable metallic screen. Moreover, an aged insulation can be rejuvenated in a limited extent using this protection.