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Pressure effect on the electrical ageing of polyethylene

The purpose of this study is to show the effect of hydrostatic pressure on the electrical ageing, by a dc voltage, on polyethylene used in submarine cables. Experimental results are obtained at 1 and 300 bar, for a temperature of 70 °C in the range of an electrical field of 1.1-4.5 MV cm-1 and for up to 1500 h of ageing. By using the Weibull statistic and the estimation of confidence bounds of 90%, the results have shown an increase of lifetime with pressure. The time dependence of the breakdown behaviour of the two materials (HDPE and XLPE) is consistent with the inverse power law model. The pressure effect may be explained by changes in the activation free energy for the formation of submicrocavities.