Behaviour of XLPE insulated medium voltage cables in long duration immersion

For a certain number of years the behaviour of medium voltage power cables with synthetic insulation in a wet environment has been discussed. More recently, some countries have tried to develop several long-duration test methods to better understand power cable behaviour under such conditions. 20 years ago, France developed a power cable model with radial and lengthwise watertightness. Despite this specificity and in order to have an input to the tests carried out in Europe, this type of power cable has been under further investigation to understand its behaviour when the insulation is in the presence of water. Tests consisted mainly of ageing the cable in water at 50°C under four times its rated voltage for two years. Residual voltage strength has been measured after six months, one year and two years. As observed in other laboratories, a drop of voltage strength mainly occurs during the first six months. This report gives detailed results from these experiments, thus updating the results presented at JICABLE 95