Development of moisture analysis for high and very high voltage XLPE and LDPE cables insulations

In France, high voltage cables with synthetic extruded insulation have been operated underground for about 30 years with a failure rate less than 0.2 defect/100 km/year. Thereby, diagnostic methods used after dielectric breakdowns showed that about 90% of the damages were caused by water penetration. Laboratory experiments showed that the presence of water trees was correlated with a large quantity of water in polyethylene insulation. That is why a development of moisture analysis of synthetic extruded insulations was made in laboratories in order to improve this method. The authors present the development of the experimental moisture measurement method applied to XLPE cable insulation of which water content was about 45-50 ppm