Research on the water absorption and insulation deterioration of insulating oil for high-voltage cable terminations

Trace water absorption in insulating oils used in high-voltage cable terminations may cause electrical property deterioration and premature insulation failure. This paper compares the short-term moisture absorption behavior and electrical performance degradation of silicone oil and polyisobutylene during 0–120 h exposure, combined with molecular-scale analysis. The results show that silicone oil exhibits faster water uptake and a higher saturated water content of about 52 ppm, following an exponential growth trend, while polyisobutylene shows slower and nearly linear moisture absorption. For both liquids, short-term water absorption increases dielectric loss, decreases volume resistivity, and weakens insulation strength. Silicone oil falls below the national breakdown strength requirement after 3 h of exposure, whereas polyisobutylene remains compliant for up to 24 h. These results provide useful guidance for the filling, application, and fault analysis of cable termination insulating oils.