Effect of moisture diffusion and heat cycling on low voltage oil-impregnated-paper insulated distribution cables

Moisture can play a critical role in the long-term failure of low-voltage oil-impregnated-paper insulated cables. The processes leading to incipient discharges and, over longer periods, to cable failure are considered. Measurements of commercially manufactured cable insulation conductivity are reported with cycling of temperature and ambient moisture levels. Moisture ingress into cable insulation is also directly measured using Karl-Fischer (KF) titration. Rapid increase in cable core temperature is shown to dramatically increase conductivity for a short period. Cycling of moisture exposure is shown to gradually increase insulation conductivity in both wet and dry states.