Dielectric response of oil-impregnated cable insulation at low temperature

The installation in northern regions of new power plants and facilities presents certain unique problems due to the very low ambient temperatures. Many electrical insulating materials commonly used become glass like under extreme cold conditions. Insulating oils such as those used in cables and transformers present the risk of becoming highly viscous or solid at low temperatures. In oil impregnated cables the freezing of the oil could create problems such as the formation of voids and a possible loss of oil pressure. The dielectric response of a mineral low viscosity oil and of an oil-impregnated kraft paper system have been examined in the temperature range from ambient to -80°C. Results at low voltage frequency response tests of the oil at frequencies up to 10⁵ Hz are presented. Cable models have also been subjected to low and high voltage tests in the same temperature range. Data on dielectric loss vs. frequency and electrical stress along with partial discharge tests are also discussed.