Insulating oil in 11 kV switches

Summary form only given. Insulating oil used in electrical power plants is subject to deterioration whilst in service by oxidation, moisture ingress and moisture generation by other processes. The permissible amount of moisture in the oil depends on the type of solid insulation used in the plant. Failure of power plant due to contamination of the oil may be hazardous, so it is important to understand the failure mechanisms and to develop safe and reliable methods of detecting and measuring the moisture content of insulating oils of site. The author describes the properties of insulating oil and how water changes the effectiveness of the oil in maintaining the integrity of the solid insulation immersed in the liquid. The similarities which exist between the mechanisms of degradation of solid insulating surfaces operating in air and oil are described