Insulating liquid properties impacting transformer performance

Sa？etak This paper briefly discusses the functions of a power transformer’s insulating liquid in achieving effective cooling and reliable performance under high voltage stress, and in having sufficient oxidation stability to maintain performance, as well as low maintenance. Low viscosity over operating temperature range, high oxidation stability and favourable streamer propagation behaviour characterized by high acceleration voltage are key aspects of a good insulating liquid. The efficiency of a power transformer can be partly improved by increased convective cooling, thanks to a lower viscosity of the liquid. Moreover, many established electrical design rules for oil/paper systems used in power transformers of today rely on the characteristics of “traditional” mineral oils, which typically have high acceleration voltage. Furthermore, the insulating liquid’s oxidation stability and ageing behaviour will have a direct impact on a transformer’s total cost of ownership for its operator