Partial discharge behavior of environmentally friendly and hardly inflammable ester liquids compared to mineral oil for power transformers

Conventional insulation systems of power transformers consist of mineral oil, cellulose paper, and pressboard. Due to the low biodegradability level of mineral oil and its susceptibility to fire, there has been an increase in the use of environmentally-friendly fluids such as synthetic esters and natural esters in recent years. To improve personal safety and to reduce the environmental impact of electrical power supply, alternative insulation fluids are demanded for large power transformers. These liquids are already used in the area of distribution transformers, but in case of large power transformers insignificant experience exists so far with alternative insulating fluids. For characterization of the insulating material and optimization of electrical design different electrical test methods (e.g. breakdown voltage, partial discharge) are used. The partial discharge behavior is a distinguishing characteristic of an insulating medium. In conclusion, it can be said that this paper shows the partial discharge behavior of alternative insulation liquids compared to commonly used mineral oil based on various investigations of an inhomogeneous test setup to generate reproducible partial discharges.