Power transformers with environmentally friendly and low flammability ester liquids

To improve personal safety and reduce the environmental impact of electrical power supply, alternative insulation fluids are demanded for large power transformers. With their biodegradability, the fact that they can be produced from renewable resources, and the high fire point properties, ester fluids are becoming potential substitutes for mineral oil. A number of companies offer such alternative insulation fluids, and in many distribution transformers they are already used satisfactorily. So far, however, there is little experience for use of these liquids in large power transformers. Even in proven high-voltage applications with mineral oil, every change in transformer design or materials needs to be evaluated. Changing such a crucial component as the insulating liquid itself, the suitability must be proven most thoroughly. This paper illustrates various issues which must be clarified in order to successfully operate power transformers filled with these environmentally friendly, renewable and barely inflammable insulating liquids.