Since many years ester liquids are in use as an alternative insulating liquid to mineral oil in distribution transformers. The major advantage, forcing the application of these fluids, is their improved environmental compatibility. But these liquids comprise several additional advantages, which are at first their lower inflammability. Power transformers contain several tons of insulating liquid, that may cause a long lasting pool fire in case of a transformer tank rupture due to winding failures. Meanwhile there are a lot of good experiences concerning the use of the ester liquid Midel 7131 in distribution transformers. This good experience encourages the manufacturer of transformers to use this liquid in power transformers. Due to larger dimensions of power transformers in comparison to distribution transformers special consideration is necessary. The contribution presents some results of investigations concerning the electric and dielectric behaviour of ester liquids in comparison to mineral based transformer oil.Furthermore the performance of ester liquid Midel 7131 and mineral oil mixtures concerning the electric behaviour is introduced.
H. Borsi, E. Gockenbach
University of Hannover, Institute of Electric Power Systems,
Division of High Voltage Engineering, Schering-Institute
Callinstr. 25 A, D 30167 Hannover GERMANY