Insulation systems for electrical distribution transformers arebeing re-evaluated based on their total life cycle cost from both aneconomical and an environmental perspective. Due to the inherentlyhigher efficiency design offered by liquid cooled transformers,development has focused on fluids having improved environmental andhealth properties while maintaining the fire resistant properties of“less-flammable” fluids. This paper reports the authors'findings from several years of research and development on alternativedielectric systems using both natural and synthetic esters. Becauseesters have lower inherent resistance to oxidation and differsignificantly in the type and magnitude of oxidation byproducts, a novelinsulation system was developed to overcome this potential handicap.Single and three phase prototype field installations using these newdielectric coolants are discussed
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