Relative properties of the new combustion-resistant vegetable-oil-based dielectric coolants for distribution and power transformers

Electrical distribution transformers insulation systems are being reevaluated based on their total life-cycle cost from economical, safety, and environmental perspectives. Due to the inherently higher efficiency design offered by liquid-cooled transformers, development has focused on fluids having improved environmental and health properties while maintaining the fire-resistant properties of "less-flammable" fluids. This paper reports our findings from several years of research and development on alternative dielectric systems using both natural and synthetic esters. Because esters have lower inherent resistance to oxidation than conventional mineral oil, a novel insulation system was developed to overcome this potential handicap. Single- and three-phase prototype field installations using these new dielectric coolants are discussed.