Natural Ester Dielectric Fluid Development Update

Since the early 1980s, Cooper Power Systems has been actively involved in exploring and developing ester-based dielectric fluids. Introduced in 1984, our first commercialized ester was a synthetic polyol ester, developed primarily as an environmentally acceptable Askarel substitute. Although its technical performance is very good, the cost is prohibitive for most applications. The desirable properties of the polyol ester spurred exploration into other, more cost-effective, ester chemistries. This led to the evaluation of a natural (vegetable oil) ester dielectric coolant having many of the same performance advantages of synthetic esters, but much more economical. The major disadvantages of the natural esters are their inherent susceptibility to oxidation and higher pour point. We undertook a massive natural ester research and development program beginning in the early 1990s. Significant improvement low temperature flow was achieved. Oxidation inhibitors together with proper method-of-use overcome the oxidation stability issues. In many ways the natural esters perform better than the less-flammable fluids they replace, and offer significant advantages for applications where naphthenic mineral oils are traditionally applied. Although initially developed for distribution transformers, application in medium and large power transformers is becoming more common. This paper summarizes our laboratory and field experience and is an update of work presented in 2006.