Aging of wire enamels in transformer oil

THERMAL aging characteristics of wire enamels aged under conditions similar to those which may be expected in sealed liquid-filled transformers have been studied and found to be quite different from results obtained by aging the same enamels in air. Enamels which have shown only fair thermal aging characteristics in air in comparison to other enamels may rate very differently when aged in a sealed system with a limited amount of oxygen present. For example, Formex (General Electric registered trademark) wire enamel which has a short life in comparison to a terephthalate polyester when aged thermally in a circulating air oven is equal or superior to the terephthalate polyester when aged in a closed system under oil.