Chapter IX insulating liquids

Massey (1) has made a comprehensive contribution in a three-part paper “The Deterioration of Transformer Oil”. Though, his discussion is based largely on. British Standard 148–1951 for transformer and switch oils, the opinions and conclusions are broadly applicable. Part I discusses transformer design, construction, and operation; and the relation of these factors to oxidation of transformer oil. Part II is a discussion, of the effect of transformer construction materials on the rate of oil deterioration. Accelerated oxidation tests were made at 150°C. using a modification of BS148. Service condition tests were made at 80°C. and 100°C. in glass containers. The transformer materials tested included about all the metals and non-metals used in transformer construction. Part III Is an assessment of BS148; and a discussion of means of improving transformer oil stability. It is concluded that, when carefully done, BS148 is a satisfactory transformer oil oxidation test. With regard to improvement of oxidation stability of transformer oils, it is said that further improvement through present refining processes is unlikely; and that when severe conditions occur, such as transformer operation at high temperature with access of air to the oil, the use of an oxidation inhibitor in the oil is a logical means of attaining increased oxidation stability. Broadly useful in Part III are discussions, with respect to BS148, of the relation between sludge formation and Wijs iodine value, and of the mechanism of oxidation catalysis in transformer oil of solid and oil soluble forms of copper. It was the most active oxidation catalyst of all the transformer materials tested.