The stability of flow-improver additives in transformer oils under oxidation and electrical discharges

Transformer oils used in the northern part of the United States and Canada must have low pour-point temperatures in order to maintain good flow characteristics under the sometimes arctic conditions encountered during the winter months. The naphthenic oils presently used meet this requirement, but they are not expected to be available any longer, as the corresponding crude oil bases are now depleted. The paraffinic oils proposed as alternatives by the oil industry have much higher pour points, which must be artificially lowered by incorporating relatively large amounts of pour depressants. The eventual use of paraffinic oils in cold climates therefore relies heavily on the quality of such additives and their stability under actual service conditions. Flow improver additives used in transformer oils are generally large molecules or polymers of the aromatic type, with long paraffinic side chains preventing the formation of crystals in oil on cooling [1]. Their resistance to oxidation, corona discharges and arcing have been examined in the present study.