Water in oils

Even just to touch on all aspects of water in insulating oils would require a paper far too long for present purposes. The remarks in this paper are confined to a few considerations of the effects of moisture in the oil-paper insulation of large power transformers filled with mineral oil. No attention is paid to other items of oil-filled plant such as cables, tapchangers, bulk oil circuit breakers, instrument transformers or bushings. The main issue covered is the behaviour of moisture in the bulk oil-impregnated paper main insulation of the transformer windings. There is no detailed examination of the paper-oil interface or the effects of water on surfaces such as barrier boards and paper-wrapped connecting leads. This paper attempts to address how moisture gets into the oil, how is it undesirable, how to measure it and how it may be removed.