Surface coatings for h.v. insulators in polluted areas

Abstract
Many years' experience in Britain has shown that petroleum jelly, used as an insulator coating, is an effective remedy against flashover in polluted localities. Following the winter of 1962–63, when some 800 pollution faults were recorded on 275 kV circuits alone, the use of petroleum jelly has been stepped up, and efforts have been intensified to improve the technique of application and develop better materials. Spraying methods have resulted which are both quick and cheap, and new petroleum jellies have been produced which resist sliding in hot weather, without sacrifice of effectiveness against flashover. Methods have been found for estimating the effective life of a coating, which may be three years for petroleum jelly, compared with one year for silicone grease in the same locality. Because of this difference in working life, the use of petroleum jelly is generally cheaper than that of silicone. Development of easier techniques for removing grease is still required; special porcelain shapes have been devised which may speed this operation. Easily strippable oily plastic coatings have been developed, but these are less successful electrically and more difficult to apply than petroleum jelly. Another solution to the problem of inhibiting pollution flashover is the use of oil-bath insulators, which have the advantage of requiring little maintenance.

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