Protective finishing of electrical equipment

This paper is a review of current practice and methods of protective finishing for electrical equipment. It covers most conditions met in normal service, but excludes the more specialized tropical and arctic conditions, which differ considerably from normal applications. The conditions under which the protective finishes are used are divided into six classes, and the service conditions for each class are described. Different types and methods of protective finishing are reviewed and described in some detail, together with reference to a number of self-protective materials. The choice of a finish for a particular piece of equipment is frequently a compromise between the various factors involved, but a broad tabulation is given with examples of the influence of particular factors in a final choice. The correct evaluation of accelerated tests on finishes is most difficult, and the necessity for correlation with field experience is stressed. Methods of testing and process control are reviewed and some of the difficulties which arise in service are illustrated. This review of the field of protective finishes shows the range of problems which must be considered by the engineer when designing and manufacturing his products, and points to the desirability of close co-operation with the industrial chemist.