Standards of Insulation and Protection for Transformers

This paper presents the reasons and the evidence which have influenced the authors to favor the proposed Recommendations on Relation of Transformer Insulation to Adjacent Line Insulation set forth in a companion paper by Messrs. Montsinger and Dann. The paper first outlines the principal considerations which govern the determination of transmission line insulation on the one hand and transformer insulation on the other, and concludes that the line insulation is a service problem requiring a unique solution whereas the transformer insulation is a manufacturing problem requiring a standardized solution. True coordination of the one with the other therefore seems impossible, indicating the need for protective measures at the point of contact. Considerations affecting the selection and characteristics of such protective measures are discussed briefly and the reasons outlined for believing that, at present, service experience is a better criterion than research tests upon which to decide such selection. Twenty-five years´ service experience on the system now controlled by the Buffalo, Niagara and Eastern Power Corporation, with protective gaps similar to those recommended as one of the proposed protective measures, is described and the conclusion drawn that the use of such gaps under suitable conditions constitutes a satisfactory protective measure.