Abridgment of electric strength of solid and liquid dielectrics

This paper was prepared by a subcommittee of the Committee on Electrical Insulation of the Division of Engineering and Industrial Research of the National Research Council. The general purpose of the committee is to foster research on dielectrics and its initial activities have been confined to the preparation of a series of summaries of the published literature on this subject. The subcommittee which presents this paper is the second one to report, it having been preceded by a paper on dielectric absorption and theories of dielectric behavior, by Chairman J. B. Whitehead, which was published by the A. I. E. E. in 1926. The second paper under the auspices of the committee was inspired by the first one, and was an original exposition of Clerk Maxwell´s theory of the double layer dielectric, by Professor Murnaghan, published by the A. I. E. E. in 1927. The present paper, like the first, is a summary of existing literature which, it is hoped, will afford a starting point for original research in many directions. It is hoped that the discussion by the Institute will bring out obscure phenomena and new interpretations of the data reviewed. The report starts with a consideration of the general subject of instability in electrical circuits, and an explanation of instability in the case of dielectrics, in terms of a stress and strain characteristic. This is followed by a discussion of distribution of stress and strain in non-uniform fields, and their relation to breakdown. The reversible and non-reversible phenomena of dielectric failure are considered, the former in relation to the electron theory and the latter in relation to the pyroelectric theory, and the bearing of both upon the time — voltage relation is indicated. The latter part of the full report is devoted to the relation of breakdown voltage to various factors, such as insulation thickness, insulation area, the electrode form, heterogeneity, temperature, rate of voltage, variation, pressure, etc. Final- conclusions are given in the full report which summarize in a few words the present state of the art, as it may be judged from published data.