Corona voltages of typical transformer insulations under oil — II

SOME 13 years ago, Doctor L. Dreyfus¹ published a paper on insulation design of transformers. In this paper, he assumed that electrical breakdown adjacent to square edges was a function of the stress and the distance over which this stress acted; in other words, that it was a function of the voltage gradient along a line of force for some indeterminate distance. By means of conformal representation, he was able to determine the field shape at the corners of structures representative of those in transformers. He could then evaluate the strength of these various structures. His paper was principally mathematical, and it is the purpose of this paper to call attention to his work, to restate some of his assumptions and the conclusions that he reached, and to furnish some experimental data.