Standard basic impulse insulation levels

This report of the joint committee
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on co-ordination of insulation of AIEE, Edison Electric Institute, and National Electrical Manufacturers Association is the culmination of more than ten years
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study to establish basic insulation co-ordination. It specifies basic impulse insulation levels in terms of a withstand voltage for a specified test wave. These values are to be the bases for various AIEE and other standards now in course of development or revision. Culminating over ten years' work on insulation co-ordination during which the fundamentals of making impulse tests were investigated and standardized, as well as basic levels set up and provisionally tried out, the joint AIEE-EEI-NEMA committee on insulation co-ordination at its meeting held in November, 1940, agreed unanimously to adopt as standard the series of basic impulse insulation levels given in table I. These are the same values given in the paper presented at the AIEE winter convention, January 22–26, 1940, “Basic Impulse Insulation Levels” by Sporn and Powel (AIEE Trans., Oct. '40 Sec., p. 596–8). The purpose of this present report is to call attention to the fact that these basic levels have now been adopted and to the general conditions under which they apply. The general principle of insulation co-ordination requires a reasonable margin between the voltage level held by the protective device (the protectable level) and the various basic levels themselves to insure that adequate protection is provided. The values in table I have been set up on this basis. It is felt that the values so set up are on a sound basis and that they are most likely to stand without change for a long time. It is the opinion of the committee, therefore, that the various technical committees working on standards can adopt the values given in this report for standardization purposes, and it is further believed that the use of these values will result in ultimate over-all benefit to the industry.