A new basis for rating power circuit breakers [includes discussion]

Recently, considerable interest has been expressed in the interpretation of American Standards and in the relative severity of the interruption of symmetrical currents and of asymmetrical currents having different degrees of asymmetry. To bring out discussions of these problems, the AIEE Committee on Switchgear arranged a session of the AIEE Winter Meeting in New York in 1952, at which session five technical papers on this subject were presented. In view both of the general interest shown at this session and the general trend towards symmetrical ratings for all apparatus, the AIEE Committee on Switchgear directed the AIEE Subcommittee on Power Circuit Breakers to investigate the methods of rating power circuit breakers and to recommend an improved method. A Working Group on Methods of Rating was formed early in 1952 to work out a basis for the change, and the task assigned to the Working Group was: 1. To recommend a new basis for rating; 2. To list the advantages of the new method of rating as compared with the old method; 3. To propose the changes in the ASA Standards that will be necessary; 4. To recommend what provisions must be made in the ASA Standards or otherwise, so that confusion does not arise over existing name-plate ratings. The Working Group was also instructed that it should be cognizant of the work of the International Electrotechnical Commission (IEC), so that, if adopted, a new standard would be a step in the direction of, or compatible with, the International Standards for alternating current circuit breakers. The Working Group has spent considerable time and effort on this assignment, and this paper constitutes its first official report and recommendation for a new basis of rating. It is hoped that this paper will be widely studied and discussed, so that the Working Group can incorporate as many improvements as possible before submitting its final report to the AIEE Subcommittee on Power Circuit Breakers.