Proposed Revisions of American Standard C37.10 AIEE Committee Report

The AIEE New Working Group on Methods of Rating Power Circuit Breakers presented at the 1959 Winter General Meeting Conference Paper 59-186, entitled " Proposed Revision of American Standard C37.4, Rating Structure for Alternating-Current Power Circuit Breakers." That paper has been further reviewed and rewritten, see page 449 of this issue. The paper presented herewith is a companion paper. It conforms to the revised Rating Structure and employs a corresponding numbering system of the various sections. Much of the information included on circuit-breaker application has heretofore not appeared in the American Standards. The methods for calculation of shortcircuit currents proposed in this paper are designed to demonstrate and make clear symmetrical as well as asymmetrical current requirements. The calculation procedure provides: 1. an E/ X (symmetrical current) simplified method, 2. an E/ X method corrected for a-c and d-c decrements, and 3. the method generally recognized in the industry as the " rigorous method," although it is probably not necessary to employ this procedure in view of the accuracy obtainable by the two easier methods. Method 2 has been developed primarily to replace the more difficult method 3, and it provides at the same time a great improvement in accuracy as compared with the simplified method of American Standard C37.5-1953, with relatively Little additional effort being required of the application engineer.