Short circuit current fundamentals: characteristics/magnitudes/definitions for high voltage circuit breaker duties

The ANSI/IEEE Standards C37 provide many sections identifying the characteristics, magnitudes and relationships for short circuit/fault currents. Also, these standards provide many sections defining the preferred ratings that circuit breakers and/or fuses are to be capable of. The goal for this paper is to provide a general/executive summary and clear definition for medium and high voltage short circuit (SC) current rating requirements for circuit breakers and present the five stages (steps) of SC current that are derived from the standards. One commercial power system analysis program calculated fundamental SC current values correctly, but did not comply with the IEEE/ANSI Standards definition for stage 2 asymmetrical values. This mis-directed the decision of the required circuit breaker rating. There is another commercial program that does provide values and definitions that comply with the Standards for all specified magnitudes in the five stages of SC current. It is important to be able to clearly understand the SC current characteristics when making circuit breaker selection. This paper provides a guide to evaluate the required circuit breaker capability/rating, per the latest ANSI/IEEE Standards, for the supplier to comply with