Short-circuit current calculation: a comparison between methods of IEC and ANSI standards using dynamic simulation as reference

A comparison is presented between two of the most significant international standards for short-circuit calculation: the IEC 909 Standard and the ANSI/IEEE C37.010-1979. The ANSI standard is more oriented toward breaker selection while the IEC standard gives general guidelines for short-circuit current computation. A set of short-circuit currents, directly extracted from the standards or obtainable after some elaborations, were determined as values useful for the comparison. A detailed dynamic analysis performed by using a well-known program for electromagnetic simulation was used as reference for the comparison between the two standards. The comparison shows that the IEC 909 is somewhat more ponderous than the ANSI standard. Hypothesis and assumptions are more numerous and more detailed in the IEC 909 than in the ANSI standard. In the former standard, more information and more formulas about the possibility of neglecting motor contributions are presented, as well as the basis for determining whether short-circuit is to be considered near or far from generators. The results of calculations confirm that both standards give satisfactory approximations of the short-circuit currents, which are mostly on the safety side