Comparison of ANSI and IEC 909 short-circuit current calculation procedures

A comparison between the American National Standards Institute (ANSI) and International Electrotechnical Commission (IEC) 909 short-circuit current calculation procedures is presented. The philosophical differences in calculation procedures are discussed. No attempt is made to present the complete method of either standard or to make judgments on the correctness of either standard. While ANSI fault calculation methods are designed to determine a value to compare to the equipment ratings, the IEC 909 Standard presents a method which inherently models the fault currents more accurately. The IEC method requires significantly more complex modeling of the power system fault contributions than the ANSI procedures