ANSI Fault Analysis
A_FAULT provides fault calculations in full compliance with the ANSI C37 standards.
It offers separate solutions for low, medium and high voltage systems and for symmetrical, momentary and interrupting calculations as defined in the standards.
For medium and high voltage systems, the momentary and interrupting values may be calculated using either the E/X or E/Z methods permitted by the standards. Both ac and dc decrement curves required by the total current rated standard (C37.5) and the symmetrical rated standard (C37.010) are used by the program.
A_FAULT Versus DAPPER Traditional Fault Analysis
A_FAULT follows ANSI C37 standards for calculating equipment ratings.
DAPPER follows a traditional Ohm’s Law calculation for fault current.
For Low voltage systems (600V and below), the calculations are the same except for two items: 1) A_FAULT calculates the X/R ratios based on separate X and R networks whereas DAPPER uses a single complex network. 2) A_FAULT uses the X/R/ ratio to adjust the calculated short circuit value to compare directly with molded case and power circuit breaker ratings based on ANSI test power factor. In other words, the calculated short circuit value is increased if the X/R/ ratio is larger that the ANSI test power factor.
For Medium and High Voltage systems (above 600Volts): The momentary calculations are similar. The largest difference is in Interrupting Calculations: A_FAULT uses the ANSI C37 tables and curves to simulate AC and DC decay for interrupting calculations, whereas DAPPER accounts for the system DC decay but ignores the AC machine decay in all cases.