SHORT‐CIRCUIT CALCULATIONS ACCORDING TO ANSI/IEEE STANDARDS FOR ARC FLASH ANALYSIS

The calculation of short‐circuit currents is the first step in the process of arc flash calculations. The IEEE 1584 Guide equations relate three‐phase bolted fault currents with arcing currents. In a multivoltage system, four types of short‐circuit calculations may be required. These are: first‐cycle (momentary) duties for fuses and low voltage circuit breakers, first‐cycle (momentary) duties for medium or high voltage (HV) circuit breakers, contact parting (interrupting) duties for HV circuit breakers (circuit breakers rated above 1 kV), and short‐circuit currents for time‐delayed relaying devices. In an attempt to harmonize ANSI/IEEE standards for HV circuit breakers with IEC, there has been considerable changes in the rating structures of the HV circuit breakers. Again, the procedures of calculations in IEEE standards are oriented for calculations of short‐circuit duties on the switching devices. Typical results of computer‐based calculations are also shown.