For a 1500kVA transformer, how do you calculate the maximum secondary fault current?

To determine the maximum secondary fault current for a transformer, it's essential to understand the relationship between the full load current, voltage, and the transformer's impedance. The correct approach involves using the full load amps of the transformer divided by its percent impedance.

The percent impedance represents the voltage drop of the transformer under full load conditions and essentially reflects how much of the transformer's capacity can go to fault current. This impedance acts like a resistance that limits the fault current during a short-circuit condition. By dividing the full load amps by the percent impedance, you calculate the maximum short-circuit current that can flow through the secondary side of the transformer.

This calculation is crucial for ensuring that protective devices are adequate for the possible maximum fault current, safeguarding the system against overcurrents that could damage equipment or create unsafe conditions.