Free Short Circuit Current Calculator
Estimate the prospective short-circuit current from the transformer kVA rating and impedance.
Prospective Short-Circuit Current
14,434 A
Prospective Short-Circuit Current vs Transformer Rating
Transformer Short-Circuit Current
The prospective short-circuit current at the transformer secondary is limited by the transformer impedance.
Formulas
I_FL = kVA x 1000 / (sqrt(3) x V) (full load current)
I_SC = I_FL / (Z%/100) (short-circuit current)
where Z% is the transformer impedance expressed as a percentage. This is the maximum fault current available at the transformer terminals, ignoring cable impedance downstream.
Example Calculation
A 500 kVA transformer, 400 V secondary, 5% impedance.
- 01I_FL = 500,000 / (1.732 x 400) = 721.7 A
- 02I_SC = 721.7 / 0.05 = 14,434 A = 14.43 kA
- 03Switchgear must have a breaking capacity above 14.43 kA.
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