Calculating the Maximum Short-Circuit Current (SCA) for the Transformer

We previously published in a post how to calculate the Percentage Impedance of a transformer.

As requested by some friends, from Z%, the maximum short-circuit current (SCA) is calculated.

Calculating the Maximum Short-Circuit Current (SCA) for the Transformer

Transformer data is as follows:  

25 MVA & 66/11 kV  

Z = 10% (Impedance)

SCA: Short Circuit Current  

FLA: Full Load Current  

1. First, calculate the maximum load current of the transformer (secondary winding):

• P = 1.73 × V × I  

• 25,000 = 1.73 × 11 × I  

Maximum Full Load Current:  

   I = 25,000 / (1.73 × 11)  

   I = 1313 A (1313 Amperes)  

2. Second, calculate the short-circuit current using the following equation:

   Full Load Current = Short Circuit Current × Impedance (Z%)  

   I (Full Load) = I (Short Circuit) × Z%  

   I (Short Circuit) = I (Full Load) / Z%  

   I (Short Circuit) = 1313 / 10%  

   I (Short Circuit) = 13130 A  

   = 13 kA