Transformer Fault Current Calculation

Description
Transformer Impedance is measured in Percent Impedance. Percent Impedance is the % of rated primary voltage that is applied to the Transformer's primary winding so that the rated secondary Full Load Current can flow in the secondary winding. The primary winding is connected to a variable supply or a Variac with the secondary winding shorted-out for this test to be performed.

There can be a variation in the transformer impedance values, but generally the transformers that Blakley Electrics use will be in the 4-5% range of primary voltage.

For calculation of the maximum fault current that can be potentially achieved within a transformer-fed circuit, we use the formula shown in the tool screenshots beginning with: zSEC=.

*Originally shared on electrical-engineering-portal.com*