Enter the rated primary volts of the transformer, and the short circuit volts into the calculator to determine the transformer impedance percentage.

Transformer Impedance Formula

The following formula is used to calculate a transformer impedance percentage. 

I = SCV / RV *100
  • Where I is the transformer impedance percentage
  • SCV is the short circuit voltage (also known as the injected voltage)
  • RV is the rated voltage

To calculate a transformer impedance percentage, divide the short circuit voltage by the rated voltage, then multiply by 100.

Transformer Impedance Definition

Transformer impedance percentage is defined as the ratio of the injected voltage to the rated voltage. The rated voltage can be the secondary short condition.

Example Problem

How to calculate transformer impedance percentage?

First, you must find the rated voltage of the transformer. This is known as the secondary short condition and will be larger than the injected voltage.

For this example problem, the rated voltage is found to be 40V.

Next, find the injected voltage.

In this case, the injected voltage is found to be 30V.

Finally, calculate the transformer impedance.

Using the formula, %I = SCV / RV *100 = 30/40*100 = 75%.