| the arithmetic difference between the no-load voltage of a winding and the voltage developed at the terminals of the same winding at a specified load and power factor, the voltage supplied to (one of) the other winding(s) being equal to:|
- its rated value if the transformer is connected on the principal tapping (the no-load voltage of the former winding is then equal to its rated value);
- the tapping voltage if the transformer is connected on another tapping.
This difference is generally expressed as a percentage of the no-load voltage of the former winding
NOTE – For multi-winding transformers, the voltage drop or rise depends not only on the load and power factor of the winding itself, but also on the load and power factor of the other windings.