When the secondary of the transformer is loaded (from no load to full load), the secondary voltage changes even though primary supply voltage is held constant at rated value.
% Voltage Regulation = (V2(no load) - V2 (full load))*100 / (V2(no load))
With the rated voltage applied to the primary winding, the secondary terminal voltage varies with the load current and power factor even the primary voltage is kept constant. This variation is called voltage regulation.
Voltage regulation depends on the voltage drop in the impedance of the transformer, load current and load power factor.
Leading and Lagging power factor regulation:
- For lagging power factor load the secondary voltage decreases with increase in the load current (when the transformer is loaded). Thus for lagging power factor loads, the regulation is positive ( voltage drop observed as the load current increases).
- For leading power factor load, the secondary voltage increases slightly with increase in the load current. This type regulation. Thus for leading power factor loads, the regulation is negative (raise in voltage as load current increases)
For better performance of the system voltage regulation should be as minimum as possible i.e, Change in secondary voltage with load should be as minimum as possible when primary voltage is kept constant.