TABLE OF CONTENTS Consider a transformer whose primary winding voltage is adjusted so that it delivers the rated load at the rated secondary terminal voltage. If we now remove the load, the secondary terminal voltage changes because of the change in the voltage drops across the winding resistances and leakage reactances. A quantity of interest is the net change in the secondary winding voltage from no load to full load for the same primary winding voltage. When the change is expressed as a percentage of its rated voltage, it is called the voltage regulation ( VR ) of the transformer. As a percent, it may be written as
where V 2 NL and V 2 FL are the effective values of no-load and full-load voltages at the secondary terminals.
The voltage regulation is like the figure-of-merit of a transformer. For an ideal transformer, the voltage regulation is zero. The smaller the voltage regulation, the better the operation of the transformer.
The expressions for the percent voltage regulation for the approximate equivalent circuits as viewed from the primary and the secondary sides are
where V 1 is the full-load voltage on the primary side and V 2 is the rated voltage at the secondary.
A 2.2-kVA, 440/220-V, 50-Hz, step-down transformer has the following parameters as referred to the primary side: R e1 = 3 ?, X e1 = 4 ?, R c1 = 2.5 k ?
