Voltage regulation of Transformer

Voltage regulation of a Transformer is defined as the change in magnitude of terminal voltage  or secondary voltage, when full load(rated load) of specified power factor supplied at rated voltage is thrown off(reduced to no load) with primary voltage and frequency held constant, as percentage of the rated terminal voltage.

Explanation of voltage regulation of transformer

If v2 is the secondary (terminal) voltage at full load at specified. Power factor and E2 is the secondary(terminal) voltage at no load,then percentage regulation is given as:

Voltage regulation of transformer at lagging power factor

From the given figure;

Angle between OC and OD may be small,so it can be neglected.Hence,

OD≅OC

Voltage regulation of transformer at leading power factor

From the given figure,

Angle between OC and OD may be small,so it can be neglected.Hence,

OD≅OC

The percentage regulation can be given as

voltage regulation of a transformer on an average is about 4 %.

Is the voltage regulation better or worse at 0.6 pf lagging than at 0.8 pf lagging for the same KVA output?

Ans:The voltage regulation will be maximum and worst when power factor becomes equal to

.since the equivalent reactance of transformer is usually more than double its equivalent resistance,the voltage regulation will increases(i.e become more and more worse) till power factor falls even below

,the voltage regulation will worsen at 0.6 pf lagging than at 0.8 pf lagging.

How the regulation of transformer is affected by the power factor of the load supplied by it?

Ans:The voltage regulation increases with the fall in power factor of the load,if the load is inductive,and becomes maximum when the power factor of the inductive load becomes equal to

The voltage regulation drops with the fall in power factor of the load,if the load is capacitive,and becomes equal to

and then increases with the fall in power factor of load in the negative direction.

condition for Zero Regulation

Regulation will be Zero if the numerator will be equal to Zero or

The negative sign indicates that Zero regulation occurs at a leading power factor.Zero voltage regulation is only possible in case of Ideal transformer.

Condition for Maximum Regulation

Regulation will be maximum if

i.e maximum regulation occurs at lagging power factor.