Voltage Regulation is the way in which the secondary terminal voltage varies with the load depends upon load current, the internal impedance and the load power factor. The change in secondary terminal voltage from no-load to full-load, with primary voltage and frequency held constant, is termed the inherent regulation.
The figure of merit which determines the voltage characteristic of a transformer is termed as voltage regulation. It is usually expressed as a percentage of the rated terminal (secondary) voltage.
It is defined as the change in magnitude of terminal (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.
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 a transformer, on an average, is about 4 percent.
From the consumer’s view point, voltage regulation due to variations in load is undesirable and should be kept smallest possible.
Condition for Zero Regulation:
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Regulation = I2 R02 cos ɸ + I2 X02 sin ɸ/E2
Regulation will be zero if the numerator will be equal to zero:
Or I2 R02 cos ɸ + I2 X02 sin ɸ = O
Or tan ɸ = -R02/X02 … (10.32)
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The -ve sign indicates that zero regulation occurs at a leading power factor.