Voltage Regulation

Author: E.E. Kimberly

The voltage regulation of a transformer depends on the magnitudes of the resistances and the reactances of the windings. The impedance of a transformer is usually specified in per cent. This designation means that, with either the primary or the secondary winding short-circuited, the specified per cent of the rated voltage applied to the other winding will cause full-load current to flow in both windings. Distribution transformers are usually designed with impedances of 2 to 4 per cent. The per cent of voltage regulation with loads of rated current or less cannot exceed the per cent of impedance. The impedance specified on the name plate of a transformer is therefore an indication of the maximum voltage regulation that may be expected of it. The voltage regulation of a transformer is based on the change in secondary voltage from full load to no load with constant primary applied voltage. Thus,