A transformer cannot work on DC supply. If a rated DC voltage is applied across the primary, a flux of constant magnitude will be set up in the core. Hence, there will not be any self-induced emf (which is only possible with the rate of change of flux linkages) in the primary winding to oppose the applied voltage. As the resistance of the primary winding is very low, the primary current will be quite high as given by the Ohm’s law.
This current is much more than the rated full-load current of primary winding. Thus, it will produce lot of heat (I2R) loss and burns the insulation of the primary winding, and consequently, the transformer will be damaged. Hence, DC is never applied to a transformer.
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