A transformer is an electro-static device used to transfer energy from one electrical system to another through the principle of electromagnetic induction. Electromagnetic induction is the process by which voltage is generated across a moving conductor when placed in a stationary magnetic field (or when a stationary conductor is placed in a changing magnetic field).
Basic working principle of transformer
Alternating current (AC) varies its magnitude with respect to time. When this AC voltage is applied to the primary of the transformer, a varying magnetic field (flux) is automatically generated in the transformer core. This varying flux will link with the secondary winding of the transformer and thereby a voltage will be generated across the secondary side. Thus the voltage is generated based on the principle of electromagnetic induction.
Can a transformer operate on DC?
The magnitude of the direct current (DC) does not change with respect to time. The transformer windings basically act like inductors. So when a DC voltage is applied across an inductor, it acts as a short circuit. That is, there won't be any potential difference across the inductor, but a current starts flowing through the inductor.
Likewise, when a DC voltage is applied across the primary of a transformer a time-invariant current starts flowing through the primary. This time-invariant current cannot create a varying magnetic field in the core of the transformer. And hence no voltage is generated across the secondary winding. As the transformer windings have very low resistance, they tend to draw excessive current from the DC supply connected to the primary. Sometimes this excessive current can result in burning out of transformer windings. So as to conclude, a transformer cannot operate with DC.
