A transformer is a device that step-up or step-down the level of AC current or voltage without changing the primary (i.e. input source) frequency.
The transformer only works on AC and can’t be operated on DC i.e. it has been designed to be operated only and only on alternating current and voltage. A transformer works on the principle of mutual induction, in which you need a varying magnetic field in a winding to induce an EMF in the secondary winding.
In DC generally change in frequency with respect to time is zero. If the primary of a transformer is connected to a d.c. supply, the primary will draw a steady current and hence produce constant flux. Consequently, no back e.m.f. will be produced. So a dc source cannot provide varying magnetic fields, hence mutual induction is not possible.
The primary winding will draw excessive current due to the low resistance of the primary. The result is that the primary will overheat and burn out or the fuses will blow. Care must be taken not to connect the primary of transformer across the DC supply.
Answer In other words
A transformer is connected to a DC supply:
- When a DC voltage is applied to the transformer's primary coil, a constant current result in constant flux.
- In the primary circuit, the induced EMF will be zero.
- The flux produced is inversely proportional to the frequency of the DC voltage, which has no frequency.
- The transformer core saturates as a result of this.
- The extra current is short-circuited by the transformer's primary coil.
- The transformer may be blown away as a result of this.
- As a result, the transformer should never be connected to DC rather than AC.
- In the magnetic environment, any change of the coil of wire will cause a voltage (emf) to be induced in the coil.