The Transformer is a static device that transfers electrical energy from one electrical circuit to another electrical circuit with same in the frequency but voltage level is usually changed.
The transformer has two winding one is called primary winding and other is called secondary winding.
Necessity of Transformer
The electrical power is generated at the voltage level of 11kv. For economical reasons, ac power is transmitted at very higher voltages over a long distance. Therefore, a step up transformer is used at generating station to raise the voltage level. Then voltages are stepped down to suitable level by a transformer at various substations. Ultimately for utilization of electrical power, the voltage is stepped down to 400/230 for safety reasons.
Transformer is a static device, owing to the lack of rotating parts. There are no friction or windage losses, so that the efficiency of a transformer is high. Typical transformer efficiencies at full load lie between 95% and 98%.
Transformer on DC
A transformer cannot operate on dc supply and never be connected to a dc source. If the primary winding of a transformer is connected to a dc supply mains the flux produced will not vary but remain constant in magnitude and, therefore no emf will be induced in the secondary winding except at the moment of switching ON. There will be no induced emf in the primary winding and therefore, a heavy current will be drawn from the supply mains which may result in the burning out of the transformer winding.