The Transformer is a static device that transfers electrical energy from one electrical circuit to another electrical circuit without change in the frequency but voltage level is usually changed. It may be stepup or step down transformer.

stepup transformer

The transformer has two winding one is called primary winding and other is called secondary winding.

  • The source is connected to the primary winding.
  • The load is connected to the secondary winding.
  • The transformer is an electromagnetic energy conversion device, since the energy received by the primary is first converted to magnetic energy and then it is reconverted into electrical energy in the secondary circuit. Thus the primary and secondary winding of a transformer are not connected electrically, but are coupled magnetically.
  • The transformers may be stepped up or stepped down. If the secondary winding has more turns than the primary winding, then the secondary voltage transformer is called a stepup transformer. If the primary winding has more turns than the secondary winding, then the secondary voltage is lower than the primary voltage and the transformer is called a step down transformer.

Necessity of Transformer

The electrical power is generated at 11kv. For economical reasons, ac power is transmitted at very high voltages over long distances. 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 safely 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.