TRANSFORMER

TRANSFORMER:

Transformer is a static device, by means of which an electrical power is transformed from one circuit to another with the desired change in voltage and current without any change in the frequency.

All parts in transformer are in stationary positions. Hence transformers are called static electric machines.

VIDEO EXPLANATION:

PRINCIPLE OF OPERATION:

The transformer operates on the principle of mutual induction.

Mutual induction:

Mutual induction is the phenomenon in which a change of current in one coil causes an induced EMF in another coil placed near the first coil.

The animations below clearly explains the mutual induction concept

The coil in which electrical energy (AC) is fed is called primary winding (P).

The other coil which is connected to load is called secondary winding (S).

The two winding of the transformer are magnetically coupled through the core.

When the primary winding is connected to AC source, the alternating current in the primary winging setup a flux (Φ) in the core. This alternating flux (Φ) completes its path through common magnetic core.

Thus, this alternating flux links with the secondary winding.

According to the Faraday’s law of electromagnetic induction, mutually induced EMF get developed in the secondary winding. If now load is connected to the secondary winding, this EMF drives a current through it.

The magnitude of the induced EMF depends up on the number of turns in the winding.

Step up transformer:

     If the secondary winding has more number of turns than the primary winding, then the secondary voltage is higher than the primary voltage and the transformer is called step up transformer.

Step down transformer:

If the secondary winding has less number of turns than the primary winding, then the secondary voltage is lower than the primary voltage and the transformer is called step down transformer.

A step-up transformer can be used as a step-down transformer, in which the secondary of step-up transformer becomes the primary of the step-down transformer.

Actually, a transformer can be termed a step-up or step-down transformer only after it has been put in to service. Therefore, when referring to the winding of a transformer, the terms high voltage winding and low voltage winding should be used instead of primary and secondary winding. 

Transformation Ratio is defined as the secondary voltage divided by the primary voltage. And it is denoted by K.

K = V_s / V _p

     = N _s / N_p

  = I _p / I_s

TRANSFORMER CONSTRUCTION:

The basic parts of a transformer are

1.     Magnetic Core

2.     Primary and Secondary Winding.

MAGNETIC CORE

The magnetic core is a stack of thin silicon – steel lamination's to reduce hysteresis loss about 0.35 mm thick for 50 Hz.

In-order to reduce the eddy current losses, these lamination's are insulated from one another by thin layer of varnish.

The core of the transformer has two portions called limb and yoke.

The vertical portion on which the coils are wound is called limb.

The top and bottom horizontal portion are called Yoke.