TRANSFORMERS

One of the main reason of adopting a.c. systemindtead of d.c. system for generation, tarnsmissionand distribution of electric power is that alternating voltage can be increased or decreased conveniently by means of transformer. In fact, for economical reasons, electric power is required to be transmitted at high voltage whereas it has to be utilized at low voltages from safetly point of view. The increase in voltage for transmission and decrease in voltage for utilization can be achived by using a transformer.

Transformer is a static device which transfer a.c. electrical power from one circuit to other at the same frequency but the voltage level is changed usually . when the voltage level is raised on the output side, the transformer is called step-up transformer, whereas, the transformer in which the voltage is lowered on the output side is called a step-up transformer.

There are two type of construction of transformer:

1. Core type transformer.
2. Shell type transformer.

AN IDEAL TRANSFORMER

An ideal transformer is one which has no ohmic resistance and no magnetic leakages flux i.e. all the flux produced in the core linkes with primary as well as secondary. Hence , transformer has no copper losses and core losses. It means an ideal transformer consists of two purely inductive coils would on a loss free core. Although is actual practicle, it is impossible to realized such as transformer yet for convenience, it is better to start with an ideal transformer and then extend it to an actual transformer.

In an ideal transformer there is no power loss, therefore, output must be equal to input.

TRANSFORMAR ON D.C.

A transformer cannot work on D.C. supply. If a rated D.C. voltage is applied across the primary a flux of constant magnitude will be set up in the core. Hence, there will not be any self induction e.m.f. in the primary winding to oppose the applied voltage. The resistance of the primary winding is very low and the primary current will be quite high as given by the Ohm’s law.

            Primary current = d.c. applied voltage/resistance of primary winding

This current is much more than the rated full load current of primary winding. Thus it will produce lot of heat loss and burn the insulation of the primary winding, and the transformer will be damaged. That is why, d.c. is never applied to a transformer.

LOSSES IN A TRANSFORMER

The losses which occur in an actual transformer are:

1. Core or iron losses.
2. Copper losses.

COPPER OR IRON LOSSES:

The alternating flux is set up in the core, therefore , hysteresis and eddy current losses occur in the magnetic core.

1. Hysteresis loss: when the magnetic material is subjected to reversal of flux, power is required for the continuous reversal of molecular magnets. This power is dissipated in the from of heat and is known as hysteresis loss. This loss can be minimized by using silicon steel material for the construction of core.
2. Eddy current loss : since the flux in a transformer core is alternating, it links with the magnetic material of the core. This induces e.m.f. in the core and circulates eddy current. Power is required to maintain these eddy current. This power is dissipated in the form of heat and is known as eddy current loss. This loss can be minimized by making the core of this laminations.

COPPER LOSSES:

Copper losses occur in both the primary and secondary winding due to their ohmic resistance .

• Written by Pankaj .
• In category General Reference.
• 14 years ago.

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