What are losses of Transformer? Draw an equivalent circuit of Transformer.

Losses of Transformer

The power losses in a transformer are of two types, namely;

1.         Core or Iron losses      2.         Copper losses

These  losses  appear  in  the  form  of  heat  and  produce  (i)  an  increase  in temperature and (ii) a drop in efficiency.

1.      Core or Iron losses (Pi)

These consist of hysteresis and eddy current losses and occur in the transformer core due to the alternating flux. These can be determined by open-circuit test.

Both hysteresis and eddy current losses depend upon (i) maximum flux density Bm  in the core and (ii) supply frequency f. Since transformers are connected to constant-frequency, constant voltage supply, both f and B_m are constant. Hence, core or iron losses are practically the same at all loads.

The hysteresis loss can be minimized by using steel of high silicon content whereas eddy current loss can be reduced by using core of thin laminations.

2.      Copper losses

These losses occur in both the primary and secondary windings due to their ohmic resistance. These can be determined by short-circuit test.

It is clear that copper losses vary as the square of load current Thus if copper losses are 400 W at a load current of 10 A, then they will be (1/2)2      400 = 100 W at a load current of 5A.

It may be noted that in a transformer, copper losses account for about 90% of the total losses.

Approximate equivalent circuit of a loaded Transformer

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