Losses In Transformer

Losses In Transformer

 An electrical transformer is an static device, hence mechanical losses (like windage or friction losses) are absent in it. A transformer only consists of electrical losses (iron losses and copper losses). Transformer losses are similar to losses in a DC machine, except that transformers do not have mechanical losses.
Losses in transformer are explained below -

(I) Core Losses Or Iron Losses

Eddy current loss and hysteresis loss depend upon the magnetic properties of the material used for the construction of core. Hence these losses are also known ascore losses or iron losses.

§  Hysteresis loss in transformer: Hysteresis loss is due to reversal of magnetization in the transformer core. This loss depends upon the volume and grade of the iron, frequency of magnetic reversals and value of flux density. It can be given by, Steinmetz formula:
W_h= ηB_max^1.6fV (watts)       where,   η = Steinmetz hysteresis constant
                                                     V = volume of the core in m³

§  Eddy current loss in transformer: In transformer, AC current is supplied to the primary winding which sets up alternating magnetizing flux. When this flux links with secondary winding, it produces induced emf in it. But some part of this flux also gets linked with other conducting parts like steel core or iron body or the transformer, which will result in induced emf in those parts, causing small circulating current in them. This current is called as eddy current. Due to these eddy currents, some energy will be dissipated in the form of heat.

 (Ii) Copper Loss In Transformer

Copper loss is due to ohmic resistance of the transformer windings.  Copper loss for the primary winding is I₁²R₁ and for secondary winding is I₂²R₂. Where, I₁ and I₂ are current in primary and secondary winding respectively, R₁ and R₂ are the resistances of primary and secondary winding respectively. It is clear that Cu loss is proportional to square of the current, and current depends on the load. Hence copper loss in transformer varies with the load.

Efficiency of Transformer

Just like any other electrical machine, efficiency of a transformer can be defined as the output power divided by the input power. That is  efficiency = output / input .Transformers are the most highly efficient electrical devices. Most of the transformers have full load efficiency between 95% to 98.5% . As a transformer being highly efficient, output and input are having nearly same value, and hence it is impractical to measure the efficiency of transformer by using output / input. A better method to find efficiency of a transformer is using, 

efficiency = (input - losses) / input = 1 - (losses / input).

Condition For Maximum Efficiency

Let,Copper loss = I₁ ²R₁ & Iron loss = Wi 

Hence, efficiency of a transformer will be maximum when copper loss and iron losses are equal.
         That is Copper loss = Iron loss.