Maximum Efficiency of Transformer

 For any system, we desire that system has minimum losses so that maximum part of input energy is transformed as output energy i.e. maximum efficiency. So that we need to determine the conditions for maximum efficiency of a transformer. 

 

We know the formula(equation) of efficiency is - 

The efficiency(η) of transformer depends upon the power factor (φ) and the load (x). 

 

Conditions for Maximum Efficiency of Transformer :

Case 1 : Power factor of load(φ) is varied. Then we have to determine the power factor at which efficiency is maximum. 

 

 So maximum  power efficiency of a transformer for fixed load occurs at unity power factor.

 Case 2 : If Load of transformer is variable, then to obtain maximum efficiency - 

So, this is the load on transformer as a fraction of full load. 

At maximum efficiency, 

So at maximum efficiency copper (Cu) loss is equal to iron loss or core loss.

Hence, Maximum Efficiency is - 

  

So the efficiency of a transformer is maximum at Unity Power Factor and at where copper loss and iron loss are same.

• All Day Efficiency 

  As efficiency depends upon the connected load of transformer and in case of Distribution Transformer the load is varied throughout the day, so that the definition of the transformer needs to be modify to have physical significance for variable load and it is termed as All Day Efficiency.

   

  

  For Power Transformer we do not calculate All Day Efficiency.