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Efficiency of Transformer and Condition for maximum Efficiency

Transformer Efficiency

The Efficiency of a transformer is defined as the ratio of useful output power to the input power.

Transformer efficiency is denoted by Ƞ.

Transformer Efficiency


  • V2 – Secondary terminal voltage
  • I2 – Full load secondary current
  • Cosϕ2 – power factor of the load
  • Pi – Iron losses = hysteresis losses + eddy current losses
  • Pc – Full load copper losses = I22Res

Consider, the x is the fraction of the full load. The efficiency of the transformer regarding x is expressed as

Transformer Efficiency

The copper losses vary according to the fraction of the load.

As the transformer is a static device, hence does not have rotational losses (such as windage and frictional losses). Therefore, a transformer can have efficiency as high as 99 %.

Maximum Efficiency Condition of a Transformer

The efficiency of transformer will be maximum when the constant losses (or iron losses) being equal to variable losses (or copper losses).

Check out the given below pdf for the details derivation on Maximum Efficiency Condition of a Transformer.


I hope the above Hindi video lecture and the handwritten note can help you understand the Transformer efficiency. Stay with us for more educational video lectures and handwritten notes with free job alerts as well.

Checkout: Types of Starter for DC Motor with Handwritten Notes in PDF

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