Effect of Power factor on Efficiency

Effect of Power factor on Efficiency
       The efficiency of a transformer is given by,

Now,              input = output + losses = V2 I2 cos Φ + losses
Using in (1),     η = 1 - (losses / (V2 I2 cos Φ + losses))
Let    losses/V2 I2 = x and using in (2),
      Thus as the power factor of the load is more i.e. cos is higher, x/cosΦ is lesser. Hence the second term in the equation (3) becomes lesser and efficiency will be more.
Key Point : As power factor increases, the efficiency increases.
       Thus the family of efficiency curves are obtained as power factor increases, as shown in the Fig.1.
Fig. 1  Effect of p.f. on efficiency


  1. please send equivalent circuit diagram of three transformer,autotransformer notes

  2. Please send me the notes on equivalent circuit of three phase transformer and auto transformer notes.
    Thank you.