What would the total loss of the 2kVA transformer corresponding to maximum efficiency be, provided the transformer has the iron of 150 W and full-load copper loss of 250W?

• A. 400 W
• B. 500 W
• C. 100 W
• D. 300 W

Answer: (D)

When variable loss becomes equal to the constant loss, efficiency is maximum.
Losses = Pi + Pc
Since copper loss is a variable loss therefore
Losses = Pi + Pi = 2pi
Thus at a maximum efficiency of this transformer total loss
= 150 x 2 = 300 W