Answer / rk

losses in transformer are 1) core loss2) copper loss
copper loss is proportional to current . the resistance of the copper changes with temperature. approximately it is 1.2 times at 85 degree celcius as compared to 40 degree ambient.so
total power consumed by the transformer during no load conditon can be read from the wattmeter connected in the primarry. this will give the core loss which varies with the loading of transformer insignificatly lets say 1000W.

now if transformer is distribution type or generation type.

maximum efficiency is when core loss = copper loss

so total loss at 50% loading is 2000w
copper loss at 100% load will be approx 4*1.2*1000=4800w( 4 due to doubling of current , copper resistance almost increases by 20% from 40 to 85 degree celsius rise


so total loss at 100% load = 1000+4800w=5800w

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