Answer Posted / pankaj rajput

The copper loss of a Transformer depends on current i.e.
I^2 R and the iron loss depends on voltage. Hence the total
losses depends on volt-ampere (VA) and not on phase angle
between voltage & current.

Therefor the losses in a transformer are independent of
power factor which is cosine of angle between voltage &
current.

That's why the rating of transformers is in KVA and not in
kW.

Now coming to Efficiency of a transformer: Yes it depends
on power factor of load. Because the
Efficiency = Output/Input
= (Input - Losses) / Input
= 1 - (Losses / Input)
= 1 - [Losses / (Vs * Is * Cos phi + Losses)]

Efficiency is inverted V curve (Y-scale) and the peak of
curve appears between 50-60% load (X-scale)for various load
power factors. Efficiency increases as the power factor
increases.

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