Question 3.18: The no-load input power to a transformer is 100 W. The no-lo...

At no-load, the input power is lost as a small amount of I² R loss in the winding and as core loss.
In an ac circuit,                        power = VI \cos Φ
Let No-load input power be W_{0}

W_{0}= V_{1}  I_{0}  \cos Φ_{0}

\cos Φ_{0}=\frac{W_{0}}{V_{1}  I_{0}}

\cos Φ_{0}=\frac{100}{230  ×  3} =0.15 lagging

\cos Φ_{0} is the no-load power factor of the transformer. At no-load, primary winding copper loss is equal to

I_{0}^{2}  R_{1}= 3^{2}  ×  0.5  =4.5   W

The wattmeter reading W_{0} indicates the power loss in the core as also in the winding.

Core loss, or iron loss,             W_{i} = W_{0}  –  I_{0}^{2}  R_{1}

= 100 − 4.5
= 95.5 W