Transformer Losses

Iron losses ( no-load) and copper losses are different. When you perform open circuit test, you will find the no load losses provided that you supply with the rated voltage. With short circuit test, you will find copper losses where by you need to set the current required to circulate full load currents as stated on your transformer name plate.

With 'no load losses' the only circulating currents magnetic and electric, are the magnetizing currents.

'No load loss' is a sum of "...Iron" and "..copper" losses. (Some people do love to give incomplete information...seems to amuse them)

Under load, these currents and associated heat losses rise.

No Load loss consists of the magnetizing coomponent and hystersis los in the magnetic portion Thisremainsconstant .The copper loss or full load is due load current and varies as square of current.for example the loss at 50% will be 1/4 of full load loss.At max eff point copper loss = noload loss which is the best point for operatin.The designer can play around with these figs