How do you perform no load magnetizing current measurement of transformer?

Answer 1

I am sure there is more than one way of doing this but what I am currently implementing in my own study of I_mag is the following: At no load perform an over excitation test where you vary the input voltage from 0 V and monitor the current flowing through the primary windings of the transformer. Over-excite the transformer until the rate at which current, I_in increases in the primary windings is relatively larger than the change in Vout , across the secondary windings (this is the point of saturation). Plot your results of voltage Vout (y- axis) against current I_in (x-axis) and you should come up with a characteristic B-H curve. (Remember that the B field is proportional to voltage and the H field is proportional to current from magnetic circuits theory) You are then to decide which point on your curve you will regard as the 'knee' point or the point at which the curve starts to deviate from the linear region. This 'knee' point will correspond to your I_mag. While I_in is not necessarily equal to I_mag at no load, at the knee point on your curve these two currents will be approximately equal.