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Question: It is desired to find the equivalent circuit parameters for a single-phase 110V AC transformer. In the short-circuit condition, the transformer can be modelled by a series resistance and inductive reactance. When 5V is applied to the transformer, it draws a current of 20A with a measured input power of 21W. Find the equivalent reactance for the transformer.

So far what I have done is:

  • I have found the total impedance of the transformer in the short circuit condition, being: Z = R + wL

  • Then, when 5V is applied, I used ohms law: I=V/R = 5/(R + wL)

to which R + wL = 5/20 = 0.25

However, this is incorrect... The total impedance is not 0.25. I am given some power values, however I am not sure how they can come into play.

I appreciate any help, Thank you.

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  • \$\begingroup\$ Hint: What's the phase angle between the magnitixing current (wL) and the copper/core losses (R)? \$\endgroup\$ – winny Apr 2 at 13:49

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