In the following, assume the voltage source is V_s = 100 V, the transformer is i

Question

In the following, assume the voltage source is V_s = 100 V, the transformer is ideal, and the secondary side is open. A student has claimed that the electrical current in the primary should be zero according to I_1 = (N1/N2) I_2 = (N1/N2) 0 = 0. However, the primary circuit is a closed loop with a non-zero voltage source and a finite reactants. As a result, we should have I_1 = 100 V/X_c where X_1 is the reactants of primary winding with N1 turns. Explain why the logic of I_1 = 100 V/X_c is not correct.

Explanation / Answer

Reactance does not consume any real power it only consume reactive power for the excitation purpose.

in case of open secondary required rective power is only for the iron circuit.

here we are considering ideal transformer so loss in magnetic circuit is zero and hence reactive power required will also be zero.

so no excitation current reuired from sourse so above logic is not corrent.

this is the reason why in practical transformer no load current is about 5% of rated supply current .( because of excitation loss in core of transformer)

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