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*I _{2}*

This secondary current sets up m.m.f( =N_{2}I_{2} ) and hence it produce magnetic flux Φ_{ 2} which is in opposition to the main primary flux Φ . The secondary ampere-turns N_{2}I_{2 }are known as demagnetizing amp-turns. The opposing secondary flux Φ_{ 2 }weakens the primary flux _{1} _{1} > E_{1}_{2}_{2})_{2}_{2}’) sets up its own flux _{ 2}_{ 2} , but is in the same direction as primary flux Φ. And flux _{ 2}_{ 2}. Hence, the two flux cancel each other out.

So, we can say that whatever the load conditions, the net flux passing through the core is approximately the same as at no-load. Due to the constancy of core flux at all loads, the core loss is also practically the same under all load conditions.
As _{ 2}= Φ_{ 2}

Hence, when transformer is no load, the primary winding has two currents in it; one is I_{0} and the other is I_{2}’ which is anti-phase with _{2}_{0 }_{2}

In Fig. shown the vector diagram of a transformer when the load is non-inductive and when the load is inductive.
If we assume voltage transformation ratio is unity , ( i.e

In the fig.-1, shown the vector diagram of a transformer when load is non-inductive

_{2}_{2}= V_{2}

I_{2}’= load component of primary current which is anti-phase with I_{2} and also equal to it in magnitude( as

I_{1}= Primary current which is vector sum of _{0} and I_{2}_{1}_{1}

In the fig.-2, shown the vector diagram of a transformer when load is inductive,

_{2}_{2 }_{2}

_{2}_{2} and also equal to it in magnitude( as

I_{1}= Primary current which is vector sum of I_{0} and I_{2}’ and lags behind V_{1} by angle φ_{1}.

It is seen from the fig.-2 that the angle _{1}_{2}

In figure , It is seen that I_{0} is neglect as compared to _{2}_{1}= φ_{2}_{1}I_{2}’= N_{2}I_{1}= N_{1}I_{2}

It is shown that under the full-load condition, the ratio of primary and secondary current is constant. The relationship is made the basis of current transformer, such a transformer which is used with a low-range ammeter for measuring currents in circuits.