This secondary current sets up m.m.f( =N2I2 ) and hence it produce magnetic flux Φ 2 which is in opposition to the main primary flux Φ . The secondary ampere-turns N2I2 are known as demagnetizing amp-turns. The opposing secondary flux Φ 2 weakens the primary flux
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.
Hence, when transformer is no load, the primary winding has two currents in it; one is I0 and the other is I2’ which is anti-phase with
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
I2’= load component of primary current which is anti-phase with I2 and also equal to it in magnitude( as
I1= Primary current which is vector sum of
In the fig.-2, shown the vector diagram of a transformer when load is inductive,
I1= Primary current which is vector sum of I0 and I2’ and lags behind V1 by angle φ1.
It is seen from the fig.-2 that the angle
In figure , It is seen that I0 is neglect as compared to
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.