MUTUAL AND LEAKAGE FLUXES:
So far, it is assumed that when AC supply is given to the primary winding of a transformer, an alternating flux is set up in the core and whole of this flux links with both the primary and secondary windings. However, in an actual transformer, both the windings produce some flux that links only with the winding that produces it.
The flux that links with both the windings of the transformer is called mutual flux and the flux which links only with one winding of the transformer and not to the other is called leakage flux.
The primary ampere turns produce some flux (∅l1)which is set up in air and links only with primary winding, as shown in Figure -1. It is called primary leakage flux.
Similarly, secondary ampere turns produce some flux(∅l2) which is set up in air and links only with secondary winding called is secondary leakage flux.
The primary leakage flux ∅ is proportional to the primary current I1 and secondary leakage flux(∅l2) is proportional to secondary current I2. The primary leakage flux ∅l1 produces self-inductance L1 (= N1∅l1/I1) which in turn produces leakage reactance X1(= 2π f L1). Similarly, secondary leakage flux(∅l2) produces leakage reactance X2 (= 2 πf L2). The leakage reactance (inductive) has been shown external to the windings in Fig – 2.