In an a.c. machine,any flux set up by the load current which does not contribute to the useful flux of the machine is a leakage flux.The effect of the leakage flux is set up a self-induced emf in the armature windings.
The leakage fluxes may be classified as follows:
2.Tooth head leakage
3.Coil-end or overhang leakage.
The voltages induced in the armature windings by the air gap flux are called air gap voltages.
The leakage fluxes also induce voltages in the armature windings.These are taken into account by introduction of leakages reactance drops.Most of the reluctances of the magnetic circuits for armature leakages fluxs are due to air paths.The fluxes are,therefore,nearly proportional to the armature currents producing them and arc in phase with these currents.For this reason,the voltage they induced in the armature winding can be taken into account by the use of constant leakage reactances for the phases,which multiplied by the phase currents,give the components voltages induced in the phases by the leakage flux.These voltages are the leakagereactance drops and lead the currents producing them by 90degree