When armature carries a current, it produces its own flux. Some part of this flux completes its path through the air around the conductors itself. Such a flux is called leakage flux. This is shown in the Fig. 1.
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| Fig. 1 Armature leakage flux |
Note : This leakage flux makes the armature winding inductive in nature. So winding possesses a leakage reacatnce, in addition to the resistance.
So if 'L' is the leakage inductance of the armature winding per phase, then leakage reactance per phase is given by XL = 2 π f L Ω/ph. The value of leakage reactance is much higher than the armature resistance. Similar to the d.c. machines, the value of armature resistance is very very small.
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