5 Armature reaction - nptel - Indian Institute of Technology Madras

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Electrical Machines I Prof. Krishna Vasudevan, Prof. G. Sridhara Rao, Prof. P. Sasidhara Rao Indian Institute of Technology Madras N S Ideal flux density Figure 18: Mmf and flux variation in an unloaded machine 44 mmf Permeance Practical Flux density
Electrical Machines I Prof. Krishna Vasudevan, Prof. G. Sridhara Rao, Prof. P. Sasidhara Rao the slotting of the armature. The no-load flux density curve can be obtained by multiplying mmf and permeance. Allowing for the fringing of the flux, the actual flux density curve would be as shown under Fig. 18. 5.0.2 MMF distribution due to armature conductors alone carrying currents S-Pole Indian Institute of Technology Madras N N-Pole A Generator Figure 19: Mmf and flux distribution under the action of armature alone carrying current S Flux mmf The armature has a distributed winding, as against the field coils which are concentrated and concentric. The mmf of each coil is shifted in space by the number of slots. For a full pitched coil, each coil produces a rectangular mmf distribution. The sum of the mmf due to all coils would result in a stepped triangular wave form. If we neglect slotting and have uniformly spaced coils on the surface, then the mmf distribution due to the armature working alone would be a triangular distribution in space since all the conductors carry equal currents. MMF distribution is the integral of the ampere conductor distribution. 45
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5 Armature reaction - nptel - Indian Institute of Technology Madras

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