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Increase in flux density at one end of the pole is less than the decrease at the other end. This is called as ____________(a) Demagnetizing mmf(b) Cross-magnetizing mmf(c) Anti-magnetizing mmf(d) Magnetizing mmfI have been asked this question during an interview for a job.The origin of the question is Armature Reaction -1 in division Armature Reaction of DC Machines

Answer»

The correct choice is (a) Demagnetizing mmf

The EXPLANATION: If the main pole EXCITATION is such that iron is in the saturated region of magnetization (this is the case in a PRACTICAL machine), the increase in flux density at one END of the poles caused by armature reaction is less than the decrease at the other end, so that there is a net reduction in the flux/pole, a demagnetizing effect.



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