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Emf produced by DC machine, for zero armature current (E1) and non-zero armature current (E2) can be related as__________(a) E1 = E2(b) E1 > E2(c) E1 < E2(d) Can’t be determinedI got this question in semester exam.Origin of the question is EMF and Torque Production in division Circuit Model, Emf and Torque of DC Machines

Answer»

Right option is (a) E1 = E2

Best explanation: In a DC machine FLUX density wave in the air gap is flat TOPPED with quarter wave symmetry as long as armature current is equal to 0. For non-zero VALUE of armature current, this quarter wave symmetry is disturbed because of armature reaction. Emf produced is independent of B-wave shape, thus we will get same value for both cases.



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