Electrical Machines
The synchronous reactance( Xs) is the

 reactance either due to armature reaction or leakage flux
 reactance due to leakage flux
 combined reactance due to armature reaction and leakage flux
 reactance due to armature reaction of the machine

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Electrical Machines
The introduction of interpoles in between the main poles improves the performance of a dc machine, because

 the inequality of air-gap flux on the top and bottom halves of the armature is removed
 the interpoles produce additional flux to augment the developed torque
 the flux waveform is improved with reduction in harmonics
 a counter-emf is induced in the coil undergoing commutation

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