Electrical Machines
A cumulatively compounded dc motor delivers rated load power at rated speed. If the series field is short-circuited, then

 Ia increases and ωm decreses
 both armature current Ia and speed ωm increase
 both decrese
 Ia remains constant but ωm increase

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

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

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Electrical Machines
No load primary current in a transformer

 leads the applied voltage by exactly 90Â&
 lags behind applied voltage somewhat less than 90Ã
 lags behind applied voltage by exactly 90Â&am
 leads the applied voltage somewhat less than 90Ã&

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