The introduction of interpoles in between the main poles improves the performance of a dc machine, because
A. the interpoles produce additional flux to augment the developed torque
B. the flux waveform is improved with reduction in harmonics
C. the inequality of air-gap flux on the top and bottom halves of the armature is removed
D. a counter-emf is induced in the coil undergoing commutation
Answer: D
Share your understanding of this question with the correct explanation.
The correct answer is D. The introduction of interpoles in a DC machine improves its performance because a counter-emf is induced in the coil undergoing commutation.
Explanation:
Interpoles, also known as commutating poles, are additional poles placed between the main poles of a DC machine. They serve the purpose of improving commutation, which is the process of reversing the current in the armature coils as the rotor rotates.
During commutation, there is a brief period when the coil undergoing commutation is short-circuited by the brushes. This short-circuiting can lead to arcing and sparking, which can cause damage to the commutator and brushes.
The interpoles are designed to generate a counter-electromotive force (emf) in the coil undergoing commutation. This counter-emf opposes the short-circuit current, aiding in the rapid reversal of current and reducing arcing and sparking. By providing this counter-emf, the interpoles help to improve the commutation process and ensure smooth operation of the DC machine.
Therefore, option D is correct as the presence of interpoles induces a counter-emf in the coil undergoing commutation, leading to improved performance of the DC machine.