Question

Consider a dc machine having its armature wound in lap fashion having 12 coils and each resistance 0.1 ohms. If it is measured resistance between two adjacent commutator segments, the result will be _________

(a) 0.092 ohms

(b) 1.1 ohms

(c) 1.8 ohms

(d) 0.92 ohms

This question was addressed to me during an online interview.

My query is from Armature Windings in section Armature Windings of Electrical Machines

Answer 1

Right choice is (a) 0.092 ohms

Explanation: There are 11 resistance which are in parallel to one resistance. So taking the equivalent resistance of 11 series connected resistance and the one single resistance of the commutator segment.

    R(eq) = 0.1||1.1 = 0.0917.