Question

What is the value of the demagnetizing coefficient if the total number of teeth is greater than 10^7?

(a) d = angle/360

(b) d = angle/240

(c) d = angle/540

(d) d = angle/720

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Question is taken from Design Preliminaries in section Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines

Answer 1

Correct answer is (d) d = angle/720

To elaborate: If the total number of teeth is greater than 10^7 then the demagnetizing coefficient become the ratio of the angle and 720. Otherwise d is one half the ratio of the maximum number of teeth that can be situated within the angle to the total number of teeth.