Question

What is the formula of the magnetic to electrical boarding ratio?

(a) magnetic to electrical boarding ratio = number of poles * permeance coefficient * flux per pole/number of conductors * armature current

(b) magnetic to electrical boarding ratio = number of poles / permeance coefficient * flux per pole*number of conductors * armature current

(c) magnetic to electrical boarding ratio = number of poles + permeance coefficient * flux per pole/number of conductors * armature current

(d) magnetic to electrical boarding ratio = number of poles * permeance coefficient / flux per pole*number of conductors * armature current

The question was asked during a job interview.

This interesting question is from Design Preliminaries in section Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines

Answer 1

The correct choice is (a) magnetic to electrical boarding ratio = number of poles * permeance coefficient * flux per pole/number of conductors * armature current

For explanation: The permeance coefficient is first calculated along with the number of poles and the flux per pole. Then the number of conductors are noted and the armature current is calculated to give the magnetic to electrical boarding ratio.