Question

What is the formula for the armature resistance?

(a) armature resistance = running armature resistance / 1.0 to 1.0

(b) armature resistance = running armature resistance * 1.3 to 1.5

(c) armature resistance = running armature resistance * 1.4 to 1.5

(d) armature resistance = running armature resistance / 1.3 to 1.3

I had been asked this question during an interview.

Question is taken from Design Steps and Considerations in chapter Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines

Answer 1

Correct option is (d) armature resistance = running armature resistance / 1.3 to 1.3

The explanation: The running armature resistance is first calculated in the PMDC motor. It is divided by 1.3 and that gives the armature resistance of the machine.