Question

For a certain machine having γ = 1.8, we are using starter with 5 steps. What will be the resistance at step 3 if step 2 resistance is equal to 2 Ω?

(a) 2.111

(b) 1.111

(c) 3.6

(d) 10.8

I have been asked this question in an internship interview.

This interesting question is from Starting of DC Motors topic in chapter DC Motors of DC Machines

Answer 1

Correct option is (b) 1.111

The explanation: γ is defined so as to calculate step resistance from the given maximum limit of current and minimum limit of the same. This γ = rn/rn-1. So, for calculating resistance at step 3 we’ll substitute the corresponding values in the equation, which will give step 3 resistance as 1.1111Ω.