Question

Which of the following is correct formula for braking torque in plugging?

(a) n (ka^2/Rb)

(b) n^2 (ka^2/Rb)

(c) n^-1 (ka^2/Rb)

(d) (ka^2/Rb)

This question was posed to me in a job interview.

My question is taken from Braking of DC Motors in section DC Motors of DC Machines

Answer 1

Correct choice is (a) n (ka^2/Rb)

Explanation: Braking torque is equal to braking power divided by speed of the motor.

 T= [(nka )^2/Rb]/n. As, Braking power is equal to Ea^2/Rb/n. By solving for the braking torque from the above equation, we get n (ka^2/Rb).