Question

Reducing the field current will give us _______________

(a) Constant torque and variable power speed control

(b) Constant torque speed control

(c) Variable power speed control

(d) Constant power speed control

I have been asked this question in an interview for job.

My question is from Ward Leonard Speed Control Method topic in portion DC Motors of DC Machines

Answer 1

The correct choice is (b) Constant torque speed control

Explanation: As seen from speed torque characteristics, reducing field current will increase the speed of the motor above base value but power will remain same. Thus, reducing armature voltage will give constant power speed control, with variable torque.