Question

For a dc machine, its commutator has a diameter of 50 c rotating at 1000 rpm. For a brush width of 1 cm, the time commutation taken by the machine will be _________

(a) 0.382 ms

(b) 0.456 ms

(c) 0.573 ms

(d) 0.312 ms

I have been asked this question by my college director while I was bunking the class.

This question is from DC Motor Starting topic in portion DC Motors of Electrical Machines

Answer 1

Right answer is (a) 0.382 ms

The best explanation: Time of commutation = brush width/peripheral velocity

                                 = 1*60/(pi*50*1000)

     = 0.382 ms.