Question

NVC will release the handle electromagnetically when ________

(a) In the case of failure of field current

(b) If the resistance is very high

(c) At the end of each rotation

(d) At the start of each rotation

This question was posed to me during an interview.

I would like to ask this question from Starting of DC Motors in section DC Motors of DC Machines

Answer 1

Right option is (a) In the case of failure of field current

To explain: In case of failure of field current (due to accidental or otherwise open circuiting) NVC coil releases the handle (held electromagnetically), which goes back to the OFF position under the spring action.