Question

DC generators are disconnected/connected from/to the busbars only under the floating condition because ____________

(a) To avoid sudden loading of the prime mover

(b) To avoid burning of all switch contacts

(c) To avoid mechanical jerk to the shaft

(d) To avoid sudden loading of the prime mover, burning of all switch contacts and avoid mechanical jerking to the shaft

This question was addressed to me in an interview.

The question is from Brushes and Commutator Assembly topic in portion DC Machines of DC Machines

Answer 1

The correct answer is (d) To avoid sudden loading of the prime mover, burning of all switch contacts and avoid mechanical jerking to the shaft

The best I can explain: Brushes are the medium between rotating and non-rotating part of the DC machine. If sudden change in connections are done, whole machine undergoes change in all electrical quantities, which may damage machine. Thus, machines are connected and disconnected only at floating condition.