Question

If the DC excitation is suddenly dropped to 0, the three phase alternator _________

(a) runs as motor

(b) stops to zero speed in few seconds

(c) continues to run as motor but at lower speed

(d) no change in the operating conditions

The question was posed to me during an internship interview.

This intriguing question originated from Excitation Systems for Synchronous Machines topic in chapter Synchronous Machines of Electrical Machines

Answer 1

Right choice is (a) runs as motor

To explain: When the dc excitation is disconnected from the supply, it will start acting as synchronous motor as the prime mover will still be mechanically coupled.