Engineering Exam question: synchronous motor excitation

[tobiascarter]

Here is a multiple choice question i was completely stumped on, and still can't find the right answer for in my textbooks...

Name 2 forms of excitation with respect to synchronous motors:
a) under and over excitation
b) dc & ac variation
c) dc excitation and load variation
d) armature and stator reversal

Any clues or certain answers would be appreciated

 

[n.karthick]

Synchronous motor can be operated in under or over excited modes. If operated in over excitation mode, it is also called as synchronous condenser, because it supplies reactive power to the source.

 

[tobiascarter]

and if it is under excited??

 

[hmparikh1990]

it is Induction motor.(it works on lagging p.f.)

 

[Bob S]

it is Induction motor.(it works on lagging p.f.)

When running as a synchronous motor, it is still synchronous, and the armature has a lagging phase. There is no phase slippage, like in an induction motor. It has synchronously-excited salient poles on the armature, not a squirrel cage like induction motors.

Bob S