When the field of a synchronous motor is under-excited, the power factor will be

When the field of a synchronous motor is under-excited, the power factor will be

Right Answer is:

Zero

SOLUTION

When the synchronous machine is operating as an under-excited motor, it has a lagging power factor due to a low field current. Here, the maximum power Pmax is small and hence the machine operation is less stable. In this case, the motor behaves like an inductive load and the motor absorbs reactive power from the 3-phase line.

Note:- The power factor at which a synchronous machine operates and its stator (armature) current can be controlled by changing its field excitation.

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