A Synchronous motor can operate at
Right Answer is:
Leading as well as lagging power factor
A synchronous motor can operate at Leading as well as lagging power factors.
For constant power output, a synchronous motor can be made to operate at either a lagging power factor, unity power factor, or leading power factor by varying the field excitation.
Normal Excitation:- When the machine is operating as a normal excited motor, it has a unity power factor due to a normal field current. Under such conditions, the motor draws the minimum stator current.
Underexcited:- 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.
Overexcited:-When the machine is operating as an overexcited motor, it has a leading power factor due to a high field current. Therefore, the maximum power Pmax is large and the machine operation is stable. An overexcited synchronous motor acts as a power factor correction device and is also known as a synchronous condenser.