The correct answer is: C. it runs as a reluctance motor at a lower speed.
When the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected, the motor will run as a reluctance motor at a lower speed. This is because the rotor will no longer be aligned with the stator field, and the motor will start to rotate at a speed that is determined by the reluctance torque. The reluctance torque is the torque that is produced by the difference in reluctance between the stator and rotor teeth. The higher the difference in reluctance, the higher the reluctance torque.
The speed of the motor will decrease until it reaches a steady-state speed. The steady-state speed will be determined by the load on the motor and the reluctance torque. The higher the load, the lower the steady-state speed.
The following are the brief explanations of each option:
- Option A: The motor stops. This is not correct because the motor will continue to rotate as a reluctance motor.
- Option B: It runs as a reluctance motor at the same speed. This is not correct because the motor will run at a lower speed.
- Option D: None of the above. This is not correct because the motor will run as a reluctance motor at a lower speed.