The correct answer is: D. Any of the above
The DC excitation of a synchronous motor controls the magnetic field produced by the stator windings. This magnetic field interacts with the rotor’s magnetic field to produce torque, which causes the motor to rotate. The amount of torque produced by the motor is proportional to the strength of the magnetic field. Therefore, changing the DC excitation will change the amount of torque produced by the motor, which will in turn change the motor speed.
The power factor of a motor is a measure of how efficiently the motor converts electrical energy into mechanical energy. A motor with a power factor of 1 is said to be 100% efficient, while a motor with a power factor of 0.5 is said to be 50% efficient. The power factor of a motor is affected by the amount of current drawn by the motor. The amount of current drawn by a motor is proportional to the strength of the magnetic field. Therefore, changing the DC excitation will change the amount of current drawn by the motor, which will in turn change the power factor of the motor.
In conclusion, changing the DC excitation of a synchronous motor will change the motor speed and the power factor of the motor.