Which of the following statements are INCORRECT about auxiliary motor starting in synchronous motors?
A) The function of the auxiliary motor is to run the synchronous motor at a speed less than its synchronous speed.
B) The rating of the auxiliary motor is much lower than that of the synchronous motor.
C) This method is used only for loaded synchronous motors.
D) Auxiliary motor starting is not a commonly used starting method in modern days.

Correct option is C

A is incorrect: The auxiliary motor's purpose is to accelerate the synchronous motor to near synchronous speed, not run it below it. 
D is incorrect: Auxiliary motor starting is still a widely used method for starting synchronous motors. 
B is correct: The auxiliary motor is much smaller in size and rating compared to the main synchronous motor because it only needs to bring the rotor close to synchronous speed. 
C is incorrect: Auxiliary motor starting can be used for both loaded and unloaded synchronous motors.