It is stated in the textbook I'm studying that if we reduce the excitation current after the rotor has reached synchronous speed , its speed will remain constant even if the excitation current becomes zero.
I know that the reason the rotor runs at synchronous speed is because the poles created by the excitation current are attracted to those of the stator. If we reduce the current to 0 though, there are no poles on the rotor to be attracted.
So how does the motor still run at synchronous speed?