How does a synchronous motor maintain its speed?

A synchronous motor maintains its speed by operating at the synchronous speed, which is determined by the frequency of the AC power supply and the number of poles in the motor. The relationship between the speed of the motor, the frequency of the electrical supply, and the number of poles is given by the formula:

[ \text{Synchronous Speed (RPM)} = \frac{120 \times \text{Frequency (Hz)}}{\text{Number of Poles}} ]

In a synchronous motor, the rotor moves in synchrony with the rotating magnetic field produced by the stator. When the motor is properly designed with a specific number of poles, it matches the speed of the magnetic field, resulting in constant speed operation as long as the frequency remains stable. This design feature effectively eliminates slip, which is the difference between the synchronous speed and the actual speed of the rotor, thereby allowing the synchronous motor to maintain its designated speed under varying load conditions.

Moreover, the other options do not effectively lead to speed maintenance in synchronous motors. Adjusting the voltage supplied could influence the torque but not the synchronous speed. A battery backup is not a standard feature in the context of synchronous motors, while varying the current in the stator impacts the motor's performance but does