Which characteristic is unique to synchronous motors?

The characteristic unique to synchronous motors is that the rotor speed matches synchronous speed. Synchronous motors are designed to operate at a constant speed which is determined by the frequency of the AC supply and the number of poles in the motor. This synchronization occurs because the rotor is magnetically locked to the rotating magnetic field produced by the stator.

In contrast to other types of motors, such as induction motors, where the rotor lags behind the magnetic field (resulting in slip), synchronous motors do not have this slip; their rotor rotates in perfect synchrony with the stator's magnetic field. This allows for precise control of speed and positioning, making synchronous motors ideal for applications requiring constant speed regardless of the load, within the motor's specifications.

Understanding this concept is crucial for anyone involved in elevator installation and maintenance, as it highlights the differences in motor function and suitability for various applications within the field.