What distinguishes synchronous motors from asynchronous motors?

Synchronous motors are fundamentally distinguished from asynchronous motors based on their operation relative to the supply frequency. A synchronous motor runs in synchrony with the frequency of the power supply, which means that its rotor speed matches the magnetic field speed created by the stator. This is essential for achieving a steady rotational speed regardless of the load conditions, making their speed consistent and directly tied to the electrical frequency.

In contrast, asynchronous motors, commonly referred to as induction motors, do not operate at the supply frequency. Instead, the rotor speed is slightly less than that of the stator's magnetic field speed, which allows them to develop torque through electromagnetic induction between the stator and rotor. This difference in operation leads to variable speeds in asynchronous motors, especially under varying load conditions.

The other statements do not accurately capture the pivotal distinction regarding synchronous operation versus asynchronous operation as defined by the relationship to supply frequency. Understanding this key difference is crucial for selecting the appropriate motor type for specific applications, particularly when consistent speed is vital.