What does the term 'synchronous speed' refer to in electrical motors?

Synchronous speed refers specifically to the speed at which the magnetic field of an alternating current (AC) motor rotates. This speed is determined by the frequency of the AC power supply and the number of poles in the motor. The formula to calculate synchronous speed is given by ( S = \frac{120 \times f}{P} ), where ( S ) is the synchronous speed in revolutions per minute (RPM), ( f ) is the frequency in hertz, and ( P ) is the number of poles.

Understanding this concept is crucial for interpreting how AC motors operate. The rotor of the motor does not actually reach this speed but instead operates at a speed slightly lower than this value due to slip, which is necessary for torque generation. Thus, the correct understanding of synchronous speed is foundational in the design and application of electrical motors, as it affects overall motor performance and efficiency.