what is synchronous speed

Synchronous speed is the speed of the revolution of the magnetic field in the stator winding of an AC motor. It is the speed at which the electromotive force is produced by the alternating machine. The synchronous speed of an AC motor is determined by the frequency of the source and the number of poles. The RPM is calculated by multiplying the frequency by 120 and dividing the result by the number of poles. The formula for synchronous speed is given as nₛ = 120f/p, where nₛ is synchronous speed in RPM, f is frequency, and p is the number of poles. Small synchronous motors are used in timing applications such as in synchronous clocks, timers in appliances, tape recorders, and precision servomechanisms in which the motor must operate at a precise speed. Accuracy depends on the power line frequency, which is carefully controlled in large interconnected grid systems.