What formula is used to calculate the speed of a rotating magnetic field of an AC Motor?

The formula used to calculate the speed of a rotating magnetic field of an AC motor is derived from the relationship between the number of poles, frequency, and speed. The correct equation expresses the synchronous speed (Ns) in terms of the number of poles (P) and the frequency (f) of the AC supply.

In this context, the formula indicates that the synchronous speed is directly proportional to the frequency of the alternating current and inversely proportional to the number of poles in the motor. Specifically, the factor of 60 is included to convert the frequency from Hertz (cycles per second) to revolutions per minute (RPM). The formula demonstrates that as the frequency increases or the number of poles decreases, the speed of the rotating magnetic field increases.

This relationship is crucial for understanding motor performance and for designing electric motors to operate efficiently under varying loads and conditions. The other formulations do not accurately represent this relationship or misuse the parameters involved, making them unsuitable for determining the synchronous speed of an AC motor.