Question 6A347

The speed of an induction motor is fundamentally determined by the interaction of these three factors. The **number of pairs of poles (A)** and the **line frequency (B)** together establish the *synchronous speed* of the rotating magnetic field in the stator. The formula for synchronous speed (in RPM) is (120 * Frequency) / Number of Poles. More poles or lower frequency results in a slower synchronous speed, while fewer poles or higher frequency results in a faster synchronous speed. However, an induction motor always operates with a "slip," meaning its rotor speed is slightly less than the synchronous speed. This **load (C)** determines the amount of slip. As the mechanical load on the motor increases, the slip increases, causing the actual rotor speed to decrease slightly relative to the synchronous speed to produce more torque. Conversely, a lighter load results in less slip and a speed closer to synchronous. Therefore, all three—poles, frequency, and load—collectively determine the actual operating speed of an induction motor.