Single-phase motor speed is determined by

Single-phase motor speed is determined by

• A. The number of stator poles
• B. The motor's power rating
• C. The size of the start capacitor
• D. The supply frequency

Answer: (A)

The speed of an AC motor is set by the rotating magnetic field the stator creates. That field has a synchronous speed that depends on how many poles the stator has and the supply frequency. For a fixed frequency, increasing the number of stator poles lowers the synchronous speed, so the rotor settles into a speed close to that value (with a small slip under load). The starting capacitor mainly affects starting torque, not running speed, and the motor’s power rating doesn’t determine how fast it runs. So, with a given frequency, the number of stator poles is the primary factor that fixes the motor’s operating speed.

The speed of an AC motor is set by the rotating magnetic field the stator creates. That field has a synchronous speed that depends on how many poles the stator has and the supply frequency. For a fixed frequency, increasing the number of stator poles lowers the synchronous speed, so the rotor settles into a speed close to that value (with a small slip under load). The starting capacitor mainly affects starting torque, not running speed, and the motor’s power rating doesn’t determine how fast it runs. So, with a given frequency, the number of stator poles is the primary factor that fixes the motor’s operating speed.