Which statement about synchronous speed concept is true?

Which statement about synchronous speed concept is true?

• A. Synchronous speed is independent of frequency.
• B. Synchronous speed increases with frequency and decreases with pole count.
• C. Synchronous speed is proportional to frequency and inversely proportional to pole count.
• D. Synchronous speed depends on load and rotor resistance.

Answer: (C)

Synchronous speed is the speed at which the stator’s rotating magnetic field turns, and it is determined only by the supply frequency and the machine’s pole count. The standard relationship is n_s = 120 f / P (in rpm), which means increasing frequency makes the synchronous speed rise, while increasing the number of poles makes it fall. Load and rotor resistance don’t set this speed for synchronous operation; the rotor will lock in step with the rotating field at n_s, though the torque it can deliver will vary with load. The best description is that synchronous speed is proportional to frequency and inversely proportional to pole count.

Synchronous speed is the speed at which the stator’s rotating magnetic field turns, and it is determined only by the supply frequency and the machine’s pole count. The standard relationship is n_s = 120 f / P (in rpm), which means increasing frequency makes the synchronous speed rise, while increasing the number of poles makes it fall. Load and rotor resistance don’t set this speed for synchronous operation; the rotor will lock in step with the rotating field at n_s, though the torque it can deliver will vary with load. The best description is that synchronous speed is proportional to frequency and inversely proportional to pole count.