What is the rotating speed of a three-phase 30 Hz 6-pole motor?

What is the rotating speed of a three-phase 30 Hz 6-pole motor?

• A. 600 rpm
• B. 1800 rpm
• C. 1200 rpm
• D. 900 rpm

Answer: (A)

Rotating speed in a polyphase motor is set by the synchronous speed, which is determined by the frequency and the number of poles. The formula is Ns = 120 f / P. With a 30 Hz supply and 6 poles, the calculation is 120 × 30 / 6 = 600 rpm. This is the speed at which the stator’s magnetic field rotates. In an induction motor, the rotor typically runs a bit slower than synchronous speed due to slip, so the actual shaft speed under load would be slightly less than 600 rpm. The same formula explains other common cases: for example, 30 Hz with 4 poles would give 900 rpm, and other combinations shift the speed accordingly.

Rotating speed in a polyphase motor is set by the synchronous speed, which is determined by the frequency and the number of poles. The formula is Ns = 120 f / P. With a 30 Hz supply and 6 poles, the calculation is 120 × 30 / 6 = 600 rpm. This is the speed at which the stator’s magnetic field rotates. In an induction motor, the rotor typically runs a bit slower than synchronous speed due to slip, so the actual shaft speed under load would be slightly less than 600 rpm. The same formula explains other common cases: for example, 30 Hz with 4 poles would give 900 rpm, and other combinations shift the speed accordingly.