The difference between two-pole and four-pole motors
The number of poles in an electric motor is a crucial parameter that reflects the speed of the motor.
The core components of an electric motor are the stator and rotor. The stator has coils embedded in it. When energized, these coils generate N and S pole magnetic fields. One N pole and one S pole determine the number of poles in the electric motor's magnetic field; each N pole and S pole forms a pole pair. A two-pole motor has 1 pole pair, and a four-pole motor has 2. So how do we know the speed of an electric motor?
An electric motor has a synchronous speed, which is the alternating speed of the magnetic field—that is, the alternating frequency of the motor multiplied by the time (seconds) and divided by the number of pole pairs.
The synchronous speed of a two-pole motor is 50Hz * 60s / 1 = 3000 rpm. Similarly, the synchronous speed of a four-pole motor is 50Hz * 60s / 2 = 1500 rpm. You can continue to calculate the motor speed. The number of poles in a motor is always even; there are no odd-numbered motors.
We know that asynchronous motors generate electromagnetic force by cutting magnetic lines of force to drive the motor to rotate. Therefore, there must be a difference in the magnetic field of the motor, that is, the speed of the rotor is lower than the synchronous speed of the motor. This speed difference is called the slip of the motor. The slip is generally 3-5% of the synchronous speed of the motor.
Once we know the synchronous speed of the motor, we can multiply it by the motor slip rate to get the motor speed.
Induction motors are induction motors, and the actual speed of the rotor lags behind the synchronous speed.
Ideal speed = frequency * 60 / number of pole pairs; Actual speed = ideal speed * (1 - slip rate).
For example, the AC frequency is 50Hz, the number of pole pairs is 2, and the slip is 0.04 (.096).
The synchronous speed of a 2-pole motor is 3000 r/min, and the asynchronous speed is 2850 r/min.
The synchronous speed of a 4-pole motor is 1500 r/min, and the asynchronous speed is 1450 r/min.
The synchronous speed of a 6-pole motor is 1000 r/min, and the asynchronous speed is 960 r/min.
The synchronous speed of the 8-pole motor is 750 r/min, and the asynchronous speed is 720 r/min.
