I would like to know how the number of poles in a motor affects its selection

The number of pole pairs primarily affects the speed of the motor; the formula is n=60*f(1-s)/p. In this formula, n represents the speed of the motor, f is the frequency of the power supply, which is 50HZ in China, s is the slip rate of the motor – and the slip rate is generally constant for each motor – while p denotes the number of pole pairs. It can be seen that the higher the number of pole pairs, the lower the speed of the motor.

The more pole pairs a motor has, the lower its speed will be, but its torque will be greater； When selecting a motor, you need to consider the amount of starting torque required by the load; for example, starting under load requires more torque than starting with no load. In the case of high-power loads that require starting, voltage reduction starting (or star-delta starting) must also be taken into account ； As for the issue of matching the speed to the load after determining the number of pole pairs in the motor, it is possible to consider using pulleys of different diameters for transmission, or employing variable-speed gears (gearboxes) for this purpose. If, after determining the number of pole pairs in the motor, the power delivered via belt or gear transmission is not sufficient to meet the load requirements, then the power capacity of the motor needs to be considered.

The more poles a motor has, the lower its speed will be, but its torque will be greater. 2 poles: about 2900 revolutions; 4 poles: about 1450 revolutions; 6 poles: about 980 revolutions; 8 poles: about 680 revolutions

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