How to adjust the speed by changing the number of pole pairs P
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We know that the speed of a rotating magnetic field is given by n=60f/p. Of course, in practice there is also the issue of slip rate s, which means that the motor’s speed is related to the values of f, s, and p. By changing f, it is possible to achieve variable frequency speed control; for this purpose, frequency conversion devices such as inverters are required； Changing s allows for speed control by varying the slip rate ； So how is variable-pole speed control achieved by changing the number of pole pairs p? What structural requirements does such speed control impose on the motor? Does any expert in electrical engineering have relevant information or examples of practical applications to share?
There are specialized multipolar motors that enable the change in the number of motor poles through the combination of windings. However, this speed control method can only achieve several fixed speeds, as the number of pole pairs must be an integer. Due to the limitations of the windings, it is also not possible to have too many pole pairs
It’s usually a two-speed motor; you can find out by searching online. Generally, two cables are required, and it operates in a manner similar to star-delta starting