Term List (PQR)

Pole

When talking about motors, we are often asked, "How many poles does the motor have?" The number of poles or the number of magnetic poles refers to the magnetic poles (NSNSNS……) that appear on the surface created by cutting the motor perpendicularly to the shaft.


Basically, the number of poles is an even number (2, 4, 6, 8......). As described on the next page, there are two winding types: distributed winding and concentrated winding. The concentrated winding is suited for brushless motors. You can easily change the number of poles by changing the connection of the coils. A six-coil stator allows two types of connection. One is used for two poles and the other for four or eight poles. However, it is unreasonable to change the number of poles of a finished motor to four or eight. The distributed winding that is often used to provide 12 poles on a nine-slot stator is suited for induction motors. In such a case, the number of poles is selected before the winding work is started.


Although small motors usually have four poles, two-pole motors are also used for high-speed applications that require 50 or 60 rotations per second. Before brushless motors were introduced, a technique was once used for changing the number of poles of squirrel-cage rotor type induction motors by modifying the connection of the complex windings that are not able to be classified as distributed winding or concentrated winding. This technique was an attempt to enable operation at two different speeds by changing the synchronous speed.

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