Rieter

Pole-changing three-phase motors

Index

Squirrel-cage motors usually have only one 4-pole or 6-pole winding. However, motors can also be produced with two windings, i.e. 4-pole and 6-pole in one motor. By switching from one winding to the other, e.g. from 4-pole to 6-pole, the speed can be reduced to 2/3, since the following relationships exist between poles, frequencies (f) and speeds:

 

f=50

f=60

Speed, rpm
6-pole
950
1 130
4-pole
1 450
1 730

Pole-changing motors are expensive and their efficiency is low since they are load-dependent.