30 Multiple pole machines and torque

30 Multiple pole machines and torque - Lecture 29 Multiple...

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Lecture 29 Multiple pole machines and Torque calculation Consider a three-phase, two-pole machine with distributed windings, Figure 1 - 2 pole machine For simplicity a single winding per phase is shown. Assuming the three phase currents flowing in the windings are balanced with frequency ω s , the magnetic field around the air gap is () ( ) max ,c o s s HtH t θω θ =− Multiple poles are used to change the speed of rotation of the magnetic field. The windings in the previous image were wound in a full pitch. That is, the winding terminals a and –a are 180 degrees from each other. Consider now a 4-pole machine as picture next. This machine is said to have half pitch because the winding terminals are shifted only 90 degrees. In this case it would be as dividing each of the windings into two separate coils.
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Figure 2 - 4 pole machine The magnetic field will be, () ( ) max ,c o s 2 s HtH t θω θ =− The number of poles (P) is always even, and the field distribution can be in general expressed as max o s 2 s P t 
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30 Multiple pole machines and torque - Lecture 29 Multiple...

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