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#47873 - 01/28/05 03:03 AM 2pole but 3 phase  
Edward  Offline
Joined: Dec 2002
Posts: 308
i saw a wood working machinary that had 4 MOTORS on it. On the name plate of each motor it was STAMPED 2 POLE however on the body of the motor it clearly said 3 phase iduction motor. And it had 3 leads going to the motor housing.
My question is what does that 2pole refer to?

Number of phases? I dont think so.

Number of poles inside???????



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#47874 - 01/28/05 07:16 AM Re: 2pole but 3 phase  
oldtimer  Offline
Junior Member
Joined: Jul 2002
Posts: 7
raymond, ohio, u.s.a.
the number of poles relates to a motor's r.p.m. 2 poles = 3600 r.p.m.
4 poles = 1800 r.p.m.
6 poles = 1200 r.p.m.
(nominal speeds with no slippage factored in)

this has to do with the number of windings in the stator and how their grouped, not whether their single-phase or three-phase.

#47875 - 01/28/05 09:35 AM Re: 2pole but 3 phase  
winnie  Offline
Joined: Sep 2003
Posts: 649
boston, ma
In particular, the number of 'poles' describes the shape of the magnetic field produced inside the motor.

In a conventional induction motor, magnetic flux threads across the 'airgap', the space between the rotor and the stator. Just like a conventional bar magnet, some parts of the stator will be north poles, and some parts will be south poles. In operation, the position of the poles rotates.

The magnetic field will rotate by one pair of poles per AC cycle. So when you feed 60Hz AC into a 2 pole motor, the magnetic field will rotate 60 times per second, or 3600 RPM. If you feed 60Hz AC into a 4 pole motor, the magnetic field only rotates half a turn per AC cycle, or 30 times per second, or 1800 RPM


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