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2 Speed 2 Winding 3 Phase Motor

clearwater

Plastic
Joined
Sep 28, 2009
Location
Boise Idaho
I am trying to understand 2 speed induction motors, so I figured the 2 speed, 2 winding, 3 phase induction motor would be simpler to understand. From what I learned in my electrical engineering classes a few years ago, the more times a conductor is wound, the stronger the magnetic field and thus the higher the torque. I was then trying to understand the workings of a 2 speed motor in our plant and I was told that the winding that resulted in more volts/winding would result in the higher speed. That means, connected to the same bus that the winding with less "winds" would actually be the faster speed and would require more power (it's powering a fan). I don't understand how this works. I mean, taken to an extreme, the fastest, most powerful configuration would then be 1 wind, and the slowest, weakest configuration would be infinity. I am sure I am looking at this wrong but I can't seem to wrap my head around it.
 
In 2 speed motor the windings give 2 poles or 4 poles depending on the connections that are used. The synchronous speed of a motor is determined ONLY by the applied frequency and the number of poles. Loaded motors run slightly below synchronous speed due to slip.
 
Not all 3 phase 2 speed motors are 2 and 4 pole, they can be 4 and 8. I have one! The reason is that the number of poles determines the speed. The frequency of the line determines the speed of an induction motor. Divide 7200 by the number of poles it will give the Synchronous Speed (speed with no load) As load increase the "slip" reduces the speed and it will be at name plate RPM when under name plate load (HP) Don't confuse their operation to the single phase type multi speed fan motor. With no load all the speed are the same, the fan will load the motor and winding are done to weaken the torque so that it will run slower but only with the fan attached.
 








 
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