What is the correct method for counting poles in a 3-phase induction motor?

  • #1
BlackMelon
43
7
(I have modified the picture a little bit for clarity)

Hi there!

I had a chat with my colleague. He believes that the 3-phase induction motor on the picture below has 2-poles.
There are 12 slots. Each phase contain 2 coils. I have showed how the coils are connected for the phase W at the bottom.
The waveform belongs to current of each phase. For notations, when the current is entering the slot W1 (crossed symbol in the hand drawing), the same current leaves the slot W2 (dotted symbol in the hand drawing).

So from the waveform, I take a sample of current flows when wt = 0 degree, where w is angular frequency (U1 = 0, W1 = positive, V1 = negative). Using the right hand rule, I founded that there are 6 poles.

I would like to know whether me or my colleague made any mistakes?Melon.

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  • #2
If you made a mistake, then it is probably observational, and we have been presented with the same data.

The ultimate test needs to be: does the unloaded motor run just below synchronous speed, or just below half twice synchronous speed.
 
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  • #3
Aren't number of poles is usually defined per phase?
 
  • #4
Averagesupernova said:
Aren't number of poles is usually defined per phase?
Well, I understand your point. You bring the phase W like I drew and then examine its number of poles (4 poles).
However, when you input the 3 phase currents into the motor, the number of poles will not be 4x3. Rather, it will still be 4, considering the directions of all the currents in the stator.
Baluncore said:
If you made a mistake, then it is probably observational, and we have been presented with the same data.

The ultimate test needs to be: does the unloaded motor run just below synchronous speed, or just below half twice synchronous speed.
Thank you for the advice. :) :)
 
  • #5
Guys, I got the answer for the question I asked. The distribution of windings' positions are incorrect. (The way I analyzed the number of poles was correct and showed abnormality). Rather, the distribution should be done as the picture below.
According to the right and rule (The thumb is the magnetic field. The rest of the fingers are the current). Please not that 6 adjacent phase zones form 1 pole in the air gap.
For example at 30 degree electrical angle, U, -V, W and -U, V, -W form a south pole.
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