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I am having trouble finding diagrams to show induction motors with poles not equal to 3x. Everything I find is 2 poles per phase. Can anyone explain and help me visualize, for example, a 4 pole 3 phase induction motor?

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4 Answers 4

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  1. Lest there be any confusion: poles always appear in pairs. The windings generate alternating N (north) and S (south) poles. As a result AC motors are 2-pole, 4-pole, 6-pole, etc. (It may help to remember that if you were to break a bar magnet in half to isolate each of the poles that new opposite poles would appear each side of the break, giving you two bar magnets each with a N-S pole pair.)
  2. On a three-phase motor the pole pattern has to be repeated for each phase. Therefore a 2=pole, 3-phase motor will have six poles.

enter image description here

Figure 1. A 2-pole, 3-phase motor.

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Figure 2. A 4-pole, 3-phase motor.

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Figure 3. A 6-pole, 3-phase motor.

Images from Basil Networks permanent magnet brushless motors page. This is worth a read as it shows the series motor connections.

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Figure 4. 4-pole, 3-phase AC induction motor illustration. Source Wikipedia: induction motor.

Figure 4 is a little clearer regarding the flux path inside the rotor.

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  • \$\begingroup\$ "Therefore a 2=pole, 3-phase motor will have six poles.", IMO that statment isn't correct, because it has 2 poles, rather it has six winding, but it would be OK if you provide a reference/citation to that statement. \$\endgroup\$ Commented Mar 27, 2016 at 15:38
  • \$\begingroup\$ my confusion was the count difference between windings and poles. thank you! \$\endgroup\$
    – blindguy
    Commented Mar 28, 2016 at 2:59
  • \$\begingroup\$ I stared at these Basil Networks diagrams for yonks trying to figure out why I couldn't get them to work. Turns out the 4-pole and 6-pole are wrong. The additional pole pairs also require additional magnetic poles. See slide 23 of pjm.com/-/media/training/nerc-certifications/gen-exam-materials/… Can anyone confirm that the additional "N N S S" labels on the Basil diagrams are incorrectly labelled? \$\endgroup\$ Commented Nov 8, 2018 at 4:25
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    \$\begingroup\$ Figure 2 shows an odd wiring setup where you have four windings, but they're wound such that two adjacent windings act together, hence "NN NN SS SS". But normally you wire each adjacent winding to act opposite the last winding, giving "NN SS NN SS". This is shown for a normal three phase four pole motor in Figure 4. \$\endgroup\$ Commented Feb 25, 2020 at 6:15
  • \$\begingroup\$ Isn't the statement "a 2=pole, 3-phase motor will have six poles" contradictory? Is that a typo? \$\endgroup\$ Commented Oct 4, 2021 at 19:39
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Because a magnet field has two poles N and S, or one pole pair. The poles number can therefore be just a number 2*N. And it is not poles per phase, but rather poles (or pole pairs). For example you have a two pole motor, or a motor with one pole pair, which is the same. The synchronous speed of a induction motor is N=f/(60*N_of_pole_pairs).

The picture below is a representation of magnetic flux of 2 pole vs. 4 pole machine. The 2 pole has poles N and S, while 4 pole has N S N S. enter image description here

Four pole induction motor animation:

enter image description here

Edit: You should search for rotating magnetic field. The current in three phase winding generates magnetic field of constant magnitude that rotates if the currents are AC. The same could be done with two phase windings with 90 degrees appart, but we would need 4 wires, meanwhile the three phase system uses only 3 wires. Therefore the number of phases isn't related to the number of pole pairs.

Edit2: Special for user JonRB that has no idea of induction motors, see there are 2,4,6,8... poles, 3 POLES DOESN'T EXIST. enter image description here

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  • \$\begingroup\$ yeah but how is a two pole 3 phase motor wired. Its easy for me to visualize a 6 pole 3 phase motor because each phase can be a pole pair \$\endgroup\$
    – blindguy
    Commented Mar 27, 2016 at 3:19
  • \$\begingroup\$ you can't have a 2pole, 3phase machine... 3pole, 3phase machine is the lowest count \$\endgroup\$
    – user16222
    Commented Mar 27, 2016 at 10:04
  • \$\begingroup\$ @JonRB If you don't know the single phase induction motor is two phase, also the stepper motor is to phase, but there is no such motor as 3 pole. \$\endgroup\$ Commented Mar 27, 2016 at 13:54
  • \$\begingroup\$ How is a single phase a 3phase as 1) asked, 2) I stated. And equally there was a typo in my comment. 3pole pair.. \$\endgroup\$
    – user16222
    Commented Mar 27, 2016 at 14:15
  • \$\begingroup\$ @JonRB "3pole, 3phase machine is the lowest count" nor 3 pole is lowest count, it's 2 pole; nor 3 phase is lowest count. \$\endgroup\$ Commented Mar 27, 2016 at 14:18
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I think you are getting confused by pole and no of winding in three phase induction moter six coil winding makes one pair of pole or two pole . If there is four pole (two pair of pole )no of winding becomes 12

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I'm a Structural Engineer and I find the arguments and discussions above confusing! So let me chip in my two cents worth and you can then attack my understanding.

In principle a two pole 3 phase stator is wound to create two magnetic poles or a pole pair when excited by three phase current hence it is called a 2 pole motor. This can be achieved with numerous winding combinations. So the number of windings counted has nothing to do with the number of poles or pole pairs!

To take an example if the motor has 6 windings it can be wound to create a NNN SSS pattern this would be a 2 pole motor.

Equally the motor could have 12 windings connected to create a NNNNNN SSSSSS pattern which would still be a 2 pole motor.

Both motors would result in a NS flux pattern which rotates at the frequency of the supply currents. i.e. Ns = 2f/P = 2f/2 =f.

It's important to note the flux pattern is different from a NS magnet. The NNN winding is supplied by a 3 phase supply (one pole per phase) out of phase by 120 degrees resulting in a circular flux pattern around the NNN poles much like that around a current carrying wire. Similarly the SSS winding results in a circular flux pattern of opposite direction.

Same applies to the NNNNNN winding and SSSSSS winding where each active phase is connected to a NN pair wired in parallel i.e. total of 3 phase supply.

Obviously the 6 winding motor produces 1/2 the flux density of the 12 winding motor but both pattern rotate at the same speed Ns =f

Consider the 4 pole 3 phase motor using 12 windings connected to create the pattern NNN SSS NNN SSS. Each NNN winding is supplied by 3 phase supply resulting in a circular flux pattern which alternates direction with the adjacent SSS winding.

The four pole flux pattern rotates a Ns = 2f/4 = f/2.

Finally consider the 6 pole 3 phase motor with 12 windings creating a NN SS NN SS NN SS pattern. Each NN pair is connected to an active phase in parallel.

The six pole flux pattern rotates at Ms = 2f/6 = f/3.

So a 12 winding stator can be wound to create a 2 pole, 4 pole or 6 pole motor!

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