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3 phase motor connection

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    #32
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    M cebee wrote: »
    there's a few ways of doing it with 12v ac supply etc
    It can also be done with a battery, connected to 1 winding and an analogue meter to another, remove battery and see the direction of the back EMF deflection, ive never tried it myself though. And by doing all windings it can be found what polarity they are relative to each other.

    But i did quick drawing of 3 phase motor and by swapping one windings polarity around with respect to other 2, im more convinced now the motor would not run right, its not the same as reversing 2 phases. I did same before as i said, but was a fair while back.

    If you were to reverse a star delta fed motor by changing connections in the connection box, you would have to swap 2 of the 3 on one side, and the 2 facing them as well. Or swap 2 phases feeding the star delta starter, which in effect swaps 2 pairs at the motor connection box. Its not the same as taking a single winding inside the motor and reversing its polarity i dont think.

    But once the 6 ends were on the terminals as they were when motor was working it doest come into it.


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    #33
    M cebee
    Closed Accounts Posts: 4,431 ✭✭✭M cebee


    yes

    godamm -have you nothing else to do:D


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    #34
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    M cebee wrote: »
    yes

    godamm -have you nothing else to do:D

    Absolutely nothing, haha i was waitin for that question, im retired now along with lots of electrical persons these days.:)


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    #35
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,591 Mod ✭✭✭✭2011


    But i did quick drawing of 3 phase motor and by swapping one windings polarity around with respect to other 2, im more convinced now the motor would not run right, its not the same as reversing 2 phases. I did same before as i said, but was a fair while back.
    I think it will run, but you have me thinking now! I will ask at work in the am. I am working with a guy that would be considered (by me) to be the last word on this kind of thing. I will let you know his view on the matter.


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    #36
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    2011 wrote: »
    I think it will run, but you have me thinking now! I will ask at work in the am. I am working with a guy that would be considered (by me) to be the last word on this kind of thing. I will let you know his view on the matter.

    Do that, will be interesting to hear.

    Id say after looking at it drawn out its near certain it wont run right. I remember exact same question on a site a few years ago, came to conclusion reversing one winding relative to others and it wont run properly. Reversing 2 phases causes 2 windins/sets of windings to change place with each other electrically, while reversing a single winding polarity just reverses its pole relative to how it was, It still has the same position in the phase rotation.

    The last word would be getting a motor, swap U1 with U2 and connect up as normal. And say it was`t you if it blows up:confused:


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    #37
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    M cebee wrote: »
    ya he's ok if the windings are connected into the block

    and the start finish face each other

    I think i mis understood you here too, you meant as long as one end of 3 windings is on one side of the connection box and other ends are on opposite side, thats definitely right in what you say there, i thought you meant both ends of each winding should be direct across from each other but of course they should be stepped on the opposite terminals.

    Windings still connected in the block is what i was assuming all along,


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    #38
    M cebee
    Closed Accounts Posts: 4,431 ✭✭✭M cebee


    http://www.scribd.com/doc/34298682/Testing-of-electrical-machines-at-Rourkela-steel-plant


    1.4.5 Determination of the star point of phases :
    1.4.5.1 This test is carried out for machines in rewinding cases.
    1.4.5.2 After rewinding, six leads (start & finish) 0f 3 phases are brought out. Connect two
    phases in series. Apply a small voltage of range 10 to 15 Volts A/C to the third phase.

    1.4.5.3 If the induced voltage across the two phases connected in series is zero then the start finish sequence of the winding is correct. If the induced voltage is other than zero the sequence of the start & finish of the winding of each phase is not correct.
    1.4.5.4 This test has to be repeated for all three windings to get correct start & finish of
    individual winding.


    i think this is the correct method


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    #39
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    M cebee wrote: »
    http://www.scribd.com/doc/34298682/Testing-of-electrical-machines-at-Rourkela-steel-plant


    1.4.5 Determination of the star point of phases :
    1.4.5.1 This test is carried out for machines in rewinding cases.
    1.4.5.2 After rewinding, six leads (start & finish) 0f 3 phases are brought out. Connect two
    phases in series. Apply a small voltage of range 10 to 15 Volts A/C to the third phase.

    1.4.5.3 If the induced voltage across the two phases connected in series is zero then the start finish sequence of the winding is correct. If the induced voltage is other than zero the sequence of the start & finish of the winding of each phase is not correct.
    1.4.5.4 This test has to be repeated for all three windings to get correct start & finish of
    individual winding.


    i think this is the correct method

    Yes it looks right, you can do the same using a 12 volt battery connected to the winding instead of the ac supply and when you remove it you will get a deflection on an analogue meter from the 2 in series windings when the start finish is not in sequence as if using the ac above.

    The reversal of one windings connections certainly affects the motor operation. It would be the same as having one winding wound in reverse direction to the other 2 windings.


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    #40
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,591 Mod ✭✭✭✭2011


    Robbie, I asked. You are correct.
    Will post details later.


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    #41
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    2011 wrote: »
    Robbie, I asked.
    Will post details later.

    Thats good anyway, not the correct bit, but to have it come up again and comfirmed properly. It was on an actual job it came up before and we came to same conclusion from drawing it out.

    If you just draw the delta shape it will be seen that swapping two phases reverses one windings phases but also swaps the phases on one end of the other 2 windings. Where as just reversing 1 winding leaves the phase rotation as it was with 1 windings pole now wrong. That was our conclusion a few years ago.

    Did he suggest the motor would stop or be very rough, our conclusion was it will not run. But we never put it to an actual test.


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    #42
    M cebee
    Closed Accounts Posts: 4,431 ✭✭✭M cebee


    afaik the motor will not run properly -as the rotating magnetic field

    will not be right

    not usually an issue for sparkies-but motor rewinders and testers would prob be well familiar


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    #43
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    M cebee wrote: »
    afaik the motor will not run properly -as the rotating magnetic field

    will not be right

    not usually an issue for sparkies-but motor rewinders and testers would prob be well familiar

    Yes i never actually had to look at a motor with the windings inside disconnected, but it came up on a job about it when we were putting in star delta connectors. It is possible to have a winding reversed by mixing up the 6 wires from the starter, it did`t happen or anything like that, but we started wondering what would happen if....

    Some lads did believe the 3 phases on one set of terminals had to be stepped over 1 place on the opposite 3 terminals which of course is incorrect as the windings should be connected internally in this way to allow links to be used straight across the terminals, and so matching phases from the star delta starter should be straight across from each other. Brown-Brown, Black-Black, Grey-Grey.


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    #44
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,591 Mod ✭✭✭✭2011


    My colleague is a very experienced electrical engineer, so I asked him about the importance of polarity with the motor windings on a 3 phase motor and the consequences of getting one of them connected in reverse. He came to the conclusion that in this case one of the phases would be opposing the other 2. This would mean that there would not be a rotating magnetic field. Just to confirm we rang a company that we deal with form time to time that specialize in rewinding and repairing motors. They asked what motor we were referring to as they assumed that they had made a mistake with a motor they had repaired for us!! They also confirmed correct polarity is essential.

    Fair play Robbie.

    Every day is a school day!!


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    #45
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    2011 wrote: »
    My colleague is a very experienced electrical engineer, so I asked him about the importance of polarity with the motor windings on a 3 phase motor and the consequences of getting one of them connected in reverse. He came to the conclusion that in this case one of the phases would be opposing the other 2. This would mean that there would not be a rotating magnetic field. Just to confirm we rang a company that we deal with form time to time that specialize in rewinding and repairing motors. They asked what motor we were referring to as they assumed that they had made a mistake with a motor they had repaired for us!! They also confirmed correct polarity is essential.

    Fair play Robbie.

    Every day is a school day!!

    It certainly is, it never ends.


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    #46
    M cebee
    Closed Accounts Posts: 4,431 ✭✭✭M cebee


    robbie7730 wrote: »
    It certainly is, it never ends.


    why's he congratulating you:D


    sure wasn't it me that told you:pac:


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    #47
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    M cebee wrote: »
    why's he congratulating you:D


    sure wasn't it me that told you:pac:
    He must of thought i was you:). Although it was only his post 19 that
    made me realise it was being suggested the motor windings had been removed from the terminals. And when he mentioned U1 and U2 being reversed as an example i thought right that wont work.

    Or will it:eek:

    Maybe dublindilbert should get the prize


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    #48
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,591 Mod ✭✭✭✭2011


    why's he congratulating you
    Sure why not?:D:D
    Ok you were right too
    Maybe dublindilbert should get the prize
    Oh yeah!


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    #49
    DublinDilbert
    Registered Users Posts: 5,379 ✭✭✭DublinDilbert


    robbie7730 wrote: »
    Maybe dublindilbert should get the prize

    Oh what do I win??? :D

    Just had a read back up the thread there, the method of joining 2 phases together and applying a small AC waveform to the 3 phase is quite clever. Its sometimes important to know the polarity of windings with fly back transformers etc, this method would work quite well for these too.


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    #50
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    DublinDilbert wrote: »
    Oh what do I win??? :D

    Just had a read back up the thread there, the method of joining 2 phases together and applying a small AC waveform to the 3 phase is quite clever. Its sometimes important to know the polarity of windings with fly back transformers etc, this method would work quite well for these too.

    Yes that will work, will work connecting and removing a 12 volt battery too and watching meter deflection on the other 2 windings seperately etc, match the deflection direction in them two and thats 2 windings polarity matched, or both windings in series will give no deflection or a big deflection depending on their relative polarity. Its a rare thing to need it though as the winding ends would need to have been removed and unmarked. Thats why i was wondering early in the thread how polarity was coming into the OP`s problem, as i did`t think they were removed. The winding ends themselves are usually marked too, although hard to read at times.


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