3ph motors over amping

Discussion in 'General Electronics Chat' started by Bburn, Jan 18, 2011.

  1. Bburn

    Thread Starter New Member

    Jan 18, 2011
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    I recently purchased used a "four head Maka oscillating chisel mortiser". It was built in Germany in 1965. There was a motor spec plate on only one of the motors. It reads - 3ph, 2.5 KV (4.1 FLA at 480V) and is indeed dual voltage. I can not speak with the former operators or maintenance people from whence it came in North Carolina.

    Since there are no motor wiring diagrams, I can only guess that they are wired 480 since they run at this voltage but not 240.

    The machine is designed to be able to run any or all (depending upon which of the manual starters are switched on) the motors during a typical 4 second cycle. While testing I noticed that one of the four motors was getting hot in only a few operation cycles. When I tested the other three motors together, they tripped the 30A panel breaker from which they're fed. I tested the draw with a clamp meter and amazingly each leg of the three read around 85 amps! I thought my meter was off so I tested my 15hp dust collector motor and after inrush it read about 20A - just right. So the meter works.

    However, despite the fact that the meter reads such a high amperage they are not blowing the 11.5A thermal protectors in their individual manual starters.

    What am I missing. I don't have a good grasp of the difference between wye and delta transformer and motor wiring. Could this be an issue?
    Also, at least two of the motors were rewired internally since there are only three motor leads rather than nine.

    I've attached a supply wiring diagram FYI

    Too much information yet?

    Thanks,

    Bill
     
  2. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    the two motors with the nine leads will tell you if your delta or Y. How did the overload/overcurrent protection come about? The individual overloads indicate low voltage, while your upstream indicate high voltage. Your 2.5KV is likely 2.5KW.

    These things were probably in storage, right? I'd be meggering them before applying any current.
     
    Last edited: Jan 18, 2011
  3. Bburn

    Thread Starter New Member

    Jan 18, 2011
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    0
    GotoDeviceInfo,

    A) The motor connections match nothing in my uglys book they are...

    L1, L2 and L3 respectively 1-4, 2-5, 3-6 with 7-8-9 tied I've attached a drawing if this doesn't make sense.

    B) The machine was retrofitted with two electric drill motors on ways that were pneumatically actuated. All the switches for these auxillary motors as well as the ones for the original motors are retrofitted to. They are contemporary off the shelf items and I don't see how they could affect the current (but I'm not an engineer). I ended up rewiring and replumbing the whole machine because the added drills complicated all the operational logic. I attached a pdf of the feed schematic on my first post.

    C) The plant manager who had no operational nor setup knowledge of the machine gave me the impression that the whole production line, of which this machine was a part, was only shut down recently. So it's not sit idle long.

    D) I've heard of meggering but don't know what is is or how to do it. Is is like buggering, which I have no knowledge of either :)

    E) If you're curious I've attached a link to the pages from which I bought the machine...
    http://www.irsauctions.com/index_lots.asp?pg=details&id=14053&bp=176649

    Thanks for all your help.

    Bill
     
  4. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
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    this is a low voltage Y. Meggering checks your insulation by applying a high voltage to the windings.

    A qualified Electrician would be a very good investment.
     
  5. BillB3857

    Senior Member

    Feb 28, 2009
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  6. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
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    would you look at that, good thing you didn't call me.
     
  7. Bburn

    Thread Starter New Member

    Jan 18, 2011
    9
    0
    BillB3857,

    That's what I thought concerning the motor connections - "where did that come from?" However, they must have gotten confused four times since I have the same problem on each motor. Again, two have been rewired dual voltage (9 wires) and two were rewired single voltage (3 wires). It appears this was fairly recently considering the quality of the insulation on the leads. The only one on which I can really see numbers was one with plastic snap on numbers.

    If I were advising someone like me, I'd say go buy some good used replacement motors. However, these are VERY special and have the tooling holders mounted on the shafts and they fit into a vertical adjustment sleeve like a huge router. The Import company told me the windings alone would run in the thousands.

    GotoDeviceIinfo,

    I would be very relieved if you are correct. That's an easy fix, but may I ask from whence your information comes? Again, I checked this against UGLYS and it's not a match for any voltage or any winding configuration they list. I hope you have some information I don't.

    Furthermore, my shop 240V three phase is transformed down from 480 so there is no High Leg. Is it possible that when I tested the motors at 240 they were looking for a high leg and found none, and therefore declined to run properly?
     
  8. Bburn

    Thread Starter New Member

    Jan 18, 2011
    9
    0
    Not sure I understand your last post. Did you see BillB3857's post and agree with him? I'd love for you to tell me "wire'm this way and your problem's solved".
     
  9. Hagen

    Active Member

    May 8, 2010
    30
    1
    The standard low voltage (240 volt) connection for a 9-lead star connected motor is L1 to 1 & 7, L2 to 2 & 8, and L3 to 3 & 9, with 4,5, and 6 joined and insulated.
     
  10. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    My bet is to get all the phase connections correct and it'll work properly.
    Although common 480V is set up as a Y most three phase motors do not want the neutral at all.
     
  11. Bburn

    Thread Starter New Member

    Jan 18, 2011
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    0
    Ok Guys,

    Thanks for all the input.

    To Hagen...

    Yes, that's what my book tells me too. But when I opened the cover they weren't arranged that way. I assumed it was running before I got it and that it was correct then. Obviously not. I'm leary of rearranging them according to ugly (your arrangement) and applying power.

    To Marshallf3...

    It looks like the either the motor connections were mislabled by the previous owner or not wired properly last time the motor was wound. If I'm reading my uglys correctly.

    To Both...

    If I'm reading the wye diagram correctly I should get continuity across...

    1-4, 3-6, 5-2 and 7-8-9

    If I do then the motor is wired star and the connections as I recived them were incorrect. I need to go back to star HV wiring.

    If I get continuity across 1-9-4, 6-3-8 and 7-2-5 then its delta and I need to wire accordingly.

    But the question is, if I identify that for example 1-4 have continuity, how do I know which is which when I wire them? Does it matter?

    And what about the two other motors that only have three wires. Must I open the case to test and what then?

    Bill
     
  12. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
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    if you have a motor that has legable wiring, as you've indicated, I would break all those connections and using a meter, confirm thier configuration. Your looking for a delta type winding which should have terminals 1-4-9 related, or a Y configuration which should have terminals 7-8-9 related.

    oops, took too long theorizing.
     
  13. Bburn

    Thread Starter New Member

    Jan 18, 2011
    9
    0
    Now we're getting somewhere,

    I tested all leads against each other and found what looks like a Wye pattern with mislabled leads. I found that according to the tags, which are slip on, I have continuity between...

    1-7, 3-9, 8-2 and 4-5-6

    If it were labled correctly wouldn't it be continuity between...

    1-4, 2-5, 3-6 and 7-8-9

    I'm tempted to wire this as a HV wye to give it a try but I don't know how to determine which is Line leg of each of the pairs. I imagine it makes a difference.

    Again it came wired as 1-4, 2-5, 3-6 and 7-8-9. So it looks like someone wired this thing like the actual wye patern rather than the wye motor connections.
     
  14. BillB3857

    Senior Member

    Feb 28, 2009
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    An old fashioned way to figure it out is to find the three windings that are tied together internally. Connect those three wires (hopefully 7-8-9) to 240 voltage. Use any existing wire numbers to connect the other three windings to create an un-powered star. (5-5-6 together). Connect only one of the second star power lines (example, 1 to 7) Power up the motor and measure voltages between 2 and 8 as well as 3 to 9. If all the windings are identified properly, there should be very little voltage. If you see significant voltages, the tags on the wires are wrong. Sort of like phasing transformers.
     
  15. Bburn

    Thread Starter New Member

    Jan 18, 2011
    9
    0
    Bill,

    Thanks, that's what I'm looking for. I'm a bit confused though. Did you mistype when you mentioned tying together 5-5-6?

    I posted the results of the continuity test just a minute ago but here it is again... 1-7, 2-8, 3-9, 4-5-6. So with that information can you be more specific in terms of the test you recommend.

    Then, what do I do with the results of the test? How do I properly lable the leads?
     
  16. BillB3857

    Senior Member

    Feb 28, 2009
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    Fat fingers and mis-direction....... Should be 4,5,6 together. Look at the y diagram from my earlier post and it will be clear.
     
  17. Bburn

    Thread Starter New Member

    Jan 18, 2011
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    That helps but...

    I'm a little thick and I can't afford mistakes. Can you draw me a picture?

    bill
     
  18. BillB3857

    Senior Member

    Feb 28, 2009
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    Just doing my morning quick e-mail check. Won't be able to get drawing done until this evening.
     
  19. Bburn

    Thread Starter New Member

    Jan 18, 2011
    9
    0
    Thanks to all for the input and help.

    The problem was that the motor leads were mis-labled. Whoever wired and numbered these wires did so using the Wye winding diagram rather than the Wye connection diagram. I had to go in and test the leads and renumber them.

    I wouldn't have been able to do it without Billb3857s suggestion. I needed specific directions which he didn't have time to supply today but found the diagnositic instruction at the following link...

    http://www.usmotors.com/Service/faq9.htm

    I don't know how you guys operate but if you could make this available to everyone else with this problem/question it would save a lot of effort.

    Thanks again,

    Bill
     
  20. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    Glad to see that you found the link. The method shown in the link, using the battery, is much better (and safer) than my old tried and true method. I've downloaded the page you linked for future reference. Thanks for doing the research.
     
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