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Thread: Delta vs Wye motor connections

  1. #1
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    Delta vs Wye motor connections

    I have been reading informatino regarding delta vs wye motor configurations but am still a little foggy on the subject. I have noticed that most of the motors in our plant are wired for a 3-wire delta configuration. If I understand correctly, a 3-wire connection is not one that can be changed, and it is what it is wheather its delta or wye.

    This brings me to the 6-wire motors which can be changed between delta and wye. I understand that a delta wired motor will have the L-L line voltage across the stator windings, and a wye configured motor will have (L-L)/1.73V across the stator windings. I've seen a high voltage and low voltage referenced when using delta / wye connectiosn but am unsure what these voltages refer to? If I have a 480V L-L system voltage, would this be a high voltage or low voltage when refering it to a 480V 6-wire motor? What is meant by these voltages.

    Aside from a wye-start / delta-run soft starting application what are some other applications where a motor would be wired for a wye configuration for starting and running? What happens if you wire a motor configured for one type the other way?

    I would appreciate any info or resources regarding this topic.

  2. #2
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    mull -
    It's too much for me to tackle all at once. i'll nibble off a couple of pieces

    Quote Originally Posted by mull982
    ...Aside from a wye-start / delta-run soft starting application what are some other applications where a motor would be wired for a wye configuration for starting and running? ...
    I'm not much on motor winding theory. But there are plenty of wye wound motors out there. When I was fingering the wires for a living, that is pretty much all I saw. 99% fell into 2 - 50hp, 9 lead dual voltage. I don't know what is common now.

    Quote Originally Posted by mull982
    ... What happens if you wire a motor configured for one type the other way? ...
    If you connect a delta wound motor as a wye, it is a lower hp motor.

    If you connect a wye wound motor as a delta -- well, I've never seen one that you could do that to. All of the wye wound motors I've seen are 9 lead or 3 lead. The 9 lead are dual voltage (usually 480/240) and the 3 lead are single voltage. The 3 lead have the wye point buried in the internals. The 9 lead has 6 coils that can be connected in series, or parallel fed. One set of three windings have the wye point already made up and buried in the internals

    carl
    Using the code for a design guide is a sign of incompetance

  3. #3
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    Assuming you are in North America, don't get hung up on the "Delta vs Wye" winding issue, it is almost completely irrelevant. A NEMA designed motor is what it is, you usually have no way of knowing, short of dissection, whether it is wound in Delta or Wye internally, nor should you care.

    Don't confuse this with Delta or Wye power systems, the issues are completely separate and not related as far as functionality goes. Aside from Y-Start / Delta-Run motors, you ALWAYS only run 3 leads to the motor, NEVER the 4th (neutral). So how it is connected internally is for the motor mfr. to worry about, not you.

    In a Wye-Start / Delta Run motor, the windings, and associated power ratings, are still based on the Delta configuration. But when you bring all of the motor leads out to the connection box and connect them in Wye, you get the 1.73 reduction factor (58%) on effective voltage across the windings. Since torque, and therefore current, follow the square of the applied voltage, you also get 33% (.58 x .58) of the normal torque and current. Since the frequency didn't change and you have less torque, you have less HP by the same ratio, so your shaft HP is down to 33% as well. Technically then, you could run a motor in Wye continuously is you are ABSOLUTELY sure the mechanical load on it is never more than 1/3 of its rating (although you must as "Why?")

    How that relates to "Leads" in single speed NEMA motors is as follows:
    "6 lead motors" are either single voltage motors, Wye or Delta wound (you won't know the difference) or they are single voltage, Wye-Dela start. They can also be dual-windings, for instance as you would use with a Part Winding starter. In some RARE instances they are dual voltage motors, but the voltage ratio is always 1.732:1, so that would be 480/277V or 575/331V; you won't see a lot of those, not worth considering.

    "9 lead motors" can be either Dual Voltage Wye or Dual Voltage Delta (again, you won't know the difference), typically 230/460V. They CANNOT be connected for Wye-start / Delta Run. In some rare cases you will see IEC motors sold in N. America as Single Voltage 9 lead motors, because they base it only on the high voltage connection (Wye only).

    "12 lead motors" are where you get into all kinds of possibilities, i.e. dual voltage, Wye-Delta starting or pretty much any lower configuration mentioned above.

    In the IEC motor world, more specifically Great Britain (and Australia / New Zealand), THEY use Delta or Wye winding configurations for voltage changing. A 380/220V motor is connected with its windings in "Star" (Wye) for 380V line supply, Delta for 220V (380 / 1.732 = 220). Their system essentially rates the motor based on the Delta configuration as well, but because you are changing the applied voltage, the power remains the same. We don't do that here in the US because we don't have the same ratios of voltage supplies.
    Last edited by Jraef; 04-14-08 at 08:06 PM.

  4. #4
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    Quote Originally Posted by Jraef
    ... "9 lead motors" can be either Dual Voltage Wye or Dual Voltage Delta (again, you won't know the difference), typically 230/460V. ...
    This confused non-Southern American is completely unsure how the motor coils of a dual voltage, 9 lead motor could be connected delta. All the ones I have seen have LV with 3 pairs individually connected to line and one trio connected. The HV connection is 3 pairs connected, and 3 leads to line. That sure looks like there is a wye point buried in the motor.

    Perhaps you could send a sketch on how the coils of a dual voltage, 9 lead motor are connected for an internal delta.

    carl
    Using the code for a design guide is a sign of incompetance

  5. #5
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    Carl, they do make a nine lead, dual voltage, delta motor. Give me a few minutes and I'll draw the diagram amd post it.

  6. #6
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    Here is what the windings and connections of the nine-lead, dual-voltage, delta motor look like.

    The high voltage connection is straight-forward. The low voltage connection isn't quite so obvious.

    Also, it is easy to tell whether one is working with a wye 9-lead or delta 9-lead by using an ohmeter to check the common leads.


  7. #7
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    Quote Originally Posted by crossman
    Carl, they do make a nine lead, dual voltage, delta motor. Give me a few minutes and I'll draw the diagram amd post it.
    I saw this picture in a 1934 motor winding handbook. but it looked like this. But, I have never seen or heard of one - and I have wired a lot (until twenty-five years ago). Is this something that has been around and common for ever, or a recent (less than twenty-five years) development, or a 1934 design that never went anywhere?

    carl
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    Using the code for a design guide is a sign of incompetance

  8. #8
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    Good question Carl. I can't say that I ever actually hooked up or even saw a motor that was wound like this. I have only seen it mentioned in the texts. I would bet that they made these years ago but don't anymore. I am on dial-up right now, otherwise I would do a search.

  9. #9
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    Carl, your picture looks like the 1/2 voltage version of crossman's picture.
    see:
    http://www.usmotors.com/products/ProFacts/1-120-7.htm

  10. #10
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    Quote Originally Posted by crossman
    Here is what the windings and connections of the nine-lead, dual-voltage, delta motor look like.

    The high voltage connection is straight-forward. The low voltage connection isn't quite so obvious.

    Also, it is easy to tell whether one is working with a wye 9-lead or delta 9-lead by using an ohmeter to check the common leads.

    That's the right diagram, I saw a lot of them when I worked in a surplus house years ago, no idea if anyone still makes or sells them.

    The connections are:
    LV: L1 to 1, 6 & 7; L2 to 2, 4, &8; L3 to 3, 5 &9
    HV: Li to 1, L2 to 2, L3 to 3, Join 4 & 7, 5 & 8, 6 & 9

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