1 phase from 3 phase

Discussion in 'The Projects Forum' started by Jim Draper, Sep 5, 2010.

  1. Jim Draper

    Thread Starter New Member

    Sep 5, 2010
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    Hi all. I'm new here and have a problem to figure out. A shop I am working for installed a 480V single phase magnaflux machine by using 2 of the wires in a 480V three phase panel. The three phase has the delta configuration. The magnaflux machine works a lot like a welder. It has transformers and rectifiers to get AC or DC, and very high Amps (should get 3,000A). The machine is operational, but only produces half of the amps it should at the maximum setting. My thought is that it needs to be wired into a single phase panel. Any ideas? Thanks in advance.
     
  2. marshallf3

    Well-Known Member

    Jul 26, 2010
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    480 doesn't come in Delta except in very rare occasions.

    What's coming into your building is commonly known as 480Y/277 meaning that there is 480V between any two of the three phases and 277V from any one of the phases to neutral. The phases are exactly 120* apart from each other.

    In any case if he grabbed two of the three hot phases he's feeding 480V into it as a single phase.

    IF this magneflux machine was designed to be operated from 480V single phase I'd be quite surprised. Small motors yes - big equipment no.

    What are the requirements listed on the label of the machine? My guess is it's supposed to get all three phases.

    If I'm correct and it requires three phase power I do hope this was installed by a qualified COMMERCIAL electrician so he can be asked to come correct his mistake. If it was installed by your physical plant guys they may have made a rather unusual mistake and shouldn't be anywhere near 480V circuitry much less a simple wall socket.
     
  3. Jim Draper

    Thread Starter New Member

    Sep 5, 2010
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    The panel is labeled 480 volts, and has 3 hot wires coming in. When checking the volts of each wire to ground, I get 150V, 550V and 350V. When checking one wire to another, I get 480 on all. The machine is labeled 220V/440V, 1 phase.
     
  4. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Sounds like it's been converted at some point through a 208Y/120 transformer up to 480 3 phase. They make these, and some of the legitimate 480V to 208Y/120 step down transformers are rated to operate in reverse.

    Considering what you're reading from each phase to ground the converter transformer has no internal neutral connection for the 480V side and really shouldn't, a good sign that it's a step-down that was wired in reverse.

    You're reading 480V between any pair of the three phase output wires.
    Machine is labeled 220V/440V single phase and I'm sure hooked up for a 440V input.

    In theory what you've described should work but I'd be darn sure that the machine itself is well bonded (connected) to an earth ground leg of the building's original power system. I mean the actual case of the machine, not any of the wires going into it.

    Now, why aren't you getting the amount of power you'd expect?

    1) You're going to have to find that transformer that's supplying the 480V three phase and find out how many KVA it's rated for, it's usually clearly marked.

    2) You're going to need to find out how much amperage the machine in question requires when running off 440V.
     
    Last edited: Sep 5, 2010
  5. Jim Draper

    Thread Starter New Member

    Sep 5, 2010
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    The transformer should be plenty big. It is in a large steel foundry, and this magnaflux machine is quite small compared to other things running in the building. My concern is, it is made to run off of a single phase 440. This would have 2 hot wires, with "phases" 180° apart. It is wired into a three phase box using 2 of the 3 hot wires. On 3 phase, the phases are 120° apart. Would this cause my problem of only getting half the output I should have out of the machine?
     
  6. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Ignore the three phase part for now, you measured 480V between two hot conductors - that's your single phase of power. Also ignore the 120* apart as that's been compensated for in the way they specify the 480V

    The transformer should be plenty big means absolutely nothing. I'm presently moving one in part of the building. It's about 2' high x 1' square and weighs about 300 lbs. It's rated at 15 KVA which means, fully loaded, it will provide me with 3 legs of 120V single phase each of which is capable of 40A. To do so it will require about 11A being fed into each leg of the 480V input.

    Were I to use that same transformer hooked up in reverse and fully fed it I'd only be able to get 10A of 480V singe phase out.

    I guess your initial statement of "The magnaflux machine works a lot like a welder. It has transformers and rectifiers to get AC or DC, and very high Amps (should get 3,000A)." means that it outputs a rather low voltage.

    The mere fact that it's working without smoke or blowing fuses makes me think it's wired in correctly. I would however feel better knowing the KVA of your step-up transformer and the nameplate amps on the machine itself.

    You previously mentioned you were able to measure some voltages that clued me in to this being powered off a step down transformer hooked up in reverse, however does your meter have a clamp-on ammeter so you can see how many amps the machine pulls when you're operating it under normal load?

    I realize all this 120* out of phase stuff is confusing but it works that way and is exactly what the equipment is expecting as an input.

    My guesses are that it doesn't have enough ampacity of the 480V to draw on (the reason I'd like to see some nameplate numbers) or that the machine itself has an internal fault such as one rectifier being open that would still allow it to funtion, just at a reduced efficiency.
     
  7. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    you say the machine produces only half the amps. I'm leaning towards that as being on it's low voltage output, and not intended to mean that it's supply is to provide that much current. As in a typical welder, a malfunctioning rectifier section will reduce your current delivered.
     
  8. Jim Draper

    Thread Starter New Member

    Sep 5, 2010
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    That is correct. The amps it is producing is on the low voltage output. It is producing 1500 amps, which is exactly half of what is should be. I will try to post pictures tomorrow afternoon. Thanks for the help.
     
  9. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    schematics would be better. Sounding more like rectifiers.
     
  10. marshallf3

    Well-Known Member

    Jul 26, 2010
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    If it's getting plenty of power then a simple ohmmeter should easily pinoint the defective rectifier.
     
  11. gerty

    AAC Fanatic!

    Aug 30, 2007
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    Have you monitored the input voltage (480) while the machine is running?
     
  12. Jim Draper

    Thread Starter New Member

    Sep 5, 2010
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    OK, I fixed it. Like a welder, it has leads that plug into the machine. The leads go to a coil instead of a ground clamp and a stinger. Anyway, I brought a lead from home and plugged it in to the machine. Got 3,000 amps, that's it. So, the connections on the old leads were not letting the full amount of power through. I looked at the label on the machine again. It is 1 phase, 220 / 440 volts. It is wired into 2 legs of a 3 phase 480 box. Thanks for all the suggestions. I'm glad it was an easy fix. Now I have to fix a 3 phase magnaflux machine with a blown transformer. Wish me luck!
     
  13. n1ist

    Active Member

    Mar 8, 2009
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    Be real cautious here. 480V at these currents can be extremely dangerous; make sure you are using the proper protective equipment (PPE - face shields, proper clothing, etc) for the available fault current, and proper lockout-tagout procedures, whenever a panel is live and opened. Arc flash can be fatal or worse.

    Those voltages you are reading to ground may also mean that you have an ungrounded system; if that is so, and isn't intentional, it should get checked out by a licensed electrician.
     
  14. marshallf3

    Well-Known Member

    Jul 26, 2010
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    The actual output of the machine is going to be at a far lower voltage much like any welder.

    It's also normal to read voltages from the supply phases to ground and in the case of what he's seing it would be typical if a 480Y step down transformer is hiding somewhere in the bulding that's been hooked up backwards such that they can get 480V when they only have 208Y coming in.

    Some of these step down transformers are rated to do that, some aren't suggested to be used as such but people do it anyway without consequence if they know what they're doing.
     
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