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Thread: Recycling Power Through a Wye-Wye Transformer

  1. #11
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    Quote Originally Posted by Besoeker View Post
    I think he means it is used to test the converter (of whatever type) at its rating and sends the converter output back to the supply. This is not altogether uncommon on test set ups, particularly if there is a lot of power involved that would otherwise be wasted.
    Yes, I'm sure that's what he means, and that can easily be accomplished with any of these:

    http://www.bing.com/search?q=electro...ox&FORM=IENTSR

    But 50KW is a whole different ball game.

    I'm not sure it can be accomplished with just a transformer, but a motor-generator with some paralleling gear to sync it to the utility would easily work at very high power levels.

    Edit: Ops, maybe all of those electronic loads don't return power back to the source, but the one we had in my college power electronics lab did. So they are available.
    Last edited by steve66; 03-10-17 at 03:38 PM.

  2. #12
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    JohnSmith1,

    The basic concept that you propose is reasonable and safe.

    As I understand it, you wish to test a device which converts input electrical power to output electrical power, without wasting the output electrical power. Instead you want to 'recycle' the output electrical power back into your supply network, or at least into the supply of the device being tested.

    We do this all the time with electric motor dynamometers. We have two motors with their shafts tied together, run by VSDs. One motor is driven as a motor, the other is in regen. The mechanical power going down the shaft is 'recirculated' on the DC bus between the two drives, to run a test we need only supply electrical loss.

    The devil, however, is always in the details. For example, how will your power conversion device tolerate voltage at both input and output when the device is off. How will you control the system to actually get power to circulate? Will your converter device adjust its output to force power to circulate, or do you need to adjust the '208V' of your simulated load to get power to circulate? Do you need some way to turn your simulated load on and off?

    In your plan, why do you need taps on both primary and secondary? Primary is connected to your 480V supply; secondary is _either_ connected to your 480V converter input or your 208V converter output. IMHO even though power would be flowing from 208V to 480V, the 480V side remains your primary since it is connected to your steady 480V bus.

    If you always connect 'primary' to 480V and 'secondary' to your converters, then you don't need the wye to wye phase matching. A conventional delta-wye connected transformer would be suitable.

    As far as actually sourcing the transformers that you need, they should be easy to build. I have been very happy with drive isolation transformers from Fargo Electric (www.fargoelectric.com). Their existing designs include devices with have 480V, 240V, and 208V taps on the primary, as well as 2.5% taps on the secondary. They are probably quite capable of building designs with 480V primary and multiply tapped secondaries.

    You could also simply 'bank' single phase transformers to create three phase transformers.

    Finally, I think that both your power converter input and output could be connected to the secondary of the _same_ transformer; I don't think you would need two transformers for each test station. You might need to add three phase variacs in 'buck/boost' configuration to adjust voltage and control your load, but that goes back to your design of your control system.

    Best of luck,
    Jon

  3. #13
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    Quote Originally Posted by steve66 View Post
    Yes, I'm sure that's what he means, and that can easily be accomplished with any of these:

    http://www.bing.com/search?q=electro...ox&FORM=IENTSR

    But 50KW is a whole different ball game.

    I'm not sure it can be accomplished with just a transformer, but a motor-generator with some paralleling gear to sync it to the utility would easily work at very high power levels.
    I've done it quite a few times for various projects.
    One of the more interesting was for testing energy storage flywheels. The problem is what to do with all the stored energy.

    A few numbers. The source was three phase mains transformed up to about 1200V with a Delta-delta wye (Ddyn11) transformer, rectified and smoothed to get an ultra low ripple 1500V, 600A supply (900kW).
    That powered up a whole bunch of flywheel motors. Initially, the stored power was just dumped in a load bank. Expensive waste of energy.
    The next phase of the project was to recover that energy - recyle it if you like. We built a step down chopper to get from 1500Vdc to 400Vdc and followed it with a mains commutated inverter to stick the energy back into the 400Vac utility supply.

    Interesting as I said, all topology we already employed, but the scale made a little more of a challenge.
    Si hoc legere scis nimium eruditionis habes.

  4. #14
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    What he proposes is not safe
    that is why some mfgs refuse to do it
    he wants to tie 480 and 208 together on the same xfmr primary
    he will have short ckts and most likely destroy the converter
    many shops will build one off's
    http://linepower.com/
    http://www.pemco.net/expertise/
    but not this design



  5. #15
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    The transformer has a fixed turn ratio and there is no guarantee that the service taps and load-influenced changes will be compatible.
    Basically the 480 and 240 need to be on different transformers. The converter can bridge from one to the other, but a direct grid connection may not make a suitable load for all tests. You still need a resistive or motor/brake load at some point.

    mobile

  6. #16
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    Quote Originally Posted by GoldDigger View Post

    The transformer has a fixed turn ratio and there is no guarantee that the service taps and load-influenced changes will be compatible.
    Basically the 480 and 240 need to be on different transformers. The converter can bridge from one to the other, but a direct grid connection may not make a suitable load for all tests. You still need a resistive or motor/brake load at some point.

    mobile
    Bingo

    he needs electrical isolation
    motor/gen
    charge batteries, invert back to grid
    caps and invert back
    Maybe use one of his 208:480 inverters

    I would never hook it up as proposed
    it would not last very long
    he's applying power to both sides of the converter



  7. #17
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    John smith u appear to want to keep the details of ur black box secret. Ok. I sent u pm with my email to reply to. We will be happy to quote and build u 7 custom xfmrs. But we will also request details on what u are trying to do in order to help u do it right. Yes, lots of ways to screw this up.

    Sent from my SM-G900V using Tapatalk

  8. #18
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    If isolation is indeed significant we can simply add a second 208v secondary to each phase instead of going back into prim winding. Same result... or perhaps no isolation is required and we just make it an auto xfmr....

    Sent from my SM-G900V using Tapatalk

  9. #19
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    I also think OP proposal to connect convertor output back to transformer primary risky as any phase reversal (say by POCO by mistake) could cause short circuit. Silly, my earlier post saying it got deleted.....
    I want to add a reverse power flow relay may solve the above issue.

  10. #20
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    Quote Originally Posted by Ingenieur View Post
    What he proposes is not safe
    that is why some mfgs refuse to do it
    he wants to tie 480 and 208 together on the same xfmr primary
    he will have short ckts and most likely destroy the converter
    many shops will build one off's
    http://linepower.com/
    http://www.pemco.net/expertise/
    but not this design
    Is that his diagram or yours?
    Si hoc legere scis nimium eruditionis habes.

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