Page 3 of 8 FirstFirst 12345 ... LastLast
Results 21 to 30 of 71

Thread: Recycling Power Through a Wye-Wye Transformer

  1. #21
    Join Date
    Jan 2016
    Location
    PA
    Posts
    2,552
    Quote Originally Posted by JohnSmith1 View Post
    ...we have developed a plan to recycle the 208V power in a very unconventional way

    custom transformer ... with 480V primary and 480V secondary
    as well as 208V taps on both the primary and secondary windings


    What we plan on doing for our 208V tests is having 480V power initially enter with relatively high current into the transformer.

    It would then be transformed into 208V, 100A, and pass through our test unit

    Once it has passed through all of these, it returns to the input side of the transformer enters the primary winding via the 208V tap.


    kVA: 75
    Qty: 7
    Primary: 480V Wye
    Secondary: 480V Wye
    Taps: 208V Wye on both primary and secondary
    Material: Aluminum
    Temp Rise: 150

    The main issue that we have is that no one is willing to make it for us.
    We have tried many custom transformer companies, and received answers ranging from, "it's not safe," ....
    his post edited for salient points
    His words put into a diagram
    the op agreed the diagram is accurate (it was previously posted) with minor comments
    see post 4
    Last edited by Ingenieur; 03-11-17 at 12:47 AM.



  2. #22
    Join Date
    Sep 2008
    Location
    UK
    Posts
    8,946
    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
    For the 900kW system I describe a few posts back the input and returned power had no isolation between them other than the Ddyn11 required for 12-pulse operation.
    Si hoc legere scis nimium eruditionis habes.

  3. #23
    Join Date
    Jan 2016
    Location
    PA
    Posts
    2,552
    Quote Originally Posted by Besoeker View Post
    For the 900kW system I describe a few posts back the input and returned power had no isolation between them other than the Ddyn11 required for 12-pulse operation.
    Interesting project but there are several points of isolation
    rectification to dc
    elec-mech with the flywheel, replaced by dc-ac inversion
    but the last step of isolation/transformation is not required in this case because the v is the original bus voltage, not a different v tied into the main bus xfmr primary

    he would be better served by this method than his proposed



  4. #24
    Join Date
    Sep 2008
    Location
    UK
    Posts
    8,946
    Quote Originally Posted by Ingenieur View Post
    Interesting project but there are several points of isolation
    rectification to dc
    elec-mech with the flywheel, replaced by dc-ac inversion
    but the last step of isolation/transformation is not required in this case because the v is the original bus voltage, not a different v tied into the main bus xfmr primary

    he would be better served by this method than his proposed
    Rectification does not usually use or require isolation.
    The flywheel drive motor acts a generator back into same common DC bus.
    The mains commutated inverter dc to ac doesn't provide electrical isolation.

    I hope that answers your points but I'd be happy to expand on any of them.
    Si hoc legere scis nimium eruditionis habes.

  5. #25
    Join Date
    Jan 2016
    Location
    PA
    Posts
    2,552
    Quote Originally Posted by Besoeker View Post
    Rectification does not usually use or require isolation.
    The flywheel drive motor acts a generator back into same common DC bus.
    The mains commutated inverter dc to ac doesn't provide electrical isolation.

    I hope that answers your points but I'd be happy to expand on any of them.
    all imo all are forms of isolation
    rectification negates any freq/phase or voltage discrepency, fresh slate when inverting back
    the flywheel is major isolation elec-mech-elec
    the field can be manipulated for control
    gen windings act as isolation, basically a rotating xfmr
    and you had a load: the motor/flywheel/load bank
    then the motor/flywheel supplying the inverterh
    he has no load, or energy storage
    he is feeding 480 bus with 208, power can't flow (at least in the desired direction)

    but the main point is that you put 400 vac synch'ed into a 400 bus
    no need for a final isolation step
    not 208 into a 480 xfmr via a common primary winding tap
    Last edited by Ingenieur; 03-11-17 at 11:39 AM.



  6. #26
    Join Date
    Sep 2008
    Location
    UK
    Posts
    8,946
    Quote Originally Posted by Ingenieur View Post
    all imo all are forms of isolation
    rectification negates any freq/phase or voltage discrepency,
    Not electrical isolation as a rule.

    Quote Originally Posted by Ingenieur View Post
    the flywheel is major isolation elec-mech-elec
    the field can be manipulated for control
    The flywheels are powered by inverter fed SCIMs. There is no seperate field to adjust. They are fed from the common 600Vdc link. These run in two quadrants. Motoring to run the flywheels up and generation to feed stored energy back into that same dc link. No isolatiion there.

    Quote Originally Posted by Ingenieur View Post
    but the main point is that you put 400 vac synch'ed into a 400 bus
    not 208 into a 480 xfmr via a common primary winding tap
    A mains (line) commutated inverter actually ties it to line frequency. Even if it varies.

    I hope that helps.

    But I'd be happy to expand on any of the points.
    Si hoc legere scis nimium eruditionis habes.

  7. #27
    Join Date
    Jan 2016
    Location
    PA
    Posts
    2,552
    Quote Originally Posted by Besoeker View Post
    Not electrical isolation as a rule.

    The flywheels are powered by inverter fed SCIMs. There is no seperate field to adjust. They are fed from the common 600Vdc link. These run in two quadrants. Motoring to run the flywheels up and generation to feed stored energy back into that same dc link. No isolatiion there.

    A mains (line) commutated inverter actually ties it to line frequency. Even if it varies.

    I hope that helps.

    But I'd be happy to expand on any of the points.
    you missed the key point
    208 into a 480 xfmr primary via a direct tap

    thought experiment
    2000 A 505 vac supply >>> than test load(?)
    100 A xfmr 480-480 with +/- 5% taps
    a vfd input is 505 output controlled to 455

    Configure as follows
    the 505 is connected to the +5% 504 vac tap (sec is 504 also)
    the sec is connected to the vfd supply
    the vfd out/load of 455 vac is connected to the xfmr -5% (456 vac) tap

    this is very similar, but not as extreme, as the op's proposal
    what is the result?
    Can i flow from the vfd 455 to the xfmr? What v is on the -5% tap?
    what induces the vfd to produce/allow power to flow?



  8. #28
    Join Date
    Sep 2008
    Location
    UK
    Posts
    8,946
    Quote Originally Posted by Ingenieur View Post
    you missed the key point
    208 into a 480 xfmr primary via a direct tap
    OK.
    Si hoc legere scis nimium eruditionis habes.

  9. #29
    Join Date
    Jan 2016
    Location
    PA
    Posts
    2,552
    Power can't flow from the 'device' output to the 480 bus
    3 ways to control power flow bus-bus
    1 sending v > receiving v
    2 line Z
    3 power angle, ph delta v sending - v receiving

    1 not the case, receiving > sending, if anything the 480 bus will flow power TO the device
    2 ignore, short cables, low voltage
    3 he stated the v's were in phase, no power can flow, but regardless could not be increased enough to overcome v delta

    increasing power angle would make things worse, now the v's on the xfmr prim are out of phase

    Imho the op needs to rethink this and consult his plant power ee



  10. #30
    Join Date
    Sep 2008
    Location
    UK
    Posts
    8,946
    Quote Originally Posted by Ingenieur View Post
    Power can't flow from the 'device' output to the 480 bus
    That's what the system I designed did. At 400V 50Hz.
    Four quad systems are fairly common in process industries. Call it recycling power or whatever.

    It's an interesting area and one that have been involved with for a very long time.
    Last edited by ActionDave; 03-11-17 at 01:01 PM.
    Si hoc legere scis nimium eruditionis habes.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •