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Thread: Ground bonding on mixed Wye /delta connection - fault protection

  1. #11
    Join Date
    Jul 2006
    Roughly 5346 miles from Earls Court
    Greg, have to checked to see if the ESTA has anything relevant? (I'll ask some of my friends in SMPTE, too.)

  2. #12
    Join Date
    Nov 2014
    Miami, Florida, USA
    Greg, I'd say wye and delta refer to how transformers are designed/connected and not how loads are connected to them....but lets leave that alone for now. You are cool on the grounding side so forget that part too for now.

    In short, your worst solution will be where you are provide a 3 phase, 5 wire drop (3 hots, a neutral and a ground) which are then split up into 120 volt circuits. You really need a separate neutral for each phase (hot). But that adds mucho money to the situation.

    You will do better with two hots and a ground (single phase 208).

    Three phase 208 is your way best solution.

    120 volt stuff with individual neutrals should "work" on utility power (but a K rated transformer might be called for). They could be a problem for a generator.

    If you buy amps rated for the Euro market they shouldn't have as much power distortion. They have much tighter regs.

    There is another solution for 120 volt loads called a "balanced power" transformer. It is code approved for recording studios. Don't know about for your needs. Wouldn't be cheap but I love them at home for those nasty digital sources. Plus now you do need to think about grounding.

    IMHO class D amps have no place in quality audio but then I use vacuum tubes, horn loaded drivers, and play vinyl

  3. #13
    Join Date
    Jul 2017
    Kirbyville, MO, USA

    Simultaneous wye/delta (line-to-line-to-line vs. line-to-neutral

    Thanks for the replies. Everything you mentioned is part of my study, and those are the issues.

    As I think I mentioned, there are some monstrous amplifiers out there that are capable of operating on a true delta connection (I'm terming them "native 3-phase"), and they solve this issue, at least as far as the neutral is concerned. Interestingly, some are manufactured by companies whose other business is large industrial motor speed controllers. Go figure.

    I have done some testing with "non-native 3-phase" (single line-to-neutral) large amplifiers and the "triple single phase 208" connection results in very well behaved current draw and obviously eliminates the neutral problem, while still providing 120v for 120V low current devices.

    I have built a test jig that can source either format (Line-to-line-to-line or line-to-neutral) and is capable of metering up to 100A line-to-line and 100A neutral; as well as line-to-line (simultaneously all three lines) voltage, and line-to neutral (selectable for leg) voltage differential. I'm using analog metering because digital display ammeters/voltmeters cannot reliably catch these peak currents and instantaneous voltage droops.

    I can quickly switch a bank (3 for the test) of amplifiers to either format. I do have to shut the amplifiers down and restart to switch formats so their power supplies can sense the new input voltage.

    Neutral-to-ground -- Yes, at the far end of long source cable runs to amp racks there are some interesting things going on with neutral-to-ground voltage where there should not be any in Wye. I believe this voltage to be the harmonic content on the neutral.

    WRT generators -- there are anecdotal reports where users are experiencing voltage swings line-to-neutral of significant magnitude running their systems on generators. It is likely that the harmonic content is driving the regulation in the generator batty. It is also likely that the users are taking the nameplate current draw ratings of the amplifiers for gospel (20,000 watts on 120V) and sizing a rental generator accordingly for lowest rental cost. Amplifiers are shutting down from over and under volt. There are anecdotal reports where users have jacked up the voltage of generators (130v+) to keep amplifiers from undervolt shutdown, with the unexpected result that they are then experiencing overvolt shutdown.

    I'll also post a schematic of a particularly scary power distribution setup.

    I really appreciate all the input on this, stay tuned.

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