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Recent content by davidbeach

  1. davidbeach

    Excitation current on induction motor as a generator via VFD

    Since an induction generator only generates power, but not voltage, where's the voltage going to come from? Even with caps to supply vars, there needs to be a solid voltage source to get any meaningful amount of power out of the generator. Don't think that's something the VFD can do. But I...
  2. davidbeach

    Carbon River Fairfax Bridge - Closed

    That will take pressure off the understaffed park.
  3. davidbeach

    Equipment Ground Conductor (EGC) on delta system with a grounding transformer

    I agree with Bill about the shield. A concentric neutral, might, maybe, be used as the ECG. Admittedly, it's been 20 years since I worked on the NEC side of the meter, but at that point there weren't any concentric neutral cables NTRL listed as 2 conductor assemblies. There were single...
  4. davidbeach

    Dominican Republic Nigh Club Roof Collapse

    There's a wide array of image sources and image qualities in Google Earth. Yes, there is undoubtedly a base of satellite imagery, but given the wide variety of sources and image quality it seems there's also a variety of elevations and focal lengths involved. If the image angle of power poles...
  5. davidbeach

    Dominican Republic Nigh Club Roof Collapse

    That's what they say. Ever actually pondered any of that imagery? If, for instance, the images are from satellites rather than vastly lower airplanes, why do the images of power poles tip soooooo far away from the base? Those images are from a few thousand feet at most. Certainly well below...
  6. davidbeach

    Dominican Republic Nigh Club Roof Collapse

    It was never satellite imagery.... geesh....
  7. davidbeach

    Transmission ground distance relaying with distribution underbuild

    Ok, the pre-fault unbalance is just a real line in the non-textbook world. Your transmission provider doesn't do much transposition and I'm going to guess that you don't either. Nobody does the "continuous transposition" thing and so balanced 3-phase systems are a useful fiction but not found...
  8. davidbeach

    Transmission ground distance relaying with distribution underbuild

    I'd be interesting in taking a look at it, you know how to reach me... Is the line in question in the regional model? If not, enough of a model that I can connect it in would be helpful.
  9. davidbeach

    Transmission ground distance relaying with distribution underbuild

    How do your Z1 and Z0 compare? I've never seen that much discrepancy between values arrived at using the more conventional rules of thumb and those arrived at using more detailed analysis. Any unmodeled ground sources in the neighborhood?
  10. davidbeach

    Heathrow power outage

    And with decent protection you detect the fault and clear the transformer long before it gets to the interesting stage.
  11. davidbeach

    Paralleling dissimilar Generators

    How big a system? The Western Interconnect has hundreds of dissimilar, random, generators all running in parallel with no particular problems… The Eastern might well have more.
  12. davidbeach

    Transmission ground distance relaying with distribution underbuild

    The distribution phase conductors have very little to do with line impedance, but that neutral is just line any other "shield" wire. Include it in your parameter calcs the same way you would an overhead shield. Also, don't blindly assume rho earth is the conventional 100 ohm meters. I find...
  13. davidbeach

    Arc detection relay Vs UFES (Ultra fast earthing switch)

    Something has to detect the fault to close the UFES…. I don’t think it’s “or” but rather “and”. The relay for detection and the UFES for quenching.
  14. davidbeach

    How to use the Variac

    From the test reports I’ve seen the transformer testing is done at ambient temperature and then corrected to the operating temperature. But those are in the size range of a few MW to hundreds of MW.

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