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  1. bdn2004

    What is the %Z of this grounding transformer given this nameplate data ?

    David, That's good advice... I will be contacting them. The transformer is brand new. And it brings up questions about the the switchboard connected to it. 480V ungrounded delta ? not seen that before.
  2. bdn2004

    What is the %Z of this grounding transformer given this nameplate data ?

    Thanks, from my sketch no, there is no load on it. But I'm assured by an old hand that's worked there many years there is a switchboard attached to it that feeds critical HVAC equipment. There's another 500 kVA transformer on site like this one performing the same function on the other incoming...
  3. bdn2004

    What is the %Z of this grounding transformer given this nameplate data ?

    It actually does have load on it ... Aux Power they call it. It's connected to a 3-phase switchboard. I've tried to draw out a completed faulted circuit to ground downstream on Phase B. Do I have this right ? The ratings on this transformer appear to be rated currents for normal operation. 29A...
  4. bdn2004

    Analyzing a 3-phase fault recorded waveform from an SEL relay on a 15kV feeder breaker, when did the breaker trip, why is VB at 0V before the fault ?

    Thanks that looks right what both of you are saying. Trying to get more info as you've suggested. I added some time references to the photo. It looks like it goes from 0 current to the max current in 0.0125 seconds, or about 3/4 of 1 cycle. The higher voltages between the two non-grounded...
  5. bdn2004

    Analyzing a 3-phase fault recorded waveform from an SEL relay on a 15kV feeder breaker, when did the breaker trip, why is VB at 0V before the fault ?

    There was fault on this feeder breaker. The instantaneous relay was set at 18000 amps. There was no load on the feeder. Was the wave decaying on it's own then it tripped ? Or is the last part of the top current wave when the breaker tripped ? Another question is ... WHY is VB at 0V before the...
  6. bdn2004

    What is the %Z of this grounding transformer given this nameplate data ?

    Below is the picture of the nameplate.... as you can see Z0 = 97.14 ohms per phase. Or can this be figured out from this info ? If so what is the calculation ?
  7. bdn2004

    Two 250 VDC 1200A rectifiers feeding multiple crane rails - is it OK to put the outputs in parallel ?

    There is discussion right now on the taps of the transformers that LionelHutz mentioned. And yes, the paralleling reality was in my original post ... this operation has been in service for literally decades - all day every day. That's why it's hard to believe it won't work now. But the goal is...
  8. bdn2004

    Asking for help making sense of a grounding transformer

    I still don't understand this ... I attempted to do what I think you are saying. I changed the 500kVA transformer to a Delta-Wye, changed the impedance to Z=3.85 and which yields 300A in the primary on a phase to ground fault at the secondary terminal of the 500kVA transformer. So that's the max...
  9. bdn2004

    Asking for help making sense of a grounding transformer

    Below is a part of an EasyPower model showing a grounding transformer at the first switchgear coming off the large 100 MVA transformer that feeds this Plant. The grounding transformer is 500 kVA, 15kV Wye impedance grounded - 480 delta. Z= 4.87 ohms. It has a 29 ohm resistor, 300A, 10 sec...
  10. bdn2004

    Two 250 VDC 1200A rectifiers feeding multiple crane rails - is it OK to put the outputs in parallel ?

    Parallel the secondaries of the two rectifier transformers? or add one at each ? These are hundreds of feet away from each other. As critical as these dc cranes are to the operation... it's gotta be that one rectifier can feed the whole line. Not really sure the parallel restriction is such a...
  11. bdn2004

    Two 250 VDC 1200A rectifiers feeding multiple crane rails - is it OK to put the outputs in parallel ?

    A little more information... below is the connection drawing of the existing installation. There are three rectifiers running in parallel. This proposed project is to separate the two on the left from the one on the right. Then add another one to the one on the right as a separate system.
  12. bdn2004

    Two 250 VDC 1200A rectifiers feeding multiple crane rails - is it OK to put the outputs in parallel ?

    We are trying to work this out with the Vendor right now. Attached is the detailed drawing of the existing unit that is desired to be paralleled with a new one. There is a mistake on the one line - the existing is a WYE-DELTA transformer as shown on the wiring diagram below. They are diodes...
  13. bdn2004

    Two 250 VDC 1200A rectifiers feeding multiple crane rails - is it OK to put the outputs in parallel ?

    A new installation is being put into this Plant that is a copy of another just like it: as described.... (2) 300 kW rectifiers feeding the power to multiple crane rails. The rectifier vendor is not recommending this saying: "You cannot connect two of these rectifiers’ outputs in parallel. They...
  14. bdn2004

    Anyone have experience with Schneider SAG fighter? how do you calculate the short circuit value of the output ?

    Thanks waross .... Here is the answer from EasyPower... Yes, the Schneider Electric Sag Fighter Power Logic DVR-225-22-0B75-40 seems to be for voltage sag regulation. The EasyPower software does not have a specific equipment type that particularly supports this device. As for arc flash, I...
  15. bdn2004

    Anyone have experience with Schneider SAG fighter? how do you calculate the short circuit value of the output ?

    A customer is installing these SAG Fighters in front of panelboards. The question is how do we model this in EasyPower power software ? From the literature it's a Dynamic Voltage Restorer...
  16. bdn2004

    Elevated cable trays - when could these be considered subject to physical damage and unsupported tray cable not allowed per the NEC?

    Thanks for the replies....realize this a real life situation. I've heard that is the excuse of the offender... There's so much stuff changing all the time - that it is hardly a place not subject to physical damage and therefore a Code violation. I have some sympathy for him - operator's of the...
  17. bdn2004

    Elevated cable trays - when could these be considered subject to physical damage and unsupported tray cable not allowed per the NEC?

    No replies... I'm disappointed. I'm going to say it's my opinion that on an existing Plant site there are always hazards that you have to look out for. They are supposed to do Job Safety Analysis (JSA's) before doing any work. If there is any chance you could hit something with your equipment-...
  18. bdn2004

    Elevated cable trays - when could these be considered subject to physical damage and unsupported tray cable not allowed per the NEC?

    A guy at an established site (not new construction) got up in a mechanical lift doing some retrofit work, that goes on continuously at this site. Many of the tray cables coming out of the elevated cable trays have only strain relief at the tray then onto their conduit that extends up from the...
  19. bdn2004

    Does this panel need to be re-wired and the grounds and neutrals separated ?

    Thanks for the reply... it's not just a disconnect - it's a fused disconnect right below the meter. So it is the Service and that cable going into the panel would be a feeder and the inside panel is a sub-panel. Yes one connection between the neutral and the ground - that is the main bonding...
  20. bdn2004

    Does this panel need to be re-wired and the grounds and neutrals separated ?

    A 200 Amp overhead service feeds an outdoor 200A fused disconnect on the outside of the house. Circa about 1960. 3 - #3/0 wires in metal conduit go from that disconnect, through the crawlspace 50', to a 200 Amp panel board in the middle of the house. The conduit is bonded with a short piece of...

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