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  1. BigJohn1

    Arc Flash Analysis -- Energized Equipment

    Where is troubleshooting most likely to occur? For example: Motor disconnects are likely to have energized troubleshooting (indoor or outdoor doesn't matter), and should be labeled. But a cabinet full of insulated splices is not, and might not need a flash label. A dry-type transformer...
  2. BigJohn1

    Does grounding a wye increase inrush?

    No, I don't have any oscillography. There are also voltage regulators between the switch and the transformer. These were in manual mode at 4L which is also the normal condition they would be in during past switching operations. I'll investigate any suggestions. I was the guy who shut down...
  3. BigJohn1

    Does grounding a wye increase inrush?

    Can you expand on this? What condition would allow a zero-sequence circuit to exist? Because that sounds like it might be a plausible answer: I know from experience that inrush on these substations will trip ground-fault protection. I don't know why, but it's a proven problem across...
  4. BigJohn1

    Does grounding a wye increase inrush?

    I don't know, those are old legacy settings and I'd have to do some digging to discover the origins. While I agree the protection seems set very tight, the trick is that this transformer repeatedly switched and loaded just fine for years as a floating wye. Once grounded it would not close in...
  5. BigJohn1

    Does grounding a wye increase inrush?

    I had to ground the low-side wye on a 5MVA 13,200Δ:480Y transformer, afterwards we began tripping out on inrush when trying to energize with no secondary load. Nothing else about the installation changed except bonding the 480V wye to ground. I don't know what inrush was when the wye was...
  6. BigJohn1

    Partial Discharge in Molded MV Products

    I can't see any rhyme or reason for what will cause partial discharge in medium voltage cabling systems: I have noticed that a lot of molded splice and termination products have very significant internal gaps between the conductor and the molding as part of their design. These seem to work...
  7. BigJohn1

    Impending Generator Failure

    Not familiar with what a research coil is? I'll have to do some reading. Also, to be clear, I'm looking at the rotor because it's the only test that is slightly "off" but I have no solid evidence that's the location of the fault. We've discussed infrared, but you can't see the stator, and can...
  8. BigJohn1

    Impending Generator Failure

    I follow where you're coming from, but can say that I have found shorted rotor poles on machines before that did not have obviously deficient vibration analysis results. It's worth a try, but in my experience that is not a guaranteed symptom.
  9. BigJohn1

    Impending Generator Failure

    It does have vibration as well as field ground and loss of field. Nothing has tripped. We could have a failing rotor pole, but I have no idea how to prove it from outside the machine.
  10. BigJohn1

    Impending Generator Failure

    Have a 12MW utility-parallel, enclosed generator that is suddenly producing a very significant "hot electrical" smell. All instruments are reporting "normal" values for temperature, current, voltage, etc. No protection has operated. Did winding resistance and insulation resistance on both...
  11. BigJohn1

    Vacuum Breaker Prestrike Blowing Fuses?

    I figured I'd give some update: We reenergized an alternate feeder that had OCBs as protection instead of fuses and the customer went online and stayed on despite having all the arrestors in place. We found a low-side ground fault in the facility that may have accounted for the original fuse...
  12. BigJohn1

    Vacuum Breaker Prestrike Blowing Fuses?

    What you describe sounds like a chain-grounded: Used to close in an ungrounded wye when no gang switch is available. I'm only familiar with it being used to prevent resonance failures. The arrestors are only rated L-N. If this were a delta, I could absolutely explain the overvoltage and...
  13. BigJohn1

    Vacuum Breaker Prestrike Blowing Fuses?

    Grounded. Floating wyes are rare as hens teeth up here so I assumed folks would assume. But if there is we can't find it. The line section passed a hipot and also will stay energized when the arrestors are disconnected. Further, I would think a fault would only blow fuses in the affected...
  14. BigJohn1

    Vacuum Breaker Prestrike Blowing Fuses?

    The only solution I have for checking for ferroresonance would be to put on as many single phase loads as possible and then try energizing into that to see if it drops the circuit impedance enough to prevent this. What say you? As far as fast switching causing it, the operation of the VCB...
  15. BigJohn1

    Vacuum Breaker Prestrike Blowing Fuses?

    I am very willing to believe it is a switching transient, and would be willing to try switching in under moderate load. But that raises a huge flag: Why? Barring a utility change that isn't showing uo in the voltage readimgs, what about this substation could've changed to cause this voltage?
  16. BigJohn1

    Vacuum Breaker Prestrike Blowing Fuses?

    We know that historically it can be very difficult to find a bad arrestor, I have seen them pass a 10kV power factor and fail in service. Knowing that, we actually took a PT and backfed these things at their 24kV MCOV to try and prove a fault, but they were all passing less than 5mA ay their...
  17. BigJohn1

    Vacuum Breaker Prestrike Blowing Fuses?

    There might be 50 feet of overhead conductor.
  18. BigJohn1

    Vacuum Breaker Prestrike Blowing Fuses?

    Very unusual problem on a 25MVA transformer 34.5kV Y : 13.8kV Δ. Has been in service for many years. Recent unexplained feeder fault blew a fuse. Now every single time the transformer is energized via the vacuum breaker it blows those same upstream feeder fuses. The transformer has so far...
  19. BigJohn1

    Temperature Correcting Cable Tests

    I'm looking for any information on temperature correcting insulation resistance and hipot values for low- and medium-voltage cable. I can find general references to correcting things to 15°C but very little in the way of correction tables or published insulation coefficients, so I'm not sure...
  20. BigJohn1

    Switchgear and Xylene?

    Have some folks who would like to use an acetone and xylene based degreaser as an all-purpose switchgear cleaner. Seeing what this stuff can do to plastic makes me believe this is a really bad idea, but I can't find much substantiation against it. I know alcohol is the industry standard and...

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