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  1. BSEE1980

    Measure Insulation Resistance Cable

    Generally it is best to measure each cable separately, disconnecting both ends, not as a system. You megger could damage connected equipment, especially in a distribution board! Now if you have a Y connected xmfr rated at 480V, you can lift the neutral and 500V or even 1000V meg between it and...
  2. BSEE1980

    Earth Fault Monitoring Equipment

    Try out this web site: http://www.deif.com/Products/applications/Switchboard_Instrumentation/Insulation_monitoring.aspx They have good descriptions on how insulation monitoring works, both for AC and DC systems. Basically, the meter circulates a small current thru the power system and back to...
  3. BSEE1980

    Excessive reactive power on a generator/transformer set

    You guys are right on: regulator problems. My guess is your AVR does not have a PF/KVAR regulator. If not, setting the droop higher might help. We paralleled for years without PF/VAR regulators: we just set the droop higher. That is, more current, less voltage. As long as you stay in the...
  4. BSEE1980

    Parameter of 3 windings transformer

    Typically 3 winding xmfs (US standards...don't know your brand) the M/Kva ratings are of the winding. You can look at it like it has 2 secondaries. One you "put in" 7.6M, one you "can get" 6.8M from and one you "can get" .8M from. We used to use these in remote substations: the third winding...
  5. BSEE1980

    Smell of ozone from MV switchgear

    I agree...you are headed for a replay of the Big Bang Theory! You say MV: what level? 5KV is much different than 15KV class. I have seen 5KV in unshielded cable: you would never do that with 15KV. When the PM's the breakers, did they use any cleaner on the insulators? I used to do a lot of...
  6. BSEE1980

    Strange currents / phase angles at co-gen site

    Took a while, but now it is working fine. I suspect the utility did some work on their system, but we may never know for sure...??? The circuit breaker had a faulty trip unit leading us to believe it might have been seeing a large unbalance. Plus it was looking at positive sequence currents...
  7. BSEE1980

    Transformers in Series, How does it effect the power?

    The xmfr z's will sum, making the voltage regulation even worse. I can see this will be a problem. Check your power system + xmfr + cable voltage drop calculations at 100% and 400% of motor current. You may end up with such poor regulation you will burn up your pump motor. Any way to start...
  8. BSEE1980

    Required Voltage Rating for Black Start Generator

    So does the inverter use the gen as the starting motor or does it run a separate motor for starting? I have seen both ways, but it makes a big difference in the inverter (LCI vs regular VFD) and the time you have to start. The amortisseur (starting) windings need to support it: most gens don't...
  9. BSEE1980

    28V Dc power output from 120 Vac, 3-phase, 400Hz

    Commercially available, off the shelf power supply should be availalbe. 400 hz might be a problem, so I would look at a switcher style, not a series pass. Many switchers, while made for 60Hz, will work on 400Hz. You will probably have to ask the mfr. Or make your own full wave bridge to get...
  10. BSEE1980

    Strange currents / phase angles at co-gen site

    Good ideas, much appreciated. I did not know that about unbalanced loads and displaced neutrals, waross, thank you. That makes sense. One of the things we need to pass on to the utility to check. Subtech: yes, I agree with you. We have asked the utility to check, but I am not sure they would...
  11. BSEE1980

    Strange currents / phase angles at co-gen site

    DSB: Technically, you are absolutely correct on var flow. But there are a lot of technical folks out there working with sync motors that think increasing excitation moves from lagging to leading because they are used to motors. Alan: You hit the nail on the head! I tried vector math on the...
  12. BSEE1980

    Information on Biogas for Electricity

    Check out COSPP magazine, they have had some good articles. There are LOTS of methane burning co-gen plants out there: almost every municipal land fill can support a 'trash burner.' Many large feedlots digest the cow's "output" into methane--and some of these can be 1Mw or more! Most of these...
  13. BSEE1980

    Generator Pitch

    May I suggest you Google "generator winding pitch" and you will find several very useful articles. No reason to re-print them here. One of the first hits is a CAT technical paper. Steve
  14. BSEE1980

    voltage presence on deenergized power cable

    It looks like induced voltage. Parallel conductors will have distributed capactance all along their path, inducing voltage from one to the other. You said something about DC: if this is from a rectifier or SCR source, the noise and thus induced voltages can be large. If the other source cannot...
  15. BSEE1980

    Strange currents / phase angles at co-gen site

    Great feedback, all, thank you! I'll try to answer your questions. Alan: I think I will ask them to get a phase angle meter and re-check PT's and CT's. Couldn't hurt. Electrical contractor was not experienced in switchgear work, either. Aleman: No loss of excitation alarms. We could be outside...
  16. BSEE1980

    How do I find wiring diagrams for a 25 year old generator

    Are you sure the points you have labeled 1, 2, 3 and where the green wire connect is not a copper neutral bar? It looks like at least one outgoing phase connection is the red taped conductor. I would clean up and try to read the labels on the wires just to be sure.
  17. BSEE1980

    Strange currents / phase angles at co-gen site

    I think you are right on track, Bill. The voltages are very close (+/- 2 volts) before we close. Utility voltage regulation is strickly by cap banks, we think. They were not sure if the 12.47Kv xmfr has a step V regulator (load tap changer) or not. We don't know the system PF/KVAR at the...
  18. BSEE1980

    Strange currents / phase angles at co-gen site

    Yea, we are helping the end user (our customer) so you could say we are acting as the gen field tech. Acting is the important word here! :) AVR is getting the correct analog signal. It drives the volts correct in order to sync (util volts higher than nominal setting, so it raises correctly)...
  19. BSEE1980

    Strange currents / phase angles at co-gen site

    We used the same CB for the load banks and got to 100% load just fine, so my first guess is the CB is OK. But those are pure signals and the CB was tripping on % current unbalance, so we have replaced the CB trip unit. We have it replaced now and are waiting to start up again. The unstability...
  20. BSEE1980

    How do I find wiring diagrams for a 25 year old generator

    I really cannot see the power connections very well, sorry. Of course, when you change the voltage, you will need to change many other things: protective settings (50, 51, 32?, 40?, 59, 27, basically any voltage or current based protection), AVR settings, etc. And if they are older...

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