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  1. JensenDrive

    MCC Bus Temperature based on 105C

    I noticed recently that Eaton sent in some submittals for 480V MCCs with bus where they say ampacity is based on 105C max operating temperature in a 40C ambient. Then they connect circuit breakers directly to the bus, and the circuit breakers have terminal temperatures limited to 75C. The also...
  2. JensenDrive

    90C Lugs for MCCBs - Why?

    Why does Eaton offer to sell me 90C lugs on standard 75C MCCBs? From what I can tell, the higher lug temperature rating does not allow me to use 90C ratings of cable since the lug passes cable temperature directly to the 75C rated breaker; the lug has no insulation effect and I still have to use...
  3. JensenDrive

    DTT for small distribution generator

    Thanks to all for the input. Will contact the utiity and SEL and get their thoughts. I sort of hesitate to recommend the gen dropping out if there is a loss of signal. I do not know how often and how long a dropout occurs. I suspect this DTT matter will kill the project. We are in the estimating...
  4. JensenDrive

    Phase displacement of 60 degree during Fault

    Hamburger: Impressively extensive answer! Interesting there is no V2. Had to talk myself into recognizing that. Guess I am so used to thinking of all the negative sequence voltage you get during SLG fault on a solidly grounded system.
  5. JensenDrive

    3V0 Detection/Protection

    Now I see the problem. There is a trick to do it with a single VT to ground. If the monitored phase goes to ground, you see low voltage. If the monitored phase is an unfaulted phase, voltage goes high. Hence, trip on any voltage off normal. I suspect a VT on every phase will give better comfort...
  6. JensenDrive

    Neutral required on 480 VAC system

    1) NEC Violation The specific section that applies is NEC 250.36. This article says high-impedance grounded neutral systems cannot have any line to neutral loads, and I would well argue that this inverter would be considered a line to neutral load (think of it as a negative impedance load)...
  7. JensenDrive

    DTT for small distribution generator

    I have a case of a small distribution generator that is sized larger then the minimum load on the line, so the generator has the ability to carry line load if the utility trips. The utility is saying a direct transfer trip (DTT) scheme will be needed to ensure the gen trips if the utility trips...
  8. JensenDrive

    3V0 Detection/Protection

    Is your 380V system a source, and you are protecting against backfeed into a fault? Is the 13kV (utility) source effectively grounded? If they have a ground fault, wouldn't they trip? If even a single fuse tripped, you would single phase the delta-delta xfmr, and on the secondary get half...
  9. JensenDrive

    Motor Differential Relay across captive motor transformer

    Your answer seems appropriate, but I would ask SEL to comment. You may want to add a ground differential that compares sum of xfmr neutral and motor neutral.
  10. JensenDrive

    Earth Fault / To determine faulted phase ?

    YOu have either current or voltage. Guess current is all that is left. Look at event report.
  11. JensenDrive

    Transformer Neutral Equipment Rating

    Not sure of the specifics of how 80kV is selected. I lack a copy of IEC 60076. Not sure of what you are saying in some the above, but a switch on the neutral cannot see phase to phase voltages. Just phase to ground. In high impedance grounded system there is a long story of how arcing ground...
  12. JensenDrive

    MV Breaker 86BF Trip

    A way to bypass wondering if the light is the source: monitor the voltage across the BF output with another relay input, and in relay logic, use another relay output to run the light.
  13. JensenDrive

    SF6 Breaker Maintanance

    Breaker test is part of 3 year relay trip check routine. I assume they do more than trip and close breakers, but likely something closer to what FrozenE mentions. Relay test routine at 3 years is pretty simple; not a full performance and control system check. Inject currents and voltages and...
  14. JensenDrive

    Percent Voltage Drop, respect to which voltage?

    The NEC says voltage drop, not voltage regulation. A side matter is voltage regulation is horribly complex. You cannot calculate voltage at the end load without a knowing voltage, current, and power factor at some location in the circuit. However, you do not typically know the load. If load...
  15. JensenDrive

    EARTH FAULT CALCULATION

    The question seems to say you need a bit more background in fault analysis than can be mentioned here. I am tempted to leave a reference to someone (me) that has experience and you can see how it is done, but I this needs to be non-commercial answers.
  16. JensenDrive

    Cable differential protection requirements

    Required is maybe not appropriate to ask. It seems recommended. You have short leads so a high impedance differential would be easy enough to add, for fairly low cost, and provides high speed that will protect the cables very well. Go for it. You would also add overcurrent backup, though.
  17. JensenDrive

    Research Lab Power Distribution

    Oh, I did not catch that you said 100A. Wow, that seems small for bus duct from my work history. Eaton, MP Husky, Square D, GE .... each have a line, but I think they stop at about 600A. I looked up Starline, and it has me intrigued, I might need to read up on that concept. It seems people have...
  18. JensenDrive

    Transformer Neutral Equipment Rating

    A lot of messy questions of grounding design fall out of this one. Some systems are run ungrounded, with grounding switches only for testing and search for ground faults. If the 115kV ground switch is run open, the load will effectively seem the same as a delta from a 115kV load pespective. If...
  19. JensenDrive

    Interesting fault video

    Hard to say, but maybe 69kV. Saw 2 ph-faults, with no obvious trip on the first ph-ph event, sort of implying impdance relaying was not in use. Assume 600A line, from size of conductors, indicating a 1000A pickup. One phase at 69kV = 40kV phase to ground. Just to pick up the overcurrent relay...
  20. JensenDrive

    Voltage Distribution on Ground Fault

    You asked about step potential, a matter that diverges from your apparent question. I am used to step potential being referred to as the step potential if there is a ground fault inside a substation, engergizing the ground grid, but with ground fault trying to return to a remote source. If the...

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