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Thread: Why do they both trip???

  1. #91
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    Quote Originally Posted by winnie View Post
    ,,,are the breaker trip ratings high enough to handle transformer inrush in all conditions or simply most.
    We will never know.

    Nobody does actual 'inrush' testing of small transformers. Everything is done theoretically. I have seen inrush tables complied assuming the transformer is an air core inductance, because the math is easier.
    Transformers are magnetic devices so hysteresis also comes into play. Where in the waveform when it was turned off, versus where it turns on can be a problem.
    Just because you can, doesn't mean you should.

  2. #92
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    Quote Originally Posted by winnie View Post
    GoldDigger has an interesting thought in post 85; the breakers handle transformer inrush _most_ of the time, so when the panel is manually switched on the breakers hold.

    But some automatic switching event happens at just the right moment in a cycle, or synchronized just wrong with a moments before shutdown, so that there is greater inrush and the breaker trips.
    What switching event? One on the 208/120 side of the transformers? Did you look at the panel directories? There are no heavy loads being switched.

    Steve brought up something in post 22 I am looking into.

    Quote Originally Posted by steve66 View Post
    Maybe when they test the generator, and when the transfer happens, if the timing is just right there is enough inrush on both feeders to cause both breakers to trip, and one also has enough to trip the main.
    Quote Originally Posted by iwire View Post
    Hmm, this exact issue has happened in the past and I was able to fix it by programing in a transition delay into the transfer switch.


    TGAREM says 7.5kVA but fed by a 100A breaker. Should that be 75kVA?
    The panel main is 100, the transformer primary breaker is 20 and has not tripped.

  3. #93
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    Quote Originally Posted by iwire View Post
    OK, more details. One thing I need to clear up right away is about the wire size, I looked at the wires over a year ago and my memory was telling me 500s in 4" .... when I looked again last Monday night it was 1/0s in 2". You wonder how I was so off? Well in this building there are 4" with 500 and 600s everywhere. So with that out of the way here are details

    Below is panel PPGM, it has the 200 amp main breaker that has tripped. The breaker at the top above the ATS has not tripped.

    The feeder to transformer TGEM is 70 amps and has tripped.

    The line coming out of the left of PPGEM is the 100 amp feeder heading to the remote building that has also been tripping.






    And the panel directories for those panels.





    Now the remote building







    e
    Thanks My money is on transformer inrush as mentioned. I take all the EM lights are LED or electronic florscent? (just checking)
    What is esoteric knowledge today will be common knowledge tomorrow.

  4. #94
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    Quote Originally Posted by iwire View Post
    The breakers have never (AFAIK) tripped when first energizing the transformers. The breakers handle the inrush of transformers just fine.





    I am willing to argue that. Transformer inrush varies based on the residual magnetism of the core and at the exact instant the sign wave was switched off and then on.
    What is esoteric knowledge today will be common knowledge tomorrow.

  5. #95
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    Quote Originally Posted by jim dungar View Post
    The NEC does not contain 'minimum' sizing of protective devices for transformers.
    In the old days, before plug-on 125A panel style branch breakers and energy effcient transformers, it was not uncommon to see 70A breakers used. Also, 80A and larger breakers cost more back then.


    I do not dispute that, but back then breakers tended to have a very high magnetic trip rating, assuming they even did in the first place. A good chunk of manufactures were thermal only. Over the years many arguments in the industry from fires to arc flash to magnetic force have resulted in breakers with substantially lower magnetic trip levels and even lower starting levels for those breaker which have adjustable settings.
    What is esoteric knowledge today will be common knowledge tomorrow.

  6. #96
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    Quote Originally Posted by mbrooke View Post
    I am willing to argue that. Transformer inrush varies based on the residual magnetism of the core and at the exact instant the sign wave was switched off and then on.
    What, from 1/2 second to 20 minutes?? If it doesn't go "click, pop" it's not gonna go on "residual magnetism" later on.

  7. #97
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    Quote Originally Posted by mbrooke View Post
    I am willing to argue that. Transformer inrush varies based on the residual magnetism of the core and at the exact instant the sign wave was switched off and then on.
    Again how does that, right or wrong, apply to my situation?

    The transformers are energized, they stay energized for months at a time and then all of sudden it is off.

    Given the fact there are no in rush loads other than the transformers themselves I am not understanding where you are heading.

  8. #98
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    Quote Originally Posted by gadfly56 View Post
    What, from 1/2 second to 20 minutes?? If it doesn't go "click, pop" it's not gonna go on "residual magnetism" later on.
    Varies in magnitude for the first few cycles- not duration. This has been proven over and over on large transformers (ie over 5MVA) however the physics remain the same for all sizes.
    What is esoteric knowledge today will be common knowledge tomorrow.

  9. #99
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    Quote Originally Posted by iwire View Post
    Again how does that, right or wrong, apply to my situation?

    The transformers are energized, they stay energized for months at a time and then all of sudden it is off.

    Given the fact there are no in rush loads other than the transformers themselves I am not understanding where you are heading.


    Correct, until the ATS transfers or there is a power blip from the POCO. At that point the inrush just happens to be more than when it was manually switched on- and thus trips. Inrush magnitude is never identical.
    What is esoteric knowledge today will be common knowledge tomorrow.

  10. #100
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    Quote Originally Posted by mbrooke View Post
    My money is on transformer inrush as mentioned.
    How?


    The transformers are not cycling unless the ATS is cycling and I can find no evidence for that.

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