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Thread: Primary Transformer Circuit Breaker Tripping on in Rush

  1. #11
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    Paul (tBF)...

    1) Since the Xfmr is already energized before load is applied, then, discussion about residual-magnetism should can be ignored!

    2) The simplest solution, if the nature of the load is known, is to set the protective device's tripping-point to about 2x the load's inrush. The inrush-current can be easily determined wiith a clamp-on!

    3) A more complex solution is to sync the inverter to the Xfmr!

    Regard, Phil Corso!

  2. #12
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    Quote Originally Posted by Phil Corso View Post
    Paul (tBF)...

    1) Since the Xfmr is already energized before load is applied, then, discussion about residual-magnetism should can be ignored!

    2) The simplest solution, if the nature of the load is known, is to set the protective device's tripping-point to about 2x the load's inrush. The inrush-current can be easily determined wiith a clamp-on!

    3) A more complex solution is to sync the inverter to the Xfmr!

    Regard, Phil Corso!
    Phil, the way I understand the description the ATS that switches between POCO and generator is connected to the primary of the bypass transformer. That means that residual flux in the primary is indeed a factor unless the generator syncs to POCO before the reverse transfer.
    The inverter is supplying power to the load continuously through both transfers as well as any momentary outage and so its synchronization or lack of it is not an issue.
    I suspect that the problem occurs only during the reverse transfer because there is a delay before the generator picks up the load at the beginning of the test and a large portion of the instantaneous flux has decayed. A simple time delay with the generator turned off before the back transfer to POCO should, I believe, resolve the problem.

    Sent from my XT1585 using Tapatalk

  3. #13
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    Breaker Frame Type

    Paul
    You said the tripping breaker is in a NF series panelboard.
    What is the breaker frame? EDB, EGB, EJB etc........?
    Can you remove the panel cover and take a closeup pic of breaker front?
    We need to find out if the inst (mag trip) setting is fixed or adjustable and
    what that value is.
    Am I in shape?? I get plenty of exercise pushing my luck!!

  4. #14
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    GoldDigger...

    Your interpretation is correct. I misinterpreted the layout!

    However, in my 64 year career, I always recommended the utility-fed Xfmr be continuously energized, so that load transfer time-delay was limited to just that of the ATS!

    Phil

  5. #15
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    Better still, a sketch or a diagram could be of great help in the analyses here.

  6. #16
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    Quote Originally Posted by ATSman View Post
    Paul
    You said the tripping breaker is in a NF series panelboard.
    What is the breaker frame? EDB, EGB, EJB etc........?
    Can you remove the panel cover and take a closeup pic of breaker front?
    We need to find out if the inst (mag trip) setting is fixed or adjustable and
    what that value is.
    AKAIK all NF breakers have fixed magnetic trip.
    I live for today, I'm just a day behind.

  7. #17
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    Quote Originally Posted by kwired View Post
    AKAIK all NF breakers have fixed magnetic trip.
    Methinks @ATSman is asking what the circuit breaker interrupting ratings are. Type EDB has an interrupting rating of 18kA, EGB = 35kA and EJB = 65kA.

  8. #18
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    Quote Originally Posted by topgone View Post
    Methinks @ATSman is asking what the circuit breaker interrupting ratings are. Type EDB has an interrupting rating of 18kA, EGB = 35kA and EJB = 65kA.
    That is how much the breaker can interrupt and is supposed to not be destroyed in the process. Magnetic trip setting is what level does it trip at when there is a rapid rise as in a short circuit, ground fault, or when an inductive load is turned on and has a temporary surge of high current. I know it is not adjustable on the EDB breakers, don't know that I have ever seen EGB or EJB so don't know if they have field adjustable settings.
    I live for today, I'm just a day behind.

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