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Calculation of Incident energy at secondary of transformer

Discussion in 'General Discussion' started by beenthere, Aug 24, 2009.

  1. beenthere New Member

    I have a 250 MCB as the primary protection which supplies a 225KVA, 5.27% Z, the transformer is 480 to 240. There is a secondary fused switch with 250V FRS 200A. I am questioning the incident energy on the secondary side between the bushing and the actual disconnect switch. I am assuming the 250 MCB will determine the incident energy. Any thoughts on calculating this value? Thnaks for reading my post.
    beenthere, Aug 24, 2009
    #1

  2. THE CABLE GUY Well-Known Member

    A really rough estimate on the secondary and the load side of the fused switch could be as high as 85 inch AFB, 12 cal/sm2 @ 18inch CAT#3@18" assuming a SC of 8.6ka.

    With my generic data the secondary SC could last a long time before tripping the breaker on a HI trip setting.

    However, if you have a low trip level the game changes. I get a 6" AFB .03 cal/cm2 @18" CAT0 @18".

    The breaker type and trip data is very important in determining your actual energy levels. The other problem is your transformer inrush which I suspect will probably be the problem to overcome.

    I am guessing your trip level is going to be high because of that.
    THE CABLE GUY, Sep 12, 2009
    #2

  3. beenthere New Member

    Thanks for the reply

    My details which were not many is at a plant I am going to in mid Ocotber. I plan to get more info I will post as I get it.
    beenthere, Sep 13, 2009
    #3

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