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Thread: overcurrent protection for utility poles.

  1. #1
    Join Date
    Dec 2004
    Location
    KY
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    785

    overcurrent protection for utility poles.

    Does anyone know the required fusing formula for cutouts, to protect a pole mounted cap bank ? Does it follow IEEE or is there another code body?

    Would I have to acount for Inrush current and oversize for about 50% ish or is there a law of the land?
    Last edited by aelectricalman; 07-18-12 at 02:59 PM. Reason: IEEE not IIIE
    Chris Hill, EE,ME,GA-CR
    Power Factor Correction

  2. #2
    Join Date
    Jan 2008
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    7,422
    For a grounded wye bank:

    Fuse link 100% rating = 1.35 * kvar_3ph / sqrt(3) / kV_LL

    For a 150% rated fuse like a NEMA T-link, divide the current value above by 1.5

    add:
    For an ungrounded wye bank:

    Fuse link 100% rating = 1.25 * kvar_3ph / sqrt(3) / kV_LL


    The 25-35% adder comes from the normal allowance of:
    10% for voltage
    5%-15% for capacitor tolerance
    5% for harmonics on ungrounded or 10% for harmonics on grounded wye
    Last edited by mivey; 07-18-12 at 05:53 PM.
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  3. #3
    Join Date
    Jan 2008
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    Quote Originally Posted by aelectricalman View Post
    Would I have to acount for Inrush current...?
    Transients from switching and lightning is addressed somewhat by the fuse type. A type T fuse can handle higher surge current than a K and would be better at the lower amp range.
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