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Thread: Excitation Transformer Sizing

  1. #1
    Associate Engineer
    Join Date
    Aug 2014
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    1

    Excitation Transformer Sizing

    Can any one help me. I am preparing a calculation sheet for sizing an Exitation transformer, so far I have this
    Generator Data:
    Rated output: Sgn = 108 MVA
    Rated voltage: Un = 13.8 kV
    Rated frequency: f = 60 Hz
    Rated speed: n = 276.9 rpm

    Preliminary Assumed Excitation Data:
    Excitation power: Pfn = 540 kW | 0.5% Sn
    Rated excitation voltage: Ufn = 320 V | adopted value
    Rated excitation current: Ifn = 1687.5 A | Pfn/Ufn

    Maximum excitation voltage: Ufmax = 640 V | 2.0*Ufn
    Maximum excitation current: Ifmax = 1856.3 A | 1.1*Ifn

    Corresponding values on the ac-side:
    Uac = 547.4 V | 1.05*1.1*[?/(3?2)]*Ufmax
    Iac = 1515.6 A | ?(2/3)*Ifmax
    S = 1436.9 kVA | ?3*Uac*Iac

    Excitation Transformer
    Rated output: Sn = 1500 kVA | adopted value
    Rated voltage at LV side: Uac = 550 V | adopted value
    Rated current at LV side: Iac = 1574.6 A | Sn/(?3*Uac)
    Rated current at HV side: In = 62.8 A | Sn/(?3*Un)
    Rated CT ratio at HV side: 100/5 A | adopted value


    My question is if there is a method to calculate the Rated excitation voltage, normally this value is given by the manufacturer. But I need to know how they calculate this value.

    Thanks
    Last edited by Kelly Bramble; 08-04-2014 at 12:56 PM. Reason: Removed html

  2. #2
    Principle Engineer Cragyon's Avatar
    Join Date
    Feb 2013
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    Newark, NJ
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    This is Residential Transformer Loading presentation.

    Transformer Sizing Presentation.pdf

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