Excitation Transformer Sizing
Excitation Transformer Sizing
(OP)
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 now hoy they calculate this value.
Thanks
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 now hoy they calculate this value.
Thanks





RE: Excitation Transformer Sizing
The voltage rating is based on the positive/negative ceiling voltage requirements set forth by your relevant grid codes. Ceiling voltages can be calculated if you want to get into power electronics theory for the thyristor bridge, taking into account the firing angles and transformer impedance. For a unit this large I would recommend working with the excitation system/transformer vendor to ensure you don't have any surprises.