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Earthing Transformer ( ZigZag wound ) sizing calculation basis and formulae(2)

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 VarmaPinnamaraju (Electrical) 12 Jul 12 5:06
 Hi, Please advise and provide for the Sizing calculation kVA of a Earthing Transformer (ZigZag wound). Inputs : Earthing Transformer is for connecting to 22kV, 3 phase 3 wire, 1250 Amp, Isc-25kA. 22kV bus Upstream is connected to 40MVA 230/22kV YNd1 Transformer. Maximum line fault current is 400 Amp for 30 Sec. thanks...
 odlanor (Electrical) 12 Jul 12 10:39
 Ig= 400; %A t= 30; %seg V=22000; %V zigzag Nzz = V * Ig/1000; % kVA- continuous power zigzag transformer Rngr = V/(sqrt(3) * Ig); %ohm- resistor resistance Pngr = Rngr * Ig ^2/1000; % kW - continuous power resistor [Nzz Rngr Pngr] %%%% zigzag transformer: 22kV- 8800kVA %%%% resistor: 13.8kV- 32 ohm - 5100 kW %or %%%% zigzag transformer: 22kV- 400A/30s %%%% resistor: 13.8kV- 32 ohm - 400A/30s
 pwrtran (Electrical) 13 Jul 12 8:32
 You can check - IEEE C62.92.4-1991 "IEEE Guide for the Application of Neutral Grounding in Electrical Utility Systems,Part IVâ€”Distribution", Annex A Specifying a Zig-Zag Grounding Transformer

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