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

[VarmaPinnamaraju]

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]

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]

You can check -
IEEE C62.92.4-1991 "IEEE Guide for the Application of Neutral Grounding in Electrical Utility Systems,Part IV—Distribution", Annex A Specifying a Zig-Zag Grounding Transformer