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//Book - Power System: Analysis & Design 5th Edition
//Authors - J. Duncan Glover, Mulukutla S. Sarma, and Thomas J. Overbye
//Chapter - 7 ; Example 7.4
//Scilab Version - 6.0.0 ; OS - Windows
clc;
clear;
Srated = 100; //rated power in MVA
V1 = 13.8; //generator supply voltage in kV
Xg = 0.15; //generator input reactance in ohm
Vline = 138; //transmission line voltage in kV
Xline = 20; //transmission line reactance in ohm
Vprtr1 = 13.8; //primary side voltage of transformer 1 in kV
Vsectr1 = 138; //secondary side voltage of transformer 1 in kV
Xt1 = 0.10; //reactance of transformer 1 in ohm
Vprtr2 = 138; //primary side voltage of transformer 2 in kV
Vsectr2 = 13.8; //secondary side voltage of transformer 2 in kV
Xt2 = 0.10; //reactance of transformer 2 in ohm
V2 = 13.8; //motor supply voltage in kV
Xm = 0.20; //motor reactance in ohm
Vf = 1.05; //pre fault voltage in per unit
Ybus = -%i*[9.9454 -3.2787; -3.2787 8.2787]; //bus admittance matrix in per unit using direct inspection from fig 7.5
Zbus = inv(Ybus); //bus impedance matrix in per unit
If1 = Vf/Zbus(1,1); //sub transient fault current at bus 1 in per unit
E1 = (1- (Zbus(1,1)/Zbus(1,1)))*Vf; //voltage at bus 1 in V
E2 = (1-((Zbus(2,1)/Zbus(1,1))))*Vf; //voltage at bus 2 in V
Xline =Xline*Srated/(Vline^2); //line impedance in ohm
I21 = ((E2-E1)/(%i*(Xline+Xt1+Xt2))); //fault current from transmission line in per unit
If2 = Vf/Zbus(2,2); //sub transient fault current at bus 2 in per unit
E3 = (1-(Zbus(1,2)/Zbus(2,2)))*Vf; //voltage at bus 3 in V
E4 = (1-(Zbus(2,2)/Zbus(2,2)))*Vf; //voltage at bus 4 in V
I12 = ((E3-E4)/(%i*(Xline+Xt1+Xt2))); //current to fault from transmission line in per unit
printf('\nThe 2*2 positive sequence bus impedance matix in pu is ');
disp (Zbus);
printf('\nThe Sub transient fault current at bus 1 is = %fi per unit',imag(I21));
printf('\nThe Sub transient fault current at bus 2 is = %fi per unit',imag(I12));
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