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+//Chapter 12
+//Example 12.12
+//page 500
+//To plot swing curves for single pole and three pole switching
+clear;clc;
+
+Xg0=0.1;Xg1=0.3;Xg2=0.15;E=1.2;H=4.167;
+Xt=0.1;
+Xl0=1.0;Xl1=0.3;Xl2=0.3;V=1;
+
+//transfer reactance during LG fault(fault not cleared) by star delta transformation is given by
+X12_fault=1.45;
+
+//transfer reactance after LG faulted line open is given by
+X12_fault_open=1.22;
+
+//transfer reactance when all the lines are healthy is given by
+X12_healthy=0.8;
+
+//power angle equations
+delta=0:0.1:180;
+
+//Prefault condition
+Pe1=(E*V)*sind(delta)/X12_healthy;
+//for an initial load of 1PU
+delta0=asind(1/1.5);
+
+//during fault
+Pe2=(E*V)*sind(delta)/X12_fault;
+
+//during single pole switching
+Pe3=(E*V)*sind(delta)/X12_fault_open;
+
+//during three pole switching
+Pe4=0;
+
+//after reclosure
+Pe5=Pe1;
+
+Pm=1.0;
+
+//xdot function defining the swing equations of machine during single poling
+function xdot=mac_1_pole(t,x,tc,tr)
+    xdot(1)=x(2);
+    if (t<=tc) then
+      xdot(2)=180*50*(Pm-(0.827*sind(x(1))))/12;  //swing equation before clearing the faulted line
+    elseif (t>tc)&(t<tr) then
+      xdot(2)=180*50*(Pm-(0.985*sind(x(1))))/12;//swing equation during single pole switching
+    elseif (t>=tr) then
+      xdot(2)=180*50*(Pm-(1.5*sind(x(1))))/12; //after reclosure
+    end
+endfunction
+
+//xdot function defining the swing equations of machine during three poling
+function xdot=mac_3_pole(t,x,tc,tr)
+    xdot(1)=x(2);
+    if (t>tc)&(t<tr) then
+      xdot(2)=180*50*(Pm-0)/4.167;//swing equation during three pole switching
+    elseif (t<=tc) then
+      xdot(2)=180*50*(Pm-(0.827*sind(x(1))))/4.167;  //swing equation before clearing the faulted line
+    elseif (t>=tr) then
+      xdot(2)=180*50*(Pm-(1.5*sind(x(1))))/4.167; //after reclosure
+    end
+endfunction
+
+//to find the solution of swing equation to draw the swing curves
+
+//to draw the swing curves for three pole switching with reclosure
+subplot(2,1,1)
+x_1_0=[41.8,0]';t0=0; T=0:0.001:0.65;T=T';
+tc=0.075;tr=0.325;
+sol1=ode(x_1_0,t0,T,mac_3_pole);
+plot(T,sol1(1,:)');
+set(gca(),"grid",[1 1]);
+title('Swing Curve for three pole switching at '+string(tc)+' s'+' and reclosure at '+string(tr)+' s','fontsize',3);
+xset("font size",3) 
+xstring(0.2,300,'MACHINE UNSTABLE');
+xlabel('Time (in seconds)----->');
+ylabel('Torque Angle (delta,deg)----->');
+
+//to draw the swing curves for single pole switching with reclosure
+subplot(2,1,2)
+x_1_0=[41.8,0]';t0=0; T=0:0.001:2.2;T=T';
+tc=0.075;tr=0.325;
+sol2=ode(x_1_0,t0,T,mac_1_pole);
+plot(T,sol2(1,:)');
+set(gca(),"grid",[1 1]);
+title('Swing Curve for single pole switching at '+string(tc)+' s'+' and reclosure at '+string(tr)+' s','fontsize',3);
+xset("font size",3) 
+xstring(1.2,50,'MACHINE STABLE');
+xlabel('Time (in seconds)----->');
+ylabel('Torque Angle (delta,deg)----->');
+
+f=get("current_figure");
+f.figure_position=[0,15];
+f.figure_size=[560,1000];
+