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+// Example 9.9
+// Determine (a) Excitation voltage (b) Power angle (c) No load voltage, 
+// assuming the field current is not changed (d) Voltage regulation (e) No load
+// voltage if the field current is reduced to 80% of its value at rated load. 
+// Page 369
+
+clc;
+clear;
+close;
+
+// Given data
+V=4800;                     // Voltage of synchronous generator
+PF=0.900;                   // Lagging power factor
+S_Mag=1000000/3;
+Xa_Mag=13.80;               // Synchronous reactance
+Xa_Ang=90;
+Vt_Ang=0;  
+
+// (a) Excitation voltage 
+Vt=V/sqrt(3);              
+Theta=acosd(PF);                // Angle
+Ia_Magstar=S_Mag/Vt;            // Magnitude of curent
+Ia_Angstar=Theta-0;             // Angle of current
+Ia_Mag=Ia_Magstar;
+Ia_Ang=-Ia_Angstar;
+
+// Ef=Vt+Ia*j*Xa
+// First compute Ia*Xa
+IaXa_Mag=Ia_Mag*Xa_Mag;
+IaXa_Ang=Ia_Ang+Xa_Ang;
+// Polar to Complex form for IaXa
+IaXa_R=IaXa_Mag*cos(-IaXa_Ang*%pi/180); // Real part of complex number
+IaXa_I=IaXa_Mag*sin(IaXa_Ang*%pi/180);  // Imaginary part of complex number
+// Vt term in polar form
+Vt_Mag=Vt;
+Vt_Ang=Vt_Ang;
+// Polar to Complex form for Vt
+Vt_R=Vt_Mag*cos(-Vt_Ang*%pi/180);      // Real part of complex number
+Vt_I=Vt_Mag*sin(Vt_Ang*%pi/180);       // Imaginary part of complex number
+// Ef in complex form
+Ef_R=IaXa_R+Vt_R;
+Ef_I=IaXa_I+Vt_I;
+Ef=Ef_R+%i*Ef_I;
+// Complex to Polar form for Ef
+Ef_Mag=sqrt(real(Ef)^2+imag(Ef)^2);        // Magnitude part
+Ef_Ang= atan(imag(Ef),real(Ef))*180/%pi;   // Angle part

+
+// (b) Power angle
+PA=Ef_Ang;
+
+// (c) No load voltage, assuming the field current is not changed 
+// From figure 9.23 (b)
+VolAxis=Vt_Mag/30;        // The scale at the given voltage axis
+Ef_loc=Ef_Mag/VolAxis;    // Location of Ef voltage
+Vnl=33.4*VolAxis;         // No load voltage
+
+// (d) Voltage regulation
+VR=(Vnl-Vt)/Vt*100;
+
+// (e) No load voltage if the field current is reduced to 80% 
+Vnlnew=31*VolAxis;
+
+// Display result on command window
+printf("\n Excitation voltage = %0.0f V ",Ef_Mag);
+printf("\n Power angle = %0.1f deg ",PA);
+printf("\n No load voltage = %0.0f V ",Vnl);
+printf("\n Voltage regulation = %0.0f Percent ",VR);
+printf("\n No load voltage when field current is reduced to 80 percent = %0.0f V ",Vnlnew);