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+//CHAPTER 7- SINGLE PHASE TRANSFORMER
+//Example 28
+
+disp("CHAPTER 7");
+disp("EXAMPLE 28");
+
+//VARIABLE INITIALIZATION
+va=10000;                             //apparent power
+v1=2500;                              //primary voltage in Volts
+v2=250;                               //secondary voltage in Volts
+f=50;
+//open circuit parameters
+Voc=250;
+Io=0.8;
+Wi=50;                               // watts HT side
+//short circuit test
+Vsc=60;
+Isc=3;
+Wc=45;                             // watts HT side 
+//
+//loads
+pf=0.8;
+//SOLUTION  
+I1=va/v1;                            //full rated current on hv side
+Psc0=Wc*(I1/Isc)^2;                  //ohmic loss/ cu loss at full load rated current
+Pc=Wi;                               // core losses
+// 1/4 load
+Psc=(1/4)^2*Psc0;
+Pout=va*pf*(1/4);
+Pin=Pout+Pc+Psc;
+eff=Pout*100/Pin;
+disp("SOLUTION (a)");
+disp(sprintf("The efficiency at 1/4 load is %f",eff));
+//
+// 1/2 load
+Psc=(1/2)^2*Psc0;
+Pout=va*pf*(1/2);
+Pin=Pout+Pc+Psc;
+eff=Pout*100/Pin; 
+disp(sprintf("The efficiency at 1/2 load is %f",eff));
+//
+// full load
+Psc=(1/1)^2*Psc0;
+Pout=va*pf*(1/1);
+Pin=Pout+Pc+Psc;
+eff=Pout*100/Pin;
+disp(sprintf("The efficiency at full load is %f",eff));
+//
+// 1 1/4 = 5/4 load
+Psc=(5/4)^2*Psc0;
+Pout=va*pf*(5/4);
+Pin=Pout+Pc+Psc;
+eff=Pout*100/Pin;
+disp(sprintf("The efficiency at 1 1/4 or 5/4 load is %f",eff));
+//
+//maximum efficiency at x, but then ohmic loss=core loss
+x=sqrt(Pc/Psc0);
+Pout=va*x*pf;
+Pin=Pout+Pc+Pc;                             //Ohmic losses = core losses at max efficiency
+eff=Pout*100/Pin;
+disp("SOLUTION (b)");
+disp(sprintf("The maximum efficiency  is %f",eff));
+//
+//short circuit
+phisc=acos(Wc/(Vsc*Isc));
+pf1=cos(phisc);
+R_e1=Vsc*pf1/Isc;
+Z_e1=Vsc/Isc;
+X_e1=sqrt(Z_e1^2-R_e1^2);  
+disp("SOLUTION (c)");
+disp(sprintf("The value of Re1 is %f Ohm",R_e1));
+disp(sprintf("The value of Ze1 is %f Ohm",Z_e1));
+disp(sprintf("The value of Xe1 is %fΩ",X_e1)); 
+//
+//ee, ex;
+er=I1*R_e1/v1;
+ex=I1*X_e1/v1;
+disp(sprintf("The value of Er is %f pu",er));
+disp(sprintf("The value of Ex is %f",ex)); 
+//
+phi=acos(pf);
+//R=ercosphi2+vx.sinphi2
+//E2=V2+I2.R
+%reg=(I1*R_e1*pf+I1*X_e1*sin(phi))*100/v1; //same as using er and ex
+disp(sprintf("The percent regulation at full load lagging is %f",%reg));
+%reg1=(I1*R_e1*pf-I1*X_e1*sin(phi))*100/v1; //same as using er and ex
+disp(sprintf("The percent regulation at full load leading is %f",%reg1));
+V21=(1-%reg/100)*v2;
+V22=(1-%reg1/100)*v2;
+disp(sprintf("The secondary terminal voltage at full load lagging is %f",V21));
+disp(sprintf("The secondary terminal voltage at full load leading is %f",V22));
+disp(" "); 
+// 
+//END