%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% tranreg.m - Calculates the full-load regulation of a transformer
%             as a function of load power factor with constant
%             load voltage applied.
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
clear;
R1=0.06; R2=0.015; X1=0.18; X2=0.045; Xm=400; Rc=1200;
V1=240; V2=120; KVA=5;
n=V1/V2; R2p=n^2*R2; X2p=n^2*X2;
npts=100; thet2=linspace(-pi/2,pi/2,npts);
Reg=zeros(1,npts); PF=Reg;
for i=1:npts
   I2=KVA*1000/V2*exp(-j*thet2(i)); E1=(R2p+j*X2p)*I2/n+n*V2;
   Im=E1/(j*Xm); Ic=E1/Rc; Io=Ic+Im; I1=I2/n+Io;
   V1=(R1+j*X1)*I1+E1;
   Zm=j*Rc*Xm/(Rc+j*Xm); Znl=R1+j*X1+Zm;
   Vnl=abs(V1*Zm/Znl);
   Reg(i)=(Vnl/n-V2)/V2*100;
end
thet2=thet2*180/pi;
plot(thet2,Reg); grid;
title('Regulation vs power factor');
xlabel('Power factor angle ( lead to lag ) - degrees');
ylabel('Regulation, %');