%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  traneqckt.m - Determines transformer equivalent circuit
%                parameters from open-circuit & short-circuit
%                test data. Assumes high voltage winding is  
%                primary and assigns subscript 1.
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
clear;
V1=480; V2=240; n=V1/V2;      % Rated voltage values
Vsc=37.2; Isc=51.9; Psc=750; scside='hgh';   % Test data
Voc=240; Ioc=9.7; Poc=720; ocside='low';
% dc resistance of windings - if not known, set R1dc=R2dc=1
R1dc=0.110; R2dc=0.029;    
if scside == 'low'         % Refer all data to high side
   Vsc=n*Vsc; Isc=Isc/n;
else; end
if ocside == 'low'
   Voc=n*Voc; Ioc=Ioc/n;
else; end
Req=Psc/Isc^2; R1=Req*R1dc/(R1dc+n^2*R2dc); R2=(Req-R1)/n^2;
Zsc=Vsc/Isc; X1=sqrt(Zsc^2-Req^2)/2; X2=X1/n^2;
Rc=Voc^2/Poc; Xm=Voc/sqrt(Ioc^2-(Voc/Rc)^2);
disp(' '); disp(['   TRANSFORMER EQUIVALENT CIRCUIT PARAMETERS - ',...
   date]);
disp('            Classical Data Reduction');
disp(' '); disp(' ')
disp([blanks(3) 'R1(ohm)' blanks(8) 'R2(ohm)' blanks(8) 'X1(ohm)' ...
      blanks(8) 'X2(ohm)']);
disp([blanks(3) num2str(R1) blanks(9) num2str(R2) ...
      blanks(8) num2str(X1) blanks(9) num2str(X2)]);
disp(' ');
disp([blanks(3) 'Rc(ohm)' blanks(8) 'Xm']);
disp([blanks(4) num2str(Rc) blanks(8) num2str(Xm)]);
% Refinement of data reduction
thetoc=acos(Poc/Voc/Ioc); Eoc=abs(Voc-(R1+j*X1)*Ioc*exp(-j*thetoc));
Poc=Poc-Ioc^2*R1; Qoc=Voc*Ioc*sin(thetoc)-Ioc^2*X1;
Rc=Eoc^2/Poc; Xm=Eoc^2/Qoc;
thetsc=acos(Psc/Vsc/Isc); Esc=abs(Vsc-(R1+j*X1)*Isc*exp(-j*thetsc));
Psc=Psc-Esc^2/Rc; Qsc=Vsc*Isc*sin(thetsc)-Esc^2/Xm;
Req=Psc/Isc^2; R1=Req*R1dc/(R1dc+n^2*R2dc); R2=(Req-R1)/n^2;
X1=Qsc/Isc^2/2; X2=X1/n^2;
disp(' '); disp(['   TRANSFORMER EQUIVALENT CIRCUIT PARAMETERS - ',...
   date]);
disp('            Refined Data Reduction');
disp(' '); disp(' ')
disp([blanks(3) 'R1(ohm)' blanks(8) 'R2(ohm)' blanks(8) 'X1(ohm)' ...
      blanks(8) 'X2(ohm)']);
disp([blanks(3) num2str(R1) blanks(9) num2str(R2) ...
      blanks(8) num2str(X1) blanks(9) num2str(X2)]);
disp(' ');
disp([blanks(3) 'Rc(ohm)' blanks(8) 'Xm']);
disp([blanks(4) num2str(Rc) blanks(8) num2str(Xm)]);