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%
%  sermtr.m - plots developed torque-speed curve for series 
%             excited dc motor with rated voltage applied.
%             Armature reaction neglected.
%
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clear; clf;
VtR=600;                      % Rated terminal voltage
PR=80;                        % Rated output horsepower
Ra=0.25;                      % Armature resistance
Rs=0.03;                      % Series field resistance
Ns=10;                        % Series field turns
nmR=1200;                     % Rated speed(rpm)
% Rated developed torque & armature current assuming 4% F&W losses
TdR=PR*746/(nmR*pi/30)/0.96; 
IaR=(VtR-sqrt(VtR^2-4*(Ra+Rs)*TdR*nmR*pi/30))/2/(Ra+Rs);

load eif   % Load stored OCC(in shunt field amps) for speed of nmR
m=length(eif); npts=200;
E=eif(1:m,1); If=eif(1:m,2);
% Create Kphip & mmf arrays
Kphip=eif(1:m,1)/(nmR*pi/30);
mmfs=eif(1:m,2)*Ns*IaR/(interp1(E,If,VtR-IaR*(Ra+Rs)));
npts=200; Ia=linspace(0.25*IaR,1.5*IaR,npts);

% Determination of Td-nm
for i=1:npts
   Kphi=interp1(mmfs, Kphip, Ns*Ia(i));
   Td(i)=Kphi*Ia(i);
   wm(i)=VtR/Kphi-Td(i)*Ra/Kphi^2;
end
nm=wm*30/pi;
subplot(2,1,1); plot(0,0,Td,nm,TdR,nmR,'o'); grid;
title('Series dc motor');
ylabel('Speed, rpm'); xlabel('Torque, N-m');
subplot(2,1,2); plot(0,0,Ia,nm,IaR,nmR,'o'); grid;
title('Series dc motor');
ylabel('Speed, rpm'); xlabel('Line current, A');