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+clc;
+v=250; // rated voltage of dc shunt motor
+n1=1200; // no load speed
+N=1000; // turns per pole in shunt field winding 
+n2=900; // reduced speed
+ia=100; // full load armature current
+rf=0.2; // series field resistance
+ra=0.1; // armature resistance
+ar=0.04; // armature reaction as afraction of main field m.m.f
+// At no load counter EMF=v therefore from magnetization curve given in fig 4.76 field current is
+IF=[ 0.38 0.58 0.8 1.1 1.36 1.76];
+EA=[125 180 215 250 275 300];
+plot(IF,EA);
+xlabel('field current');
+ylabel('counter EMF');
+title('Magnetising curve');
+ifs1=1.1; // field current
+Ats1=ifs1*N; // ampere turns for field current
+Ea2=v-ia*(ra+rf); // counter EMF at full load 
+// magnetization curve is for 1200 rpm, therefore full load counter EMF corresponding to it is 
+Ea2=Ea2*(n1/n2);
+// corresponding to above counter EMF field current from magnetization curve is 
+ifs2=1.62;
+Ats2=(ifs2*N)/(1-ar); // ampere turns for field current at full load
+at=Ats2-Ats1; // series field
+t=at/ia; 
+printf('Number of series turns per pole to reduce speed to %f rpm is %f ',n2,ceil(t));