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+clc;
+P=20000; // rated power of induction motor
+v=400; // rated voltage of motor
+f=50; // frequency
+m=3; // number of phases
+p=4; // number of poles
+r1=0.2; // stator resistance
+x=0.45; // stator/rotor leakage reactance
+xm=18; // magnetising reactance
+s=0.04; // slip
+pg=P/(1-s); // air gap power
+pr=s*pg; // rotor copper loss
+vp=v/sqrt(3); // per phase voltage
+ve=(vp*xm)/(x+xm); // Thevenin voltage
+re=(r1*xm)/(x+xm); // Thevenin resistance
+xe=(x*xm)/(x+xm); // Thevenin reactance
+// using Thevenin's theorrm and rotor copper loss expression we get a quadratic equation in r2 (rotor resistance) whose terms are
+t1=pr/s^2;
+t2=((2*pr*re)/s)-(m*ve^2);
+t3=pr*((xe+x)^2+re^2);
+t=[ t1 t2 t3];
+r2=roots(t);
+disp('case a');
+ws=(4*%pi*f)/p; // synchronous speed
+Tm=(m*ve^2)/(ws*2*(re+sqrt(re^2+(x+xe)^2)));
+printf('Maximum internal torque is %f Nm\n',Tm);
+Ti=(m*ve^2*r2(1))/(ws*((re+r2(1))^2+(x+xe)^2));
+printf('Initial starting torque is %f Nm\n',Ti);
+disp('case b');
+sm=r2(1)/(sqrt(re^2+(xe+x)^2));
+printf('Slip at maximum torque is %f ',sm);