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+

+clc;

+Pout=40000;//output power

+V=250;//supply voltage in volts

+r=0.2;//sum of armature circuit resistance & series field circuit resistance

+n=1500;//speed of dc series motor at rated current

+

+//PART(a)-

+

+Ir=Pout/V;//rated current

+Ea=V-Ir*r;//counter emf at rated load

+Wm=(2*%pi*n)/60;//angular speed of rotation of motor

+Te=round((Ea*Ir)/Wm);//rated electromagnetic torque in Nm.

+//Now the relation giving the torque speed characteristics of series motor must be developed.

+//Since the magnetic saturation is neglected

+//Te=Ka*phi*I

+//Te=K1*Ia^2

+K1=Te/(Ir^2);//Ia=rated current

+//Ea=K2*phi*n=K2*Ia*n

+K2=Ea/(Ir*n);// values of constant of proportionality 

+//The values of constants k1 & K2 are obtained from rated conditions

+//Ia=(V-Ea)/r & Ea=K2*Ia*n ; Ia=1250-0.00454*Ia*n

+//Ia=1250/(1+0.00454n) ....(1); Ia=armature current at any speed

+//Te=K1*Ia^2

+n=[1400 1450 1500 1550 1600 1650 1700];

+Te=K1.*(((V/r)^2)./(1+(K2/r).*n).^2); // Electromagnetic torque

+Tl=5.*sqrt(n); // load torque

+plot(Te,n,Tl,n);

+xlabel('T(Nm)');

+ylabel('Speed(rpm)');

+title('Speed-torque characteristics for Series-motor and for load');

+

+//THE INTERSECTION OF SERIES MOTOR & LOAD CHARACTERISTICS GIVES THE OPERATING POINT

+

+//From the curve the operating point is obtained at 1591 rpm & torque is 199.5 Nm

+disp('The operating speed of motor is 1591 rpm.');

+

+//PART(b)-

+//Current drawn from the source is -

+Ia=(V/r)/(1+(K2/r)*1591);//From equation (1)

+printf('Current drawn from the source is %f A.',Ia);