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// Example 11.2
// Computation of (a) Shunt field current (b) Armature current (c) Developed
// torque (d) Armature current if a resistor inserted in series with the shunt
// field circuit caused the speed to increase to 900 r/min (e) External
// resistance required in series with the shunt field circuit to operate
// at 900 r/min
// Page No. 450
clc;
clear;
close;
// Given data
HP=125;
perratedload=0.854; // Percentage rated load
VT=240; // Voltage value of motor
RF=49.2; // Resistance of shunt motor
Nf=577; // Turns per pole of the shunt motor
Ns=4.5;
Ra=0.0172; // Armature resistance
RIP=0.005; // Interpole winding resistance
Rs=0.0023; // Resistance of series field winding
n1=850; // Speed of shunt motor
n2=900;
F2=4000;
// (a) Shunt field current
IF=VT/RF; // Field current
// (b) Armature current
Pin=HP*746/perratedload; // Input power
IT=Pin/VT; // Total current
Ia1=IT-IF;
// (c) Developed torque
Racir=Ra+RIP+Rs;
Ea=VT-Ia1*Racir; // Armature emf
Pmech=Ea*Ia1; // Mechanical power
TD=Pmech*5252/n1/746; // Torque developed
// (d) Armature current if a resistor inserted in series with the shunt field
// circuit caused the speed to increase to 900 r/min
Ia2=Ia1*n2/n1;
//(e) External resistance required in series with the shunt field circuit to
// operate at 900 r/min
IF2=(F2-0.90*Ns*Ia2)/Nf;
Rx=(VT/IF2)-RF;
// Display result on command window
printf("\n Shunt field current = %0.2f A ",IF);
printf("\n Armature current = %0.2f A ",Ia1);
printf("\n Developed torque = %0.1f lb-ft ",TD);
printf("\n Armature current if a resistor inserted in series = %0.0f A ",Ia2);
printf("\n External resistance required = %0.1f Ohm ",Rx);
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