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// Example 11.4
// Computation of resistance using linear approximation and values are
// compared with results obtained in example 11.1
// Page No. 456
clc;
clear;
close;
// Given data
HP=40; // hp rating of the device
%ratedload=0.902; // Percentage rated load
VT=240; // Voltage value of motor
RF=99.5; // Resistance of shunt motor
Nf=1231; // Turns per pole of the shunt motor
Ra=0.0680; // Armature resistance
RIP=0.0198; // Interpole winding resistance
Rs=0.00911; // Resistance of series field winding
Bp1=0.70; // Flux density for a net mmf
n1=1150; // Speed of shunt motor
n2=1.25*n1;
IT=137.84;
// Computation of resistance using linear approximation and values are
// compared with results obtained in example 11.1
IF=VT/RF; // Field current
Ia1=IT-IF; // Armature current
Fnet1=Nf*IF; // Net mmf
Racir=Ra+RIP+Rs; // Armature circuit resistance
Fnet2=Fnet1*(n1/n2)*((VT-Ia1*Racir*1.15)/(VT-Ia1*Racir));
IF1=Fnet2/Nf; // Field current
Rx=(VT/IF1)-RF; // External resistance required
// Display result on command window
printf("\n The resistance rating of an external resistance = %0.2f Ohm ",Rx);
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