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// Example 12.1
// Determine (a) Field circuit resistance (b) Field rheostat setting that will
// provide no load voltage of 140V (c) Armature voltage if the rheostat is set
// to 14.23 ohm (d) Field rheostat setting that will cause critical resistance
// (e) Armature voltage at 80 percent rated speed (f) Rheostat setting required
// to obtain no load armature voltage of 140V if shunt field is separately
// excited from a 120V DC source
// Page No. 479
clc;
clear;
close;
// Given data
Ea=156; // No load voltage
If=4.7; // Shunt field current
If140=2.35; // New field current at Ea=140V
Eanew=140; // No load voltage
Ifnew=3.2; // Field current corresponding to no load voltage
Ea1=0; // First arbitrary voltage
Ea2=100; // Second arbitrary voltage
Vf=120;
V=130; // Intersection of I1 and I2
Rrheonew=14.42; // Rheostat set to new settings
Va=116; // Intersection of field resistance line with the low
// speed magnetization curve
//(a) Field circuit resistance
Rf=Ea/If; // Field circuit resistance
// (b) Field rheostat setting that will provide no load voltage of 140V
Rrheo=(Eanew/Ifnew)-Rf;
//(c) Armature voltage if the rheostat is set to 14.23 ohm
Rnew=Rf+Rrheonew; // New field resistance
If1=Ea1/(Rf+Rrheo); // Field current corresponding to first arbitrary voltage
If2=Ea2/(Rf+Rrheo); // Field current corresponding to second arbitrary voltage
// (d) Field rheostat setting that will cause critical resistance
Rcr=Eanew/If140; // Critical resistance
// (e) Armature voltage at 80 percent rated speed
// Ea80=0.80*Ea;
Ea80=116;
//(f) Rheostat setting required to obtain no load armature voltage of 140V if
// shunt field is separately excited from a 120V DC source
Rrheo1=(Vf/Ifnew)-Rf;
// Display result on command window
printf("\n Field circuit resistance = %0.2f Ohm",Rf);
printf("\n Field rheostat setting that will provide no load voltage of 140V = %0.2f Ohm ",Rrheo);
printf("\n Armature voltage if the rheostat is set to 14.23 ohm = %0.0f V ",V);
printf("\n Field rheostat setting that will cause critical resistance = %0.1f Ohm ",Rcr);
printf("\n Armature voltage at 80 percent rated speed (V)= %0.0f ",Ea80);
printf("\n Rheostat setting required = %0.2f Ohm ",Rrheo1);
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