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// Example 5.11
// Determine (a) Rotor frequency (b) Slip at which TDmax occurs (c) Rotor speed
// at 1/2 rated torque load (d) Required rheostat resistance (e) Rated torque
// Page No. 201
clc;
clear;
close;
// Given data
S=0.0159; // Slip
Fbr=50; // Rated frequency
R1=0.00536; // Motor resistance
R2=0.00613;
X1=0.0383; // Motor reactance
X2=0.0383;
Rrhe=0; // Initial rheostat resistance
P=4; // Number of poles
NR=1000; // Rated speed
s1=0.0159; // Slip of rheostat
a=2; // Stator to rotor turns ratio
hp=400; // Motor horsepower
// (a) Rotor frequency
fr=S*Fbr;
// (b) Slip at which TDmax occurs
Stdmax=(R2+Rrhe)/(sqrt(R1^2+(X1+X2)^2));
// (c) Rotor speed at 1/2 rated torque load
s=S*(0.5)*(R2/R2); // Rotor speed at 1/2 rated torque
ns=120*Fbr/P;
nr=ns*(1-s); // Rotor speed
// (d) Required rheostat resistance
s2=(ns-NR)/ns;
Rrhe2=((s2/s1)*(1/0.5)*(R2+Rrhe))-R2; // rheostat resistance
Rrheostat=Rrhe2/a^2;
// (e) Rated torque
nr1=ns*(1-s1); // Rated speed
T=hp*5252/nr1;
// Display result on command window
printf("\n Rotor frequency = %0.3f Hz",fr);
printf("\n Slip at which TDmax occurs = %0.4f ",Stdmax);
printf("\n Rotor speed at 1/2 rated torque = %0.0f r/min",nr);
printf("\n Required rheostat resistance = %0.4f Ohm/phase",Rrheostat);
printf("\n Rated torque = %0.0f lb-ft",T);
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