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// Example 10.12
// Determine (a) Rated torque (b) Armature current at locked rotor if no
// starting resistance is used (c) External resistance required in the armature
// circuit that would limit the current and develop 200 percent rated torque
// when starting (d) Assuming the system voltage drops to 215V, determine the
// locked rotor torque using the external resistor in (c)
// Page No. 433
clc;
clear;
close;
// Given data
n=1750; // Rotor speed
P=15; // Hp rating of motor
VT=230; // Rated voltade of the machine
Ea=0;
Racir=0.280; // Armature circuit loss
Rf=137; // Field resistance
ItRated=56.2; // Total current drawn
VT1=215; // Rated voltage after drop
// (a) Rated torque
Trated=P*5252/n;
// (b) Armature current
Ia=(VT-Ea)/Racir;
// (c) External resistance required
If=VT/Rf; // Field current
IaRated=ItRated-If; // Rated armature current
Ia2=IaRated*2; // Armature current for 200% rated torque
Rx=((VT-Ea)/Ia2)-Racir; // External resistance required
// (d) Locked rotor torque
If215=VT1/Rf; // Field current at 215V
Ia215=(VT1-Ea)/(Racir+Rx); // Armature current at 215V
TD2=Trated*( (If215*Ia215) / (If*IaRated) );
// Display result on command window
printf("\n Rated torque = %0.1f lb-ft ",Trated);
printf("\n Armature current = %0.1f A ",Ia);
printf("\n Armature current for 200 percent rated torque = %0.1f A ",Ia2);
printf("\n External resistance required = %0.2f Ohm ",Rx);
printf("\n Locked rotor torque = %0.1f lb-ft ",TD2);
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