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// Example 5.18
// Computation of (a) Locked rotor torque and the expected average in rush
// current (b) Repeat part (a) assuming motor is started at reduced voltage
// with 65% tap (c) In rush line current line current when starting at reduced
// voltage
// Page No. 231
clc;
clear all;
close;
// Given data
P=125; // Rated Voltage
n=1141; // Speed of machine
hp=125; // Horsepower rating of device
Vline=460; // Line voltage
ns=1200; // Stator speed
s=0.125; // Slip
ILS=683; // Current at low side
// (a) Locked rotor torque and the expected average in rush current
Trated=P*5252/(n); // Rated torque
Tlr=1.25*Trated; // Locked rotor torque
kVA=(6.3+7.1)/2;
Ilr=(kVA*1000*hp)/(Vline*sqrt(3)); // In-rush current
// (b) Locked rotor torque and the expected average in rush current when motor
// is started at reduced voltage
V2=0.65*Vline; // Voltage impressed across the stator
I=Ilr*0.65; // Average in-rush current
T2=Tlr*(V2/Vline)^2; // Locked rotor toreque
nr=ns*(1-s);
// (c) In rush line current line current when starting at reduced voltage
a=1/0.65; // Bank ratio of autotransformer
IHS=ILS/a;
// Display result on command window
printf("\n Locked rotor torque = %0.1f lb-ft ",Tlr);
printf("\n Expected average in-rush current = %0.0f A ",Ilr);
printf("\n Locked rotor torque when motor is started at reduced voltage = %0.1f lb-ft ",T2);
printf("\n In-rush line current = %0.0f A",IHS);
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