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//Chapter 6:Induction Motor Drives
//Example 16
clc;
//Variable Initialization
//Ratings of the Delta connected slipring Induction motor
f=50 // frequency in HZ
Vl=400 //line voltage in V
P=6 // number of poles
SR=2.2 //ratio of stator to rotor
//Parameters referred to the stator
Xr_=1 // rotor winding reactance in ohm
Rr_=0.2 // resistance of the rotor windings in ohm
s=0.04 // given slip when motor runs at full load
//Solution
Ns=120*f/P //synchronous speed
Wms=2*%pi*Ns/60
x=(Rr_/s)**2+Xr_**2
Tf=(3/Wms)*(Vl)**2*(Rr_/s)/x //full load torque
K=Tf/(Ns*(1-s))**2
N=850 //speed of the motor in rpm
Tl=K*N**2 //torque at the given speed N
s=(Ns-N)/Ns //slip at the given speed N
y=Tl*(Wms/3)/Vl**2 //y=X/(X**2+Xr_**2) and X=(Re+Rr_)/s
mprintf("\nThe torque at the given speed of 850rpm is:%d N-m",Tl)
mprintf("\nWith a slip of s:%.2f",s)
mprintf("\nTo find the external resistance connected the given quadratic equation is X**2-6.633X+1=0")
mprintf("\nWith X=(Re-Rr_)/s where Re is the required external resistance")
a = 1
b = -1/y
c = 1
//Discriminant
d = (b**2) - (4*a*c)
X1 = (-b-sqrt(d))/(2*a)
X2 = (-b+sqrt(d))/(2*a)
//Results
mprintf("\nThe solutions for X are %.4f and %.4f",X1,X2)
Re1=X1*s-Rr_
Re2=X2*s-Rr_
if (Re1>0) then :
mprintf("\nThe number Re1:%.3f ohm is feasible",abs(Re1))
R=Re1/SR**2
mprintf("\nRotor referred value of the external resistance is:%.3f ohm",R)
end
if (Re2>0) then
mprintf("\nThen Re2:%.3f ohm is feasible",abs(Re2))
R=Re2/SR**2
mprintf("\nHence Rotor referred value of the external resistance is:%.3f ohm",R)
end
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