# Chapter04: Control of Electric Motors¶

## Ex4_1:pg-441¶

In :
#Electric Drives:concepts and applications by V.subrahmanyam
#Publisher:Tata McGraw-Hill
#Edition:Second
#Ex4_1
import math
Eb=50;# voltage in V
V=120;# voltage in V
f=50;#frequency in Hz
R=10;# Resistance in ohm
a=math.asin(Eb/(math.sqrt(2)*V));
Alpha=(a*180)/math.pi;
pf=0.9556;
Iavg=(1/(2*math.pi*R))*((2*math.sqrt(2)*V*pf)-(Eb*(math.pi-(2*Alpha))));
print Iavg,"=Iavg:"
#answer wrong in the textbook due to error in calculation

29.9336056693 =Iavg:


## Ex4_3:pg-442¶

In :
#Electric Drives:concepts and applications by V.subrahmanyam
#Publisher:Tata McGraw-Hill
#Edition:Second
#Ex4_3
import math
P=10000;
V=240;# voltage in V
N=1000;#Speed in rpm
Eff1=0.87;#Effeciency in %
Vs=250;# voltage in V
f=50;#frequency in Hz
Alpha=0.5;#angle
R=0.40;# Resistance in ohm
Fdf=1;#fundamental displacement factor
df=0.9;#distortion factor
pf=0.9;#the power factor
Pi=P/Eff1;
I=Pi/V;
Eb=V-(I*R);
Vi=0.9*Vs;
Eb1=Vi-(I*R);
N1=(Eb1/Eb)*N;
Pi1=V*I*pf*(10)**(-3);
Pi2=(Pi1*N1)/N;
Vc=0.9*Vs*Alpha;
Eb2=Vc-(I*R);
N2=(N*Eb2)/Eb;
P0=((Pi1*N2)/N)*1000;
Pi0=Vc*I;
Eff=(P0/Pi0)*100;
print Eff,"=Effeciency in % "
#Result vary due to roundoff error

81.1519777932 =Effeciency in %


## Ex4_4:pg-442¶

In :
#Electric Drives:concepts and applications by V.subrahmanyam
#Publisher:Tata McGraw-Hill
#Edition:Second
#Ex4_4
import math
V=250;# voltage in V
f=50;#frequency in Hz
R=1.5;# Resistance in ohm
L=30;#inductance in mH
Eb=100;#Back emf in V
Alpha=0.866;#angle
Vc=0.9*V*Alpha;
Id=(Vc-Eb)/R;
P=Vc*Id*10**(-3);
pf=0.9*Alpha;
print pf,"=powerfactor "

0.7794 =powerfactor


## Ex4_5:pg-443¶

In :
#Electric Drives:concepts and applications by V.subrahmanyam
#Publisher:Tata McGraw-Hill
#Edition:Second
#Ex4_5
import math
N=1800;#Speed in rpm
I=60;#Current in A
V=400;# voltage in V
E=185;#Back emf in V
N2=900;#Speed in rpm
R=0.5;# Resistance in ohm
Vs=V/2.34;
Vl=V/1.35;
Vi=V-(I*R);
V=E+(I*R);
a=math.acos(V/(2.34*Vs));
Alpha=(a*180)/math.pi;
print Alpha,"=The firing angle in deg "

57.4863853668 =The firing angle in deg


## Ex4_6:pg-444¶

In :
#Electric Drives:concepts and applications by V.subrahmanyam
#Publisher:Tata McGraw-Hill
#Edition:Second
#Ex4_6
import math
V=500;# voltage in V
Vs=250;# voltage in V
I=181;#Current in A
N=1500;#Speed in rpm
R=0.1;# Resistance in ohm
f=50;#frequency in Hz
Eb=Vs-(I*R);
Eb1=Eb/3;
A1=math.acos(Vs/(1.35*V));
Alpha1=(A1*180)/math.pi;
Ia2=I/9;
V2=Eb1+(Ia2*R);
A2=math.acos(V2/(1.35*V));
Alpha2=(A2*180)/math.pi;
Vl=Vs/1.35;
A3=math.acos(V2/(1.35*Vl));
Alpha3=(A3*180)/math.pi;
print Alpha3,"=The firing angle in deg "

71.5063230096 =The firing angle in deg


## Ex4_7a:pg-445¶

In :
#Electric Drives:concepts and applications by V.subrahmanyam
#Publisher:Tata McGraw-Hill
#Edition:Second
#Ex4_7a
import math
V=300;# voltage in V
Vt=363.25;# voltage in V
f=60;#frequency in Hz
Rd=0.02;# Resistance in ohm
La=0.002;#inductance in H
Id=500;#Current in A
N=1500;#Speed in rpm
Eb=Vt-(Id*Rd);
A=math.acos(Vt/(1.35*V));
Alpha=(A*180)/math.pi;
print Alpha,"=The firing angle in deg "

26.2447091004 =The firing angle in deg


## Ex4_7b:pg-445¶

In :
#Electric Drives:concepts and applications by V.subrahmanyam
#Publisher:Tata McGraw-Hill
#Edition:Second
#Ex4_7b
import math
V=300;# voltage in V
Vt=363.25;# voltage in V
f=60;#frequency in Hz
Rd=0.02;# Resistance in ohm
La=0.001;#inductance in H
Id=500;#Current in A
N=1500;#Speed in rpm
Xc=2*math.pi*f*La;
Z=Rd+((3*Xc)/math.pi);
Eb=Vt-(Id*Z);
print Eb,"=The back emf in V "

173.25 =The back emf in V


## Ex4_8:pg-446¶

In :
#Electric Drives:concepts and applications by V.subrahmanyam
#Publisher:Tata McGraw-Hill
#Edition:Second
#Ex4_8
import math
V=600;# voltage in V
R=0.16;# Resistance in ohm
Ia=210;#Current in A
N=600;#Speed in rpm
n=10;#no of unit
Eb=V-(Ia*R);
Td=((Eb*Ia)/(2*math.pi*n));
W=(2*math.pi*N)/60;
A=Td/(W)**2;
print A,"=The constant A "

0.479515813953 =The constant A


## Ex4_9:pg-447¶

In :
#Electric Drives:concepts and applications by V.subrahmanyam
#Publisher:Tata McGraw-Hill
#Edition:Second
#Ex4_9
import math
V1=500;# voltage in V
V2=450;# voltage in V
Vs=420;# voltage in V
V=400;# voltage in V
I=60;#Current in A
R=1.5;# Resistance in ohm
R1=5;# Resistance in ohm
Eb=20;#Back emf in V
f=50;#frequency in Hz
Vl=V2+Eb;
A=math.acos(Vl/(1.35*Vs));
Alpha1=(A*180)/math.pi;
Eb1=V2-(I*R);
print Eb1,"=The back emf in V "
V3=-V2-(I*R);
Vc=-V2+Eb;
A1=math.acos(Vc/(1.35*Vs));
Alpha2=(A1*180)/math.pi;
print Alpha2,"=The firing angle1 in deg "
Eb2=-V-(I*R);
Vc1=-V+Eb+(R1*I);
A2=math.acos(Vc1/(1.35*Vs));
Alpha3=(A2*180)/math.pi;
print Alpha3,"=The firing angle2 in deg "

360.0 =The back emf in V
139.321363317 =The firing angle1 in deg
98.1111258306 =The firing angle2 in deg


## Ex4_10:pg-448¶

In :
#Electric Drives:concepts and applications by V.subrahmanyam
#Publisher:Tata McGraw-Hill
#Edition:Second
#Ex4_10
import math
V=500.0;# voltage in V
I=15.0;#Current in A
t=0.6;#time in sec
f=80;#frequency in Hz
Vav=V*t;
Vi=V-Vav;
Ton=t/f;
L=Vi*(Ton/I);
print L,"=The inductance in Henry "

0.1 =The inductance in Henry


## Ex4_14:pg-449¶

In :
#Electric Drives:concepts and applications by V.subrahmanyam
#Publisher:Tata McGraw-Hill
#Edition:Second
#Ex4_14
import math
V=440;# voltage in V
R1=0.07;# Resistance in ohm
R2=0.05;# Resistance in ohm
X=0.2;#Reactance in ohm
N=1420;#Speed in rpm
Xm=20;#Reactance in ohm
S1=80;#slip in rpm
S2=500;#slip in rpm
Ra=((S2/S1)*R2)-R2;
R=2*Ra;
Ra1=4*R2;
T=(Ra1*2)/R;
print T,"=The time ratio "

0.8 =The time ratio


## Ex4_15:pg-450¶

In :
#Electric Drives:concepts and applications by V.subrahmanyam
#Publisher:Tata McGraw-Hill
#Edition:Second
#Ex4_15
import math
P=1000;
N=1500;#Speed in rpm
R2=0.06;# Resistance in ohm
I2=125.6;#Current in A
T=1.5;#Time in sec
N1=1420;#Speed in rpm
S=(R2*P)/N;
K=((S/(2*math.pi*N))*(I2)**2*T)/(N1)**2;
T1=K*(N1)**2;
N2=750;#Speed in rpm
T2=K*(N2)**2;
X1=(T2*S)/T1;
A=math.acos(-S0/S2);
Alpha=(A*180)/math.pi;
print Alpha,"=The firing angle in deg "

115.887603041 =The firing angle in deg


## Ex4_20:pg-452¶

In :
#Electric Drives:concepts and applications by V.subrahmanyam
#Publisher:Tata McGraw-Hill
#Edition:Second
#Ex4_20
import math
R=0.05;# Resistance in ohm
N0=1000.0;#Speed in rpm
Rf=46.0;# Resistance in ohm
I1=75.0;#Current in A
I2=150;#Current in A
I3=250.0;#Current in A
V=230;# voltage in V
Eb=230;#Back emf in V
If=V/Rf;
Ia1=I1-If;
Eb1=V-(Ia1*R);
N1=(Eb1/Eb)*N0;
print N1,"=The speed N1 in rpm "
Ia2=I2-If;
Eb2=V-(Ia2*R);
N2=(Eb2/Eb)*N0;
print N2,"=The speed N2 in rpm "
Ia3=I3-If;
Eb3=V-(Ia3*R);
N3=(Eb3/Eb)*N0;
print N3,"=The speed N3 in rpm "

984.782608696 =The speed N1 in rpm
968.47826087 =The speed N2 in rpm
946.739130435 =The speed N3 in rpm