Chapter 6 : DC Machines¶

Example 6.1 Page No : 6.3¶

In :
# Variables
P = 4;				#no. of poles
c = 2;				#no. of parallel paths
p = 4./2;				#no. of pair of poles
S = 51;				#no. of slots
C = 12;				#conductors per slot
N = 900;				#rpm(speed)
fi = 25./1000;				#Wb

# Calculations
Z = S*C;				#total no. of conductors
E = 2*Z/c*N*p/60*fi;				#V

# Results
print "Generated emf(V): %.2f"%E
Generated emf(V): 459.00

Example 6.2 Page No : 6.4¶

In :
# Variables
P = 8.;				#no. of poles
c = 8.;				#no. of parallel paths
p = 8./2;				#no. of pair of poles
E = 260.;				#V(generated emf)
fi = 0.05;				#Wb
S = 120;				#no. of slots
N = 350;				#rpm(speed)

# Calculations
Z = E/(2./c*N*p/60*fi);				#V

# Results
print "No. of conductors per slot",int(Z)
No. of conductors per slot 891

Example 6.3 Page No : 6.6¶

In :
# Variables
Ra = 0.1;				#ohm(Armature Resistance)
Vs = 250;				#V(supply voltage)

# Calculations and Results
#part(a)
I = 80;				#A
Vdrop = Ra*I;				#V
emf = Vs+Vdrop;				#V(Generated emf)
print "Part(a) Generated emf(V) : %.2f"%emf

#part(b)
I = 60;				#A(current taken by Motor)
Vdrop = Ra*I;				#V
emf = Vs-Vdrop;				#V(Generated emf)
print "Part(b) Generated emf(V) : %.2f"%emf
Part(a) Generated emf(V) : 258.00
Part(b) Generated emf(V) : 244.00

Example 6.4 Page No : 6.7¶

In :
# Variables
P = 4;				#no. of poles
Vs = 440;				#V
c = 2;				#no. of parallel paths
p = 4./2;				#no. of pair of poles
Ia = 50;				#A
Ra = 0.28;				#ohm
Z = 888;				#conductors
fi = 0.023;				#Wb

# Calculations
emf = Vs-Ia*Ra;				#V
N = emf/(2*Z/c*p/60*fi);				#rpm

# Results
print "Speed in rpm",round(N)
Speed in rpm 626.0

Example 6.5 Page No : 6.7¶

In :
import math

# Variables
N = 900;				#rpm
Vs = 460.;				#V
Vs_new = 200;				#V
fi_ratio = 0.7;				#ratio of new flux to original flux

# Calculations
kfi = Vs/N;				#for original flux
Nnew = Vs_new/kfi/fi_ratio;				#rpm(new speed)

# Results
print "Speed in rpm",round(Nnew)
Speed in rpm 559.0

Example 6.6 Page No : 6.8¶

In :
import math

# Variables
Ia = 110;				#A
Vs = 480;				#V
Ra = 0.2;				#ohm
P = 6.;				#no. of poles
c = 6.;				#no. of parallel paths
p = P/2;				#no. of pair of poles
Z = 864;				#no. of conductors
fi = 0.05;				#Wb

# Calculations and Results
emf = Vs-Ia*Ra;				#V
N = emf/(2*Z/c*p/60*fi);				#rpm
print "(a) Speed in rpm",round(N)

Pm = Ia*emf;				#W(Mechanical power developed)
M = Pm/(N/60)/(2*math.pi);				#Nm(Torque)
print "(b) Gross torque developed(Nm) : %.f"%M
(a) Speed in rpm 636.0
(b) Gross torque developed(Nm) : 756

Example 6.7 Page No : 6.9¶

In :
import math

# Variables
N = 15;				#rps
M = 2*1000;				#Nm(Torque required)
Loss = 8*1000;				#W

# Calculations
P = 2*math.pi*M*N;				#W(Power required)
Pa = P-Loss;				#W(Power generated in armature)

# Results
print "Power generated in armature(kW) : %.2f"%(Pa/1000)
Power generated in armature(kW) : 180.50