CHAPTER 9 - ELEMENTS OF DC MACHINE DESIGN

Example E1 - Pg 195

#Caption:Find the dimensions of D and L
#Exa:9.1
import math
P=15000.#Power of shunt motor(in watt)
V=440.#Supplied voltage to motor(in volts)
n=1500.#Speed of motor(in r.p.m)
e=88.#Efficiency(in %)
B=0.65#Average flux density(in webers/m**2)
q=30000.#Specific electric loading(ampere conductors/m)
p=4.#Number of poles
R_f=220.#Field resistance(in ohms)
P_i=P/(e/100.)
I=P_i/V
I_f=V/R_f
D=170.#Choosing the diameter(in mm)
L=(P_i)/((math.pi**2.)*((D**2.)*(10.**(-6.)))*B*q*(n/60.)*(10.**(-3.)))
print '%s %.1f' %('Required dimensions of L (min)=',L)
print '%s %.f' %('                       D(in mm)=',D)

Required dimensions of L (min)= 122.6
                       D(in mm)= 170

Example E2 - Pg 198

#Caption: Find values of the 5 steps in a 6 stud starter for a d.c. shunt motor
#Exa:9.2
P_o=3730.#Output power(in watt)
V=200.#Voltage supplied to motor(in volts)
e=88.#Efficiency(in%)
P_i=P_o/(e/100.)
I=P_i/V#Full load current
I_a=I#Neglecting field current
L=P_i-P_o
Cu=(1./2.)*L#Copper loss is half the total loss(Given)
R_a=Cu/(I**2.)
I_m=(2.*I)#Maximum current is twice full load current(Given)
R_1=V/I_m
g=(R_1/R_a)**(1./5.)
R_2=R_1/g
r1=R_1-R_2
R_3=R_2/g
r2=R_2-R_3
R_4=R_3/g
r3=R_3-R_4
R_5=R_4/g
r4=R_4-R_5
R_6=R_5/g
r5=R_5-R_6
print '%s %.2f' %('Required resistances r1 (ohms)=',r1)
print '%s %.2f' %('                     r2 (ohms)=',r2)
print '%s %.2f' %('                     r3 (ohms)=',r3)
print '%s %.2f' %('                     r4 (ohms)=',r4)
print '%s %.2f' %('                     r5 (ohms)=',r5)
print '%s %.2f' %('                     R_a (ohms)=',R_a)

Required resistances r1 (ohms)= 1.63
                     r2 (ohms)= 1.07
                     r3 (ohms)= 0.70
                     r4 (ohms)= 0.46
                     r5 (ohms)= 0.30
                     R_a (ohms)= 0.57