Chapter 8: DC Motors¶

Example 8.1: page 137:¶

In :
from __future__ import division
import math

#given  data  :
s=22;#  shaft  of  the  motor  in  hp
Tsh=210;#  torue  in  hp

#calculations:
N=(s*60*746)/(2*math.pi*Tsh);

#Results
print  "speed,N(rpm)  =  ",N
speed,N(rpm)  =   746.300264578

Example 8.2: Page 143:¶

In :
from __future__ import division
import math

#given  data  :
N=955;#  in  r.p.m
V=230;#  voltage  in  volts
I=72;#  current  in  A
s=968;#  stray  losses
Rsh=115;#  shunt  field  resistance  in  ohm
Ra=0.5#  armature  resistance  in  ohm

#calculations:
W=V*I;
Ish=V/Rsh#  shunt  field  resistance
Ia=I-Ish;
Eb=V-(Ia*Ra)#  back  emf  in  volts
Dpd=Eb*Ia#  driving  power  developed
Mpo=Dpd-s;
bhp=Mpo/746;
c_losses=W-Dpd;
Ta=(9.55*Eb*Ia)/N;
Tsh=(bhp*60*746)/(2*math.pi*N);
Tl=Ta-Tsh;
eta=(Mpo/W)*100;

#Results
print  "(a)bhp  =  ",bhp
print  "(b)copper  losses(W)  =  ",c_losses
print  "(c)torque  armature,Ta(N-m)  =  ",Ta
print  "(d)shaft  torque,Tsh(N-m)  =  ",round(Tsh,2)
print  "(e)lost  torque,Tl(N-m)  =  ",round(Tl,2)
print  "(f)commercial  efficioency,eta(%)  =  ",round(eta,2)
(a)bhp  =   17.0
(b)copper  losses(W)  =   2910.0
(c)torque  armature,Ta(N-m)  =   136.5
(d)shaft  torque,Tsh(N-m)  =   126.81
(e)lost  torque,Tl(N-m)  =   9.69
(f)commercial  efficioency,eta(%)  =   76.58

Example 8.3: page 144:¶

In :
from __future__ import division
import math

#given data:
V=230#  in  volts
I=5  #  in  amperes
rpm=914#turns
ra=0.5#resistance  of  armature  in  ihms
rsh=115#shunt  field  in  ohms
Il=30#  in  amperes
ar=10#  in  percent

#calculations:
Ish=V/rsh#  in  amperes
anl=I-Ish#armature  current  in  amperes  at  no  load
ph1=100#
ph2=90#

#Results
print  "speed  when  loaded  in  rpm is ",Ns
speed  when  loaded  in  rpm is  960.0

Example 8.4: page 144:¶

In :
from __future__ import division
import math

#given data:
V=110#  in  volts
I=5    #  in  amperes  without  load
ra=0.5#armature  resistance  in  ohms
rsh=110#shunt  field  in  ohms

#calculations:
Ish=V/rsh#  in  ampere
anl=I-Ish#armature  current  in  amperes  at  no  load
Dp=Eb1*anl#driving  power  at  no  load  in  watt
Dpl=Eb2*al#driving  power  at  load  in  watt
mo=Dpl-Dp#out  of  motor  in  watt
bhp=mo/746#horse  power
mi=V*Il#input  power  in  watt
n=(mo/mi)*100#efficiency  in  percentage

#Results
print  "(a)stray  losses  in  watt is",Dp
print  "(b)horse  power  in  ampere  is",round(bhp,1)
print  "(c)efficiency  of  motor  when  it  is  work  on  full  ,load  in  percentage  is",round(n,2)
#answer(c)  is  wrong  in  the  textbook
(a)stray  losses  in  watt is 432.0
(b)horse  power  in  ampere  is 7.0
(c)efficiency  of  motor  when  it  is  work  on  full  ,load  in  percentage  is 57.24

Example 8.5: page 146¶

In :
from __future__ import division
import math

#given data:
V=230#  in  volts
I=60#  in  amperes
rpm=955#turns
ra=0.2#resistance  of  armature  in  ihms
rsh=0.15#shunt  field  in  ohms
sl=604#stray  losses  in  watts

#calculations:
Rm=ra+rsh#  in  ohms
Eb=(V-I*Rm)#  back  emf  in  volts
Dp=Eb*I#driving  power  in  watts
mi=V*I#input  power  in  watts
Cl=mi-Dp#  copper  losses  in  watts
mo=Dp-sl#output  of  motor
bhp=mo/746#  horse  power  in  bhp
Ta=(9.55*Eb*I)/rpm#total  torque  in  N-m
Ts=(bhp*60*746)/(2*math.pi*rpm)#shaft  torque  in  N-m
Tl=Ta-Ts#lost  torque  in  N-m
nc=(mo/mi)*100#commercial  efficiency  in  percentge

#Results
print  "(a)back  emf  in  volts is",Eb
print  "(b)copper  losses  in  watts is ",Cl
print  "(c)horse  power    is", bhp
print  "(d)total  torque  in  N-m is",Ta
print  "(e)shaft  torque  in  N-m is",round(Ts,1)
print  "(f)lost  torque  in  N-m is",round(Tl,1)
print  "(g)commercial  efficiency  in  percentge is",round(nc,2)
(a)back  emf  in  volts is 209.0
(b)copper  losses  in  watts is  1260.0
(c)horse  power    is 16.0
(d)total  torque  in  N-m is 125.4
(e)shaft  torque  in  N-m is 119.4
(f)lost  torque  in  N-m is 6.0
(g)commercial  efficiency  in  percentge is 86.49

Example 8.6: page 146:¶

In :
from __future__ import division
import math

#given data:
V=220#  in  volts
I=60#  in  amperes
rpm=728#turns
Ts=150#shaft  torque  in  N-m
nc=80#commercial  efficiency  in  percentge

#calculations:
I=((Ts*2*math.pi*rpm*746)/(60*746*(nc/100)*V))#  CURRENT  TAKEN  IN  AMPERES

#Results
print  "current  taken  in  amperes  is",round(I,1)
current  taken  in  amperes  is 65.0

Example 8.7: page 147:¶

In :
from __future__ import division
import math

#given data:
V=220#  in  volts
rpm=2100#turns
ra=0.5#resistance  of  armature  in  ihms
rsh=220#shunt  field  in  ohms
Il=21#  in  amperes
R1=220#  in  ohms
ph1=50#
ph2=100#

#calculations:
Ish=V/rsh#  in  amperes
Ifs=V/(rsh+R1)#shunt  field  current  in  second  case  in  ampere
n2=(rpm*ph2)/ph1#speed  in  rpm

#Results
print  "speed  in  rpm  is",n2
speed  in  rpm  is 4200.0