# Chapter 8: DC Motors¶

### Example 8.1: page 137:¶

In [1]:
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 [2]:
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 [3]:
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 [4]:
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 [5]:
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 [6]:
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 [7]:
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