# CHAPTER 7- Rating and Heating Motors¶

## EXAMPLE 7.1 - PG NO.140¶

In [1]:
#Example 7.1, page 140
import math
G=500.#in kg
h=700.# in j/kg/c
s_lambda=math.pi*.7*1*12.5
h=(G*h)/s_lambda
#disp(h)
L=((10*1000.)/.9)-10000.
w=1111.
T=w/s_lambda
print'%s %.1f %s' %("Final tempearture rise is =",T,"degree C")

Final tempearture rise is = 40.4 degree C


## EXAMPLE 7.2 - PG NO. 153¶

In [1]:
#example 7.2
#page no. 153
#calculate peak rating of motor,equivalent continous rating based on rms torque,and on rms power.
import math
print('i) peak rating is found from the given figure as 61.64 kW')
Teq=4205.3
Peq=(4205.3*2.*3.14*60.)/60000.
print'%s %.2f %s' %('ii) Peq =',Peq,'kW')
Peq2=434.31#
print'%s %.1f %s' %('iii) The mean square power =',math.sqrt(Peq2),'kW')

i) peak rating is found from the given figure as 61.64 kW
ii) Peq = 26.41 kW
iii) The mean square power = 20.8 kW


## EXAMPLE 7.3 - PG NO.155¶

In [2]:
#Example 7.3, page 155
import math
alpha=0.9
N=.5#in hr
tou=1.5#in hr
pr=25.#in kw
px=pr*math.sqrt(((1.+alpha)/(1.-math.exp(-N/tou)))-.9)
print'%s %.2f %s %s %d %s' %("Power is=",px,"kw",'say',round(px),'kw')

Power is= 60.22 kw say 60 kw


## EXAMPLE 7.4 - PG NO.157¶

In [3]:
#example 7.4, page 157
import math
pr=100.#in kw
N=18.#in min
tou=90.#in min
R=30.#in min
tou_1=120.#in min
a=N/tou
b=R/tou_1
px=pr*math.sqrt((1-math.exp(-(a+b)))/(1-math.exp(-(a))))
print'%s %.1f %s %s %d %s' %("The power is =",px,"kw",'say',round(px),'kw')
#answers in textbook are less accurate due to approximations

The power is = 141.4 kw say 141 kw


## EXAMPLE 7.5 - PG NO.161¶

In [4]:
#Example 7.5 , page 161
import math
Tr=(50.*1000.*60.)/(2.*math.pi*960.)
#print(Tr)
Tmax=2.*Tr
Tmin=300.#in nm
Tlh=1500.+Tmin
t=10.#in sec
ws=(2.*math.pi*1000.)/60.#angular f
wr=(2.*math.pi*960.)/60.#angular f
temp=math.log((Tlh-Tmin)/(Tlh-Tmax))
j=(Tr/(ws-wr))*(t/temp)
#disp(j)
r=.9#in m
wt=j/r**2
#disp(wt)
print'%s %.2f %s' %("Weight of fly wheel is=",wt,"kg")
#Part b
Tmax=994.72
Tmin=700
TL1=300
temp=math.log((Tmax-TL1)/(Tmin-TL1))
t=(j*temp*(ws-wr))/Tr
print'%s %.2f %s' %("The estimated time is =",t,"s")
#question number in textbook is printed wrong i.e 7.5 is printed as 5.7
#answer in textbook is wrong due to approximations

Weight of fly wheel is= 2356.60 kg
The estimated time is = 8.87 s