# Chapter16 Faults and Protection¶

## Example16.1,Pg.no.57¶

In [8]:
import math
from math import sqrt
V=415.0      #AC input voltage
Vf=2.53      #voltage safety factor
PIV=2*sqrt(2)*V*Vf        #peak inverse voltage of the device
PIV=round(PIV,2)
print 'peak inverse voltage of the device=PIV=',PIV,'Volts'

peak inverse voltage of the device=PIV= 2969.71 Volts


## Example16.2,Pg.no.57¶

In [9]:
import math
from math import sqrt
V=415.0        #AC input voltage in volts
PIV=1350.0     #peak inverse voltage of the device in volts
Vf=PIV/(sqrt(2)*V)         #voltage safety factor of the device
Vf=round(Vf,2)
print 'voltage safety factor of the device=Vf=',Vf

voltage safety factor of the device=Vf= 2.3


## Example16.3,Pg.no.58¶

In [10]:
import math
P=100.0           #input power in KVA
Xt=0.04           #limiting ac reactance value
Fov=2.0           #current ovarload factor
Pc=Xt*P*Fov       #choke power of the converter in KVA
print 'choke power of the converter=Pc=',Pc,'KVA'

choke power of the converter=Pc= 8.0 KVA


## Example16.4,Pg.no.58¶

In [11]:
import math
from math import sqrt
Ls=0.1              #stray inductance in the circui t in milli Henry
L=2*Ls              #inductance required for the snubber ckt for protection in mH
Im=250.0            #mean value of current in amp
C=2.5*Im            #capacitance required for the snubber ckt in nano Farads
print 'capacitance in snubber circuit=C=',C,'nanofarads'
R=2*100*sqrt(L/C)   #resistance in snubber circ uit in Kilo Ohms
R=round(R,2)
print 'Resistance in snubber circuit=R=',R,'Kilo Ohms'
Pdif=1*30.0         #permissible dv/dt of the circuit
print 'Permissible dv/dt of the circuit=',Pdif,'MV/s'

capacitance in snubber circuit=C= 625.0 nanofarads
Resistance in snubber circuit=R= 3.58 Kilo Ohms
Permissible dv/dt of the circuit= 30.0 MV/s


## Example16.5,Pg.no.59¶

In [12]:
import math
V=240.0           #dc input voltage in volts
Vh=25.0           #each selenium plate handling voltage in volts
N=V/Vh            #number of plates in series in the circuit
print 'number of plates in series in the circuit=N=',N
print 'So,we will use 10 plates in the circuit'

number of plates in series in the circuit=N= 9.6
So,we will use 10 plates in the circuit


## Example16.6,Pg.no.59¶

In [13]:
import math
V=230.0            #ac input voltage in volts
Vh=30.0            #each selenium plate handling voltage in volts
N=(V/Vh)+1      #number of plates in series in each direction in the ckt
N=round(N,0)
print 'number of plates in series in each direction =N=',N
Nt=2*N             #total number of plates in series in the circuit
Nt=round(Nt,0)
print 'total number of plates in series in both directions=Nt=',Nt

number of plates in series in each direction =N= 9.0
total number of plates in series in both directions=Nt= 18.0


## Example16.7,Pg.no.59¶

In [14]:
import math
V=415.0       #ac input voltage in volts
Vdc=440.0     #supplied voltage to dc motor in volts
Vh=30.0       #each selenium plate handling voltage in volts
N=Vdc/Vh      #number of plates in series in each direction in the ckt
N=15.0
print 'number of plates in each branch=N=',N
Nt=3*N        #total number of plates in series in the circuit
Nt=round(Nt,0)
print 'total number of plates=Nt=',Nt
Ipa=136.0     #peak armature current in amperes
T=30.0        #time constant in milliseconds
R=0.175       #Armature resistance in Ohms
L=T*R         #Armature circuit Inductance in milliHenry
L=round(L,2)
print 'Armature circuit inductance=L=',L,'mH'
Es=0.5*L*Ipa**2*10**-3            #Energy stored in armature circuit in wattsec
Es=round(Es,2)
print 'Energy stored in armature circuit=Es=',Es,'wattsec'
Ed=Es/N       #Energy dissipated per plate in wattsec
Ed=round(Ed,2)
print 'Energy dissipated per plate=Ed=',Ed,'wattsec'

number of plates in each branch=N= 15.0
total number of plates=Nt= 45.0
Armature circuit inductance=L= 5.25 mH
Energy stored in armature circuit=Es= 48.55 wattsec
Energy dissipated per plate=Ed= 3.24 wattsec