In [1]:

```
from __future__ import division
#Variable declaration:
I = 1500 #rated current of circuit breaker(A)
MVA = 1000 #MVA rating of CB
V = 33 #voltage rating of circuit breaker(kV)
#Calculation:
Is = MVA*10**6/(3**0.5*33*1000) #Rated symmetrical breaking current(A,rms)
Im = 2.55*Is #Rated making current(A,peak)
#Result:
print "(i) Rated normal current is",I,"A"
print "(ii) Breaking capacity is",MVA,"MVA"
print "(iii) Rated symmetrical breaking current is",round(Is),"A (peak)"
print "(iv) Rated making current is",round(Im),"A (peak)"
print "(v) Short-time rating is",round(Is),"for 3 seconds"
print "(vi) Rated service voltage is",V,"kV (r.m.s)"
```

In [1]:

```
from __future__ import division
import math
#Variable declaration:
f = 50 #supply frequency(Hz)
V = 11 #voltage rating of generator(V)
C = 0.01 #distributed capacitance upto ckt breaker b/w phase and neutral(uF)
XL = 5 #reactance of neatral to earth(ohm)
#Calculation:
L = round(XL/(2*math.pi*f),4) #Inductance per phase(H)
Emax = round(2**0.5*V/3**0.5,2) #Maximum value of recovery voltage (phase to neutral)(V
E = 2*Emax #Peak re-striking voltage(kV)
fn = 1/(2*3.14*(L*C*10**-6)**0.5) #frequency of oscillations(Hz)
#Since peak re-striking voltage occurs at a time t given by
t = 1/(2*fn) #s
r = E/t #kV/sec
#Result:
print "(i) Peak re-striking voltage is",round(E,2),"kV"
print "(ii) Frequency of oscillations is",round(fn),"Hz"
print "(iii)The average rate of rise of re-striking voltage"
print " upto the first peak is",math.floor(r/1000),"*10**3 kV/sec"
```

In [3]:

```
#Variable delaration:
t = 50*10**-6 #time to reach the peak re-striking voltage(s)
Vp = 100 #the peak re-striking voltage(kV)
#Calculation:
R = Vp/t #Average RRRV(kV/sec)
fn = 1/(2*t) #Natural frequency of oscillations(Hz)
#Result:
print "Average RRRV is",R/10**6,"* 10**6 kV/sec"
print "Natural frequency of oscillations is",fn,"Hz"
```

In [10]:

```
from __future__ import division
#Variable declaration:
Im = 11 #magnetising current of transformer(A)
Ic = 7 #chopped instantaneous value of current(A)
L = 35.2 #inductance (H)
C = 0.0023 #capacitance(uF)
#Result:
e = Ic*(L/(C*10**-6))**0.5 #Voltage across breaker contacts at chopping(V)
#Result:
print "Voltage across breaker contacts at chopping is",round(e/1000),"kV"
```