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{
"metadata": {
"name": "",
"signature": "sha256:34f21e34d56021d11e412854716405b885521e02b7e263afa0b62d127f14da0d"
},
"nbformat": 3,
"nbformat_minor": 0,
"worksheets": [
{
"cells": [
{
"cell_type": "heading",
"level": 1,
"metadata": {},
"source": [
"Chapter 19: Circuit Breakers"
]
},
{
"cell_type": "heading",
"level": 3,
"metadata": {},
"source": [
"Example 19.1, Page Number: 483"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"from __future__ import division\n",
"\n",
"#Variable declaration:\n",
"I = 1500 #rated current of circuit breaker(A)\n",
"MVA = 1000 #MVA rating of CB\n",
"V = 33 #voltage rating of circuit breaker(kV)\n",
"\n",
"\n",
"\n",
"#Calculation:\n",
"Is = MVA*10**6/(3**0.5*33*1000) #Rated symmetrical breaking current(A,rms)\n",
"Im = 2.55*Is #Rated making current(A,peak)\n",
"\n",
"\n",
"#Result:\n",
"print \"(i) Rated normal current is\",I,\"A\"\n",
"print \"(ii) Breaking capacity is\",MVA,\"MVA\"\n",
"print \"(iii) Rated symmetrical breaking current is\",round(Is),\"A (peak)\"\n",
"print \"(iv) Rated making current is\",round(Im),\"A (peak)\"\n",
"print \"(v) Short-time rating is\",round(Is),\"for 3 seconds\"\n",
"print \"(vi) Rated service voltage is\",V,\"kV (r.m.s)\""
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"(i) Rated normal current is 1500 A\n",
"(ii) Breaking capacity is 1000 MVA\n",
"(iii) Rated symmetrical breaking current is 17495.0 A (peak)\n",
"(iv) Rated making current is 44613.0 A (peak)\n",
"(v) Short-time rating is 17495.0 for 3 seconds\n",
"(vi) Rated service voltage is 33 kV (r.m.s)\n"
]
}
],
"prompt_number": 1
},
{
"cell_type": "heading",
"level": 3,
"metadata": {},
"source": [
"Example 19.2, Page Number: 484"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"from __future__ import division\n",
"import math\n",
"\n",
"#Variable declaration:\n",
"f = 50 #supply frequency(Hz)\n",
"V = 11 #voltage rating of generator(V)\n",
"C = 0.01 #distributed capacitance upto ckt breaker b/w phase and neutral(uF)\n",
"XL = 5 #reactance of neatral to earth(ohm)\n",
"\n",
"\n",
"#Calculation:\n",
"L = round(XL/(2*math.pi*f),4) #Inductance per phase(H)\n",
"Emax = round(2**0.5*V/3**0.5,2) #Maximum value of recovery voltage (phase to neutral)(V\n",
"E = 2*Emax #Peak re-striking voltage(kV)\n",
"fn = 1/(2*3.14*(L*C*10**-6)**0.5) #frequency of oscillations(Hz)\n",
"\n",
"#Since peak re-striking voltage occurs at a time t given by\n",
"t = 1/(2*fn) #s\n",
"r = E/t #kV/sec\n",
"\n",
"\n",
"\n",
"#Result:\n",
"print \"(i) Peak re-striking voltage is\",round(E,2),\"kV\"\n",
"print \"(ii) Frequency of oscillations is\",round(fn),\"Hz\"\n",
"print \"(iii)The average rate of rise of re-striking voltage\"\n",
"print \" upto the first peak is\",math.floor(r/1000),\"*10**3 kV/sec\""
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"(i) Peak re-striking voltage is 17.96 kV\n",
"(ii) Frequency of oscillations is 12628.0 Hz\n",
"(iii)The average rate of rise of re-striking voltage\n",
" upto the first peak is 453.0 *10**3 kV/sec\n"
]
}
],
"prompt_number": 1
},
{
"cell_type": "heading",
"level": 3,
"metadata": {},
"source": [
"Example 19.3, Page Number: 484"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"#Variable delaration:\n",
"t = 50*10**-6 #time to reach the peak re-striking voltage(s)\n",
"Vp = 100 #the peak re-striking voltage(kV)\n",
"\n",
"\n",
"#Calculation:\n",
"R = Vp/t #Average RRRV(kV/sec)\n",
"fn = 1/(2*t) #Natural frequency of oscillations(Hz)\n",
"\n",
"\n",
"#Result:\n",
"print \"Average RRRV is\",R/10**6,\"* 10**6 kV/sec\"\n",
"print \"Natural frequency of oscillations is\",fn,\"Hz\""
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Average RRRV is 2.0 * 10**6 kV/sec\n",
"Natural frequency of oscillations is 10000.0 Hz\n"
]
}
],
"prompt_number": 3
},
{
"cell_type": "heading",
"level": 3,
"metadata": {},
"source": [
"Example 19.4, Page Number: 485"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"from __future__ import division\n",
"\n",
"#Variable declaration:\n",
"Im = 11 #magnetising current of transformer(A)\n",
"Ic = 7 #chopped instantaneous value of current(A)\n",
"L = 35.2 #inductance (H)\n",
"C = 0.0023 #capacitance(uF)\n",
"\n",
"\n",
"#Result:\n",
"e = Ic*(L/(C*10**-6))**0.5 #Voltage across breaker contacts at chopping(V)\n",
"\n",
"\n",
"#Result:\n",
"print \"Voltage across breaker contacts at chopping is\",round(e/1000),\"kV\""
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Voltage across breaker contacts at chopping is 866.0 kV\n"
]
}
],
"prompt_number": 10
}
],
"metadata": {}
}
]
}
|
