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"worksheets": [
{
"cells": [
{
"cell_type": "heading",
"level": 1,
"metadata": {},
"source": [
"Chapter 7: DC Generators"
]
},
{
"cell_type": "heading",
"level": 3,
"metadata": {},
"source": [
"Example 7.1: Page 114:"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"\n",
"from __future__ import division\n",
"import math\n",
"\n",
"# given data:\n",
"p=8; # number of poles\n",
"a1=p; # in lap winding\n",
"a2=2; # in wave winding\n",
"fi=15*10**-3;# in wb\n",
"N=500;# rev/min\n",
"Z=800;# number of conductors on armature\n",
"\n",
"#calculations:\n",
"emf1=(fi*Z*N*p)/(60*a1)# when the armature is lap wound\n",
"emf2=(fi*Z*N*p)/(60*a2)# when the armature is wave wound\n",
"\n",
"#Results\n",
"print \"when the armature is lap wound, emf(V) = \",emf1\n",
"print \"when the armature is wave wound, emf(V) = \",emf2"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"when the armature is lap wound, emf(V) = 100.0\n",
"when the armature is wave wound, emf(V) = 400.0\n"
]
}
],
"prompt_number": 1
},
{
"cell_type": "heading",
"level": 3,
"metadata": {},
"source": [
"Example 7.2: Page 119:"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"\n",
"from __future__ import division\n",
"import math\n",
"\n",
"#given data:\n",
"Vt=200# terminal voltage in volts\n",
"Rsh=100;#shunt fieldresistance in ohm\n",
"Ra=0.1;# armature resistance in ohm\n",
"l=60;# number of lamps\n",
"w=40 # in watt\n",
"N=4; # number of poles\n",
"\n",
"#calculations:\n",
"total_l=l*w# in watt\n",
"Il=total_l/Vt# load current\n",
"Ish=Vt/Rsh# shunt field current\n",
"Ia=Il+Ish;\n",
"I=Ia/N;\n",
"Va=Ia*Ra#armature voltage drop \n",
"Vb=1+1;# brush contact drop for 2 pair of poles\n",
"E=Vt+Va+Vb;\n",
"\n",
"#Results\n",
"print \"(a)armature current,Ia(A) = \",Ia\n",
"print \"(b)current per path in a armature,I(A) =\",I\n",
"print \"(c)emf,E(Volts) = \",E"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"(a)armature current,Ia(A) = 14.0\n",
"(b)current per path in a armature,I(A) = 3.5\n",
"(c)emf,E(Volts) = 203.4\n"
]
}
],
"prompt_number": 2
},
{
"cell_type": "heading",
"level": 3,
"metadata": {},
"source": [
"Example 7.3: Page 119:"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"\n",
"from __future__ import division\n",
"import math\n",
"\n",
"# given data:\n",
"W=10 # output of the generator in k-w\n",
"V=250;# voltage in volts\n",
"R=0.07;# in ohm\n",
"Rsh=63.2;# shunt resistance in ohm\n",
"Ra=0.05;# armature resistance in ohm\n",
"Vb=2;# brush contact drop\n",
"\n",
"#calculations:\n",
"Il=(W*1000)/V# load current in A\n",
"Vf=Il*R# voltage drop in feeder\n",
"Vt=V+Vf;\n",
"Ish=Vt/Rsh;\n",
"Ia=Il+Ish;\n",
"Vd=Ia*Ra# voltage drop in the armature\n",
"E=Vt+Vd+Vb;\n",
"#Results\n",
"print \"(a)terminal voltage,Vt(V) = \",Vt \n",
"print \"(b)emf,E(V) = \", E"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"(a)terminal voltage,Vt(V) = 252.8\n",
"(b)emf,E(V) = 257.0\n"
]
}
],
"prompt_number": 3
},
{
"cell_type": "heading",
"level": 3,
"metadata": {},
"source": [
"Example 7.4: page 129:"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"\n",
"from __future__ import division\n",
"import math\n",
"\n",
"# given data:\n",
"W=20000# in watt\n",
"V=200;# in volts\n",
"R=0.08;# in ohm\n",
"Rs=0.02;# series field resistance in ohm\n",
"Rsh=42;# shunt ield resistance in ohm\n",
"Ra=0.04;# armature resistance in ohm\n",
"iron_losses=309.5;# iron and friction losses\n",
"\n",
"#calculations:\n",
"I=W/V;# in A\n",
"Vf=I*R;\n",
"Vs=I*Rs;\n",
"V1=Vf+Vs;# voltage drop of feeder and series field\n",
"Vg=V+V1;\n",
"Ish=Vg/Rsh# shunt field current\n",
"Ia=I+Ish;\n",
"Vd=Ia*Ra;\n",
"emf=Vg+Vd;\n",
"Ed=emf*Ia# in watt\n",
"copper_losses=Ed-W;\n",
"mech_in=W+copper_losses+iron_losses;\n",
"Bhp=mech_in/735.5;\n",
"efficiency=(W/mech_in)*100;\n",
"\n",
"#Results\n",
"print \"(a)terminal voltage,Vg(V) = \",Vg\n",
"print \"(b)emf(V) =\",emf\n",
"print \"(c)copper losses(Watt) = \",copper_losses\n",
"print \"(d)bhp metric of the primemover,Bhp = \",Bhp \n",
"print \"(e)efficiency(%) = \",round(efficiency,1)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"(a)terminal voltage,Vg(V) = 210.0\n",
"(b)emf(V) = 214.2\n",
"(c)copper losses(Watt) = 2491.0\n",
"(d)bhp metric of the primemover,Bhp = 31.0\n",
"(e)efficiency(%) = 87.7\n"
]
}
],
"prompt_number": 4
},
{
"cell_type": "heading",
"level": 3,
"metadata": {},
"source": [
"Example 7.5: page 129:"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"\n",
"from __future__ import division\n",
"import math\n",
"\n",
"# given data:\n",
"n=3 # number of motors\n",
"n1=4 # number of parallel path in winding\n",
"i=30;#current in A\n",
"Bhp=65# in hp\n",
"Rsh=44;# shunt field resistance\n",
"Ra=0.08;# armature resistance in ohm\n",
"V=440;# voltage in V\n",
"Vb=2 # we know , brush contact drops\n",
"\n",
"#calculations:\n",
"I=i*n# current taken by three motors\n",
"Ish=V/Rsh# shunt field current\n",
"Ia=I+Ish;\n",
"I1=Ia/n1# current in each path\n",
"Va=Ia*Ra;# armature drop\n",
"E=V+Va+Vb;\n",
"E_power=E*Ia;\n",
"W=V*I# in watt\n",
"M_power=Bhp*746# assume Bhp=746 W\n",
"Copper_losses=E_power-W;\n",
"S_loses=M_power-E_power;\n",
"eta_e=(W/E_power)*100;\n",
"eta_c=(W/M_power)*100;\n",
"eta_m=(E_power/M_power)*100;\n",
"\n",
"#Results\n",
"print \"(a)total armature current,Ia(A) =\",Ia\n",
"print \"(b)current in each path,I1(A) = \",I1\n",
"print \"(c)emf,E(V) = \",E # answer is wrong in a book \n",
"print \"(d)electrical power developed in watt = \",E_power # answer is wrong in a book \n",
"print \"(e)copper losses (W) = \",Copper_losses\n",
"print \"(f)stray losses(W) = \",S_loses\n",
"print \"(g1)electrical efficiency,eta_e(%) = \",eta_e\n",
"print \"(g2)commercial efficiency,eta_c(%) = \",round(eta_c,2)\n",
"print \"(g3)mechanical efficiency,eta_m(%) = \",round(eta_m,1)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"(a)total armature current,Ia(A) = 100.0\n",
"(b)current in each path,I1(A) = 25.0\n",
"(c)emf,E(V) = 450.0\n",
"(d)electrical power developed in watt = 45000.0\n",
"(e)copper losses (W) = 5400.0\n",
"(f)stray losses(W) = 3490.0\n",
"(g1)electrical efficiency,eta_e(%) = 88.0\n",
"(g2)commercial efficiency,eta_c(%) = 81.67\n",
"(g3)mechanical efficiency,eta_m(%) = 92.8\n"
]
}
],
"prompt_number": 5
}
],
"metadata": {}
}
]
}