{ "metadata": { "name": "", "signature": "sha256:ac3a59420eccf69d53afe1c1ef464227b351f7373720d9486cbc62a929140766" }, "nbformat": 3, "nbformat_minor": 0, "worksheets": [ { "cells": [ { "cell_type": "heading", "level": 1, "metadata": {}, "source": [ "CHAPTER20 : DC MACHINES " ] }, { "cell_type": "heading", "level": 2, "metadata": {}, "source": [ "Example E02 : Pg 770" ] }, { "cell_type": "code", "collapsed": false, "input": [ "# a\n", "import math \n", "Vt = 230.; # (in volts)\n", "Ia = 73.; # armature current (in amps)\n", "If = 1.6; # feild current (in amps)\n", "Ra = 0.188; # armature circuit resistance(in ohms)\n", "n = 1150.; # rated speed of the rotor(in rpm)\n", "Po = 20.*746.; # output power (in watts)\n", "\n", "Ea = Vt - (Ia*Ra); # armature voltage \n", "wm = 2.*math.pi*n/60.; # rated speed of the rotor (in rad/sec)\n", "T = Ea*Ia/wm ; # electromagnetic torque \n", "\n", "print '%s' %(\"a\")\n", "print '%s %.2f' %(\"electromagnetic torque = \",T)\n", "\n", "# b\n", "a = 4.; # no. of parallel armature paths \n", "p = 4.; # no. of poles\n", "z = 882.; # no. of armature conductors\n", "flux = Ea*60.*a/(p*z*n); # flux per pole (in Wb)\n", "\n", "print '%s' %(\"b\")\n", "print '%s %.2f' %(\"flux per pole = \",flux)\n", "\n", "# c\n", "Prot = (Ea*Ia) - Po; # rotational loss (in watt)\n", "print '%s' %(\"c\")\n", "print '%s %.2f' %(\"rotational losses = \",Prot)\n", "\n", "# d\n", "losses = Prot + (Ia**2. * Ra) + (Vt * If) ; \n", "Pi = (Ea*Ia) + (Ia**2. * Ra) + (Vt * If); # input power\n", "efficiency = 1. - (losses/Pi);\n", "\n", "print '%s' %(\"d\")\n", "print '%s %.2f' %(\"efficiency = \",efficiency)" ], "language": "python", "metadata": {}, "outputs": [ { "output_type": "stream", "stream": "stdout", "text": [ "a\n", "electromagnetic torque = 131.10\n", "b\n", "flux per pole = 0.01\n", "c\n", "rotational losses = 868.15\n", "d\n", "efficiency = 0.87\n" ] } ], "prompt_number": 1 }, { "cell_type": "heading", "level": 2, "metadata": {}, "source": [ "Example E03 : Pg 771" ] }, { "cell_type": "code", "collapsed": false, "input": [ "# final flux = 0.8*initial flux\n", "Ia1 = 73.; # initial armature current (in amps)\n", "Vt = 230.; # (in volts)\n", "Ra = 0.188; # armature circuit resistance \n", "n1 = 1150.; # initial rotor speed (in rpm)\n", "Ea1 = 216.3; # initial armature voltage \n", "\n", "Ia2 = (1./0.8)*Ia1 ; # final armature current \n", "Ea2 = Vt - (Ia2*Ra); # final armature voltage \n", "\n", "n2 = (Ea2/Ea1)*(1./0.8)*n1; # final rotor speed \n", "\n", "print '%s %.2f' %(\"final rotor speed(in rpm) = \",n2)" ], "language": "python", "metadata": {}, "outputs": [ { "output_type": "stream", "stream": "stdout", "text": [ "final rotor speed(in rpm) = 1414.54\n" ] } ], "prompt_number": 2 }, { "cell_type": "heading", "level": 2, "metadata": {}, "source": [ "Example E04 : Pg 780" ] }, { "cell_type": "code", "collapsed": false, "input": [ "# a\n", "rop = 0.4; # ratio of ON time T0 to cycle time Tp\n", "Vb =550.; # rated terminal voltage of the dc motor\n", "Ia = 30.; # current drawn by the motor (in amps)\n", "Ra = 1.; # armature circuit resistance (in ohms)\n", "ts = 5.94; # torque and speed parameter of the motor (in N-m/A)\n", " \n", "Vm = rop*Vb; # average value of the armature terminal voltage \n", "Ea = Vm - (Ia*Ra); # induced armature voltage \n", "\n", "wm = Ea/ts; # motor speed (in rad/s)\n", "print '%s' %(\"a\")\n", "print '%s %.2f' %(\"motor speed (in rad/s) = \",wm)\n", "\n", "# b\n", "deltaI = 5.; # change of armature current during the ON period \n", "La = 0.1; # armature winding inductance (in H)\n", "To = La*deltaI/(Vb - Ea); # ON time \n", "Tp = To/rop; # cycle time \n", "\n", "f = 1./Tp ; # required pulses per second \n", "print '%s' %(\"b\")\n", "print '%s %.2f' %(\"required pulses per second = \",f)\n", "\n", "# c\n", "rop = 0.7; # new ratio of ON time T0 to cycle time Tp\n", "Vm = rop*Vb; # average value of the armature terminal voltage\n", "Ea = Vm - (Ia*Ra); # induced armature voltage \n", "\n", "wm = Ea/ts; # motor speed (in rad/s)\n", "print '%s' %(\"c\")\n", "print '%s %.2f' %(\"motor speed with To/Tp equal to 0.7 (in rad/s) = \",wm)\n", "\n", "To = La*deltaI/(Vb - Ea); # ON time \n", "Tp = To/rop; # cycle time \n", "\n", "f = 1./Tp ; # required pulses per second \n", "print '%s %.2f' %(\"required pulses per second with To/Tp equal to 0.7 = \",f)" ], "language": "python", "metadata": {}, "outputs": [ { "output_type": "stream", "stream": "stdout", "text": [ "a\n", "motor speed (in rad/s) = 31.99\n", "b\n", "required pulses per second = 288.00\n", "c\n", "motor speed with To/Tp equal to 0.7 (in rad/s) = 59.76\n", "required pulses per second with To/Tp equal to 0.7 = 273.00\n" ] } ], "prompt_number": 3 } ], "metadata": {} } ] }