Page 239 - Solutions Manual to accompany Electric Machinery Fundamentals

The power converted from electrical to mechanical form is
P conv  E I  AA 228.6 V 76 A  17,370 W

Since the rotational losses are ignored, this is also the output power of the motor. The induced torque is

P 17,370 W

 ind   m   899 r/min    2 rad      1 min 60 s    185 N m
conv
1 r 
If I = 10 1.3 A, then
A
E  A V  T I A R  A R S   240 V   101.3 A 0.09   0.06    224.8 V


The magnetomotive force is F  NI  A 33 turns 101.3 A   3343 A turns , which produces a voltage
E of 252 V at n o = 900 r/min. Therefore the speed of the motor at these conditions is
Ao
E 224.8 V
n  A n    900 r/min  803 r/min
E Ao o 252 V

The power converted from electrical to mechanical form is
P conv  E I  AA 224.8 V 101.3 A   22,770 W

Since the rotational losses are ignored, this is also the output power of the motor. The induced torque is
P 22,770 W

  conv   271 N m
ind
 m  803 r/min    2 rad      1 min 60 s  
1 r 
(b) A M T
A LAB program to plot the torque-speed characteristic of this motor is shown below:

% M-file: series_ts_curve.m
% M-file to create a plot of the torque-speed curve of the
% the series dc motor in Problem 8-14.

% Get the magnetization curve. Note that this curve is
% defined for a speed of 900 r/min.
l oad prob8_14_mag.dat
mmf_values = prob8_14_mag(:,1);
ea_values = prob8_14_mag(:,2);
n_0 = 900;

% First, initialize the values ne eded in this program.
v_t = 240; % Termin al voltage (V)
r _a = 0.15; % Armature + field resistance (ohms)
i_a = 15:1:76; % Armature (line) currents (A)
n_s = 33; % Number of series turn s on fiel d

% Calculate the MMF for each load
f = n_s * i_a;

% Calculate the internal generate v oltage e_a.
e_a = v_t - i_a * r_a;

% Calculate the resulting internal generated vol tage at
% 900 r/min by interpol ating the motor's magneti zation
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