Page 231 - Solutions Manual to accompany Electric Machinery Fundamentals

From Figure P8-1, this field current would produce an internal generated voltage E of 229 V at a speed
Ao
n of 1200 r/min. Therefore,
o
 E   235.8 V 
n   A  n o     1200 r/min  1236 r/min
 E Ao   229 V 

At I = 40A, the internal generated voltage E is
A A
E  I  V  R R   240 V   40 A 0.21   231.6 V
A T A A S
The equivalent field current is
N 14 turns
I *  I  SE I  0.96 A   40 A  0.753 A
F
F
N F A 2700 turns
From Figure P8-1, this field current would produce an internal generated voltage E of 214 V at a speed
Ao
n o of 1200 r/min. Therefore,
 E   231.6 V 
n   A  n o     1200 r/min  1299 r/min
 E Ao   214 V 

At I A = 60A, the internal generated voltage E is
A

E  A T I A  V  A R S R   240 V   60 A 0.21   227.4 V
The equivalent field current is
N 14 turns
I *  I  SE I  0.96 A   60 A  0.649 A
F
F
N F A 2700 turns
From Figure P8-1, this field current would produce an internal generated voltage E of 196 V at a speed
Ao
n o of 1200 r/min. Therefore,
 E   227.4 V 
n   A  n o     1200 r/min  1392 r/min
 E Ao   196 V 

(c) The torque-speed characteristic can best be plotted with a MATLAB program. An appropriate
program is shown below.

% M-file: prob8_12.m
% M-file to create a plot of the torque-speed curve of the
% a cumulatively compounded dc motor without
% armature reaction.

% Get the magnetization curve. Note that this curve is
% defined for a speed of 1200 r/min.
load p81_mag.dat
if_values = p81_mag(:,1);
ea_values = p81_mag(:,2);
n_0 = 1200;

% First, initialize the values needed in this program.
v_t = 240; % Terminal voltage (V)
r_f = 75; % Field resistance (ohms)
r_adj = 175; % Adjustable resistance (ohms)
r_a = 0.21; % Armature + series resistance (ohms)
i_l = 0:1:110; % Line currents (A)
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