Page 228 - Solutions Manual to accompany Electric Machinery Fundamentals


E  I  V  R R   24 0 V   109 A 0.21   217.1 V
A T A A S
The equivalent field current is
N 14 turns
I *  I  SE I  0.96 A   109 A  1.53 A
F
F
N F A 2700 turns
From Figure P8-1, this field current w ould produce an internal generated voltage E of 279 V at a speed
Ao
n of 1200 r/min. Therefore,
o
 E   217.1 V 
n   A  n o     1200 r/min  934 r/min
 E Ao   279 V 
The speed regulation is


n  n 1195 r/min 934 r/min
SR  nl fl  100%   100% 27.9%

n 934 r/min
fl
The torq ue-spe ed characteristic can best be plotted with a MATLAB program. An appropriate program is
shown below.

% M-file: p rob8_10.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, init ialize the values needed in this program.
v_t = 240; % Terminal voltage (V)
r_f = 75; % Field resistance (ohms)
r_adj = 175; % Adjustable resistance (o hms)
r_a = 0.21; % Armature + series resistance (ohms)
i_l = 0:1:110; % Line currents (A)
n_f = 2700; % Number of turns on shunt field
n_se = 14; % Number of turns on series field

% Calculate the armature current for each load.
i_a = i_l - v_t / (r_f + r_adj);

% Now calculate the internal gener ated voltage for
% each armature current.
e_a = v_t - i_a * r_a;

% Calculate the effectiv e field current for each armature
% current.
i_f = v_t / (r_f + r_adj) + (n_se / n_f) * i_a;

% Calculate the resulting internal generated volt age at
% 1200 r/min by interpolating the motor's magnetization
% curve.

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