Page 236 - Solutions Manual to accompany Electric Machinery Fundamentals

% Get the magnetization curve. Note that this curve is
% defined for a speed of 1200 r/min.
load p85_mag.dat
if_values = p85_mag(:,1);
ea_values = p85_mag(:,2);
n_0 = 1200;

% First, initialize the values needed in this program.
v_t = 120; % Terminal voltage (V)
r_a = 0.36; % Armature + field resistance (ohms)
i_a = 9:1:58; % Armature (line) currents (A)

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

% Calculate the resulting internal generated voltage at
% 1200 r/min by interpolating the motor's magnetization
% curve. Note that the field current is the same as the
% armature current for this motor.
e_a0 = interp1(if_values,ea_values,i_a,'spline');

% Calculate the motor's speed, using the known fact that
% the motor runs at 1050 r/min at a current of 58 A. We
% know that
%
% Ea2 K' phi2 n2 Eao2 n2
% ----- = ------------ = ----------
% Ea1 K' phi1 n1 Eao1 n1
%
% Ea2 Eao1
% ==> n2 = ----- ------ n1
% Ea1 Eao2
%
% where Ea0 is the internal generated voltage at 1200 r/min
% for a given field current.
%
% Speed will be calculated by reference to full load speed
% and current.
n1 = 1050; % 1050 r/min at full load
Eao1 = interp1(if_values,ea_values,58,'spline');
Ea1 = v_t - 58 * r_a;

% Get speed
Eao2 = interp1(if_values,ea_values,i_a,'spline');
n = (e_a./Ea1) .* (Eao1 ./ Eao2) * n1;

% Calculate the induced torque corresponding to each
% speed from Equations (8-55) and (8-56).
t_ind = e_a .* i_a ./ (n * 2 * pi / 60);

% Plot the torque-speed curve
figure(1);
plot(t_ind,n,'b-','LineWidth',2.0);
hold on;
xlabel('\bf\tau_{ind} (N-m)');

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