Page 96 - Solutions Manual to accompany Electric Machinery Fundamentals

% M-file: prob4_4e.m
% M-file to calculate and plot the terminal voltage
% of a synchronous generator as a function of load
% for power factors of 0.8 lagging, 1.0, and 0.8 leading.

% Define values for this generator
EA = 7967; % Internal gen voltage
I = 0:20.92:2092; % Current values (A)
R = 0.20; % R (ohms)
X = 2.50; % XS (ohms)

% Calculate the voltage for the lagging PF case

VP_lag = sqrt( EA^2 - (X.*I.*0.9 - R.*I.* 0.6512).^2 ) ...
- R.*I.*0.9 - X.*I.* 0.6512;
VT_lag = VP_lag .* sqrt(3);

% Calculate the voltage for the leading PF case
VP_lead = sqrt( EA^2 - (X.*I.*0.9 + R.*I.* 0.6512).^2 ) ...
- R.*I.*0.9 + X.*I.* 0.6512;
VT_lead = VP_lead .* sqrt(3);

% Calculate the voltage for the unity PF case
VP_unity = sqrt( EA^2 - (X.*I).^2 );
VT_unity = VP_unity .* sqrt(3);

% Plot the terminal voltage versus load
plot(I,abs(VT_lag)/1000,'b-','LineWidth',2.0);
hold on;
plot(I,abs(VT_unity)/1000,'k--','LineWidth',2.0);
plot(I,abs(VT_lead)/1000,'r-.','LineWidth',2.0);
title ('\bfTerminal Voltage Versus Load');
xlabel ('\bfLoad (A)');
ylabel ('\bfTerminal Voltage (kV)');
legend('0.9 PF lagging','1.0 PF','0.9 PF leading');
%axis([0 2200 0 20]);
grid on;
hold off;

The resulting plot is shown below:

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