Page 90 - Solutions Manual to accompany Electric Machinery Fundamentals

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S  3V I   A  3 7967 V 2092 A  50 MVA
A MATLAB program that plots this capability diagram is shown below:

% M-file: prob4_2.m
% M-file to display a capability curve for a
% synchronous generator.

% Calculate the waveforms for times from 0 to 1/30 s
Q = -76.17;
DE = 110;
S = 50;

% Get points for stator current limit
theta = -95:1:95; % Angle in degrees
rad = theta * pi / 180; % Angle in radians
s_curve = S .* ( cos(rad) + j*sin(rad) );

% Get points for rotor current limit
orig = j*Q;
theta = 65:1:115; % Angle in degrees
rad = theta * pi / 180; % Angle in radians
r_curve = orig + DE .* ( cos(rad) + j*sin(rad) );

% Plot the capability diagram
figure(1);
plot(real(s_curve),imag(s_curve),'b','LineWidth',2.0);
hold on;
plot(real(r_curve),imag(r_curve),'r--','LineWidth',2.0);

% Add x and y axes
plot( [-75 75],[0 0],'k');
plot( [0,0],[-75 75],'k');

% Set titles and axes
title ('\bfSynchronous Generator Capability Diagram');
xlabel('\bfPower (MW)');
ylabel('\bfReactive Power (MVAR)');
axis( [ -75 75 -75 75] );
axis square;
hold off;
The resulting capability diagram is shown below:

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