Page 277 - Solutions Manual to accompany Electric Machinery Fundamentals

en d;

% Plot the t erminal characteristic
figure(1);
plot(i_l,v_t,'b-','LineWidth',2.0) ;
xlabel('\bf\itI_{L} \rm\bf(A)');
ylabel('\bf\itV_{T} \rm\bf(V)');
string = ['\bfTerminal Characteristic of a Differentially' ...
'Compou nded DC Generator'];
title (stri ng);
hold off;
axis([ 0 5 0 0 120]);
grid on;
The resulting terminal characteristic is shown below. Compare it to the terminal characteristics of the
cumulatively compounded dc generator in Problem 9-28 and the shunt dc generators in Problem 9-25 (d).

8-29. A cumulatively compounded dc generator is operating properly as a flat-compounded dc generator. The
machine is then shut down, and its shunt field connections are reversed.
(a) If this generator is turned in the same direction as before, will an output voltage be built up at its
terminals? Why or why not?
(b) Will the voltage build up for rotation in the opposite direction? Why or why not?

(c) For the direction of rotation in which a voltage builds up, will the generator be cumulatively or
differentially compounded?

SOLUTION
(a) The output voltage will not build up, because the residual flux now induces a voltage i n the opposite
direction, which causes a field current to flow that tends to further reduce the residual flux.
(b) If the motor rotates in the opposite direction, the voltage will build up, because the reversal in
voltage due to the change in direction of rotation causes th e voltage to produce a field current that
increases the residual flux, starting a positive feedback chain.
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