*'!

SYNCHRONOUS INDUCTION GENERATOR 197

frequency, /i, and the speed is /0 = /2 - /i. In this case, the
machine consumes mechanical power, since it is driven against
the torque given by it as induction motor, and we have:

Electric power input -f- mechanical power input ~ electric
power output = fl -r- /0 -f- /2.

That is, the three powers, primary electric, secondary electric,
and mechanical, are proportional to their respective frequencies.

As stated, the secondary frequency, /2, is also produced by p

driving the machine above synchronism, /i,. that is, with a
negative slip, /2, or at a speed, /0 = /i + /2. In this case, the
machine is* induction generator, that is, the primary circuit
generates electric power at frequency /i, the secondary circuit
generates electric power at frequency /2, and the machine con-
sumes mechanical power, arid the three powers again are propor-
tional to their respective frequencies:

Primary electric output -4- secondary electric output -f-
mechanical input = /i -*- /2 -=- /0..

Since in this case of oversynchronous rotation, both electric
circuits of the machine generate, it can not be called a frequency
converter, but is an electric generator, converting mechanical
power into electric power at two different frequencies, /i and
/2, and so is called a synchronous-induction machine, since
the sum of the two frequencies generated by it equals the fre-
quency of rotation or speed—that is, the machine revolves in
synchronism with the sum of the two frequencies generated
by it.

It is obvious that like all induction machines, this synchro-
nous-induction generator requires a reactive lagging current for
excitation, which has to be supplied to it by some outside source,
as a synchronous machine, etc.

That is, an induction machine driven at speed, /o, when sup-
plied with reactive exciting current of the proper frequency,
generates electric power in the stator as well as in the rotor, at
the two respective frequencies, /i ancl/2, which are such that their
sum is in synchronism with the speed, that is:

fi +/2 =/o;
otherwise the frequencies, fi and /2, are entirely independent.
That is, connecting the stator to a circuit of frequency, /i, the
rotor generates frequency,/2 = /o — /i, or connecting the rotor to