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ELECTRICAL APPARATUS

exciter is a synchronous motor, and the synchronous-induction
generator produces power in the stator and in the rotor circuit.
In this case, the power is produced by the generated e.m.f., E
(e.m.f. of mutual induction, or of the rotating magnetic field),
of the induction machine, and energy flows outward in both
circuits, in the stator into the receiving circuit, of terminal
voltage, Eij in the rotor against the impressed e.m.f. of the
synchronous motor exciter, EQ. The voltage of one receiving-
circuit, the stator, therefore, is controlled by a voltage impressed
upon another receiving circuit, the rotor, and this results in some
interesting effects in voltage regulation.
Assume the voltage, EQ, impressed upon the rotor circuit as
the nominal generated e.m.f. of the synchronous-motor exciter,
that is, the field corresponding to the exciter field excitation,
and assume the field excitation of the exciter, and therewith
the voltage, EQ, to be maintained constant.
Reducing all the voltages to the stator circuit by the ratio of
their effective turns and the ratio of their respective frequencies,
the same e.m.f., E, is generated in the rotor circuit as in the
stator circuit of the induction machine.
At no-load, neglecting the exciting current of the induction
machine, that is, with no current, we have EQ = E = EI.
If a load is put on the stator circuit by taking a current, I,
from the same, the terminal voltage, EI, drops below the gene-
rated e.m.f., Ej by the drop of voltage in the impedance, Z\, of
the stator circuit. Corresponding to the stator current, /i, a
current, I2, then exists in the rotor circuit, giving the same
ampere-turns as Ji, in opposite direction, and so neutralizing the
m.m.f. of the stator (as in any transformer). This current, Jo,
exists in the synchronous motor, and the synchronous motor
e.m.f., EQ, accordingly drops below the generated e.rn.L, E, of
the rotor, or, since EQ is maintained constant, E rises above EQ
with increasing load, by the drop of voltage in the rotor impedance,
Z2, and the synchronous impedance, Z0, of the exciter.
That is, the stator terminal voltage, EI, drops with increasing
load, by the stator impedance drop, and rises with increasing
load by the rotor and exciter impedance drop, since the latter
causes the generated e.m.f., E, to rise.
If then the impedance drop in the rotor circuit is greater than
that in the stator, with increasing load the terminal voltage,
EI, of the machine rises, that is, the machine automatically