SYNCHRONOUS INDUCTION GENERATOR 207
overcompounds, at constant-exciter field excitation, and if the
stator and the rotor impedance drops are equal, the machine
compounds for constant voltage.
In such a machine, by properly choosing the stator and rotor
impedances, automatic rise, decrease or constancy of the terminal
voltage with the load can be produced.
This, however, applies only to non-inductive load. If the
current, I, differs in phase from the generated e.m.f., E} the
corresponding current, Is, also differs; but a lagging component
of Ii corresponds to a leading component in I2, since the stator
circuit slips behind, the rotor circuit is driven ahead of the
rotating magnetic field, and inversely, a leading component of
/i gives a lagging component of /2. The reactance voltage of
the lagging current in one circuit is opposite to the reactance
voltage of the leading current in the other circuit, therefore
does not neutralize it, but adds, that is, instead of compounding,
regulates in the wrong direction.
123. The automatic compounding of the synchronous induc-
tion generator with low-frequency synchronous-motor excitation
so fails if the load is not non-inductive.
Let:
Zi — ri + jxi = stator self-inductive impedance,
Z2 = r2 + jx% = rotor self-inductive impedance, reduced to the
stator circuit by the ratio of the effective turns, t = 2, and the
n\
ratio of frequencies, a = /;
ZQ — TO + j#o = synchronous impedance of the synchronous-
motor exciter;
Ei = terminal voltage of the stator, chosen as real axis, = 61;
EQ = nominal generated e.m.f. of the synchronous-motor
exciter, reduced to the stator circuit;
E = generated e.m.f. of the synchronous-induction generator
stator circuit, or the rotor circuit reduced to the stator circuit.
The actual e.m.f. generated in the rotor circuit then is Ef =
taE, and the actual nominal generated e.m.f. of the synchronous
exciter is 25"o = taEv.
Let;
/! = i — fa = current in the stator circuit, or the output
current of the machine,