REVIEW 461
verter slightly changes with the load, by the slip of the induction
machine.
Induction Motor with Low-frequency Synchronous Exciter.—47.
The synchronous exciter in this case is of small capacity, and
gives speed control and power-factor compensation.
InductionGenerator with Low-frequency Exciter.—110,121. Syn-
chronous induction generator. Stanley induction generator. In
this case, the low-frequency exciter may be a synchronous or a
commutating machine or any other source of low frequency.
The phase rotation of the exciter may be in the reverse direc-
tion of the main machine, or in the same direction. In the first
case, the couple may be considered as a frequency converter
driven backward at many times synchronous speed, the exciter
is motor, and the generated frequency less than the speed. In
the case of the same phase rotation of exciter and main machine,
the generated frequency is higher than the speed, and the
exciter also is generator. This synchronous induction generator
has peculiar regulation characteristics, as the armature reaction
of non-inductive load is absent.
3. A Synchronous Commutating Machine.—112. The couple
is synchronous, and called motor converter. It has the advantage
of lower frequency commutation, and permits phase control by
the internal reactance of the induction machine. It has higher
efficiency and smaller size than a motor-generator set, but is
larger and less efficient than the synchronous converter, and
therefore has not been able to compete with the latter.
4. A direct-current commutating machine, as exciter, 41. This
converts the induction machine into a synchronous machine
(Danielson motor). A good induction motor gives a poor syn-
chronous motor, but a bad induction motor, of very low power-
factor, gives a good synchronous motor, of good power-factor,
etc.
5. An alternating-current commutating machine, as low-fre-
quency exciter, 52. The couple then is asynchronous. This
permits a wide range of power-factor and speed control as motor.
As generator it is one form of the Stanley induction generator
discussed under (2).
6. A Condenser.—This permits power-factor compensation,
55, and speed control, 11. The power-factor compensation
gives good values with very bad induction motors, of low power-
factor, but is uneconomical with good motors, Speed control