MNGLE-PHAtiE COMMUTATOR MOTORS 373
and therefore the compensation fails, and with the high ratio of
armature turns to field turns, without compensation, the field
distortion is altogether too large to give satisfactory commutation,
except in small motors.
The inductively compensated series motor with secondary ex-
citation, or inverted repulsion motor, 3, takes an intermediary
position between the series motors and the repulsion motors; it
is a series motor in so far as the armature is in the main supply
circuit, but magnetically it has repulsion-motor characteristics,
that is, contains a lagging quadrature flux. As the field exci-
tation consumes considerable voltage, when supplied from the
compensating winding as secondary circuit, considerable voltage
must be generated in this winding, thus giving a corresponding
transformer flux. With increasing speed and therewith decreas-
ing current, the voltage consumed by the field coils decreases,
and therewith the transformer flux which generates this voltage.
Therefore, the inverted repulsion motor contains a transformer
flux which has approximately the intensity and the phase re-
quired for commutation; it lags behind the main flux, but less
than 90°, thus contains a component in phase with the main
flux, as reversing flux, and decreases with increase of speed.
Therefore, the commutation of the inverted repulsion motor is
very good, far superior to the ordinary series motor, and it can
be operated without resistance leads; it has, however, the serious
objection of a poor power-factor, resulting from the lead of the
field flux against the armature current, due to the secondary ex-
citation, as discussed in V. To make such a motor satisfactory
in power-factor requires a non-inductive shunt across the field,
and thereby a waste of power. For this reason it has not come
into commercial use.
B. Repulsion Motors
208. Repulsion motors are characterized by a lagging quadra-
ture flux, which transfers the power from the compensating wind-
ing to the armature. At standstill, and at very low speeds, re-
pulsion motors and series motors are equally unsatisfactory in
commutation; while, however, in the series motors the commu-
tation remains bad (except when using commutating devices),
in the repulsion motors with increasing speed the commutation
rapidly improves, and becomes perfect near synchronism. As
the result hereof, under average conditions a much inferior com-