SINGLE-PHASE COMMUTATOR MOTOtfS 343

A, the compensating winding by C, and the field winding by F,
shown in Fig. 164.

Primary Secondary

A + F

A +C + F

A+F C

A C +F

C + F
C

A+F,C
A,C + F

A

A +F

Series motor.

Conductively compensated
series motor. (1)

Inductively compen sated
series motor. (2)

Inductively compensated
series motor with second-
ary excitation, or inverted
repulsion motor. (3)

Repulsion motor. (4)

Repulsion, motor with sec-
ondary excitation. (5)

Series repulsion motors.
(6) (7)

Since in all these motor types all three circuits are connected,
directly or inductively in series with each other, they all have.
the. same general characteristics as the direct-current series
motor; that is, a speed which increases with a decrease of load,
and a torque per- ampere input which increases with increase of
current, and therefore with decrease of speed, and the different
motor types differ from each other only by their commutation
as affected by the presence or absence of a.magnetic flux at the
brushes, and indirectly thereby in their efficiency as affected by
commutation losses.
In the conductively compensated series motor, by the choice
of the ratio of armature and compensating turns, overcompensa- .
tion, complete compensation, or undercompensation can be pro-
duced. In all the other types, armature and compensating
windings are in inductive relation, and the compensation there-
fore approximately complete.
A second series of motors of the same varying speed charac-
teristics results by replacing the stationary field coils by arma-
ture excitation, that is, introducing the current, either directly
or by transformer, into the armature by means of a second set
of brushes at right angles-to the main brushes. Such motors
are used to some extent abroad. They have the disadvantage of