SINGLE-PHASE COMMUTATOR MOTORS 375

higher speed than the repulsion motor, that is, above synchron-
ism. With the total supply voltage impressed upon the compen-
sating winding, the transformer flux equals the commutating
flux at synchronism. At n times synchronous speed the corn-
mutating flux should be —3 of what it is at synchronism, and by

IV

impressing —^ of the supply voltage upon the compensating wind-
ing, the rest on the armature, the transformer flux is reduced
to —^ of its value, that is, made equal to the required commuta-

Tb"

ting flux at n times synchronism.

In the series repulsion motor, by thus gradually shifting the
supply voltage from the compensating winding to the armature
and thereby reducing the transformer flux, it can be maintained
equal to the required commutating flux at all speeds from syn-
chronism upward; that is, the series repulsion motor arrange-
ment permits maintaining the perfect commutation, which the
repulsion motor has near synchronism, for all higher speeds.

With regard to construction, no essential difference exists be-
tween the different motor types, and any of the types can be
operated equally well on direct current by connecting all three
circuits in series. In general, the motor types having primary
and secondary circuits, as the repulsion and the series repulsion
motors, give a greater flexibility, as they permit winding the
circuits for different voltages, that is, introducing a ratio of trans-
formation between primary and secondary circuit. Shifting one
motor element from primary to secondary, or inversely, then
gives the equivalent of a change of voltage or change of turns,
Thus a repulsion motor in which the stator is wound for a higher
voltage, that is, with more turns, than the rotor or armature,
when connecting all the circuits in series for direct-current opera-
tion, gives a direct-current motor having a greater field excita-
tion compared with the armature reaction, that is, the stronger
field which is desirable for direct-current operating but not per-
missible with alternating current.

209. In general, tthe constructve differences between motor
types are mainly differences in connection of the three circuits.
For instacne, let F = field circuit, A = armature circuit, C =
compensating circuit, T = supply transformer, R = resistance
used in starting and at very low speeds. Connecting, in.Fig. 181,
the armature, A, between field F and compensating winding, C.

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