360

ELECTRICAL APPARATUS

is impressed upon the commutating winding, C, which produces
the quadrature field, and in the direct repulsion motor, 4, the
quadrature field increases with the speed, as the voltage consumed
by the main field F decreases, and that left for the compensating
winding, C, thus increases with the speed, while to give proper
commutating flux it should decrease with the square of the speed.
It thus follows that the commutation of the repulsion motors
improves with increase of speed, up to that speed where the
quadrature field is just right for commutating field—which is
about at synchronism—but above this speed the commutation
rapily becomes poorer, due to the quadrature field being far in
excess of that required for commutating.
In the series repulsion motors, 6 and 7, a quadrature field also
exists, just as in the repulsion motors, but this quadrature field
depends upon that part of the total voltage which is impressed
upon -the commutating winding, C, and thus can be varied by
varying the distribution of supply voltage between the two cir-
cuits; hence, in this type of motor, the commutating flux can be
maintained through all (higher) speeds by impressing the total
voltage upon the compensating circuit and short-circuiting the
armature circuit for all speeds up to that at which the required
commutating flux has decreased to the quadrature flux given by
the motor, and from this speed upward only a part of the supply
voltage, inversely proportional (approximately) to the square of
the speed, is impressed upon the compensating circuit, the rest
shifted over to the armature circuit. The difference between
6 and 7 is that in 6 the armature circuit is more inductive, arid
the quadrature flux therefore lags less behind the main flux than
in 7, and by thus using more or less of the field coil in the arma-
ture circuit its inductivity can be varied, and therewith the
phase displacement of the quadrature flux against the main flux
adjusted from nearly 90° lag to considerably less lag, hence not
only the proper intensity but also the exact phase of the required
commutating flux produced.
As seen herefrom, the difference between the different motor
types of IV is essentially found in their different actions regarding
commutation.
It follows herefrom that by the selection of the motor-type
quadrature fluxes, <£i, can Be impressed upon the motor, as cam-
mutating flux, of intensities and phase displacements against
the main flux, 3>, varying over a considerable range. The main