PHASE CONVERSION 215
axis of the monocyclic system, and e0 the quadrature or wattless
axis. That is, from the axis, e} power can be drawn, within
the limits of the power-generating system back of the supply
voltage. If, however, an attempt is made to draw power from
the monocyclic quadrature voltage, e0, this voltage collapses.
If then the two voltages, e and e0, are impressed upon a quarter-
phase induction motor, this motor will not take power equally
from both phases, e and eQ, but takes power essentially only from
phase, e. In starting, and at heavy load, a small amount of
power is taken also from the quadrature voltage, e0, but at light-
load, power may be returned into this voltage, so that in general
the average power of e0 approximates zero, that is, the voltage,
CQ, is wattless.
A monocyclic system thus may be defined as a system of poly-
phase voltages, in which one of the power axis, the main axis
or energy axis, is constant potential, and the other power axis,
the auxiliary or quadrature axis, is of dropping characteristic
and therefore of limited power. Or it may be defined as a poly-
phase system of voltage, in which the power available in the one
power axis of the system is practically unlimited compared with
that of the other power axis.
A monocyclic system thus is a system of polyphase voltage,
which at balanced polyphase load becomes unbalanced, that is,
in which an unbalancing of voltage or phase relation occurs
when all phases are loaded with equal loads of equal inductance
factors.
In some respect, all methods of conversion from single-phase
to polyphase might be considered as monocyclic, in so far as the
quadrature phase produced by the transforming device is limited
by the capacity of the transforming device, while the main
phase is limited only by the available power of the generating
system. However, where the power available in the quadrature
phase produced by the phase converter is sufficiently large not
to constitute a limitation of power in the polyphase device sup-
plied by it, or in other words, where the quadrature phase-pro-
duced by the phase converter gives essentially a constant-poten-
t al voltage under the condition of the use of the device, then the
system is not considered as monocyclic, but is essentially
polyphase.
In the days before the general introduction of three-phase
power generation, about 20 years ago, monocyclic systems were