216

ELECTRICAL APPARATUS

extensively used, and monocyclic generators built. These were
single-phase alternating-current generators, having a small
quadrature phase of high inductance, which combined with the
main phase gives three-phase? or quarter-phase voltages. The
auxiliary phase was of such high reactance as to limit the quadra-
ture power and thus make the flow of energy essentially single-
phase, that is, monocyclic. The purpose hereof was to permit
the use of a small quadrature coil on the generator, and thereby
to preserve the whole generator capacity for the single-phase
main voltage, without danger of overloading the quadrature
phase in case of a high motor load on the system. The general
introduction of the three-phase system superseded the mono-
cyclic generator, and monocyclic devices are today used only
for local production of polyphase voltages from single-phase
supply, for the starting of small single-phase induction motors,
etc. The advantage of the monocyclic feature then consists in
limiting the output and thereby the size of the device, and making
it thereby economically feasible with the use of the rather expen-
sive energy-storing devices of inductance (and capacity) used in
this case.
The simplest and most generally used monocyclic device con-
sists of two impedances, Zi and Z2, of different inductance factors
(resistance and inductance, or inductance and capacity), con-
nected across the single-phase mains, A and B. The common
connection, C, between the two impedances, Zi and Za, then is dis-
placed in phase from the single-phase supply voltage, A and #,
and gives with the same a system of out-of-phase voltages, AC,
CB and AS, or a—more or less unsymmetrical—three-phase
triangle. Or, between this common connection, C, and the
middle, D, of an autotransformer connected between the single-
phase mains, AjB, a quadrature voltage, CD, is produced.
This "monocyclic triangle" ACJ5, in its application as single-
phase induction motor-starting device, is discussed in Chapter V.
Two such monocyclic triangles combined give the monocyclic
square, Fig. 67.
128. Let then, in the monocyclic square shown diagrammatic-
ally in Fig. 67:
YI = gi — jbi = admittance AC and DB]
Y% — g% — jb2 = admittance CB and AD;
and let:
Yo = 0o — jbQ = admittance of the load on