PHASE CONVERSION

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duction phase converter has been discussed in the preceding, and
the synchronous phase converter has similar characteristics, but
as a rule a better regulation, that is, gives a better constancy of
voltage, and can be made to operate without producing lagging
currents, by exciting the fields sufficiently high.
However, a phase converter alone can not distribute single-
phase load so as to give a balanced polyphase system. When
transferring power from the motor phase to the generator phase,
the terminal voltage of the motor phase equals the induced vol-
tage plus the impedance drop in the machine, that of the gen-
erator phase equals induced voltage minus the impedance drop,
and the voltage of the motor phase thus must be higher than that
of the generator phase by twice the impedance voltage of the
phase converter (vectorially combined).
Therefore, in converting single-phase to polyphase by phase
converter, the polyphase system produced can not be balanced
in voltage, but the quadrature phase produced by the converter
is less than the main phase supplied to it, and drops off the more,
the greater the load.
In the reverse conversion, however, distributing a single-phase
load between phases of a polyphase system, the voltage of the
generator phase of the converter must be higher, that of the motor
phase lower than that of the polyphase system, and as the gen-
erator phase is lower in voltage than the motor phase, it follows,
that the phase converter transfers energy only when the poly-
phase system has become unbalanced by more than the voltage
drop in the converter. That is, while a phase converter may
reduce the unbalancing due to single-phase load, it can never
restore complete balance of the polyphase system, in voltage and
in the flow of power. Even to materially reduce the unbalancing,
requires large converter capacity and very close voltage regula-
tion of the converter, and thus makes it an uneconomical machine.
. To balance a polyphase system under single-phase load, there-
fore, requires the addition of a phase balancer to the phase
converter. Usually a synchronous phase balancer, would be
employed in this case, that is, a small synchronous machine of
opposite phase rotation, on the shaft of the phase converter,
and connected in series thereto. Usually it is connected into
the neutral of the phase converter. By the phase balancer, the
voltage of the motor phase of the phase converter is raised
above the generator phase so as to give a power transfer sufficient