m

228 ELECTRICAL APPARATUS

. .. e ee ee2 , e ee2 ec _

rotation: «-» —» --- and 75* -0-» -7:* where € = </l =

The unbalancing of voltage caused by a single-phase load of
impedance voltage, e = is, thus is the same as that caused by
two three-phase impedance voltages, e/2, of which the one has
the same, the other the opposite phase rotation as the three-phase
supply system. The former can be neutralized by raising the
supply voltage by e/2, by potential regulator or generator excita-
tion. This means, regulating the voltage for the average drop.
It leaves, however, the system unbalanced by the impedance
voltage, e/2, of reverse-phase rotation. The latter thus can be
compensated, and the unbalancing eliminated, by inserting into
the three-phase system a set of three-phase voltages, e/2, of re-
verse-phase rotation. Such a system can be produced by a three-
phase potential regulator by interchanging two of the phases.
Thus, if Aj B, C are the three three-phase supply voltages, im-
pressed upon the primary or shunt coils a, b, c of a three-phase
potential regulator, and 1, 2, 3 are the three secondary or series
coils of the regulator, then the voltages induced in 1, 3, 2 are
three-phase of reverse-phase rotation to A, B, C, and can be in-
serted into the system for balancing the unbalancing due to
single-phase load, in the resultant voltage: .A + 1, J3 + 3, C + 2.
It is obviously necessary to have the potential regulator turned
into such position, that the secondary voltages 1, 3, 2 have the
proper phase relation. This may require a wider range of turn-
ing than is provided in the potential regulator for controlling
balanced voltage drop.
It thus is possible to restore the voltage balance of a three-
phase system, which is unbalanced by a single-phase load of im-
pedance voltage, e', by means of two balanced three-phase poten-
tial regulators of voltage range, e'/2, connected so that the one
gives the same, the other the reverse phase rotation of the main
three-phase system.
Such an apparatus producing a balanced polyphase system of
reversed phase rotation, for inserting in series into a polyphase
system to restore the balance on single-phase load, is called a
phase balancer, and in the present case, a stationary induction
phase balancer.
A synchronous machine of opposite phase rotation to the main
system voltages, and connected in series thereto, would then be
a synchronous phase balancer.