pick up the voltage drops from the resistor-reactor
When operating the control switch from the
MANUAL to the AUTOMATIC position, you should
combination. The output potential terminals of these
pause in the TEST position. This allows the transient
transformers (X1, X2 and Y1, Y2) are connected in
current in the regulator coil circuit to disappear without
series with the ac potential leads. These leads are
effecting the ac generator output voltage. The transient
between the secondaries of the two 440/110-volt open
current is caused by the sudden connection of the
delta potential transformers and the three-phase,
damping transformer primary across the exciter
full-wave rectifier. This rectifier supplies direct current
armature.
for the regulator coil. The compensator is designed to
supply compensating voltages in two legs of the
Cross-Current Compensator
three-phase regulator potential circuit. This ensures that
a balanced three-phase voltage is applied to the regulator
When two or more regulator-controlled ac
element.
generators operate in parallel on the same bus, you must
The taps on the autotransformer are connected to
equalize the amount of reactive current carried by each
two DIAL SWITCHES (not shown) on the compensator
generator. This equalization of reactive current is
accomplished by giving the regulator a drooping
faceplate. One of these switches provides a coarse
characteristic. This is done by a cross-current
adjustment. The other provides a fine adjustment of the
compensator provided with each ac generator and
compensator. A total of 24 steps is available on the two
associated regulator.
switches. In the case of the standard 12-percent
compensation, this gives a one-half percent change in
The compensator (fig. 8-2) consists of a tapped
compensation per step. The 12 percent compensation is
autotransformer connected across a resistor-reactor
based on four amperes supplied from the current
combination The autotransformer is energized from a
transformer. If the current transformer ratio should
current transformer. It is connected in the B phase of
give some other value of secondary current,
the ac generator between the generator terminals and
the compensation settings will be affected
the bus. Two isolation transformers, with a 1-to-1 ratio,
Figure 8-5.--A Silverstat voltage regulator on an ac generator.
8-8
