9
When the module is used in parallel operation
attention should be paid to the settings of U
s
,
T1 and T2 as follows:
Us
All voltage regulating modules operating in parallel must have the same
voltage setting as they control transformers feeding the same busbar. If the
U
s
value of one of the voltage regulating modules is higher than that of the
others, the resulting voltage level will be higher than desired, because it will
be determined by the mean value of the U
s
settings of all the voltage regu-
lating modules. In this case the transformer controlled by the higher setting
value will feed circulating current to the busbar.
T1, T2
The minimum recommended setting of the delay times T1 and T2 is 10 s
when definite time delay is used, and 25 s when inverse time delay is used.
Inverse time is recommended in order to avoid unnecessary operation and
wear of the tap-changer.
When the module is used in parallel operation
in accordance with the negative reactance prin-
ciple, attention should be paid to the settings
of U
r
%, U
x
%, stability and load phase-shift as
follows:
U
r
%, U
x
%
Setting as for single operation, except for the calculation of the values, which
is made on the basis of the common network.
Stability
The "gain" of the parallel operation. The setting should be proportional to
the rated currents of the parallel operating transformers. Start with small
values and increase them to obtain the optimal voltage regulation.
Load phase-shift
The expected phase-shift of the load. This setting value is calculated as an
average of the phase-shiftvalues appearing in the load.
When the module is used in parallel operation
in accordance with the minimizing circulating
current principle, attention should be paid to
the settings of U
r
%, U
x
%, stability, I
nt
and I
nt
/
I
ct
, as follows:
U
r
%, U
x
%
Setting as for single operation, except for the calculation of the values, which
is made on the basis of the common network.
Stability
The "gain" of the parallel operation. The same setting should be used for
all the parallel operating regulators. Start with small values and increase
them to get the optimal voltage regulation.
I
nt
The rated current of the power transformer should be set, when the mini-
mizing circulating current principle is used.
I
nt
/I
ct
Matching transformer compensation should be set, when the minimizing
circulating current principle is used.
