ABB REC670 Applications Manual page 426

Section 14
Control
420
Figure 175, shows a vector diagram where the principle of reverse reactance has been
introduced for the transformers in figure 174. The transformers are here supposed to be
on the same tap position, and the busbar voltage is supposed to give a calculated
compensated value V that coincides with the target voltage VSet.
L
I =I =(I +I
T1 T2 T1
ANSI06000485 V1 EN-US
Figure 175: Vector diagram for two transformers regulated exactly on target
voltage.
A comparison with figure
purpose of reverse reactance control is made with a value with opposite sign on X
hence the designation "reverse reactance" or "negative reactance". Effectively this
means that, whereas the line voltage drop compensation in figure
drop along a line from the busbar voltage V
voltage drop compensation in figure
adjusting the ratio X /R
L L
will be approximately equal to the length of V
itself. Thus in principal the difference between the vector diagrams in figure
figure 175 is the sign of the setting parameter X
If now the tap position between the transformers will differ, a circulating current will
appear, and the transformer with the highest tap (highest no load voltage) will be the
source of this circulating current. Figure
on a higher tap than T2.
R I =R I
L T1 L T2
jX I =jX I
L T1 L T2
V
B
)/2
T2
en06000485_ansi.vsd
172 gives that the line voltage drop compensation for the
to a load point voltage V
B
175 gives a voltage increase (actually, by
with respect to the power factor, the length of the vector V
) from V
B
.
L
176 below shows this situation with T1 being
1MRK 511 401-UUS A
172 gave a voltage
, the line
L
up towards the transformer
B
172
Bay control REC670 2.2 ANSI
Application manual
,
L
L
and