ABB RET670 Applications Manual page 670

Section 3
IED application
664
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 282 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.
I
cc....T2
T1
I
cc....T1
I I
T2
T1
V
B
I L
Load
V
L
ANSI06000491 V1 EN
Figure 283: Circulating current caused by T1 on a higher tap than T2.
The circulating current I
transformers. The impact of I
increases the current in T1 (the transformer that is driving I
the same time as it introduces contradictive phase shifts, as can be seen in figure 283.
The result is thus, that the line voltage drop compensation calculated voltage V
will be higher than the line voltage drop compensation calculated voltage V
279 gives that the line voltage drop compensation for the
to a load point voltage V
B
282 gives a voltage increase (actually, by
with respect to the power factor, the length of the vector V
) from V
B
L
283 below shows this situation with T1 being
T2
is predominantly reactive due to the reactive nature of the
cc
on the individual transformer currents is that it
cc
1MRK504116-UUS C
279 gave a voltage
, the line
L
up towards the transformer
B
.
R I
L T2
jX I
L T2
V
-I
I
B
cc
T2
(I +I )/2
T1 T2
I
I
T1
cc
en06000491_ansi.vsd
) and decreases it in T2 at
cc
Application manual
,
L
L
279 and
RI
T1
jX I
L T
1
for T1
L
for T2, or
L