Figure 287, shows a vector diagram where the principle of reverse reactance has been
introduced for the transformers in figure 286. 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
L
that coincides with the tar
get voltage VSet.
en06000485_ansi.vsd
V
B
R
L
I
T1
=R
L
I
T2
jX
L
I
T1
=jX
L
I
T2
I
T1
=I
T2
=(I
T1
+I
T2
)/2
V
L
1
=
V
L
2
=
V
s
e
t
ANSI06000485 V1 EN-US
Figure 287: Vector diagram for two transformers regulated exactly on target
voltage.
A comparison with figure
284 gives that the line voltage drop compensation for the
purpose of reverse reactance control is made with a value with opposite sign on X
L
,
hence the designation “reverse reactance” or “negative reactance”. Effectively this
means that, whereas the line voltage drop compensation in figure 284 gave a voltage
drop along a line from the busbar voltage V
B
to a load point voltage
V
L
, the line
voltage drop compensation in figure
287 gives a voltage increase (actually, by
adjusting the ratio X
L
/R
L
with respect to the power factor
, the length of the vector V
L
will be approximately equal to the length of V
B
) from V
B
up towards the transformer
itself. Thus in principal the difference between the vector diagrams in figure
284 and
figure 287 is the sign of the setting parameter X
L
.
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
288 below shows this situation with T1 being
on a higher tap than T2.
Section 15 1MRK 502 071-UUS A
Control
608 Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062
Application manual
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