ABB RELION RET670, Руководство по применению

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Figure 368 , shows a vector diagram where the principle of reverse reactance has been
introduced for the transformers in figure 367 . 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 target 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
L1
=V
L2
=V
set
ANSI06000485 V1 EN-US
Figure 368: Vector diagram for two transformers regulated exactly on target
voltage.
A comparison with figure 365 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
365 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 368 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 365 and
figure 368 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
369 below shows this situation with T1 being
on a higher tap than T2.
1MRK 504 163-UUS A
Section 15
Control
Transformer protection RET670 2.2 ANSI 767
Application manual