ABB Relion REC670 Applications Manual page 312

Section 13
Control
T1
U
B
U
L
IEC06000486 V1 EN-US
Figure 155: Parallel transformers with equal rated data.
In the reverse reactance method, the line voltage drop compensation is used. The original of
the line voltage drop compensation function purpose is to control the voltage at a load point
further out in the network. The very same function can also be used here to control the voltage
at a load point inside the transformer, by choosing a negative value of the parameter
Figure 156, shows a vector diagram where the principle of reverse reactance has been
introduced for the transformers in figure 155. The transformers are here supposed to be on
the same tap position, and the busbar voltage is supposed to give a calculated compensated
value U
L
IEC06000485 V3 EN-US
Figure 156: Vector diagram for two transformers regulated exactly on target voltage.
A comparison with figure
reverse reactance control is made with a value with opposite sign on X
"reverse reactance" or "negative reactance". Effectively this means that, whereas the line
voltage drop compensation in figure
voltage U
voltage increase (actually, by adjusting the ratio X
length of the vector U
transformer itself. Thus in principal the difference between the vector diagrams in figure
and figure
306
T2
I
I
T2
T1
I L
Load
en06000486.vsd
that coincides with the target voltage
U
I =I =(I +I )/2
T1 T2 T1 T2
153 gives that the line voltage drop compensation for the purpose of
to a load point voltage U
B
will be approximately equal to the length of U
L
156 is the sign of the setting parameter X
USet .
R I =R I
L T1 L T2
jX I =jX I
L T1 L T2
B
IEC06000485_2_en.vsd
153 gave a voltage drop along a line from the busbar
, the line voltage drop compensation in figure
L
/R with respect to the power factor, the
L L
.
L
1MRK 511 358-UEN A
Xline .
, hence the designation
L
156 gives a
) from U up towards the
B B
153
Application manual