ABB Relion 670 Series Applications Manual page 373

1MRK 511 358-UUS A
ANSI06000626 V1 EN-US
Figure 175: Transformer with reverse reactance regulation and no circulating current
The voltage DV=V
less than -90°, then V
of the transformer load current I
control regulates the voltage towards a set target value, representing a voltage magnitude,
without considering the phase angle. Thus, V
said to be on the target value.
Assume that we want to achieve that j
D = ´
V Z I
ß
0
-
j 90
D
Ve
ß
0
j
- =
90
1
ß
j j
= - -
1
EQUATION1983-ANSI V1 EN-US
If for example cosj = 0.8 then j = arcos 0.8 = 37°. With the references in figure 175, j will be
negative (inductive load) and we get:
j = - -
( 37 ) 90
1
EQUATION1939 V1 EN-US
To achieve a more correct regulation, an adjustment to a value of j2 slightly less than -90° (2 – 4°
less) can be made.
The effect of changing power factor of the load will be that j2 will no longer be close to -90°
resulting in V
Application manual
Rline
j
1
Xline Zline
j
I
T
Rline +j I
-V =I *
B L T
will have approximately the same length as V
L
j j j j +
j j j ( )
= ´ =
Ze Ie ZIe
1 1
j
+
0
90
- = -
0 0 0
53
being smaller or greater than V
L
Xline has the argument j2 and it is realised that if j2 is slightly
*
T
(indicated with the dashed line). The automatic tap change
T
as well as V
B
= -90°, then:
2
if the ratio Rline/Xline is not adjusted.
B
I *Rline
T
V
L
jI *Xline
T
DV
V
j
B
2
en06000626_ansi.vsd
regardless of the magnitude
B
and also the dashed line could all be
L
Section 13
Control
(Equation 128)
(Equation 129)
367