ABB Relion REC670 Applications Manual page 333

1MRK 511 358-UEN A
method and with no circulation (for example, assume two equal transformers on the same tap
position). The load current lags the busbar voltage U
argument of the impedance
IEC06000626 V1 EN-US
Figure 162: Transformer with reverse reactance regulation and no circulating current
The voltage DU=U
slightly less than -90°, then U
magnitude of the transformer load current I
tap change control regulates the voltage towards a set target value, representing a voltage
magnitude, without considering the phase angle. Thus, U
line could all be said to be on the target value.
Assume that we want to achieve that j
D = ´
U Z I
ß
-
j 90
D
Ue
ß
0
- =
90
ß
j j
= - -
1
EQUATION1938 V1 EN-US
If for example cosj = 0.8 then j = arcos 0.8 = 37°. With the references in figure 162, 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.
Application manual
Rline and Xline is designated j1.
Rline
j
1
Xline Zline
j
I
T
Rline +j I
-U =I *
B L T
will have approximately the same length as U
L
0
j j j j
j j j (
= ´ =
Ze Ie ZIe
1
j j
+
1
0
90
- = -
0 0 0
53
with the power factor j and the
B
Xline has the argument j2 and it is realised that if j2 is
*
T
(indicated with the dashed line). The automatic
T
= -90°, then:
2
+
)
1
I *Rline
T
U
L
jI *Xline
T
DU
U
j
B
2
en06000626.vsd
regardless of the
B
as well as U and also the dashed
B L
Section 13
Control
(Equation 127)
(Equation 128)
327