ABB RELION RER670, Applications Manual

Page: 331 / 506

U
B
jI
T
* Xline
U
L
Xline
Rline
Zline
I
T
I
T
* Rline
j
j
1
j
2
D
U
en06000626.vsd
IEC06000626 V1 EN-US
Figure 135: Transformer with reverse reactance regulation and no circulating
current
The voltage
D
U=U
B
-U
L
=I
T
* Rline +j I
T
* Xline has the argument
j
2 and it is realised
that if
j
2 is slightly less than -90°, then U
L
will have approximately the same
length as U
B
regardless of the magnitude of the transformer load current I
T
(indicated with the dashed line). The automatic tap change control regulates the
voltage towards a set target value, representing a voltage magnitude, without
considering the phase angle. Thus, U
B
as well as U
L
and also the dashed line could
all be said to be on the target value.
Assume that we want to achieve that
j
2
= -90°, then:
0
1 1
( ) 90
0
1
0
1
90
90
j j j j
U Z I
Ue Ze Ie ZIe
j j j j
j j
j j
+ -
D = ´
ß
D = ´ =
ß
-
= +
ß
= - -
EQUATION1938 V1 EN-US
(Equation 76)
If for example cos
j
= 0.8 then
j
= arcos 0.8 = 37°. With the references in
figure 135 ,
j
will be negative (inductive load) and we get:
0 0 0
1
( 37 ) 90 53
j
= - - - = -
EQUATION1939 V1 EN-US
(Equation 77)
1MRK 506 375-UEN A
Section 12
Control
Railway application RER670 2.2 IEC 325
Application manual