U
B
jI
T
*Xline
U
L
Xline
Rline
Zline
I
T
I
T
*Rline
j
j
1
j
2
DU
en06000626.vsd
IEC06000626 V1 EN-US
Figure 82: Transformer with reverse reactance regulation and no circulating
current
The voltage DU=U
B
-U
L
=I
T
*Rline+j I
T
*Xline has the argument j2 and it is realised
that if j2 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 55)
If for example cosj = 0.8 then j = arcos 0.8 = 37°. With the references in
figure 82, j will be negative (inductive load) and we get:
0 0 0
1
( 37 ) 90 53
j
= - - - = -
EQUATION1939 V1 EN-US (Equation 56)
Section 11 1MRK 504 169-UEN A
Control
228 Transformer protection RET650 2.2 IEC
Application manual
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