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SEMOD154453-267 v4
C
B
BC
IEC09000160-3-en.vsd
A
IEC09000160 V3 EN-US
Figure 143: Example of tapped line with Auto transformer
This application gives rise to similar problem that was highlighted in section
, that is, increased measured impedance due to fault current infeed. For
example, for faults between the T point and B station the measured impedance at A and C will
be
A
C
A
AT
TF
A
I
I
Z
Z
Z
I
+
=
+
×
EQUATION2302 V1 EN-US
(Equation 187)
2
A
C
C
Trf
CT
TF
C
I
I
U2
Z
Z
Z
Z
I
U1
+
=
+
+
×
×
æ
ö æ
ö
ç
÷
ç
÷ è ø
è
ø
IECEQUATION1750 V1 EN-US
(Equation 188)
where
Z
AT
and Z
CT
is the line impedance from the A respective C station to the T point.
I
A
and I
C
is fault current from A respective C station for fault between T and B.
U2/U1
Transformation ratio for transformation of impedance at U1 side of the
transformer to the measuring side U2 (it is assumed that current and voltage
distance function is taken from U2 side of the transformer).
For this example with a fault between T and B, the measured impedance from the T point to
the fault will be increased by a factor defined as the sum of the currents from T point to the
fault divided by the IED current. For the IED at C, the impedance on the high voltage side U1
has to be transferred to the measuring voltage level by the transformer ratio.
Another complication that might occur depending on the topology is that the current from one
end can have a reverse direction for fault on the protected line. For example, for faults at T the
Section 7
1MRK 505 343-UEN B
Impedance protection
230
Application manual
Содержание Relion 670 series
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