ABB REL670 2.2 IEC - Page 230

M17048-245 v4
C
B
BC
IEC09000160-3-en.vsd
A
IEC09000160 V3 EN-US
Figure 118: Example of tapped line with Auto transformer
This application gives rise to similar problem that was highlighted in section "Fault
infeed from remote end" , 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
ZA =ZAT + ·ZTF
IA + IC
IA
DOCUMENT11524-IMG3509 V3 EN-US
(Equation 124)
Z Z Z
I I
I
Z
U
U
C Trf CT
A C
C
TF
= + +
+
⋅






⋅






2
1
2
DOCUMENT11524-IMG3510 V3 EN-US (Equation 125)
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).
Z
TF
is the line impedance from the T point to the fault (F).
Z
Trf
Transformer impedance
Section 8 1MRK 506 369-UEN B
Impedance protection
224 Line distance protection REL670 2.2 IEC
Application manual