ABB RELION 670 SERIES Applications Manual page 298

Section 8
Impedance protection
292
A
I
A
Z<
DOCUMENT11524-IMG869 V1 EN
Figure 145: Example of tapped line with Auto transformer
This application gives rise to similar problem that was highlighted in section
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
I + I
A C
Z =Z +
A AT
I
A
DOCUMENT11524-IMG3509 V3 EN
æ
I
A
+ +
=
Z Z Z
ç
C Trf CT
è
EQUATION1783-ANSI V1 EN
Where:
ZAT and ZCT is the line impedance from the B respective C station to the T point.
IA and IC is fault current from A respective C station for fault between T and B.
V2/V1 Transformation ratio for transformation of impedance at V1 side of the transformer to the
measuring side V2 (it is assumed that current and voltage distance function is taken
from V2 side of the transformer).
T
I
C
Z<
C
·Z
TF
ö 2
+
I æ V 2 ö
C
× ×
Z
÷ ç
÷
TB
I è V 1 ø
ø
C
1MRK 506 369-UUS -
B
I
B
Z<
-I
B
en05000224.vsd
"Fault infeed
Line distance protection REL670 2.2 ANSI
Application manual
(Equation 204)
(Equation 205)