ABB RELION RET670 Applications Manual page 310

Section 8
Impedance protection
304
A
I
A
Z<
DOCUMENT11524-IMG869 V1 EN-US
Figure 147: Example of tapped line with Auto transformer
This application gives rise to similar problem that was highlighted in section
infeed from remote end"
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-US
æ
I
A
+ +
=
Z Z Z
ç
C Trf CT
è
EQUATION1783-ANSI V1 EN-US
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
that is, increased measured impedance due to fault current
·Z
TF
ö 2
+
æ ö
I V 2
C
× ×
Z
÷ ç
÷
TB
è V 1 ø
I
ø
C
1MRK 504 163-UUS A
B
I
B
Z<
-I
B
en05000224.vsd
Transformer protection RET670 2.2 ANSI
Application manual
SEMOD154680-267 v2
"Fault
(Equation 173)
(Equation 174)