ABB RET670 Applications Manual page 181

1MRK504116-UUS C
Application manual
Ensure that the underreaching zones from both line ends will overlap a sufficient
amount (at least 10%) in the middle of the protected circuit.
Tapped line application
A
I
21
ANSI05000224 V1 EN
Figure 57: 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 V2 EN
+
I I
A
= + +
Z Z (Z
C Trf CT
I
C
EQUATION1714 V1 EN
A
T
I
C
21
C
, that is increased measured impedance due to fault current
·Z
TF
V2
C
× × 2
Z ) ( )
TB
V1
Section 3
IED application
B
I
B
21
-I
B
en05000224_ansi.vsd
"Fault
(Equation 74)
(Equation 75)
175