ABB RET670 - Page 181

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
B
21 21
21
C
T
IC
IA
IB
-IB
en05000224_ansi.vsd
ANSI05000224 V1 EN
Figure 57: 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 V2 EN (Equation 74)
A C
2
C Trf CT TB
C
I I V2
Z Z (Z Z ) ( )
V1
I
+
= + + × ×
EQUATION1714 V1 EN (Equation 75)
1MRK504116-UUS C Section 3
IED application
175
Application manual