ABB REL650 series, Applications Manual

Page: 131 / 516

Ensure that the underreaching zones from both line ends will overlap a sufficient amount
(at least 10%) in the middle of the protected circuit.
6.1.2.6 Tapped line application
A B
21 21
21
C
T
I
C
I
A
I
B
-I
B
en05000224_ansi.vsd
ANSI05000224 V1 EN
Figure 60: 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
Z
A
=Z
AT
+ ·Z
TF
I
A
+ I
C
I
A
DOCUMENT11524-IMG3509 V2 EN
(Equation 46)
A C
2
C Trf CT TB
C
I I V2
Z Z (Z Z ) ( )
V1
I
+
= + + × ×
EQUATION1714 V1 EN
(Equation 47)
1MRK 506 334-UUS A
Section 6
Impedance protection
125
Application manual