Tapped Line Application - ABB RELION RET670 Applications Manual

1MRK 504 163-UUS A
8.1.2.7
Transformer protection RET670 2.2 ANSI
Application manual
( )
×
Im A X
( )
=
Im K
U
( )
2
é ù
+
Re A
ë û
EQUATION1288 V2 EN-US
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

ANSI05000224 V2 EN-US
Figure 78: 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 is as follows:
2
m 0
( )
2
é ù
Im A
ë û
A
that is, increased measured impedance due to fault current
Impedance protection
B
C
ANSI05000224-2-en.vsd
Section 8
(Equation 49)
SEMOD168232-266 v2
SEMOD168232-268 v2
BC
"Fault
203