ABB RELION RET670, Applications Manual

Page: 313 / 1016

from adjacent lines at remote end are considerable higher than the fault current at the
IED location.
The setting shall generally not exceed 80% of the following impedances:
• The impedance corresponding to the protected line, plus the first zone reach of the
shortest adjacent line.
• The impedance corresponding to the protected line, plus the impedance of the
maximum number of transformers operating in parallel on the bus at the remote
end of the protected line.
If the requirements in the dotted paragraphs above gives a zone2 reach less than 120%,
the time delay of zone2 must be increased by approximately 200ms to avoid unwanted
operation in cases when the telecommunication for the short adjacent line at remote
end is down during faults. The zone2 must not be reduced below 120% of the protected
line section. The whole line must be covered under all conditions.
The requirement that the zone 2 shall not reach more than 80% of the shortest adjacent
line at remote end is highlighted wit a simple example below.
If a fault occurs at point F, the IED at point A senses the impedance:
Z
V
I
Z
I I
I
Z
I I I
I
R Z
I
I
Z
AF
A
A
AC
A C
A
CF
A C B
A
F
AC
C
A
C
= = +
+
⋅ +
+ +
⋅ = + +





 ⋅
1
F F
C B
A
F
I I
I
R + +
+





 ⋅
1
EQUATION302 V5 EN-US
(Equation 176)
A
B
21
C
I A
IB
Z AC
Z CB
Z CF
IA+ IB
ANSI05000457-2-en.vsd
F
ANSI05000457 V2 EN-US
Figure 148:
8.5.3.4 Setting of reverse zone
SEMOD154704-33 v3
The reverse zone is applicable for purposes of scheme communication logic, current
reversal logic, weak-end-infeed logic, and so on. The same applies to the back-up
protection of the bus bar or power transformers. It is necessary to secure, that it always
1MRK 504 163-UUS A
Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI 307
Application manual