ABB Relion 670 series, Applications Manual

Page: 286 / 760

Larger overreach than the mentioned 80% can often be acceptable due to fault current infeed
from other lines. This requires however analysis by means of fault calculations.
If any of the above indicates a zone 2 reach less than 120%, the time delay of zone 2 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 zone 2
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 in the example below.
If a fault occurs at point F see figure 173 , 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 272)
A B
Z<
C
I
C
Z
AC
Z
CB
Z
CF
I
A
+ I
C
IEC09000256-2-en.vsd
F
I
A
I
B
IEC09000256 V2 EN-US
Figure 173: Setting of overreaching zone
7.9.3.4 Setting of reverse zone
GUID-0EDCDC8F-A2C9-4625-A6BD-0E7D2B4B1F04 v1
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 covers the overreaching
zone, used at the remote line IED for the telecommunication purposes.
Consider the possible enlarging factor that might exist due to fault infeed from adjacent lines.
Equation 273 can be used to calculate the reach in reverse direction when the zone is used for
blocking scheme, weak-end infeed etc.
rem L
1.2 Z2 Z
-
rev
Z
³ ×
EQUATION2314 V1 EN-US
(Equation 273)
Where:
Z
L
is the protected line impedance
Z2
rem
is zone 2 setting at remote end of protected line.
In many applications it might be necessary to consider the enlarging factor due to fault
current infeed from adjacent lines in the reverse direction in order to obtain certain sensitivity.
Section 7 1MRK 505 343-UEN B
Impedance protection
280
Application manual