ABB REL670 2.2 IEC, Applications Manual

Page: 233 / 908

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.
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 gives 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 119 , 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 127)
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 119: Setting of overreaching zone
8.3.3.4 Setting of reverse zone
SEMOD55087-74 v4
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.
1MRK 506 369-UEN B
Section 8
Impedance protection
Line distance protection REL670 2.2 IEC 227
Application manual