•
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
, 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 148)
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 134: Setting of overreaching zone
7.3.3.4
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.
Consider the possible enlarging factor that might exist due to fault infeed from adjacent lines.
Equation
can be used to calculate the reach in reverse direction when the zone is used for
blocking scheme, weak-end infeed, and so on.
(
)
1.2
2
³
×
-
Zrev
ZL Z rem
EQUATION1525 V5 EN-US
(Equation 149)
Where:
ZL
is the protected line impedance
Z2rem is zone 2 setting at remote end of protected line.
Section 7
1MRK 505 343-UEN B
Impedance protection
212
Application manual
Содержание Relion 670 series
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