If the chosen zone 2 reach gives such a value that it will interfere with zone 2 on adjacent lines,
the time delay of zone 2 must be increased by approximately 200 ms to avoid unwanted
operation in cases when the telecommunication for the short adjacent line at the 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 402)
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 234: Setting of overreaching zone
7.13.4.4
Setting of reverse zone
GUID-C08EC148-B90C-4A20-8993-707E63545946 v2
The reverse zone (zone RV) 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.
The 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.
Z
rev
1.2 × (Z2
rem
- ZL)
>
_
GUID-ABFB1C53-F12A-45D5-90CC-907C9FA0EFC3 V1 EN-US
(Equation 403)
Where:
ZL
is the protected line impedance.
Z2rem is the zone 2 setting (zone used in the POTT scheme) at the remote end of the protected line.
In many applications it might be necessary to consider the enlarging factor due to the fault
current infeed from adjacent lines in the reverse direction in order to obtain certain sensitivity.
7.13.4.5
Series compensated and adjacent lines
GUID-33C23BA9-5807-4E9E-859A-12D6A76304C0 v1
Section 7
1MRK 505 343-UEN B
Impedance protection
354
Application manual
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