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Section 8
Impedance protection
8.13.4.4
394
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 218, the IED at point A senses the impedance:
+
V
I
I
A
A
C
=
=
+
Z
Z
AF
AC
I
I
A
A
EQUATION302 V5 EN-US
A
I
A
Z<
IEC09000256 V2 EN-US
Figure 218:
Setting of overreaching zone
Setting of reverse zone
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
1.2 × (Z2
- ZL)
rem
rev
GUID-ABFB1C53-F12A-45D5-90CC-907C9FA0EFC3 V1 EN-US
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.
+
+
I
I
I
A
C
B
⋅
+
⋅
=
Z
R
CF
F
I
A
Z
Z
AC
CB
C
Z
CF
I
+ I
A
C
I
C
1MRK 506 369-UEN B
I
C
+
1
+
⋅
+
1
+
Z
Z
AC
C
F F
I
A
F
I
B
B
IEC09000256-2-en.vsd
GUID-C08EC148-B90C-4A20-8993-707E63545946 v2
Line distance protection REL670 2.2 IEC
Application manual
+
I
I
C
B
⋅
R
F
I
A
(Equation 379)
(Equation 380)
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