Table of Contents
Advertisement
Section 8
Impedance protection
8.12.3.2
8.12.3.3
348
Setting of zone 1
The different errors mentioned earlier usually require a limitation of the
underreaching zone (normally zone 1) to 75 - 90% of the protected line.
In case of parallel lines, consider the influence of the mutual coupling according to
section
"Parallel line application with mutual coupling"
are valid in the particular application. By proper setting it is possible to compensate
for the cases when the parallel line is in operation, out of service and not earthed
and out of service and earthed in both ends. The setting of earth-fault reach should
be selected to be <95% also when parallel line is out of service and earthed at both
ends (worst case).
Setting of overreaching zone
The first overreaching zone (normally zone 2) must detect faults on the whole
protected line. Considering the different errors that might influence the
measurement in the same way as for zone 1, it is necessary to increase the reach of
the overreaching zone to at least 120% of the protected line. The zone 2 reach can
be even higher if the fault infeed from adjacent lines at remote end is considerable
higher than the fault current at the IED location.
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 180, 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
+
+
I
I
I
A
C
B
⋅
+
⋅
=
Z
R
CF
F
I
A
1MRK 506 369-UEN B
GUID-ABD9A3B1-E420-471E-A798-4A56371E715E v1
and select the case(s) that
GUID-8D7D4C9D-468B-465F-85D9-3D64500474DB v2
I
C
+
1
+
⋅
+
1
+
Z
Z
AC
C
F F
I
A
Line distance protection REL670 2.2 IEC
Application manual
+
I
I
C
B
⋅
R
F
I
A
(Equation 312)
Advertisement
Table of Contents
