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This K
N1
setting for zone 1 only affects the reach for earth faults while the reach
for two and three-phase faults are unaffected.
For case 2, when the parallel line is out of operation but not earthed, the zone 1
nominal reach for earth faults is reduced. The measured impedance can be
calculated:
1
0
1
1
1
1
1
3
N
Z
x Z
K
Z
Z
Z
+
= ×
+
-
×
IECEQUATION14015 V1 EN-US
(Equation 174)
The reduced reach must be taken into account when using a permissive
underreaching scheme.
For case 3, when the parallel line is in service, the reach for earth faults can further
reduce because of the mutual coupling. The measured impedance can be
calculated:
1
0
1
1
1
1
1
3
2
N
Nm
Z
x Z
K
Z
Z
x
K
Z
x
+
= ×
+
-
+
-
×
IECEQUATION14014 V1 EN-US
(Equation 175)
This reduction of the reach is most pronounced with no in-feed in the line terminal
nearest fault. When the reach is reduced at one line end, it is extended in the
opposite one. Therefore, this reach reduction does not affect a permissive
underreaching scheme.
Setting of overreaching zone
GUID-1C500D3E-12A2-4F0F-A5A8-A8054677DF4D v1
Zone 1 is not allowed to overreach under any condition. Overreaching zones 2 and
3 are not allowed to underreach the whole line under any condition.
Setting of zone 2
GUID-DB83C2EF-A40F-4E18-BFC5-D617CE0C0438 v2
The overreaching zone 2 for backup or permissive overreaching distance protection
schemes must at least safely cover 100% of the line with a safety margin of about
20%. This must be guaranteed for the most unfavorable condition of case 3.
The earth-fault compensation factor must be adjusted to the case of parallel line in
service (case 3) where the highest earth-fault impedance occurs.
0
1
2
1
3
N
Nm
K
Z
Z
K
Z
=
-
-
IECEQUATION14019 V1 EN-US
(Equation 176)
For case 1, the measured impedance can be calculated by the following expression:
1MRK 506 369-UEN B
Section 8
Impedance protection
Line distance protection REL670 2.2 IEC
255
Application manual
Содержание REL670 2.2 IEC
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