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1MRK 506 369-UEN B
Line distance protection REL670 2.2 IEC
Application manual
This K
setting for zone 1 only affects the reach for earth faults while the reach
N1
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:
-
Z
Z
0
1
+
1
3
Z
×
1
= ×
Z
x Z
1
+
1
K
N
1
IECEQUATION14015 V1 EN-US
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:
-
Z
Z
+
0
1
+
1
3
Z
×
1
= ×
Z
x Z
1
+
1
K
IECEQUATION14014 V1 EN-US
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
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
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.
-
Z
Z
-
0
1
K
=
K
N
2
Nm
3
Z
1
IECEQUATION14019 V1 EN-US
For case 1, the measured impedance can be calculated by the following expression:
x
K
Nm
-
2
x
N
1
Section 8
Impedance protection
(Equation 174)
(Equation 175)
GUID-1C500D3E-12A2-4F0F-A5A8-A8054677DF4D v1
GUID-DB83C2EF-A40F-4E18-BFC5-D617CE0C0438 v2
(Equation 176)
255
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