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•
Zone 2 should overreach all terminals of the protected circuit by an acceptable
margin (typically 20% of highest impedance seen) for all fault conditions and
for all intended modes of system operation
•
As far as possible, zone 2 reach should be less than zone 1 coverage of all
adjacent lines to minimize the required zone 2 time delay setting.
It is necessary to consider the underreaching effects of zero sequence mutual
coupling on earth-fault impedance measurement when setting the reach of zone 2
distance protection to meet the primary reach criterion for parallel circuits.
8.4.3.5
Setting of zone 3
GUID-9FAC19EC-3334-4CA5-80A7-4CF8404E9383 v1
Zone 3 distance elements must be set according to the following criteria where
possible:
•
Zone 3 should overreach the remote terminal of the longest adjacent line by an
acceptable margin (typically 20% of highest impedance seen) for all fault
conditions and in feed conditions associated with all intended modes of system
operation
•
Zone 3 reach should be less than the zone 2 protection coverage of the shortest
adjacent transmission circuit, and it should not see through power transformers
into distribution systems in order to minimize the required zone 3 time delay
setting.
8.4.3.6
Setting of reverse zone
GUID-F79912AC-E34A-4A6B-90B4-5F4619613CE5 v1
The criterion for setting zone 4 reverse reach would be as under.
•
The zone 4 reverse reach must adequately cover expected levels of apparent
bus bar fault resistance when allowing for multiple in feeds from other circuits.
It is difficult to precisely apply the above criterion and in such cases the practice is
to set zone 4 reverse reach to about 25% of the associated zone 1 forward reach.
With a reverse reach setting of less than the zone 1 reach of distance protection for
the shortest line connected to the local bus bar, the zone 4 time delay would only
need to co-ordinate with bus bar main protection fault clearance and with zone 1
fault clearance for lines out of the same substation. This would be according to the
zone 2 time setting guidelines.
Parallel line in service
Setting of zones for parallel line application
GUID-27298DF4-E681-47D4-BD44-709F76B85344 v2
The distance protection zone reaches vary with the switching state of the parallel
line configuration. Below the configurations and the corresponding formulas for
the reach calculation are given for the most important cases. In these equations,
x
stands for ratio of distance to fault and length of the line, and
Z
stands for the
impedance seen by the relay.
1MRK 506 369-UEN B
Section 8
Impedance protection
Line distance protection REL670 2.2 IEC
251
Application manual
Содержание REL670 2.2 IEC
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