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.
8.4.3.3 Setting of zone 2
Zone 2 distance elements must be set according to the following criteria:
• 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
ground fault impedance measurement when setting the reach of zone 2 distance protection
to meet the primary reach criterion for parallel circuits.
8.4.3.4 Setting of zone 3
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.
8.4.3.5 Setting of reverse zone
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.
Section 8 1MRK 506 369-UUS -
Impedance protection
268 Line distance protection REL670 2.2 ANSI
Application manual
To Next Page
Loading...
