GE D60 Instruction Manual page 533

10 APPLICATION OF SETTINGS 10.2 DISTANCE ELEMENTS (STEPPED DISTANCE SCHEME)
d) GROUND DISTANCE ZONE 2
To ensure that the zone 2 can see 100% of the line, inter-circuit mutual effects must be considered, as they can contribute
to a significant under-reach. Typically this may occur on double circuit lines, when both lines may carry the same current.
An analytical study should be carried out to determine the appropriate reach setting.
The main purpose of this element is to operate for faults beyond the reach of the local zone 1 element, and therefore a time
delay must be used similar to the phase fault case.
e) GROUND DISTANCE ZONE 3
This remote back up function must have a reach which is set to account for any infeed at the remote bus, plus the imped-
ance of the longest line which terminates on this remote bus. Similar to the phase fault case, a zone 3 element must be
time coordinated with timed clearances on the next section.
f) GROUND DISTANCE ZONE 4
As a further contribution to a remote backup philosophy, the reach of this element must be set to account for any infeed at
the remote bus. The time delay must coordinate with other time-delayed protections on the next line. The use of a lens
characteristic or load encroachment element may be advantageous if load limits are a problem. To avoid extremely large
reach settings the D60 has the ability to implement any element, so that it is reverse looking. This strategy can be beneficial
if the reduced reach enhances the discrimination between the load and fault conditions. It should be recognized however
that, if adopted, this approach must be implemented at both ends of the protected line.
g) GROUND DISTANCE ZONE 5
An additional fifth ground distance zone can be used in special applications. This zone may be start zone for arming trip-
ping from all other zones, in both forward and reverse directions of the of protected line. This zone may also be used as an
additional reverse-looking zone for implementation of two reverse-looking zones, thus providing two zone backup reverse-
looking protection. The fifth distance zone can be used as an alarm zone, indicating that load impedance is approaching
the zone characteristic.
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GE Multilin D60 Line Distance Protection System 10-5