GE Multilin D60 Line Distance Protection System 10-510 APPLICATION OF SETTINGS 10.2 DISTANCE ELEMENTS (STEPPED DISTANCE SCHEME)10d) GROUND DISTANCE ZONE 2To ensure that the zone 2 can see 100% of the line, inter-circuit mutual effects must be considered, as they can contributeto 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 timedelay must be used similar to the phase fault case.e) GROUND DISTANCE ZONE 3This 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 betime coordinated with timed clearances on the next section.f) GROUND DISTANCE ZONE 4As a further contribution to a remote backup philosophy, the reach of this element must be set to account for any infeed atthe remote bus. The time delay must coordinate with other time-delayed protections on the next line. The use of a lenscharacteristic or load encroachment element may be advantageous if load limits are a problem. To avoid extremely largereach settings the D60 has the ability to implement any element, so that it is reverse looking. This strategy can be beneficialif the reduced reach enhances the discrimination between the load and fault conditions. It should be recognized howeverthat, if adopted, this approach must be implemented at both ends of the protected line.g) GROUND DISTANCE ZONE 5An 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 anadditional 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 approachingthe zone characteristic.
