GE L90 Instruction Manual page 598

10.4 DISTANCE BACKUP/SUPERVISION 10 APPLICATION OF SETTINGS
e) 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 L90 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.
f) 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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10-16 L90 Line Current Differential System GE Multilin