GE UR Series L90, Instruction Manual, Page: 396 / 846

5-258 L90 Line Current Differential System GE Multilin
5.7 CONTROL ELEMENTS 5 SETTINGS
5
• TRIP PILOT PRIORITY : This setting is used to set an interval equal to the inter-relay channel communications time,
plus an appropriate margin, during which outputs are not asserted. This delay permits fault identification information
from a remote terminal to be used instead of local data only.
• REVERSE FAULT : This setting should be used to guarantee accuracy of single-pole tripping under evolving external to
internal faults. When a close-in external fault occurs, the relay is biased toward very fast operation on a following inter-
nal fault. This is primarily due to depressed voltages and elevated currents in response to the first, external fault. The
phase selector can exhibit some time lag compared to the main protection elements. This can potentially result in a
spurious three-pole operation on a single-line-to-ground internal fault. Delaying tripping on internal faults that follow
detection of reverse faults solves the problem.
As long as the operand indicated under this setting is asserted the trip action is delayed by
TRIP DELAY ON EVOLV
FAULTS
time. Typically this operand should combine reverse zone indications (such as zone 4 pickup) with a half-cycle
pickup delay, and two-cycle dropout delay. This setting should be used only in single-pole tripping applications, when
evolving faults are of importance, and slightly delayed operation on evolving faults could be traded for enhanced accu-
racy of single-pole tripping.
• TRIP DELAY ON EVOLV FAULTS : Use this setting in conjunction with the
REVERSE FAULT
setting (see above). Typi-
cally this value is set around half a power system cycle. Use it only in single-pole tripping applications, when evolving
faults are of importance, and slightly delayed operation on evolving faults could be traded for enhanced accuracy of
single-pole tripping.