GE L90 Instruction Manual page 560

9.5 SINGLE-POLE TRIPPING
The response of the system from this point is as described above for the second trip, except the autorecloser will go to lock-
out upon the next initiation (depending on the number of shots programmed).
c) SLG FAULT EVOLVING INTO LLG
When an AG fault occurs the events unfold initially as in the previous example. If the fault evolves quickly, the phase selec-
tor will change its initial assessment from AG to ABG fault and when the trip request is placed either by the zone 1 or the
POTT scheme, a three-pole trip will be initiated. If this is the case, all three
asserted. The command is passed to the breaker control element and results in a three-pole trip. At the same time the
recloser is initiated as per settings of the trip output. As the
the open pole is not activated. Because the
If the fault evolves slowly, the sequence is different: The relay trips phase A as in the previous example. The phase selector
resets, the open pole detector is activated and forces the zone 1 and zone 2 AG, AB, CA and negative-sequence overcur-
rent elements to reset. If the zone 1 BG element picks up, or the zone 2 BG element picks up resulting in operation of the
POTT scheme, no trip command will be issued until the
first trip. If at this time or any time later a request for trip is placed (due to an evolving fault), a three-pole trip is initiated. The
operand is de-asserted by the
TRIP 1-POLE
are opened.
When the dead time expires, the recloser signals the breaker control to close the breaker. At this time all the protection ele-
ments are operational, as the open pole detector is not blocking any elements. If the line-side VTs are used, the line pickup
element is armed as well. If there is a fault on the line, these elements will pickup the fault and issue next request for trip.
This request results in three-pole trip as the
The response of the system from this point is as described above for the second trip, except the recloser will go to lockout
upon the next initiation (depending on the number of shots programmed).
9
9-36
TRIP 3-POLE
in progress is asserted, the phase selector is blocked as well.
AR RIP
AR FORCE 3-P TRIP
operand, resetting the open pole detector. Shortly all three-poles
TRIP 3-POLE
is still asserted.
AR FORCE 3-P TRIP
L90 Line Current Differential System
9 THEORY OF OPERATION
, and
TRIP PHASE A B
operand is asserted (not the
TRIP 1-POLE
is asserted. This happens 1.25 cycles after the
operands will be
C
operand)
GE Multilin