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2.3 PROTECTION SETTINGS
714: FUSEFAIL - Potential Fuse Failure Blocking
Since a distance or directional function may operate for a full or partial loss of AC potential caused by one or
more blown fuses, FUSEFAIL is provided to block distance and directional function tripping when a fuse failure
is detected. If the backup overcurrent functions 50, 50G, and 51G are nondirectional they will be allowed to
trip. If 50, 50G or 51G are directional, then they will not be allowed to trip. The figure below shows the func-
tional logic for the FUSEFAIL function.
2
If AC potential is lost, the positive-sequence voltage detector V1 drops out, NOT1 produces a logic 1 output,
and the upper input is present at AND1. The V1 pickup setting is fixed at 75% of RATEDVOLTS. The middle
input to AND1 is present if load current is sufficient to operate the current detector IB, while the bottom input is
dependent upon whether the fault detector FD has operated or whether one or more poles of the breaker are
open. When the POLE DISAGREEMENT logic detects that one or more poles of the circuit breaker(s) are
open, FUSEFAIL is disabled.
If AC potential is lost for any reason, including a blown fuse or fuses, and there is no disturbance on the power
system, so that the fault detector has not operated, AND1 produces an output that causes timer TL1 to time out
and produce a FUSEFAIL output via OR2. The output of OR2 is routed to AND2 to seal in the FUSEFAIL out-
put, based on the output of V1, so that FUSEFAIL output is maintained as long as the potential is below nor-
mal. When the potential returns to normal, V1 and NOT1 reset to remove the seal-in, allowing the FUSEFAIL
output to reset.
When a fault occurs, with an attendant drop in potential, the V1 function resets, but the fault detector operates
to prevent an output from AND1. FUSEFAIL does not operate on fault conditions.
FUSEFAIL can be set to NO or YES. If BLOCK is selected, then an output will be prevented from any function
that requires potential to operate (distance, directional and any directionally controlled function). If NO is
selected, nothing will be blocked in the event a potential failure occurs.
2-
30
V1
1
VOLTAGE
DETECTOR
IB
CURRENT
DETECTOR
FD
1
FAULT
DETECTOR
P.D.
POLE DISAGREEMENT
Single-Pole Schemes only
Figure 2–10: FUSEFAIL FUNCTION LOGIC DIAGRAM
LPS-D Line Protection System
2 CALCULATION OF SETTINGS
2
2
3
1
0
FUSEFAIL
GE Power Management
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