10-48 L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
SINGLE-POLE TRIPPING CHAPTER 10: THEORY OF OPERATION
10
10.5.4 Permissive echo signaling
The “echo” feature can reduce the response time of an over-reaching scheme when a terminal is disconnected from the
line. In this condition, a zone 2 element at the terminal that remains in-service can detect a fault, but cannot trip, as a
permissive signal is not received from the remote terminal. This feature is provided in the permissive over-reaching transfer
trip and hybrid permissive over-reaching transfer trip schemes.
10.5.4.1 Permissive over-reaching transfer trip scheme
When used, this feature “echoes” a reliable received permissive signal back to the originating terminal when a line-end-
open condition is identified by the line pickup logic. The permissive echo is programmed as a one-shot logic. The echo is
sent only once and then the echo logic locks out for a settable period. The duration of the echo pulse does not depend on
the duration or shape of the received Rx signals but is settable.
The echo is sent back only if none of the overreaching protection elements operates.
10.5.4.2 Hybrid permissive over-reaching transfer trip permissive echo
When used, this feature “echoes” a reliable received permissive signal back to the originating terminal if the line-end-open
condition is recognized by the line pickup scheme and the fault is not identified as a reverse fault by the zone 4 or the
ground directional overcurrent function (if used). The permissive echo is programmed as a one-shot logic. The echo is sent
only once and then the echo logic locks out for a settable period. The duration of the echo pulse does not depend on the
duration or shape of the received Rx signal but is settable as
ECHO DURATION.
0 0 1 1 0 0 0 0 BG AG, AB, ABG, CA, CAG,
3P, unrecognized
DCUB TRIP B
00 0100 0 0
11 0000 0 0 AG BG
01 0000 0 0
00 0011 0 0 CG
00 0001 0 0
00 0000 1 1 MULTI-P
00 0000 0 1
0 0 0 0 1 1 0 0 CG CG, BC, BCG, CA, CAG,
3P, unrecognized
DCUB TRIP C
00 0001 0 0
11 0000 0 0 AG CG
01 0000 0 0
00 1100 0 0 BG
00 0100 0 0
00 0000 1 1 MULTI-P
00 0000 0 1
1 1 0 0 0 0 0 0 AG BC, BCG DCUB TRIP 3P
01 0000 0 0
0 0 1 1 0 0 0 0 BG CA, CAG
00 0100 0 0
0 0 0 0 1 1 0 0 CG AB, ABG
00 0001 0 0
0 0 0 0 0 0 1 1 MULTI-P 3P or unrecognized
00 0000 0 1
Remote data Local data
Bit pattern received Remote
determinatio
n of fault
type
Local determination
of fault type
Trip output
RX1 LOG1 RX2 LOG2 RX3 LOG3 RX4 LOG4
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