664
D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
SINGLE-POLE TRIPPING
CHAPTER 15: THEORY OF OPERATION
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.
When used with the permissive overreaching transfer trip (POTT) scheme, this feature will
echo 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 user-
specified period. The duration of the echo pulse does not depend on the duration or shape
of the received RX signals but is user-programmable. The echo is sent back only if none of
the overreaching protection elements operates.
When used with the hybrid permissive overreaching transfer trip (hybrid POTT) scheme,
this feature will echo 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
0
0
0
1
0
0
0
0
BG
AG, AB, ABG, CA,
CAG, 3P,
unrecognized
DCUB TRIP B
1
1
0
0
0
0
0
0
AG
BG
DCUB TRIP B
0
1
0
0
0
0
0
0
AG
BG
DCUB TRIP B
0
0
0
0
1
1
0
0
CG
BG
DCUB TRIP B
0
0
0
0
0
1
0
0
CG
BG
DCUB TRIP B
0
0
0
0
0
0
1
1
MULTI-P
BG
DCUB TRIP B
0
0
0
0
0
0
0
1
MULTI-P
BG
DCUB TRIP B
0
0
0
0
1
1
0
0
CG
CG, BC, BCG, CA,
CAG, 3P,
unrecognized
DCUB TRIP C
0
0
0
0
0
1
0
0
CG
CG, BC, BCG, CA,
CAG, 3P,
unrecognized
DCUB TRIP C
1
1
0
0
0
0
0
0
AG
CG
DCUB TRIP C
0
1
0
0
0
0
0
0
AG
CG
DCUB TRIP C
0
0
1
1
0
0
0
0
BG
CG
DCUB TRIP C
0
0
0
1
0
0
0
0
BG
CG
DCUB TRIP C
0
0
0
0
0
0
1
1
MULTI-P
CG
DCUB TRIP C
0
0
0
0
0
0
0
1
MULTI-P
CG
DCUB TRIP C
1
1
0
0
0
0
0
0
AG
BC, BCG
DCUB TRIP 3P
0
1
0
0
0
0
0
0
AG
BC, BCG
DCUB TRIP 3P
0
0
1
1
0
0
0
0
BG
CA, CAG
DCUB TRIP 3P
0
0
0
1
0
0
0
0
BG
CA, CAG
DCUB TRIP 3P
0
0
0
0
1
1
0
0
CG
AB, ABG
DCUB TRIP 3P
0
0
0
0
0
1
0
0
CG
AB, ABG
DCUB TRIP 3P
0
0
0
0
0
0
1
1
MULTI-P
3P or unrecognized DCUB TRIP 3P
0
0
0
0
0
0
0
1
MULTI-P
3P or unrecognized DCUB TRIP 3P
Remote data
Local data
Bit pattern
Remote
determination of
fault type
Local
determination of
fault type
Trip output
RX
1
LO
G1
RX
2
LO
G2
RX
3
LO
G3
RX
4
LO
G4