Pilot Schemes - GE L60 Instruction Manual

5.6 CONTROL ELEMENTS
a) PERMISSIVE OVERREACHING TRANSFER TRIP (POTT)
PATH: SETTINGS CONTROL ELEMENTS
POTT SCHEME
5
This scheme is intended for two-terminal line applications only. It uses an over-reaching zone 2 distance element to essen-
tially compare the direction to a fault at both the ends of the line. Ground directional overcurrent functions available in the
relay can be used in conjunction with the zone 2 distance element to key the scheme and initiate its operation. This pro-
vides increased coverage for high resistance faults.
For proper scheme operation, the zone 2 phase and ground distance elements must be enabled, configured, and set per
the rules of distance relaying. The line pickup element should be enabled, configured and set properly to detect line-end-
open/weak-infeed conditions. If used by this scheme, the selected ground directional overcurrent function(s) must be
enabled, configured, and set accordingly.
• POTT PERMISSIVE ECHO: If set to "Enabled" this setting will result in sending a permissive echo signal to the remote
end. The permissive signal is echoed back upon receiving a reliable
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 of time (
duration of the echo pulse does not depend on the duration or shape of the received
.
ECHO DURATION
• POTT RX PICKUP DELAY: This setting enables the relay to cope with spurious receive signals. The delay should be
set longer than the longest spurious
delay will increase the response time of the scheme.
• TRANS BLOCK PICKUP DELAY: This setting defines a transient blocking mechanism embedded in the POTT
scheme for coping with the exposure of a ground directional overcurrent function (if used) to current reversal condi-
tions. The transient blocking mechanism applies to the ground overcurrent path only as the reach settings for the zone
2 distance functions is not expected to be long for two-terminal applications, and the security of the distance functions
is not endangered by the current reversal conditions. Upon receiving the
anism allows the
5-210

PILOT SCHEMES

POTT SCHEME
FUNCTION: Disabled
POTT PERMISSIVE
MESSAGE
ECHO: Disabled
POTT RX PICKUP
MESSAGE
DELAY: 0.000 s
TRANS BLOCK PICKUP
MESSAGE
DELAY: 0.020 s
TRANS BLOCK RESET
MESSAGE
DELAY: 0.090 s
ECHO DURATION:
MESSAGE
0.100 s
ECHO LOCKOUT:
MESSAGE
0.250 s
LINE END OPEN PICKUP
MESSAGE
DELAY:
POTT SEAL-IN
MESSAGE
DELAY:
GND DIR O/C FWD:
MESSAGE
Off
POTT RX:
MESSAGE
Off
signal that can occur simultaneously with the zone 2 pickup. The selected
TX
signal to be passed and aligned with the
RX
L60 Line Phase Comparison Relay
POTT SCHEME
Range: Disabled, Enabled
Range: Disabled, Enabled
Range: 0.000 to 65.535 s in steps of 0.001
Range: 0.000 to 65.535 s in steps of 0.001
Range: 0.000 to 65.535 s in steps of 0.001
Range: 0.000 to 65.535 s in steps of 0.001
Range: 0.000 to 65.535 s in steps of 0.001
Range: 0.000 to 65.535 s in steps of 0.001
0.050 s
Range: 0.000 to 65.535 s in steps of 0.001
0.400 s
Range: FlexLogic™ operand
Range: FlexLogic™ operand
POTT RX
POTT RX
GND DIR O/C FWD
5 SETTINGS
5.6.9 PILOT SCHEMES
signal from the remote end while the
setting). The
ECHO LOCKOUT
signal but is settable as
POTT RX
signal, the transient blocking mech-
indication only for a period of time
GE Multilin