Pilot Schemes - GE L90 Instruction Manual

5 SETTINGS
a) PERMISSIVE OVER-REACHING TRANSFER TRIP (POTT)
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PATH: SETTINGS CONTROL ELEMENTS
# POTT SCHEME
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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 POTT RX signal from the remote end while the
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 POTT RX signal but is settable as
.
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 TX signal that can occur simultaneously with the zone 2 pickup. The selected
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 POTT RX signal, the transient blocking mech-
anism allows the RX signal to be passed and aligned with the
GE Multilin
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PILOT SCHEMES

POTT SCHEME
POTT SCHEME
FUNCTION: Disabled
POTT PERMISSIVE
ECHO: Disabled
POTT RX PICKUP
DELAY: 0.000 s
TRANS BLOCK PICKUP
DELAY: 0.020 s
TRANS BLOCK RESET
DELAY: 0.090 s
ECHO DURATION:
0.100 s
ECHO LOCKOUT:
0.250 s
LINE END OPEN PICKUP
DELAY: 0.050 s
POTT SEAL-IN
DELAY: 0.400 s
GND DIR O/C FWD:
Off
POTT RX:
Off
GND DIR O/C FWD
L90 Line Differential Relay
5.6 CONTROL ELEMENTS
5.6.8 PILOT SCHEMES
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
Range: 0.000 to 65.535 s in steps of 0.001
Range: FlexLogic™ operand
Range: FlexLogic™ operand
ECHO LOCKOUT
indication only for a period of time
5
setting). The
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