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L60 LINE PHASE COMPARISON SYSTEM – INSTRUCTION MANUAL
CONTROL ELEMENTS
CHAPTER 5: SETTINGS
5
5.7.10 Pilot schemes
5.7.10.1 Permissive overreaching transfer trip (POTT)
SETTINGS
CONTROL ELEMENTS
PILOT SCHEMES
POTT SCHEME
This scheme is intended for two-terminal line applications only. It uses an over-reaching zone 2 distance element to
essentially 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
provides increased coverage for high resistance faults.
For proper scheme operation, enable and configure the zone 2 phase and ground distance elements per the rules of
distance relaying. Enable and configure the line pickup element to detect line-end-open/weak-infeed conditions. If used by
this scheme, enable and configure the selected ground directional overcurrent functions accordingly.
POTT PERMISSIVE ECHO
— When "Enabled," this setting results in a permissive echo signal being sent 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 (
ECHO LOCKOUT
setting). The 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. Set the delay longer than the
longest spurious
TX
signal that can occur simultaneously with the zone 2 pickup. The selected delay increases 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 conditions. 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
POTT SCHEME
POTT SCHEME
FUNCTION: Disabled
Range: Disabled, Enabled
POTT PERMISSIVE
ECHO: Disabled
Range: Disabled, Enabled
POTT RX PICKUP
DELAY: 0.000 s
Range: 0.000 to 65.535 s in steps of 0.001
TRANS BLOCK PICKUP
DELAY: 0.020 s
Range: 0.000 to 65.535 s in steps of 0.001
TRANS BLOCK RESET
DELAY: 0.090 s
Range: 0.000 to 65.535 s in steps of 0.001
ECHO DURATION:
0.100 s
Range: 0.000 to 65.535 s in steps of 0.001
ECHO LOCKOUT:
0.250 s
Range: 0.000 to 65.535 s in steps of 0.001
LINE END OPEN PICKUP
DELAY: 0.050 s
Range: 0.000 to 65.535 s in steps of 0.001
POTT SEAL-IN
DELAY: 0.400 s
Range: 0.000 to 65.535 s in steps of 0.001
GND DIR O/C FWD:
Off
Range: FlexLogic operand
POTT RX:
Off
Range: FlexLogic operand
POTT SCHEME TARGET:
Self-reset
Range: Self-reset, Latched, Disabled
POTT SCHEME EVENT:
Disabled
Range: Disabled, Enabled