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5-236 L60 Line Phase Comparison System GE Multilin

5.6 CONTROL ELEMENTS 5 SETTINGS

5.6.10 PILOT SCHEMES

a) PERMISSIVE OVERREACHING TRANSFER TRIP (POTT)

PATH: SETTINGS ÖØ CONTROL ELEMENTS ÖØ PILOT SCHEMES ÖØ POTT SCHEME

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 functions 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 (

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. 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.

 POTT SCHEME



POTT SCHEME

FUNCTION: Disabled

Range: Disabled, Enabled

MESSAGE

POTT PERMISSIVE

ECHO: Disabled

Range: Disabled, Enabled

MESSAGE

POTT RX PICKUP

DELAY: 0.000 s