5-322 L60 LINE PHASE COMPARISON SYSTEM – INSTRUCTION MANUALCONTROL ELEMENTS CHAPTER 5: SETTINGS55.7.10 Pilot schemes5.7.10.1 Permissive overreaching transfer trip (POTT)SETTINGS CONTROL ELEMENTS PILOT SCHEMES POTT SCHEMEThis scheme is intended for two-terminal line applications only. It uses an over-reaching zone 2 distance element toessentially compare the direction to a fault at both the ends of the line. Ground directional overcurrent functions availablein the relay can be used in conjunction with the zone 2 distance element to key the scheme and initiate its operation. Thisprovides increased coverage for high resistance faults.For proper scheme operation, enable and configure the zone 2 phase and ground distance elements per the rules ofdistance relaying. Enable and configure the line pickup element to detect line-end-open/weak-infeed conditions. If used bythis 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. Thepermissive signal is echoed back upon receiving a reliable POTT RX signal from the remote end while the line-end-opencondition is identified by the line pickup logic. The permissive echo is programmed as a one-shot logic. The echo is sentonly once and then the echo logic locks out for a settable period of time (ECHO LOCKOUT setting). The duration of the echopulse 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 thelongest spurious TX signal that can occur simultaneously with the zone 2 pickup. The selected delay increases the responsetime of the scheme.TRANS BLOCK PICKUP DELAY — This setting defines a transient blocking mechanism embedded in the POTT scheme forcoping with the exposure of a ground directional overcurrent function (if used) to current reversal conditions. The transientblocking mechanism applies to the ground overcurrent path only as the reach settings for the zone 2 distance functions isnot expected to be long for two-terminal applications, and the security of the distance functions is not endangered by the POTT SCHEME POTT SCHEMEFUNCTION: DisabledRange: Disabled, Enabled POTT PERMISSIVEECHO: DisabledRange: Disabled, Enabled POTT RX PICKUPDELAY: 0.000 sRange: 0.000 to 65.535 s in steps of 0.001 TRANS BLOCK PICKUPDELAY: 0.020 sRange: 0.000 to 65.535 s in steps of 0.001 TRANS BLOCK RESETDELAY: 0.090 sRange: 0.000 to 65.535 s in steps of 0.001 ECHO DURATION:0.100 sRange: 0.000 to 65.535 s in steps of 0.001 ECHO LOCKOUT:0.250 sRange: 0.000 to 65.535 s in steps of 0.001 LINE END OPEN PICKUPDELAY: 0.050 sRange: 0.000 to 65.535 s in steps of 0.001 POTT SEAL-INDELAY: 0.400 sRange: 0.000 to 65.535 s in steps of 0.001 GND DIR O/C FWD:OffRange: FlexLogic operand POTT RX:OffRange: FlexLogic operand POTT SCHEME TARGET:Self-ResetRange: Self-Reset, Latched, Disabled POTT SCHEME EVENTS:DisabledRange: Disabled, Enabled
