GE L90 Instruction Manual

Also see for L90: Communications manual Communications guide Instruction manual Instruction manual Instruction manual

Contents

5-246 L90 Line Current Differential System GE Multilin5.7 CONTROL ELEMENTS 5 SETTINGS5This 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 therelay 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 perthe 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 beenabled, configured, and set accordingly.• POTT PERMISSIVE ECHO: If set to "Enabled" this setting will result in sending a permissive echo signal to the remoteend. The permissive signal is echoed back upon receiving a reliable POTT RX signal from the remote end while theline-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). Theduration of the echo pulse does not depend on the duration or shape of the received POTT RX signal but is settable asECHO DURATION.• POTT RX PICKUP DELAY: This setting enables the relay to cope with spurious receive signals. The delay should beset longer than the longest spurious TX signal that can occur simultaneously with the zone 2 pickup. The selecteddelay will increase the response time of the scheme.• TRANS BLOCK PICKUP DELAY: This setting defines a transient blocking mechanism embedded in the POTTscheme 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 zone2 distance functions is not expected to be long for two-terminal applications, and the security of the distance functionsis 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 GND DIR O/C FWD indication only for a period of timedefined as TRANS BLOCK PICKUP DELAY. After that the ground directional overcurrent path will be virtually disabled for aperiod of time specified as TRANS BLOCK RESET DELAY.The TRANS BLOCK PICKUP DELAY should be long enough to give the selected ground directional overcurrent functiontime to operate, but not longer than the fastest possible operation time of the protection system that can create currentreversal conditions within the reach of the selected ground directional overcurrent function. This setting should takeinto account the POTT RX PICKUP DELAY. The POTT RX signal is shaped for aligning with the ground directional indica-tion as follows: the original RX signal is delayed by the POTT RX PICKUP DELAY, then terminated at TRANS BLOCK PICKUPDELAY after the pickup of the original POTT TX signal, and eventually, locked-out for TRANS BLOCK RESET DELAY.• TRANS BLOCK RESET DELAY: This setting defines a transient blocking mechanism embedded in the POTT schemefor coping with the exposure of a ground directional overcurrent function (if used) to current reversal conditions (seealso the TRANS BLOCK PICKUP DELAY). This delay should be selected long enough to cope with transient conditionsincluding not only current reversals but also spurious negative and zero-sequence currents occurring during breakeroperations. The breaker failure time of the surrounding protection systems within the reach of the ground directionalfunction used by the POTT scheme may be considered to make sure that the ground directional function is not jeopar-dized during delayed breaker operations.• ECHO DURATION: This setting defines the guaranteed and exact duration of the echo pulse. The duration does notdepend on the duration and shape of the received POTT RX signal. This setting enables the relay to avoid a permanentlock-up of the transmit/receive loop.• ECHO LOCKOUT: This setting defines the lockout period for the echo logic after sending the echo pulse.• LINE END OPEN PICKUP DELAY: This setting defines the pickup setting for validation of the line end open conditionsas detected by the Line Pickup logic through the LINE PICKUP LEO PKP FlexLogic™ operand. The validated line endopen condition is a requirement for the POTT scheme to return a received echo signal (if the echo feature is enabled).The value of this setting should take into account the principle of operation and settings of the line pickup element.MESSAGE POTT SCHEME TARGET:Self-ResetRange: Self-Reset, Latched, DisabledMESSAGE POTT SCHEME EVENTS:DisabledRange: Disabled, Enabled