9-10 D60 Line Distance Protection System GE Multilin9.3 PROTECTION SIGNALING SCHEMES 9 APPLICATION OF SETTINGS9c) LOSS-OF-GUARD OPERATIONThe loss-of-guard operation picks under the following conditions:• The scheme is enabled (DCUB FUNCTION is “Enabled” and DCUB BLOCK is “Off”), and• any loss-of-guard signal is received without its associated RX signal, and• a fault is seen in the forward zone 2 distance elements or ground directional forward function (if configured), and• the reverse zone 4 distance elements or ground directional reverse function (if configured) did not pickup to set thetransient blocking.If these conditions are met, then the DCUB LOG PICKUP DELAY timer is started. After this timer times out, the trip table is run,operating the scheme and asserting the DCUB OP FlexLogic operand. The trip table with the aid of the local phase selectorand loss-of-guard signals will determine what tripping operands will be operated. The DCUB LOG PICKUP DELAY timer allowsfor any and all channel(s) to transition from guard to permissive before operating due to loss-of-guard in the presence of aforward fault. The time window of allowing the scheme to operate when no DCUB RX signal is received when any loss-of-guard was received is the difference between the DCUB LOG TRIP WINDOW and DCUB LOG PICKUP DELAY timers. When usingdefault settings, this value is 150 – 8 = 142ms. This means the scheme is unblocked and can trip during this time window ifa forward fault is sensed.d) KEYING OF THE CARRIER(S) UNDER NORMAL CONDITIONSThe keying signals, which allows the relay to key the permissive channel during normal permissive scheme operation bymeans of the DCUB TX1 through DCUB TX4 signals, are established as follows:• The scheme is enabled (DCUB FUNCTION is “Enabled” and DCUB BLOCK is “Off”), and• a fault is seen in the forward zone 2 distance elements or ground directional forward function (if configured), and• the reverse zone 4 distance elements or ground directional reverse function (if configured) did not pickup to set thetransient blocking.If these conditions are met, then the scheme will key the channel(s) by means of asserting transmit signals DCUB TX1through DCUB TX4 with the aid of the local phase selector or zone 2 distance elements.e) KEYING OF THE CARRIER DURING ECHO CONDITIONSThe echo signal, which allows the relay to key the permissive channel(s) through the DCUB TX1 through DCUB TX4 transmitoperands during echo conditions when the local breaker opened, will key the carrier(s) during the following conditions:• The scheme is enabled (DCUB FUNCTION is “Enabled” and DCUB BLOCK is “Off”), and• the DCUB PERMISSIVE ECHO setting is “Enabled”, and• the LINE PICKUP LEO PKP operand that detects the local breaker to be open picks up for a time set by LINE END OPENPICKUP DELAY, and• any permissive signal DCUB RX1 through DCUB RX4 is received and any LOG1 to LOG4 is received, and• a fault is not seen in the forward zone 2 distance elements or ground directional forward function (if configured) for atleast 100 ms, and• the reverse zone 4 distance elements or ground directional reverse function (if configured) did not pickup to set thetransient blocking.If these conditions are met, then the scheme will echo (transmit the DCUB TX1 through DCUB TX4 operands) the receivedpermissive DCUB RX signal(s) back to the remote relay based on the echo table.The keying or transmit signals DCUB TX1 through DCUB TX4 consist of all normal keying or echo keying conditions.The scheme DCUB TRIP A , DCUB TRIB B , DCUB TRIP C, and DCUB TRIP 3P output operands are hard-wired to the trip outputscheme. As such, if the trip output or breaker control operands (if the breaker control function is used) are used for tripping,the scheme fully operational. The permissive key carrier signals DCUB TX1 through DCUB TX4 must still be assigned to thetripping/operating logic, and to output contacts as per the usual D60 logic/output assignments.
