5-314 F60 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUALMONITORING ELEMENTS CHAPTER 5: SETTINGS5internal faults on the protected line are identified, the blocking action can be removed through FORCE TX STOP1-2 inputs.This is done to cope with evolving faults when an external fault is followed by an internal fault. Do not set the TRANS BLOCKPICKUP DELAY longer than the fastest possible trip time for faults on an adjacent line so that the extended blocking actioncan be established. Take into account the pickup time of the reverse-looking elements of the scheme. Do not set the delaytoo short, in order to avoid locking up a spurious reverse fault indication that can occur during internal fault conditions.TRANS BLOCK RESET DELAY — This setting defines a transient blocking mechanism embedded in the blocking scheme forcoping with the exposure of the overreaching protection functions to current reversal conditions (see also the TRANS BLOCKPICKUP DELAY). Set this delay long enough to cope with transient conditions including not only current reversals but alsospurious negative and zero-sequence currents occurring during breaker operations.DCB3 SEAL-IN DELAY — The output FlexLogic operand (DCB3 OP) is produced according to the Blocking scheme logic. TheDCB3 SEAL-IN DELAY defines a minimum guaranteed duration of the DCB3 OP pulse.DCB3 DIR FWD1-3 — This setting defines the FlexLogic operand of a protection element to identify forward faults on theprotected line, and thus, for initiating operation of the scheme. Good directional integrity is the key requirement for anover-reaching forward-looking protection element.Even though any FlexLogic operand can be used as DIR FWD, enabling the user to combine responses of variousprotection elements or to apply extra conditions through FlexLogic equations, DIR FWD entries are primarily meant to bethe output operand from the Negative-Sequence Directional FWD IOC, Neutral Directional FWD IOC, and the forward-looking distance over-reaching elements.DCB3 DIR REV1-3 — This setting defines the FlexLogic operand of a protection element to identify reverse faults, and thus, toinitiate the blocking signal. Reverse-looking directional overcurrent protection elements or reverse-looking distanceelements can be used as DIR REV.Even though any FlexLogic operand can be used as DIR REV, enabling the user to combine responses of various protectionelements or to apply extra conditions through FlexLogic equations, DIR REV entries are primarily meant to be the outputoperand from the Negative-Sequence Directional REV IOC, Neutral Directional REV IOC, non-directional IOC, or reverse-looking distance elements.The selected protection element (or elements in combination) need to be coordinated with the selection of DIR FWD. For allthe forward external faults seen by an element used as DIR FWD at one end of the line, the reverse-looking element usedas DIR REV at the other end needs to pick up and provide a blocking signal.DCB3 FORCE TX STOP1-2 — This setting defines the FlexLogic operand of a protection element that is used to identify internalfaults on the protected line, and thus, to stop the blocking signal. Typically, forward-looking under-reach protectionelements are used as FORCE TX STOP.DCB3 RX — This setting selects the FlexLogic operands to represent the receive signals for the scheme. Contact inputsinterfacing with a signaling system(s) are used typically.
