To achieve fast clearing of faults on the whole line, when no communication channel is available, local acceleration logic (ZCLCPLAL) can be used. This logic enables fast fault clearing during certain conditions, but naturally, it can not fully replace a communication channel.

　　The logic can be controlled either by the autorecloser (zone extension) or by the loss-of-load current (loss-of-load acceleration).

　　Scheme communication logic for residual overcurrent protection ECPSCH

　　To achieve fast fault clearance of earth faults on the part of the line not covered by the instantaneous step of the residual overcurrent protection, the directional residual overcurrent protection can be supported with a logic that uses communication channels.

　　In the directional scheme, information of the fault current direction must be transmitted to the other line end. With directional comparison, a short operate time of the protection including a channel transmission time, can be achieved. This short operate time enables rapid autoreclosing function after the fault clearance.

　　The communication logic module for directional residual current protection enables blocking as well as permissive under/overreaching schemes. The logic can also be supported by additional logic for weak-end infeed and current reversal, included in Current reversal and weak-end infeed logic for residual overcurrent protection (ECRWPSCH) function.

　　Current reversal and weak-end infeed logic for residual overcurrent protection ECRWPSCH

　　The Current reversal and weak-end infeed logic for residual overcurrent protection ECRWPSCH is a supplement to Scheme communication logic for residual overcurrent protection ECPSCH.

　　To achieve fast fault clearing for all earth faults on the line, the directional earth-fault protection function can be supported with logic that uses communication channels.

　　The 670 series IEDs have for this reason available additions to scheme communication logic.

　　If parallel lines are connected to common busbars at both terminals, overreaching permissive communication schemes can trip unselectively due to fault current reversal. This unwanted tripping affects the healthy line when a fault is cleared on the other line. This lack of security can result in a total loss of interconnection between the two buses. To avoid this type of disturbance, a fault current reversal logic (transient blocking logic) can be used.

　　Permissive communication schemes for residual overcurrent protection can basically operate only when the protection in the remote IED can detect the fault. The detection requires a sufficient minimum residual fault current, out from this IED. The fault current can be too low due to an opened breaker or high-positive and/or zero-sequence source impedance behind this IED. To overcome these conditions, weak-end infeed (WEI) echo logic is used.

　　Logic

　　Tripping logic SMPPTRC

　　A function block for protection tripping is provided for each circuit breaker involved in the tripping of the fault. It provides a settable pulse prolongation to ensure a trip pulse of sufficient length, as well as all functionality necessary for correct co-operation with autoreclosing functions.

　　The trip function block also includes a settable latch functionality for evolving faults and breaker lock-out.

　　Trip matrix logic TMAGGIO

　　Trip matrix logic TMAGGIO function is used to route trip signals and other logical output signals to different output contacts on the IED.

　　TMAGGIO output signals and the physical outputs allows the user to adapt the signals to the physical tripping outputs according to the specific application needs.

　　Fixed signal function block

　　The Fixed signals function (FXDSIGN) generates a number of pre-set (fixed) signals that can be used in the configuration of an IED, either for forcing the unused inputs in other function blocks to a certain level/value, or for creating certain logic.
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