currents have been above the set value MinCurr for more than setting tLowCurr, anoverreaching zone will be allowed to trip "instantaneously" during a fault conditionwhen one or two of the phase currents will become low due to a three-phase trip atthe opposite IED, see figure 206. The current measurement is performed internallyand the internal STILL signal becomes logical one under the described conditions.The load current in a healthy phase is in this way used to indicate the tripping at theopposite IED. Note that this function will not operate in case of three-phase faults,because none of the phase currents will be low when the opposite IED is tripped.IEC05000158 V1 EN-USFigure 206: Loss-of-load acceleration - simplified logic diagramBreaker closing signals can if decided be connected to block the function duringnormal closing.M13819-14 v213.4 Scheme communication logic for residualovercurrent protection ECPSCH IP14711-1 v213.4.1 IdentificationM14882-1 v2Function description IEC 61850identificationIEC 60617identificationANSI/IEEE C37.2device numberScheme communication logic forresidual overcurrent protectionECPSCH - 8513.4.2 Functionality M13918-4 v11To achieve fast fault clearance of earth faults on the part of the line not covered bythe instantaneous step of the residual overcurrent protection, the directionalresidual overcurrent protection can be supported with a logic that usescommunication channels.In the directional scheme, information of the fault current direction must betransmitted to the other line end. With directional comparison, a short operate time1MRK 505 394-UEN A Section 13Scheme communicationLine differential protection RED650 2.2 IEC 417Technical manual
