The pick-up timer tLowCurr determine the window needed for pick-up of the minimumcurrent value used to release the function. The timer is by default set to 200 ms, which isjudged to be enough to avoid unwanted release of the function (avoid unwanted trip).12.5 Scheme communication logic for residual overcurrentprotection ECPSCH (85)12.5.1 IdentificationFunction description IEC 61850identificationIEC 60617identificationANSI/IEEE C37.2device numberScheme communication logic forresidual overcurrent protectionECPSCH - 8512.5.2 ApplicationTo achieve fast fault clearance of ground faults on the part of the line not covered by theinstantaneous step of the residual overcurrent protection, the directional residualovercurrent protection can be supported with a logic that uses communication channels.One communication channel is used in each direction, which can transmit an on/off signalif required. The performance and security of this function is directly related to thetransmission channel speed and security against false or lost signals.In the directional scheme, information of the fault current direction must be transmitted tothe other line end.With directional comparison in permissive schemes, a short operate time of the protectionincluding a channel transmission time, can be achieved. This short operate time enablesrapid autoreclosing function after the fault clearance.The communication logic module enables blocking as well as permissive under/overreaching schemes. The logic can also be supported by additional logic for weak-endinfeed and current reversal, included in the Current reversal and weak-end infeed logic forresidual overcurrent protection (ECRWPSCH, 85) function.Metallic communication paths adversely affected by fault generated noise may not besuitable for conventional permissive schemes that rely on signal transmitted during aprotected line fault. With power line carrier, for example, the communication signal maybe attenuated by the fault, especially when the fault is close to the line end, therebydisabling the communication channel.1MRK 506 334-UUS A Section 12Scheme communication407Application manual
