To overcome the lower dependability in permissive schemes, an unblocking function canbe used. Use this function at older, less reliable, power line carrier (PLC) communication,where the signal has to be sent through the primary fault. The unblocking function uses aguard signal CRG, which must always be present, even when no CR signal is received.The absence of the CRG signal during the security time is used as a CR signal. This alsoenables a permissive scheme to operate when the line fault blocks the signal transmission.Set the tSecurity to 35 ms.12.5.3 Setting guidelinesThe parameters for the scheme communication logic for residual overcurrent protectionfunction are set via the local HMI or PCM600.The following settings can be done for the scheme communication logic for residualovercurrent protection function:Operation: Disabled or Enabled.SchemeType: This parameter can be set to Off , Intertrip, Permissive UR, Permissive ORor Blocking.tCoord: Delay time for trip from ECPSCH (85) function. For Permissive under/overreaching schemes, this timer shall be set to at least 20 ms plus maximum reset time ofthe communication channel as a security margin. For Blocking scheme, the setting shouldbe > maximum signal transmission time +10 ms.tCoord: Delay time for trip from ECPSCH (85) function. For Permissive under/overreaching schemes, this timer can be set to 0. For Blocking scheme, the setting shouldbe > maximum signal transmission time +10 ms.Unblock: Select Off if unblocking scheme with no alarm for loss of guard is used. Set toRestart if unblocking scheme with alarm for loss of guard is used.12.6 Current reversal and weak-end infeed logic for residualovercurrent protection ECRWPSCH (85)12.6.1 IdentificationFunction description IEC 61850identificationIEC 60617identificationANSI/IEEE C37.2device numberCurrent reversal and weak-end infeedlogic for residual overcurrent protectionECRWPSCH - 85Section 12 1MRK 506 334-UUS AScheme communication408Application manual