13.4.2 Application M13919-3 v6To 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.One communication channel is used in each direction, which can transmit an on/offsignal if required. The performance and security of this function is directly relatedto the transmission channel speed and security against false or lost signals.In the directional scheme, information of the fault current direction must betransmitted to the other line end.With directional comparison in permissive schemes, a short operate time of theprotection including a channel transmission time, can be achieved. This shortoperate time enables rapid 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 forweak-end infeed and current reversal, included in the Current reversal and weak-end infeed logic for residual overcurrent protection (ECRWPSCH) function.Metallic communication paths adversely affected by fault generated noise may notbe suitable for conventional permissive schemes that rely on signal transmittedduring a protected line fault. With power line carrier, for example, thecommunication signal may be attenuated by the fault, especially when the fault isclose to the line end, thereby disabling the communication channel.To overcome the lower dependability in permissive schemes, an unblockingfunction can be 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 a guard signal CRG, which must always be present,even when no CR signal is received. The absence of the CRG signal during thesecurity time is used as a CR signal. This also enables a permissive scheme tooperate when the line fault blocks the signal transmission. Set the tSecurity to 35ms.13.4.3 Setting guidelines M13920-4 v7The parameters for the scheme communication logic for residual overcurrentprotection function are set via the local HMI or PCM600.The following settings can be done for the scheme communication logic forresidual overcurrent protection function:Operation: Off or On.SchemeType: This parameter can be set to Off , Intertrip, Permissive UR,Permissive OR or Blocking.Section 13 1MRK 505 393-UEN BScheme communication290 Line differential protection RED650 2.2 IECApplication manual
