Typical LDCM communication delay between two IEDs is in order of 30-40 ms. Note thatfor disconnector status this delay will not pose any practical problems. However, timedelay caused by LDCM communication can be crucial for circuit breakers status. In suchcases it is strongly recommended that at least the circuit breaker closing command fromevery circuit breaker is directly wired to all three phases/IEDs to minimize any risk forunwanted operation of the busbar differential protection zones due to late inclusion ofrespective bay current into the differential measuring circuit.17.1.3 Setting guidelinesChannelMode: This parameter can be set Normal or Blocked. Besides this, it can be setOutOfService which signifies that the local LDCM is out of service. Thus, with thissetting, the communication channel is active and a message is sent to the remote IED thatthe local IED is out of service, but there is no COMFAIL signal and the analog and binaryvalues are sent as zero.TerminalNo: This setting shall be used to assign an unique address to each LDCM, in allcurrent differential IEDs. Up to 256 LDCMs can be assigned a unique number. Considera local IED with two LDCMs:• LDCM for slot 302: Set TerminalNo to 1 and RemoteTermNo to 2• LDCM for slot 303: Set TerminalNo to 3 and RemoteTermNo to 4In multiterminal current differential applications, with 4 LDCMs in each IED, up to 20unique addresses must be set.The unique address is necessary to give high security against incorrectaddressing in the communication system. Using the same number forsetting TerminalNo in some of the LDCMs, a loop-back test in thecommunication system can give incorrect trip.RemoteTermNo: This setting assigns a number to each related LDCM in the remote IED.For each LDCM, the parameter RemoteTermNo shall be set to a different value thanparameter TerminalNo, but equal to the TerminalNo of the remote end LDCM. In theremote IED the TerminalNo and RemoteTermNo settings are reversed as follows:• LDCM for slot 302: Set TerminalNo to 2 and RemoteTermNo to 1• LDCM for slot 303: Set TerminalNo to 4 and RemoteTermNo to 3The redundant channel is always configured in the lower position, forexampleSection 17 1MRK 505 337-UUS -Remote communication458Application manual
