6.1.2.2 Analog signal transfer for line differential protection M13647-3 v8The line differential protection function can be arranged as a master-master systemor a master-slave system alternatively. In the former, current samples areexchanged between all IEDs, and an evaluation is made in each IED. This meansthat a 64 kbits/s communication channel is needed between every IED included inthe same line differential protection zone. In the latter, current samples are sentfrom all slave IEDs to one master IED where the evaluation is made, and tripsignals are sent to the remote ends when needed. In this system, a 64 kbit/scommunication channel is only needed between the master and each one of theslave IEDs. The Master-Slave condition for the differential function appearsautomatically when the setting Operation for the differential function is set to Off.For line differential protection we recommend that all feeder endsuse the same version of RED650 or RED670 and the line datacommunication module LDCM. The line differential protection inthe latest version of RED650 is compatible with older versions ofRED670 and RED650. Older versions than RED670 1.2.3 must beverified with ABB.Current samples from IEDs located geographically apart from each other, must betime coordinated so that the current differential algorithm can be executedcorrectly, this is done with the echo method.The communication link is continuously monitored, and an automatic switchoverto a standby link is possible after a preset time.Section 6 1MRK 505 394-UEN ADifferential protection86 Line differential protection RED650 2.2 IECTechnical manual
