13.3 IEC/UCA 61850-9-2LE communication protocolSEMOD172279 v313.3.1 Introduction SEMOD166571-1 v2SEMOD166590-5 v5Every IED can be provided with communication interfaces enabling it to connect tothe process buses in order to get data from analog data acquisition units close to theprocess (primary apparatus), commonly known as Merging Units (MU). Theprotocol used in this case is the IEC/UCA 61850-9-2LE communication protocol.The IEC/UCA 61850-9-2LE standard does not specify the quality of the sampledvalues. Thus, the accuracy of the current and voltage inputs to the merging unit andthe inaccuracy added by the merging unit must be coordinated with the requirementfor the actual type of protection function.Factors influencing the accuracy of the sampled values from the merging unit are,for example, anti aliasing filters, frequency range, step response, truncating, A/Dconversion inaccuracy, time tagging accuracy etc.In principle, the accuracy of the current and voltage transformers, together with themerging unit, will have the same quality as the direct input of currents andvoltages.The process bus physical layout can be arranged in several ways, described inAnnex B of the standard, depending on what are the needs for sampled data in asubstation.1MRK 511 423-UEN A Section 13Station communicationBay control REC650 2.2 IEC 239Application manual
