20.3 IEC/UCA 61850-9-2LE communication protocol20.3.1 IntroductionEvery 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). The protocolused 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 and theinaccuracy added by the merging unit must be coordinated with the requirement forthe actual type of protection function.Factors influencing the accuracy of the sampled values from the merging unit are, forexample, 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 and voltages.The process bus physical layout can be arranged in several ways, described in AnnexB of the standard, depending on what are the needs for sampled data in a substation.IEC06000537 V1 ENFigure 325: Example of a station configuration with separated process bus andstation bus1MRK 502 071-UEN - Section 20Station communicationGenerator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 685Application manual
