ABB Relion 670 Series Applications Manual page 352

Section 23
Requirements
• Independent of asymmetry.
23.6 IEC/UCA 61850-9-2LE Merging unit requirements
The merging units that supply the IED with measured values via the process bus must fulfill the
IEC/UCA 61850-9-2LE standard.
This part of the IEC 61850 is specifying "Communication Service Mapping (SCSM) – Sampled
values over ISO/IEC 8802", in other words – sampled data over Ethernet. The 9-2 part of the IEC
61850 protocol uses also definitions from 7-2, "Basic communication structure for substation and
feeder equipment – Abstract communication service interface (ACSI)". The set of functionality
implemented in the IED (IEC/UCA 61850-9-2LE) is a subset of the IEC 61850-9-2. For example the
IED covers the client part of the standard, not the server part.
The standard does not define the sample rate for data, but in the UCA users group
recommendations there are indicated sample rates that are adopted, by consensus, in the
industry.
There are two sample rates defined: 80 samples/cycle (4000 samples/sec. at 50Hz or 4800
samples/sec. at 60 Hz) for a merging unit "type1" and 256 samples/cycle for a merging unit
"type2". The IED can receive data rates of 80 samples/cycle.
Note that the IEC/UCA 61850-9-2LE standard does not specify the quality of the sampled values,
only the transportation. Thus, the accuracy of the current and voltage inputs to the merging unit
and the inaccuracy added by the merging unit must be coordinated with the requirement for
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/D conversion inaccuracy, time
tagging accuracy etc.
In principle the accuracy of the current and voltage transformers, together with the merging unit,
shall have the same quality as direct input of currents and voltages.
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1MRK 511 407-UUS Rev. J
SEMOD166590-11 v5
Phasor measurement unit RES670
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