Iec 61850-9-2Le Merging Unit Requirements - ABB Relion REC670 Applications Manual

1MRK 511 358-UEN A
• Independent synchronization, asynchronous mapping
• The actual SDH port must be set to allow transmission of the master clock from the PDH-
system via the SDH-system in transparent mode.
• Maximum clock deviation <±50 ppm nominal, <±100 ppm operational
• Jitter and Wander according to ITU-T G.823 and G.825
• Buffer memory <100 μs
• Format: Transparent
• Maximum channel delay
• Loop time <40 ms continuous (2 x 20 ms)
IED with echo synchronization of differential clock (without GPS clock)
• Both channels must have the same route with maximum asymmetry of 0,2-0,5 ms,
depending on set sensitivity of the differential protection.
• A fixed asymmetry can be compensated (setting of asymmetric delay in built in HMI or the
parameter setting tool PST).
IED with GPS clock
• Independent of asymmetry.
22.5

IEC 61850-9-2LE Merging unit requirements

The merging units that supply the IED with measured values via the process bus must fulfill the
IEC61850-9-2LE standard.
This part of the IEC61850 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
IEC61850 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 (IEC61850-9-2LE) is a subset of the IEC61850-9-2. 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 61850-9-2 LE 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.
Application manual
Section 22
Requirements
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