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

Section 24
Requirements
24.6
608
• 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.

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.
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