Siemens SIPROTEC 6MU805 User Manual page 38

Functions
2.2 Merging Unit
• parameter 0460 PPS Synchro is set to OFF, no matter time sync signal is received at the time sync interface
• or the physical time sync signal is never received by 6MU805
Then the distributed IEC61850-9-2 SVs (sample values) are not synchronized to time sync signal and are
flagged as not synchronized. Although the SV is not synchronized, they are suitable for protection functions
which need SVs only from one Merging Unit.
If parameter 0460 PPS Synchro is set to ON, 6MU805 will check whether received time sync signals are accu-
rate. After detecting, checking and stabilizing the time sync signals 6MU805 transmits SVs which are flagged
as synchronized and accurate to s (microseconds). For PPS/IRIG-B it takes a few seconds, for GPS this pro-
cedure takes about a few minutes.
The 6MU805 distinguishes automatically PPS or IRIG-B signal arriving at the PPS / IRIG-B module.
Parameter 0485 IEC61850Ed2Sync determines which value is included in IEC61850-9-2 SV-telegrams when
6MU805 is local synchronized for IEC61850Edition 2. If GPS is used, no Local mark is supported.
When the time sync signal is lost, 6MU805 starts the Holdover Time. During the Holdover Time (currently fixed
to 2 minutes) the Sample Value synchronization algorithm runs based on the last valid time sync signal pulses
and the IEC61850-9-2 SV is flagged still as synchronized. In this situation, 6MU805 ensures an appropriate
accuracy of the SVs better than +/-10 us. If time sync signal occurs again during the Holdover Time 6MU805
stops the timer of the Holdover Time.
If the holdover time is expired SVs will be flagged as not synchronized. A reoccurrence of the sync signal pulse
will cause a resynchronization of the SV-generation and IEC61850-9-2 SV will be flagged as synchronized
again. Every reoccurrence of time sync signal will be checked by the SV synchronization algorithm to meet the
accuracy conditions.
Sample Value Distribution
The MU device 6MU805 converts the digital sample values to sample value telegrams according to IEC 61850-
9-2 standard and the current draft of IEC61869.
The information transmitted from the MU to the bay level equipment is mainly about the sample data of the
current and voltage of the primary system and quality information.The quality information is defined in
IEC61869. Based on these data, the bay level equipment can supervise the status of the primary system.
Therefore, a high reliabiability is required in the information sent to the bay level equipment.
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SIPROTEC, 6MU805, Manual
C53000-G1140-C380-5, Release date 06.2018