Functions
2.2 Merging Unit
SIPROTEC, 7SC805, Manual
C53000-G1140-C380-1, Release date 05.2014
34
If parameter
460
PPS Synchro
is set to
ON
, 7SC805 will check whether received time sync signals are accurate.
After detecting, checking and stabilizing the time sync signals 7SC805 transmits SVs which are flagged as syn-
chronized and accurate to us (microseconds). For PPS/IRIG-B it takes a few seconds, for GPS it takes about
a few minutes.
The 7SC805 distinguishes automatically PPS or IRIG-B signal arriving at the PPS / IRIG-B module and sup-
ports the specific Global- and Local time synchronization marks.
Parameter
485
IEC61850Ed2Sync
determines which value is included in IEC61850-9-2 SV – telegrams when
7SC805 is local synchronized for IEC61850Edition 2. If GPS is used no Local mark is supported.
When the time sync signal is lost, 7SC805 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, 7SC805 ensures an appropriate ac-
curacy of the SVs better than +/-10 us. If time sync signal occurs again during the Holdover Time 7SC805 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 7SC805 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.