Functions
2.2 Merging Unit
SIPROTEC, 7SC805, Manual
C53000-G1140-C380-1, Release date 05.2014
33
2.2.1
Functional Description
Acquisision and Mergence of Multichannel Data
The MU device 7SC805 supports to digitize sample values of 4 currents (1 A/5 A) and 4 voltages (100 V/ 110
V) with 80 samples per cycle for 50 Hz or 60 Hz power grid systems.
The device acquires and merges the sample values from instrument transfomers synchronnously. Current and
voltage measurements are merged into one device and a digital stream is generated from sample values, which
can then serve as an input signal for other protection relays.
Sample Value Synchronization
The main feature of a Merging Unit is generating sample values synchronized by an external synchronization
signal PPS, GPS or IRIG-B. When digitizing sample values, the synchronization of MU is very important for
protection application , which need sample values from different MUs,e.g. differential protection applications. If
there are more than one MU running in the substation, those SMV are synchronized via a common synchroni-
zation signal, so the synchronization signals sent to different MUs should keep high synchronization accuracy.
Synchronization signals must be compatible with the international standard IEC61869. SMV synchronization
signals, such as PPS, GPS or IRIG-B signal, are supervised and stabilized before they are used for synchro-
nization of the sample value generation.
The Sample Value Synchronization is active only when:
• parameter
460
PPS Synchro
is configured as
ON
• equipped time sync signal module (PPS / IRIG-B module or GPS module )
• accurate time sync signal is received at PPS / IRIG-B module or GPS module
The Sample Value synchronization is independent from the time synchronization settings.
Sample value are generated based on the crystal tact of 7SC805 in one of the following cases:
• parameter 460
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 7SC805
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.