Omicron CMGPS - Standard Accuracy Mode

GPS Syncronization Unit CMGPS
30
5.1 Standard Accuracy Mode
If such a protection scheme is to be reliably tested, it has to be tested as a
complete system, i.e. the relays on both sides of the transmission line, the
signal link and the functional interaction of all the components have to be tested.
Using two CMC test sets — one at the beginning of the transmission line and
one at the end — performs this function. The two devices are synchronized by
means of a CMGPS.
After the CMGPS synchronization units have received signals from a sufficient
number of satellites, they can determine the exact time.
Figure 5-2:
Timing Relationship
when using CMGPS
and multiple CMC test
sets
The GPS output pulse is issued at the same time (+/- 1 µs
1
) from the GPS
receivers in both substations. The test sets have a 100 µs sampling rate for
reading the status of the binary inputs, which also applies to the external input
for the GPS output signal. The timing of the binary input sampling is not
synchronized between the two test sets. Due to this, a time difference of up to
100 µs can appear between the pickup of the GPS pulse by the two test sets.
This can result in an equivalent phase difference of a maximum of 1.8 ° at 50 Hz
or a maximum of 2.16 ° at 60 Hz.
1. Depending on set accuracy (configuration in software)
GPS output pulse
Binary input
sampling of
the CMC at
substation A
Binary input
sampling of
the CMC at
substation B
100 μs
The CMC at substation A
picks up the GPS pulse
The CMC at substation B
picks up the GPS pulse
Time difference
< 100 μs
Falling slope is within
± 1 μs to
programmed time at both sides