ABB RES670 Technical Manual page 778

Section 22
Basic IED functions
772
predefined is meant that it is not mandatory to have a predefined synchronization tree,
as the master (Grand Master) may shift.
Consider instead PTP as a synchronization grouping, i.e. all devices connected to the
PTP group will be synchronized to the same source or, if there is no external source the
group will at least maintain a common time. The group is synchronized by connecting
one or more "Grand Master" clocks to it. The clocks can be part of the devices in the
group or be specialized synchronization devices, as for instance a GPS clock or similar.
If several synchronization devices are connected to the group, the "Best Master
Algorithm" in the PTP protocol will assure that only one is the "Grand Master". The
IED can act as a synchronization device and supply any synchronization source (like
SNTP, IRIG-B, SPA etc) as clock input, that will synchronize the whole PTP group if
there is no better source available in the group. The IED can be connected to several
groups and thereby connect them to each other, by acting as a "Boundary Clock". If
PTP is "On" on several Access Points, the IED connects the Access Points via a
boundary clock. If PTP is "On" on redundant Access Points, the IED acts as a
"Transparent Clock".
In a network there may be variety of possible masters that are connected together
where the masters by selection, using the priority of PTP (also called the Best Master
Algorithm, or BMC) to determine which of them that is the best master.
Priority order according to PTP
1. Priority 1
setting for each device, default 128, set to a lower number if this device shall be
the Grand Master.
2. GM class
given from the type of device, for instance "6" for a GPS clock, "7" for a GPS
clock that has lost synch during a hold-over time, "187" for a clock that can also
be a slave.
3. GM Accuracy
how accurate the time is as a enumerated value
4. Offset Scaled Variance
calculated value that shows the oscillator quality
5. Priority 2
setting for each device, default 128, set to a lower number if this device is
preferred to be the Grand Master, if Priority 1, GM class, GM accuracy and
OffsetScaledVariance are the same for all devices.
6. Identity, that is the MAC-adress of the port.
MAC address of the access points can be seen in LHMI under the
settings of each access point.
1MRK 511 408-UUS A
Phasor measurement unit RES670 2.2 ANSI
Technical manual