Process Bus Iec/Uca 61850-9-2Le Synchronization - ABB Relion 650 Series Technical Manual

Section 15
Basic IED functions
15.1.3.4
15.1.3.5
624

Process bus IEC/UCA 61850-9-2LE synchronization

When process bus communication (IEC/UCA 61850-9-2LE protocol) is used, it is
essential that the merging units are synchronized with the hardware time of the IED
(see Technical manual, section Design of the time system (clock synchronization) ).
To achieve this, PTP, PPS or IRIG-B can be used depending of the facilities of the
merging unit.
If the merging unit supports PTP, use PTP. If PTP is used in the IED and the
merging unit cannot be synchronized from the IED, then use GPS-based clocks to
provide PTP synch as well as sync to the merging unit.
If synchronization of the IED and the merging unit is based on GPS, set the
parameter LostSyncMode to BlockOnLostUTC in order to provide a block of
protection functions whenever the global common time is lost.
If PTP is not used, use the same synchronization method for the HwSyncSrc as the
merging unit provides. For instance, if the merging unit provides PPS as
synchronization, use PPS as HwSyncSrc. If LDCM in GPS-mode is used, that is,
the hardware and software clocks are connected to each other, HwSyncSrc is not
used and other means to synchronize the merging unit to the IED is required. For
instance, FineSyncSource is set to the same source that the merging unit uses.
Precision Time Protocol (PTP)
PTP according to IEEE 1588-2008 and specifically its profile IEC/IEEE 61850-9-3
for power utility automation is a synchronization method that differs from SNTP,
for instance, by providing much better accuracy and by being not predefined. By
not 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, SPA) 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.
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