ABB Relion 650 Series Technical Manual page 624

Section 15
Basic IED functions
618
The echo mode of the line differential protection function is based on the hardware
clock. Thus, there is no need to synchronize the hardware clock and the software
clock.
Synchronization of the hardware clock to the software clock is necessary only
when IRIG B 00X with optical fiber, IEEE 1344 is used for differential protection.
The two clock systems are synchronized by a special clock synchronization unit
with two modes, fast and slow. A special feature, an automatic fast clock time
regulator is used. The automatic fast mode makes the synchronization time as short
as possible during start-up. The Fast and Slow settings are also available on the
local HMI.
SyncLostMode is not required to set as Block/BlockonLostUTC when differential
protection is based on ECHO mode.
Fast clock synchronization mode
At start-up and after interruptions in the IRIG B time signals, the deviation between
the external time system and the internal differential time system can be
substantial. A new start-up is also required, for example, after maintenance of the
auxiliary voltage system.
When the time difference is > 16 μs, the line differential protection function is
blocked and the time regulator for the hardware clock automatically uses a fast
mode to synchronize the clock systems. Time adjustment is made with an
exponential function, that is, with big time adjustment steps in the beginning, and
then smaller steps until a time deviation of < 16 μs between the external time
system and the internal differential time system has been reached. The protection
function is then enabled and the synchronization remains in fast mode or switches
to slow mode depending on the setting.
Slow clock synchronization mode
During normal service, a setting with slow synchronization mode is used. This
prevents the hardware clock to make too big a time steps (> 16 µs) emanating from
the requirement of correct timing in the line differential protection function.
Synchronization principle
From a general point of view synchronization can be seen as a hierarchical
structure. A function is synchronized from a higher level and provides
synchronization to lower levels.
1MRK 511 424-UEN B
M11346-83 v4
Bay control REC650 2.2 IEC
Technical manual