ABB RELION REX640 Technical Manual page 123

1MRS759142 F
Real-time clock at power off
During power off, the system time is kept in a separate capacitor-backed RTC. This
RTC provides a millisecond resolution and digital temperature compensation for
the crystal oscillator. Typical accuracy is 5 ppm which means the time may drift
maximum 0.5 seconds per day. This RTC runs on a stored charge in a supercapacitor
at least for 48 hours. After the capacitor has been discharged, the time is lost.
Real-time clock at power-up
At startup, the initial system time is recovered from the capacitor-backed RTC or set
to 01-01-2010 if the RTC time was lost. The clock is free-running until the selected
synchronization source becomes available. The first synchronization message sets
the time to an accurate value and later synchronization messages additionally
discipline the clock so that the time drift between synchronization messages is
minimized. If the synchronization source is lost, the drift can be 0.25 ppm if the
external clock source was a high-quality clock and the surrounding temperature is
constant.
The setting
set to "None", the clock is free-running and the settings
to set the time manually. In this mode the typical accuracy is 5 ppm and the time
may drift maximum 0.5 seconds per day.
Other setting values activate a communication protocol that provides the time
synchronization. Only one synchronization method can be active at a time. Both IEEE
1588 v2 and SNTP provide time master backup functionality.
Line differential communication
When using line differential communication between the protection relays, the
time synchronization messages can be received from the other line end protection
relay within the protection telegrams. The protection relay begins to synchronize
its RTC with the remote end protection relay's time if the "Line differential"
time synchronization source is selected. This does not affect the protection
synchronization used in the line differential protection or the selection of the
remote end protection relay's time synchronization method. It is expected that
the remote end protection relay has another time synchronization source activated
and therefore operates as a time gateway. Line differential time synchronization is
available only for X6 port.
GNRLLTMS supervision functionality depends on the synchronization source. This
means that the GNRLLTMS supervision signal values and their combinations have
different meanings depending on the used synchronization source.
SNTP
The relay can use one of two SNTP servers, the primary or the secondary server. The
primary server is mainly in use, whereas the secondary server is used if the primary
server cannot be reached or a KoD response is received. While using the secondary
SNTP server, the relay tries to switch back to the primary server on every third SNTP
request attempt. If both SNTP servers are offline, event time stamps have the time
invalid status.
REX640
Technical Manual
Synch source determines the method for synchronizing the RTC. If it is
Connect at least one measurement channel in Application Configuration
in PCM600 either from the hardware (AIM or SIM) or from SMVRCV to
ensure that the time system works correctly.
Basic functions
Date and Time can be used
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