Siemens SIPROTEC 4 Manual page 48

Time Synchronization
4.2 Time Synchronization with Modbus TCP
NOTE
i
i
For time synchronization with NTP or Modbus TCP, at least one NTP server must be configured in the IEC
61850 System Configurator (see
If Modbus TCP time synchronization is enabled, the Modbus TCP master shall perform time synchronization
to the slave periodically every 55 s to 61 s, because the time-control algorithm in the SIPROTEC 4 devices is
based on a cyclical synchronization within this time period.
The module-specific setting EnableTimeSynchronization determines whether NTP is used or not for time
synchronization:
Source
Time Synchronization
Selection in DIGSI 4
Ethernet NTP
Other, e.g. IRIG B,
GPS
48
Figure 2-22
)
NTP Server is Configured
in Station Configurator
Yes
No
Not relevant
Setting
EnableT104TimeSynch
= 0: NTP is used
= 1: Modbus TCP is used
Not relevant
Not relevant
SIPROTEC 4, Modbus TCP Profile, Manual
C53000-L1840-C582-1, Edition 07.2015
Result
Device is synchronized from
NTP (time telegrams from
Modbus TCP master are
rejected)
Device is synchronized from
Modbus TCP master
No time synchronization
(time telegrams from
Modbus TCP master are
rejected)
Device is synchronized from
the selected source
(telegrams from Modbus
TCP master are rejected)