GE MiCOM P40 Agile, Technical Manual, Page: 604 / 962

communication functionality such as Ethernet. The IRIG-B connection is presented by a connector is a BNC
connector. IRIG-B signals are usually presented as an RF-modulated signal. There are two types of input to our
IRIG-B boards: demodulated or modulated. A board that accepts a demodulated input is used where the IRIG-B
signal has already been demodulated by another device before being fed to the IED. A board that accepts a
modulated input has an on-board demodulator.
To set the device to use IRIG-B, use the setting IRIG-B Sync cell in the DATE AND TIME column.
The IRIG-B status can be viewed in the IRIG-B Status cell in the DATE AND TIME column.
9.2 SNTP
SNTP is used to synchronise the clocks of computer systems over packet-switched, variable-latency data
networks, such as IP. SNTP can be used as the time synchronisation method for models using IEC 61850 over
Ethernet.
The device is synchronised by the main SNTP server. This is achieved by entering the IP address of the SNTP server
into the IED using the IEC 61850 Configurator software described in the settings application software manual. A
second server is also configured with a different IP address for backup purposes.
This function issues an alarm when there is a loss of time synchronisation on the SNTP server. This could be
because there is no response or no valid clock signal.
The HMI menu does not contain any configurable settings relating to SNTP, as the only way to configure it is using
the IEC 61850 Configurator. However it is possible to view some parameters in the COMMUNICATIONS column
under the sub-heading SNTP parameters. Here you can view the SNTP server addresses and the SNTP poll rate in
the cells SNTP Server 1, SNTP Server 2 and SNTP Poll rate respectively.
The SNTP time synchronisation status is displayed in the SNTP Status cell in the DATE AND TIME column.
9.2.1 LOSS OF SNTP SERVER SIGNAL ALARM
This function issues an alarm when there is a loss of time synchronization on the SNTP server. It is issued when the
SNTP sever has not detected a valid time synchronisation response within its 5 second window. This is because
there is no response or no valid clock. The alarm is mapped to IEC 61850.
9.3 IEEE 1588 PRECISION TIME PROTOCOL
The MiCOM P40 modular products support the IEEE C37.238 (Power Profile) of IEEE 1588 Precision Time Protocol
(PTP) as a slave-only clock. This can be used to replace or supplement IRIG-B and SNTP time synchronisation so
that the IED can be synchronised using Ethernet messages from the substation LAN without any additional
physical connections being required.
A dedicated DDB signal (PTP Failure) his provided to indicate failure of failure of PTP.
9.3.1 ACCURACY AND DELAY CALCULATION
A time synchronisation accuracy of within 5 ms is possible. Both peer-to-peer or end-to-end mode delay
measurement can be used.
In peer-to-peer mode, delays are measured between each link in the network and are compensated for. This
provides greater accuracy, but requires that every device between the Grand Master and Slaves supports the
peer-to-peer delay measurement.
In end-to-end mode, delays are only measured between each Grand Master and Slave. The advantage of this
mode is that the requirements for the switches on the network are lower; they do not need to independently
calculate delays. The main disadvantage is that more inaccuracy is introduced, because the method assumes that
forward and reverse delays are always the same, which may not always be correct.
Chapter 21 - Communications P446SV
572 P446SV-TM-EN-1