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15.15
Date Code 20171006
Instruction Manual
SEL-400 Series Relays
Communications Interfaces
Ethernet Communications
ESNTP = UNICAST
In unicast mode of operation the SNTP client in the relay requests time updates
from the primary (IP address setting SNTPPIP) or backup (IP address setting
SNTPBIP) NTP server at a rate defined by setting SNTPRAT. If the NTP server
does not respond with the period defined by the sum of setting SNTPTO and
SNTPRAT then the relay tries the other SNTP server. When the relay success-
fully synchronizes to the primary NTP time server, Relay Word bit TSNTPP
asserts. When the relay successfully synchronizes to the backup NTP time server,
Relay Word bit TSNTPB asserts.
ESNTP = MANYCAST
In manycast mode of operation the relay initially sends an NTP request to the
broadcast address contained in setting SNTPPIP. The relay continues to broad-
cast requests at a rate defined by setting SNTPRAT. When a server replies, the
relay considers that server to be the primary NTP server, and switches to UNI-
CAST mode, asserts Relay Word bit TSNTPP, and thereafter requests updates
from the primary server. If the NTP server stops responding for time SNTPTO,
the relay deasserts TSNTPP and begins to request time from the broadcast
address again until a server responds.
ESNTP = BROADCAST
Setting SNTPPIP = 0.0.0.0 while ESNTP = BROADCAST, the relay will listen
for and synchronize to any broadcasting NTP server. If setting SNTPPIP is set to
a specific IP address while setting ESNTP = BROADCAST, then the relay will
listen for and synchronize to only NTP server broadcasts from that address.
When synchronized the relay asserts Relay Word bit TSNTPP. Relay Word bit
TNSTPP deasserts if the relay does not receive a valid broadcast within the
SNTPT0 setting value after the period defined by setting SNTPRAT.
SNTP Accuracy Considerations
SNTP time synchronization accuracy is limited by the accuracy of the SNTP
Server and by the networking environment. The highest degree of SNTP time
synchronization can be achieved by minimizing the number of switches and rout-
ers between the SNTP Server and the relay.
When installed on a network with low burden configured with one Ethernet
switch between the relay and the SNTP Server, and when using
ESNTP = UNICAST or MANYCAST, the relay time synchronization error to
the SNTP server is typically less than ±1 millisecond.
Precision Time Protocol (PTP)
If the optional Ethernet card is installed and it includes ports A and B, then the
relay supports Precision Time Protocol version 2 (PTPv2) as a slave-only clock
as defined by IEEE-1588-2008 on ports A and B. PTP provides high accuracy
timing over an Ethernet network, eliminating the need for a separate IRIG-B
cable and connection. To achieve the best accuracy (<1 µs), it is necessary to have
one or more PTP master clocks and that all intervening equipment (e.g., Ethernet
switches) need to be 1588-aware (i.e. all intervening network devices need to be
transparent or boundary clocks).
Содержание SEL-421-4
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