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11.3
Date Code 20171006
Instruction Manual
SEL-400 Series Relays
Time and Date Management
PTP Timekeeping
regardless of validity. Because of this, all SEL devices (and other slave devices
that share this behavior) synchronized with the GM will retain relational accuracy
with each other even if, in certain cases, the GM may be incorrect in relation to UTC.
The announce message may also include the current TAI to Local offset value
(required in the C37.238 profile). In accordance with IEEE 1588-2008 16.3.3.4,
this value must include the TAI to UTC offset to reflect local time at the node, or
slave device. If the relay receives a TAI to Local offset value that does not include
the TAI to UTC offset, it may incorrectly calculate UTC and Local time. Also, if
the announce message does not include the TAI to Local offset value, the relay
will use its configured Time and Date settings (UTCOFF, BEG_DST, and
END_DST) to calculate local time. This is one reason that the relay Time and
Date settings must match the settings in the GM clock, or devices that are syn-
chronized may have issues with time alignment.
To use PTP, the relay part number must include the Ethernet card option that sup-
ports PTP and PTP must be enabled in Port 5 settings (EPTP = Y) and properly
configured. The relay must be connected to a network containing an appropriate
PTP master, and all intervening switches must be IEEE 1588 aware. For all
SEL-400 series relays, PTP is only available on Ethernet Ports 5A and 5B.
PTPPORT is an analog quantity that can be used to identify the active port.
PTPPORT = 1 if Port A is the active port, PTPPORT = 2 if Port B is the active
port, and PTPPORT = 0 if PTP is not synchronized. See
for more information on configuring the relay and the
Ethernet network for PTP.
To achieve basic synchronization to PTP, the master clock sync and announce interval
must not exceed four seconds. The Relay Word bit PTP_TIM indicates that this basic
level of synchronization has been achieved. If the master clock reports an accuracy of
1
s or better and the network is not introducing excessive jitter in the time-
synchronized messages, PTP_OK will be set indicating the presence of high-accuracy
time synchronization. The analog quantity PTPSTEN can be used to indicate the state
of the PTP Port as follows: 1 = Initializing, 2 = Faulty, 3 = Disabled, 4 = Listening,
8 = Uncalibrated, 9 = Slave.
Depending on the Port 5 configurations, the supported PTP profile may be restricted to
C37.238 power profile. When PTP time synchronization is configured on the process
bus ports (NETPORT = C or D), the only available PTP profile is C37.238. Refer to
Station Bus and Process Bus on page 17.19
for definitions of a process bus.
PTP Over PRP Networks
SEL-400 series relays support PTP time synchronization over a PRP network. When
the relay operates in this network mode, the only available PTP profile is C37.238.
The SEL-400 series relays support PTP time synchronization over Parallel Redundancy
Protocol (PRP) networks. In a PRP network, a dual attached node (DAN) receives a
pair of duplicated packets. It processes the first frame and discards the duplicated frame
based on the information in the redundancy controller trailer (RCT).
This method of using RCTs to distinguish packets does not apply to PTP messages.
PTP messages that transverse through two distinct networks suffer a different amount of
delays.
shows that path delays via LAN A and LAN B are different. These
delays include link delays and residence time. PTP-capable Ethernet switches in these
LANs should update PTP messages with the actual residence time and request/reply to
path delay messages. It should not alter PTP messages by appending RCTs. The dual
attached slave clock receives two different sets of PTP messages, as shown in
. The two ports independently determine its port state.
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