7.5
Date Code 20170927 Instruction Manual SEL-751 Relay
Communications
Communications Interfaces
On startup, the relay communicates via NETPORT (primary port) selected. If
the SEL-751 detects a link failure on the primary port, it activates the standby
port after the failover time, FTIME, elapses. If the link status on the primary
link returns to normal before the failover time expires, the failover timer resets
and uninterrupted operation continues on the primary network port.
Setting FTIME = OFF allows fast port switching (with no intentional delay).
Fast port switching can occur within one processing interval (typically 4 ms to
5 ms) and can help with IEC 61850 GOOSE performance.
After failover, while communicating via standby port, the SEL-751 checks the
primary link periodically and continues checking until it detects a normal link
status. The relay continues to communicate via the standby port even after the
primary port returns to normal. The relay reevaluates the port of choice for
communication upon a change of settings, at failure of the standby port, or
upon reboot. The relay returns to operation on the primary link under those
conditions if it detects a normal link status. When the active and backup links
both fail, the relay alternates checking for the link status of the primary and
standby ports.
Unmanaged Switch Mode
If you have a network configuration where you want to use the relay as an
unmanaged switch, set NETMODE to SWITCHED. In this mode, both links
are enabled. The relay responds to the messages it receives on either port. All
the messages received on one network port that are not addressed to the relay
are transmitted out of the other port without any modifications. In this mode,
the relay ignores the NETPORT setting.
Fixed Connection Mode
If you have a single network and want to use only one network port, or if you
have both ports connected but want to force usage of only one port for various
reasons, set NETMODE to FIXED and set NETPORT to the port you want to
use. Only the selected network port operates, and the other port is disabled.
PRP Connection Mode
Parallel Redundancy Protocol (PRP) is part of an IEC standard for high
availability automation networks (IEC 62439-3). The purpose of the protocol
is to provide seamless recovery from any single Ethernet network failure.
The basic concept is that the Ethernet network and all traffic are fully
duplicated with the two copies operating in parallel.
Make the following settings for Port 1 to configure the relay for PRP mode.
➤ NETMODE = PRP
➤ PRPTOUT = desired timeout for PRP frame entry
➤ PRPADDR = PRP destination MAC address LSB (least
significant byte of “01-15-4E-00-01-XX,” converted to decimal
and entered as 0–255)
➤ PRPINTV = desired supervision frame transmit interval
When NETMODE is not set to PRP, the following settings are hidden.
NOTE: If you change settings for the
host port in the relay and the standby
network port is active, the relay
resets and returns to operation on
the primary port.
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