615 relays with process bus based applications use IEEE 1588
for high accuracy time synchronization.
For redundant Ethernet communication, the relay offers either
two optical or two galvanic Ethernet network interfaces. A third
port with galvanic Ethernet network interface is also available.
The third Ethernet interface provides connectivity for any other
Ethernet device to an IEC 61850 station bus inside a switchgear
bay, for example connection of a Remote I/O. Ethernet network
redundancy can be achieved using the high-availability
seamless redundancy (HSR) protocol or the parallel
redundancy protocol (PRP) or a with self-healing ring using
RSTP in managed switches. Ethernet redundancy can be
applied to Ethernet-based IEC 61850, Modbus and DNP3
protocols.
The IEC 61850 standard specifies network redundancy which
improves the system availability for the substation
communication. The network redundancy is based on two
complementary protocols defined in the IEC 62439-3 standard:
PRP and HSR protocols. Both the protocols are able to
overcome a failure of a link or switch with a zero switch-over
time. In both the protocols, each network node has two
identical Ethernet ports dedicated for one network connection.
The protocols rely on the duplication of all transmitted
information and provide a zero switch-over time if the links or
switches fail, thus fulfilling all the stringent real-time
requirements of substation automation.
In PRP, each network node is attached to two independent
networks operated in parallel. The networks are completely
separated to ensure failure independence and can have
different topologies. The networks operate in parallel, thus
providing zero-time recovery and continuous checking of
redundancy to avoid failures.
GUID-334D26B1-C3BD-47B6-BD9D-2301190A5E9D V1 EN
Figure 11. Parallel redundancy protocol (PRP) solution
HSR applies the PRP principle of parallel operation to a single
ring. For each message sent, the node sends two frames, one
through each port. Both the frames circulate in opposite
directions over the ring. Every node forwards the frames it
receives from one port to another to reach the next node. When
the originating sender node receives the frame it sent, the
sender node discards the frame to avoid loops. The HSR ring
with 615 series relays supports the connection of up to 30
relays. If more than 30 relays are to be connected, it is
recommended to split the network into several rings to
guarantee the performance for real-time applications.
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