ABB RELION REX640 Technical Manual page 82

Basic functions
Figure 10: Parallel redundancy protocol solution
In case a laptop or a PC workstation is connected as a non-PRP node to one of
the PRP networks, LAN A or LAN B, it is recommended to use a redundancy box
device or an Ethernet switch with similar functionality between the PRP network
and SAN to remove additional PRP information from the Ethernet frames. In some
cases, default PC workstation adapters are not able to handle the maximum-length
Ethernet frames with the PRP trailer.
There are different alternative ways to connect a laptop or a workstation as SAN to a
PRP network.
• Via an external redundancy box (RedBox) or a switch capable of connecting to
PRP and normal networks
• By connecting the node directly to LAN A or LAN B as SAN
• By connecting the node to the protection relay's interlink port
HSR
HSR applies the PRP principle of parallel operation to a single ring, treating the
two directions as two virtual LANs. For each frame sent, a node, DAN, sends two
frames, one over each port. Both frames circulate in opposite directions over the
ring and each node forwards the frames it receives, from one port to the other.
When the originating node receives a frame sent to itself, it discards that to avoid
loops; therefore, no ring protocol is needed. Individually attached nodes, SANs, such
as laptops and printers, must be attached through a "redundancy box" that acts as
a ring element. For example, a REX640 protection relay with HSR support can be
used as a redundancy box.
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LAN A LAN A
Each protection relay has a 50-μs store-and-forward delay. To fulfil
the performance requirements for fast horizontal communication for
protection applications using GOOSE and SMV, the ring size is limited
to 30 protection relays.
1MRS759142 F
LAN B LAN B
Technical Manual
REX640