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Electric Energy T&D - Index

Electric Energy T&D - EE Magazine March / April - Index

Circle 30 on Reader Service Card
Installed Configuration
In the following example, two feeder relays
are been connected back-to-back through a
serial server which provides a TCP/IP tunnel
or conversion and transport of serial peerto-peer
messages. While having a unique IP
address, each serial server has also in records
the destination IP address of the adjacent serial
server to complete the TCP/IP tunnel.
It is important to note that TCP is recommended
over UDP protocol because of the deterministic
characteristics of TCP versus the broadcast
approach of UDP and its ability to provide
secure packet transfers.
The serial servers are connected to Ethernet
switches used as the communications backbone
between the substations, with 1GB fiber links in
a mesh configuration to provide redundancy.
The use of Ethernet technology enables the
following features:
• Enhanced Rapid Spanning Tree Protocol
(eRSTP TM ) dynamically reroutes the network
traffic in the event of a fiber break or
equipment failure.
• Dedicated VLAN ensures interferencefree
performance of the high speed relay
communications.
• Quality of Service (QoS) gives higher priority
to packets containing peer-to-peer messages.
The communication circuit performance
provided by the serial server has proven to
be transparent to the operation of the relays,
whether performing under fault conditions
or simply monitoring the heartbeat of the
companion relay.
Performance Measures
before: Round trip time of peer-to-peer
messages was 160ms (9-10 cycles) using
legacy FSK equipment leased lines or the
SONET-based Multiplexer.
lab tests: Round trip time was measured at
40ms ( .5 cycles). The lab test consisted
of feeder relays connected back-to-back
through serial servers. The serial servers
were connected to a standard Ethernet
switch with no other network traffic present
during the test.
7 I March-April 2008 Issue
present: In live production using Ethernet
switches between sites over Ethernet at
1GB speeds, the round trip time was less
than 30ms ( cycles) over an approximate
ome-way circuit distance of seven miles.
The total distance was 14 miles round trip
in this installation.
Note: To provide accurate line fault protection,
one substation relay must send a request to
trip to the other substation relay and receive
permission to trip within 9 or 10 cycles.
Conclusion
Based upon performance test results, serial
servers have proven to be an effective
alternative to transport peer-to-peer messages
using proprietary protocols between relays
over an Ethernet Network. This will replace
existing frequency shift keying (FSK) systems
over leased lines that provide this service
hence reducing the overall operating cost.
The main goal of moving substation
communications to the fiber Ethernet network
has now been achieved.