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Electric Energy T&D - Index

Electric Energy T&D - EEMag March / April 2008 - Index

Early communication circuits used dedicated
copper leased circuits as the medium of
transportation for the Frequency Shift Keying
(FSK) relay equipment. In the late 1990’s,
they began installing fiber optic cables
between the substations to enhance the relay
protection system communications, in some
cases utilizing Multiplexers on SONET using
channel division at T1 speeds. Both of these
methods are still in use today because a
cost effective solution may not be available
that could be used to retrofit existing
configurations without the need to replace
the relays to new, more advanced models that
support Ethernet communications.
In early 000’s the need to consolidate
substation communications to one common
network platform was identified. The main
reason for considering a change was simply to
take advantage of additional benefits enabled
by new technologies such as Ethernet. With
time, Ethernet over fiber optics has been
selected by many utilities as the medium
to provide a communications highway;
however, not all the Protection and Control
devices currently in service have Ethernet
connectivity. As previously stated, Serial
Servers are probably the simplest and most
economical method to bring serial devices to
the local area network.
Once at the Local Area Network level,
substation hardened Ethernet switches are
also chosen due to their ability to provide a
stable solution over fiber at link speeds of up
to 1GB. SCADA RTUs, IP-based surveillance
cameras, AMI meter collection nodes,
protective relay engineering access and
oscillography can be moved to the Ethernet
network for integrated communications,
allowing information to reach other stake
holders within the Utility Enterprise.
In many situations, the move to Ethernet
does not, however, provide an immediate
solution to replace the legacy copper leased
circuits for high-speed POTT relaying.
Relay vendors choose to use proprietary
rather then open protocols which, in most
cases, are incompatible with standard serial
communications parameters, preventing use
of Ethernet for communications. Without
an immediate solution to transport such
protocols across Ethernet within the relayrequired
timing parameters, utilities must
find methods to use existing relays over an
Ethernet communications structure.
As described above, serial servers are used to
create an IP tunnel between two serial servers
across an Ethernet infrastructure. Once the
data transfer is possible through the IP tunnel
using the any standard or proprietary protocol
over the network, users may find themselves
facing timing and data integrity issues.
March-April 2008 Issue I
figure 4 Network Topology
Since serial servers have proven their
ability to transport data between relays,
serial servers and relay vendors are working
together to enhance their products to
accurately transmit proprietary protocols over
Ethernet. Bench tests have confirmed the
solution to be effective. Initial tests proved
that timing performance can be even better
than expected, with confirmed data integrity
for secure high-speed relay protection.
Circle 23 on Reader Service Card
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