| It's been
at least six years since some industry pundits began to toll
the death knell for remote terminal units (RTUs), the stalwart
substation-based data acquisition device used for more than 30
years in thousands of utilities around the world. Many
industry professionals felt the introduction of programmable
logic controllers (PLCs), digital relays and a host of other
electronic devices would spell the end of the RTUs' existence.
To prove the
doomsdayers wrong, RTU manufacturers fought hard to retain the
role of the RTU by adding features, improving functionality,
opening up protocols and lowering prices. These efforts have
paid off as RTU sales have held steady and some areas have
even shown slow growth in revenue.
RTUs remain a viable
component of substation SCADA and distribution automation
systems for several reasons. In response to user demand, RTU
manufacturers have adapted RTU technology to meet the changing
needs of the utility market. The incorporation of digital
signal processor (DSP) technology, followed by the use of
32-bit processors and distributed architecture, along with the
implementation of open protocols such as DNP and other
achievements such as the development of basic quality
measurement capability, have saved the day against an
onslaught of early interest in PLC technology.
The annual world
market for general purpose (substation and pole-top) RTU sales
to electric utilities stands at about US $145 million-160
million. The market has remained in this range for the past
few years, with decreasing expenditures for high-end
transmission class RTUs, steady expenditures for distribution
substations and increasing investments in low-point count
remote terminal units designed for field use in distribution
automation schemes.
Key RTU Market Segments
The RTU supplier community is somewhat
fragmented and segmented. Companies such as GE/Harris,
Hathaway SNW and Valmet provide the bulk of high-point count
RTUs for use in transmission and key distribution substations
in North America. Internationally, these firms are joined by
ABB, Siemens, Schneider Groupe, Landis & Gyr, Motorola,
and more than a dozen other suppliers.
In the mid-range
SCADA RTU areas, the SCADA systems suppliers themselves lead
in shipments of distribution substation RTUs. In North
America, suppliers such as Landis & Gyr, Valmet, Advanced
Control Systems, QEI, and Ilex each ship from several hundred
to more than one thousand RTUs annually. These systems
integrators/manufacturers are joined by RTU specialists such
as DAQ and G&W Dacscan.
In the smaller but
growing segment of pole-top RTU applications, GE Harris with
its DART products and Valmet with its Polecat offering have
developed early, strong positions, domestically and
internationally. Several of the other RTU manufacturers
mentioned in this article are also becoming active in the
pole-top or DA RTU segment.
When spending for
special purpose, applications-specific RTUs or RTU-like
intelligent electronic devices (IEDs) is considered, another
US$5 million-7million can be added to the North American
totals while about US$20 million worldwide is being spent for
such communicating data acquisition and control devices. This
class of devices includes remote controls for switches, as
well as capacitor bank controllers. Additional applications
include controls for sectionalizers, tap changers, reclosers
and interchange tie closers.
Trends in the Business
Distributed architecture RTUs are being
offered by some suppliers, especially those companies active
in the substation automation business area. After many years,
American utilities are beginning to place more reliance on,
and faith in, field devices to perform local control. This has
resulted in the development of additional specific control
logic into RTUs. In fact, some PLC functions are now being
implemented via hardware cards into RTUs.
For many utilities,
RTUs are becoming more than data acquisition devices. In fact,
the RTU is now serving a second vital role—that of a
field-based communications processor. In this role, the
communications flexibility of an RTU is paramount. Incoming
signals may be received by an RTU via radio, power line
carrier, wire, cable and fiber while outbound communications
may be via leased lines, fiber and satellite. The RTU of today
can function well as a local area communications network
handler and can continue to improve on its capabilities to
provide multi-ported, wide area networking.
With all of these
ongoing developments, RTUs should continue to adapt to
changing needs in the T&D world to ensure its existence
well into the next century.
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