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 protocolssuch as DNP and other achievements such as the development of basic power 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-7 million 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 closures.
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.
Chuck Newton can be reached at Newton-Evans Research Co., Ellicott City, Maryland, U.S., (410) 465-7316 or via e-mail at [email protected] The company's Web site address is http://www.newton-evans.com.