Plantwide data networks leverage digital technology to the max

Although digital technology has pervaded industrial and postindustrial societies, power plants are not yet fully reaping its benefits. Many individual process control systems have gone digital, and even nuclear plants are beginning to apply the technology in nonsafety-related systems, but most have not reaped the full benefits of an integrated network.

In power plants, digital systems and networks dominate, or are common in, the functional areas of communications, security, operator support, and environmental health and safety. However, for the most part these key pieces of plant infrastructure are used and managed by separate (and, often, disparate) departments. Reason: The systems and networks were designed and implemented independently, with little if any thought to having them work in concert. Surprisingly, that’s often the case even for systems designed for new plants.

Case in point: At several U.S. nuclear plants, separate departments have deployed their own data networks throughout the facility, at significant cost. At one plant, the health physics department and the operations group actually installed separate fiberoptic networks at about the same time. Each project cost over a million dollars.

Although fossil-fueled plants are not as prone to “silo disease,” inattention to integration can lead to similar waste. More and more plant functions now can be performed better by digital systems, some with wireless capability. However, when different departments act unilaterally to satisfy their functionality needs, the result is multiple, incompatible networks.

Most designers of new fossil-fueled plants have come to realize that siloed functions and piecemeal integration are short-sighted tactics that produce islands of automation, which cannot deliver all of the benefits that digital technology offers. Segregating functionalities also works counter to a key goal of plant design: ensuring that data systems are robust, flexible, expandable, and upgradable well into the future.

It’s high time for the power generation industry to recognize that digital control and communications systems deserve to be linked by a plantwide data network (PDN). The PDN’s role is similar to that of the plant’s electrical distribution system: It provides the backbone and protocols to support all digital systems within the plant (and beyond, if it is part of a fleet). Just as you wouldn’t entrust your electrical buses to the corporate IT department (because—if for no other reason—real-time processing isn’t IT’s strength), the PDN should be designed and managed as a plant system, not just as another tentacle of the corporate IT network.

In addition to process control (distributed control systems, programmable logic controllers, etc.) and plant communications (public address, radios, cell phones, pagers, etc.), other functions that can benefit from linking to the PDN backbone include:

  • Process monitoring (vibration and temperature sensors, chemical monitors, predictive analytics and diagnostic systems).
  • Operator support (maintenance management systems, logs of shifts and rounds).
  • Plant security (closed-circuit video cameras, access-control and personnel tracking systems).
  • Supplemental monitoring/testing (nuclear dosimetery, portable radiation monitors, wireless sensors).

It’s the network!

To get your mental arms around the concept of a PDN, stop thinking about traditional process control techniques and start thinking about how other industries, such as telecommunications, use networks. The Verizon television commercial with the geeky guy in big black glasses and his crowd of network specialists following the customer around is an apt visual.

A high-speed PDN can move critical information into and out of digital systems in near-real time and onto the screens of the operators and engineers able to maximize its utility. Though the capabilities of such networks were originally designed to meet the needs of telecommunication carriers, they have since expanded considerably. As the major computer networking companies like Cisco Systems and Hewlett-Packard have upgraded the speed and refined the practical implementation of such systems for industrial applications, suppliers of process control and plant distributed control systems to the power industry have been moving in the same direction.

The basic foundation of a PDN is physical: its fiberoptic backbone (commonly called a cable plant). Higher in the hierarchy are multiple layers of physical and logical networks. The physical networks embody actual cable and wire and intelligent network switches, while the functionality of the logical networks is defined by the programming of switches to effect specific types of data transfers at the right time.

In a telecom network, cell phone signals jump on and off the hard-wired landline network as necessary. Similarly, a PDN should provide connectivity for wired devices, wireless devices and communications, and enough bandwidth for expanded capabilities in the future.

Can you hear me now? A layered plantwide data network for wireless communications and sharing of equipment control and performance data. Source: Hurst Technologies

Nuclear PDN

Although the safety systems at a U.S. nuclear plant probably won’t be linked by a PDN any time soon, designers of the nonsafety systems are already taking full advantage of the technology. The figure shows a typical PDN architecture that segregates a control network, a performance network, and a support network (all examples of physical networks) but integrates all three via “core” switches to allow plantwide sharing of the data and functionality of all connected devices.

The topology shown is known as an “inverted tree,” with the core switches serving as the trunk and the zone switches providing the limbs extending throughout a plant. Core switches are fed by redundant fail-safe power supplies, typically instrumentation-related power sources. Zone switches generally require only one power supply, but they also can also be dual-powered if necessary. Components considered “mission critical” are powered by two independent supplies. Each of the three networks is itself fully redundant, with dual fiberoptic cables running between its core switches and zone switches.

Usually, devices on the control network support the real-time operation of the plant and thus are considered critical. Devices on the other two networks are deemed less important. The performance network typically plays two roles: keeping track of long-term plant performance and handling monitoring of less-critical equipment. The support network provides two important, but less-time-critical, functions: plantwide communications and integration of all the plant’s diagnostic and maintenance-related systems.

The figure illustrates only one possible PDN topology. Other architectures may be better suited to the layout of a specific plant and/or the extent of its wireless networks. They include the STAR, point-to-point, and mesh configurations, each of which has advantages and disadvantages. The PDN representation shown in the figure was included in a recent utility application for a combined construction and operating license (COL) for a new nuclear unit.

Diagnostic capabilities are inherent in modern digital networks because people and machines are increasingly dependent on the data they deliver. As traffic increases, so does the importance of availability and maintaining bandwidth. PDNs that use high-bandwidth fiberoptic cables and modular network switches are the most reliable, as well as the most scalable to meet expanded needs for data and voice (and video) in the future.

New plant to old: Can we talk?

A presentation at this June’s annual ISA/EPRI Power Industry Symposium provided a peek at the promising future of PDNs at fossil-fueled plants. It describes how Lower Colorado River Authority (LCRA) integrated the digital control and communications infrastructures of a state-of-the-art plant it had recently acquired with those of a nearby power plant it had owned and operated for 40 years.

Three years after acquiring the two-year-old Lost Pines Power Park in 2003, LCRA integrated its facilities (and staff) with those of Sim Gideon Power Plant, whose three units were commissioned between 1965 and 1972 (see POWER, June 2007, "Old plant, new mission"). Eventually, LCRA would like the two plants to share the same communications infrastructure, so the combined staff can conduct day-to-day operations at both sites.

The first step toward that goal was the installation of a layered WiMax/WiFi wireless communications infrastructure covering both plants. The protocols were chosen largely to “future-proof” the system against technology obsolescence. The system—developed jointly by the asset performance management specialist Invensys Process Systems (www.ips.invensys.com) and the industrial wireless networking specialist Apprion Inc. (www.apprion.com)—is reportedly the first of its kind deployed at a large power station.

The system has the following features:

  • A 360-degree WiMax “umbrella” plantwide wireless network accessible by the entire site. It is powered by wide- and medium-bandwidth transceivers, logical integration terminals (which physically connect to the existing fiber IT systems at both plants), and WiFi access points.
  • A wireless plant intercom system with “push to talk” capabilities. It integrates with a PBX (private branch exchange) using VoIP (voice over Internet protocol).
  • The use of wireless communication badges and noise-cancelling headsets by staffers.
  • WiMax connectivity to a remote fuel oil tank farm.

Although the initial deployment simply focused on providing a common communications infrastructure for the staffs of two plants of very different vintage, LCRA’s plans for future use of the wireless PDN are what make it noteworthy. The following functionalities are currently envisioned: noncritical closed-loop level controls and alarming for auxiliary plant equipment, equipment health and condition monitoring, and remote video surveillance. Others will undoubtedly follow, after the system demonstrates what it can do best.

Only the beginning

With digital systems now common in new and old power plants alike, the need to collect and communicate more information reliably continues to grow. One way to make a plant more competitive is to seek new and better ways to improve the performance of equipment and the productivity of personnel.

Recent history makes clear that digital controls and wireless communication are quite capable of helping plant owners achieve both goals. If they are to support the digital systems, digital networks must no longer be treated as afterthoughts by utility management; they should be designed and managed with the same care that other plant systems receive because they are equally important. Although digital networks are new by power industry standards, they are maturing quickly and now command more attention during the design and operation of both fossil-fueled and nuclear power plants.

—Timothy E. Hurst, PE ([email protected]) is president of Hurst Technologies (www.hcinc.com), a consulting engineering firm specializing in instrumentation and control systems for nuclear and fossil-fueled power stations. He also is a POWER contributing editor.

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