Upgrading condition monitoring is an excellent goal, but it usually demands making difficult and sometimes impossible connections. This is where wireless links can make their greatest contributions and prove their worth.
For instance, is the Tennessee Valley Authority recently implemented WirelessHART to reach and interact with dozens of new sensors and other instruments at each of its eight combined-cycle plants. These added wireless links allowed the utility to improve and expand condition monitoring at the facilities by implementing Etapro performance monitoring and predictive maintenance software. This solution creates physical models to continuously monitor heat rates and steam flows, and increase overall operating efficiencies, improve reliability, recognize abnormalities and reduce downtime—but the wireless network connections had to be made first (Figure 1).
"We originally considered using wired 4-20 mA, serial, analog HART or Foundation fieldbus, but the quantity of instruments involved and networking costs quickly increased to $2-3 million. To minimize these expenses, we settled on using WirelessHART to monitor the 40-60 new instruments we added at each plant," says Susan Hobbie, PE, senior I&C engineer, Merrick & Co., an engineering services firm in Greenwood Village, Colo., that collaborated with TVA on the project. Hobbie presented "TVA uses wireless as backbone for performance monitoring" at the 2019 Emerson Global Users Exchange in Nashville, Tenn. "These plants also had all different layouts, with two or three units each and control rooms in different locations, so that was another challenge in designing wireless solutions for them."
This article is part of the Wireless Wish List series on industrial wireless networks. View the rest of the series here.
Hobbie reports that digital modernization with WirelessHART lets it serve as the combined-cycle plants' measurement backbone, and create the physical models that TVA wanted to measure applications, including wireless heat recovery steam generator (HRSG) monitoring, wireless circulation water monitoring, wireless leak valve detection, and wireless weather monitoring. The wireless networks at TVA's eight combined-cycle plants use Emerson's 1410 gateways with antennas that can be 600 feet away from the transmitters and other devices trying connect with them to deliver their data. The Etapro software only needs updates from the instruments about once per minute, which will enable their batteries to last eight to 10 years.
"We estimate wireless saved more than $580,000 over the eight plants, which was 15-20% of the total project's material and construction costs. No wire or conduit was needed, minimal downtime was required, and there were no new or extended outages," adds Hobbie. "These savings were achieved even though the different control room locations and other unique features required custom WirelessHART designs for each facility. Even though we used our existing DCS infrastructure wherever possible, we realized we couldn't design all of these wireless networks ourselves. It was a big help that Emerson came to every site and helped us select the right antennas, such as determining when extended-range was needed."
Hobbie concludes that TVA can now create physical performance models as ambient conditions change, which will affect how much steam and power can be produced. "By implementing these wireless technologies, TVA now has a digital infrastructure that can be expanded with minimal cost," she says. "And, with just a 1.5% increase in efficiency at one unit, we could save millions of dollars, and achieve project payback in one year."
