By Kathleen Davis, Senior Editor
Powerful and speedy electricity transmission is simple. While other parts of the power equation (inside the power plant, inside the substation, inside your home) overflow with complications and details, transmission remains in a unique zen category: It’s 99 percent big towers and long, long wires.
In the U.S., we tend to keep the rather technical name of transmission towers. Canadians prefer hydro towers because they often carry power from hydro plants. People in the UK and throughout most of Europe call them pylons. The best name for a tower comes from Australia, where they”Ëœre referred to as ironmen.
To ensure a healthy and well-fed transmission system, most utilities and transmission system owners have to maintain only those two big ticket items—towers and wires. Sounds simple, but it’s not.
If a Transmission Tower Falls in the Woods, How Much Does that Cost?
Four types of transmission towers exist: suspension (the most common), terminal, tension and transposition. Sometimes one sole ironman can juggle multiple tower types. In addtion, transmission tower manufacturers use four major elements to craft a transmission tower: wood, concrete, steel and aluminum. Most transmission towers are steel, with lattice steel framework leading the way. These towers look like someone basket-weaved steel cross poles up the structure. They might remind a viewer of the Eiffel Tower in Paris, which is probably the most famous lattice tower in the world.
Ironmen are also tall, with an average height between 50 and 180 feet. That’s a lot of tower to manage, especially when paired with the fact that most of the transmission infrastructure is getting old. Many were erected in the 1960s and 1970s.
Utilities are, therefore, dealing with a lot of aging steel that has been exposed to the elements for many years and is beginning to corode. That means many face a lot of maintenance issues with budgets that have been drastically reduced by recession.
Waiting to deal with the rust problem rather than addressing it sooner can cost a company more in the long run, said Steve Feldman, national sales director, protective coatings, North America for PPG, a protective coatings company. PPG recently released a white paper on corrosion. The company discovered shareholder profits had reduced utilities’ investments in transmission tower maintenance, which ultimately produces higher long-term costs, Feldman said.
“As a prominent supplier to utility companies, we see first-hand how a reactive, fix-as-needed approach to tower repairs can actually double or triple long-term maintenance costs,” he said.
The PPG white paper indicates that the towers on which a utility needs to focus aren’t necessarily the oldest towers. They need to focus on those in transition. Some towers can last 20, 30 or even 50 years, depending on the environment, before showing signs of corrosion. Once those signs are prominent, however, a utility has little time to act.
PPG estimates a tower with less than 5 percent rust can hit the failure point within 10 years (see figure). Paralleling the quick slide to failure is the rising repair costs as oxidation continues.
PPG catagorizes transitional corrosion phases into four types. Phase 1 is merely cosmetic. Towers look old but have only about 5 percent rust, mostly around edges and bolts. Phase 2 includes abrasive rust, as well as rust that has moved past edges and bolts to the tower’s horizontal flat areas. Phase 3 includes extensive rust, and Phase 4 is the ultimate downer: The tower falls (see photos of Phases 1 and 2, this page, and Phases 3 and 4, Page 58).
The best and cheapest place to address a corrosion issue is in Phase 1. It requires minimal cleaning and a coat of paint and typically costs less than $3,000 per tower. As the phases go up, so does the cost. Phase 2 needs more cleaning, primer and paint and costs usually top $5,000. Phase 3 is more work, cleaning and paint. Costs can easily climb to $9,000. While Phase 1 is a utility’s best bet in coming in frugal overall, budget issues and the recession make corrosion decisions more difficult. Sometimes, maintenance is put off until absolutely critical.
In the end, though, PPG suggests a wider look at long-term costs is necessary when making today’s maintenance budget decisions.
If your utility has 5,000 towers in Phase 1, it may cost you $14 million to repair. If you let those 5,000 towers drift into the disrepair of Phase 2, however, your price tag is now $28 million. If you continue that wait until Phase 3, costs can reach $44 million (based on the cost numbers per pole listed in the previous paragraph), Feldman said.
“The key is not to focus on the towers and poles that need the most or least significant repairs,” Feldman said. “The most cost-effective approach is to fix towers that are closest to transitioning from one phase of corrosion to the next. That not only saves several thousand dollars in repair costs per tower, but also helps owners identify which towers should be budgeted for immediate repairs and those that can wait one, five or 10 years.”
The right maintenance plan, therefore, can prevent towers from tumbling down.
What about the other half of that transmission equation? Every ironman needs his sidekick—in this case, the wires. Inspection of those thousands of miles of power line in the U.S. transmission system consums much time, manpower, equipment, cash and even aircraft. EPRI, however, has a solution.
EPRI has developed a transmission line inspection robot nicknamed “Ti.” Ti can be permanently installed and cover about 80 miles of line a couple of times each year as it “crawls” along the line identifying numerous issues from grass and trees too close to the right-of-way to just how components along the line are weathering the wilds (see photos of Ti below).
Ti moves along on a shield wire and dodges obstacles like marker balls by using bypasses installed along the line. Ti can automatically unhook itself from the shield wire, transfer to the bypass, navigate around the marker and then return itself to the shield wire.
EPRI is testing and refining Ti’s prototype at its Lenox, Mass., lab. Ti is equipped with high definition and infrared cameras and can be rigged with light detection and ranging (LiDAR) sensors. Ti’s job is to pass along information to the utility about what’s going on along the line, along with specific location information that comes from his global positioning system.
Ti will also reach out electronically to remote sensors along the wire to collect discharge activity data for follow-up by field personnel. Radio frequency sensors built in conjunction with Ti can talk to him about insulators’, conductors’ and connectors’ statuses. EPRI pictures these sensors being environment-specific—lightning sensors in high lightning areas, vibration sensors in high wind areas, etc.
Ti, along with the system’s sensors, can provide a comprehensive picture of line and equipment information that EPRI expects will optimize line maintenance and improve reliability. EPRI has even suggested that purchasing Ti and his eventual robot family in place of large maintenance manpower could move expenses in these areas into capital costs rather than sticking with the operations and maintenance budget plan.
Ti is currently designed to inspect about 12 765kV spans and related structures a day and can reach speeds around five miles an hour. He moves by harvesting power off the line itself and storing it in onboard batteries. In the future, EPRI hopes to make Ti more mobile, allowing him to navigate obstacles without installed bypasses and allowing Ti to be hooked onto most existing transmission line.
EPRI says placing the bypasses for Ti’s system onto new lines is fairly low cost.
Ti’s future looks sunny. EPRI plans to add solar panels, make him smaller and reshape the overall design as he moves through future stages of development toward potential commercial availability in about three years.
American Electric Power will partner with EPRI on a first field implementation of Ti. The utility’s engineers are planning to include Ti and his systems in a 765kV line to be built in 2014.
Whether maintenance is completed by people with paintbrushes or Ti with his robot sensors, many options are available to keep our ironmen and their wire sidekicks up and running for a long time.
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