All posts by Amy Nordrum

An Oft-Struck Mountaintop Tower Gets a New Lightning Sensor

Post Syndicated from Amy Nordrum original

Säntis Tower in the Swiss Alps is struck by lightning more than 100 times a year

Atop a rocky peak in the Swiss Alps sits a telecommunications tower that gets struck by lightning more than 100 times a year, making it perhaps the world’s most frequently struck object. Taking note of the remarkable consistency with which lightning hits this 124-meter structure, researchers have adorned it with instruments for a front-row view of these violent electric discharges.

On Wednesday, a small team installed a new gadget near Säntis Tower in their years-long quest to better understand how lightning forms and why it behaves the way it does. About two kilometers from the tower, they set up a broadband interferometer that one member, Mark Stanley of New Mexico Tech, had built back in his lab near Jemez, New Mexico.

“You can’t really go to a company and find an instrument that’s built just for studying lightning,” says Bill Rison, Stanley’s collaborator who teaches electrical engineering at New Mexico Tech. “You have to build your own.”

The one Stanley built has three antennas with bandwidth from 20 to 80 megahertz (MHz) to record powerful electromagnetic pulses in the very high-frequency range that lightning is known to produce. The device also has a fourth antenna to measure sferics, which are low-frequency signals that result from the movement of charge that occurs with a strike or from storm activity within clouds“Basically, lightning is a giant spark,” Rison explains. “Sparks give off radio waves and the interferometer detects the radio waves.” 

To anyone who has witnessed a lightning strike, everything seems to happen all at once. But Stanley’s sensor captures several gigabytes of data about the many separate pulses that occur within each flash. Those data can be made into a video that replays, microsecond by microsecond, how “channels” of lightning form in the clouds.

By mapping lightning in this way, the Säntis team, which hired Stanley and Rison to haul their interferometer to Switzerland, hopes to better understand what prompts lightning’s “initiation”—that mysterious moment when it cracks into existence.  

So far, measurements have raised more questions than they’ve answered. One sticking point is, in order for a thunderstorm to emit a lightning strike, the electric field within it must build to an intensity on the order of several megavolts per meter. But while researchers have sent balloons into thunderstorms, no one has measured a field beyond 200 kilovolts per meter, or one-tenth of the required value, says Farhad Rachidi of the Swiss Federal Institute of Technology (EPFL), who co-leads the Säntis research team.  

“The conditions required for lightning to be started within the clouds never seem to exist based on the measurements made in the clouds,” says Marcos Rubinstein, a telecommunications professor at Switzerland’s School of Business and Engineering Vaud and co-leader of the Säntis team with Rachidi. “This is a big, big question.”

In his own research at New Mexico Tech, Rison has laid some groundwork that could explain how small electric fields can produce such big sparks. In 2016, he and his colleagues published a paper in Nature Communications that described experimental evidence showing that a process known as fast positive breakdown can create a series of streamers, or tiny sparks, and may arise from much stronger local electric fields that occur in small pockets within a storm.

If enough streamers occur in quick succession and within close vicinity to one another, they make more streamers, adding up to a streamer “avalanche” that turns into positive leaders, or mini-bolts that branch toward clouds or the ground.

“We haven’t hit any roadblocks yet to say, this is something that isn’t the process for the initiation of lightning,” Rison says. With his evidence in hand, theorists are now trying to explain exactly how and why these fast positive breakdowns occur in the first place.

Meanwhile, the Säntis team wants to adapt a mathematical technique called time-reversal, which was originally pioneered for acoustics, to better understand lightning’s initiation. With this method, they intend to use data gathered by the tower’s many instruments (which include a collection of six antennas called a lightning mapping array, two Rogowski coils to measure current, two B-Dot sensors to measure the current time-derivative, broadband electric and magnetic field sensors, and a high-speed camera) to reconstruct the total path of strikes soon after they happen, tracing the electromagnetic radiation all the way back to its original source.

As has been true of past lightning research, their findings may someday inform the design of airplanes or electric grids, and help protect people and equipment against lightning strikes and other sudden power surges. The Säntis team’s work has held particular relevance for wind farm operators. That’s because most strikes recorded at the tower are examples of upward lightning—which travels from ground-to-cloud instead of cloud-to-ground.

Upward lightning often originates from tall buildings and structures, which can actually create a lightning bolt that shoots skyward, and this process can damage wind turbines. In 2013, the team published one of the most extensive descriptions to date of this type of flash.

More recently, their work has raised questions about why industry safety certifications for aircraft are based on data about downward strikes, instead of upward ones, which commonly occur with aircraft and cause particular kinds of damage that look more like lightning damage reported by pilots and mechanics.

By the end of this year, the Säntis team expects to record its 1,000th lightning strike at the tower. And there’s one more elusive scientific matter with massive practical implications they hope to someday resolve. “If we understand how lightning is initiated, we could take a big step forward on one of the other questions we’ve been trying to solve for a long time, and that’s to be able to predict lightning before it happens,” says Rubinstein.  

Transmission Failure Causes Nationwide Blackout in Argentina

Post Syndicated from Amy Nordrum original

Preliminary reports suggest problems with several 500-kilovolt transmission lines disrupted the flow of electricity from two dams to Argentina’s grid

A preliminary company memo suggests that problems with at least two 500-kilovolt transmission lines were the proximate cause of nationwide blackouts in Argentina on Sunday 16 June. The lines connect a pair of hydroelectric dams to Argentina’s grid. Parts of Brazil, Paraguay, and Uruguay also experienced power outages, though the total number of people affected is not yet clear. 

Government authorities have not yet determined what caused the disconnect and investigations are ongoing. Officials are expected to issue a more comprehensive report within 10 days.

In a statement on Sunday morning, the Secretariat of Energy attributed the blackouts, which began at 7:07 AM local time, to the “collapse of the Argentine Interconnection System (SADI).” The SADI is a high-voltage transmission network operated by Transener that transports electricity from generators, including power plants and dams, to distribution networks that serve tens of millions of customers.

According to a public statement by Edesur, one of Argentina’s largest electricity distributors, the failure occurred along a critical route of Argentina’s interconnection system that supplies the nation’s grid with power generated by the Yacyreta Dam in Paraguay and the Salto Grande Dam on the Uruguay River.

ABB & Siemens Test Subsea Power Grids for Underwater Factories

Post Syndicated from Amy Nordrum original

Putting a power-distribution station on the ocean floor could allow more raw materials to be processed down there

Slowly but surely, oil- and gas-drilling technology is migrating from floating platforms to the seafloor. Pumps moved down there decades ago. More recently, compressors (which boost pressure in a well to keep gas flowing) and separators (which isolate oil from water and silt) have relocated to the murky depths.

Putting this equipment closer to wells makes them more productive and energy efficient. Some oil and gas companies even aspire to build subsea factories that extract and process oil and natural gas directly on the seafloor. These factories would be safe from hazards such as icebergs and hurricanes. They would be controlled remotely, reducing labor costs. Eventually, some believe, offshore platforms could be phased out entirely.

However, all of this sunken gear requires electricity. Today, operators typically string power lines from power plants or diesel generators aboard nearby oil rigs to every piece of subsea equipment they install. That works for a few machines, but it’s impractical to string dozens of umbilicals, as they’re known, to the ocean floor.

Industry suppliers ABB and Siemens are now putting the finishing touches on competing versions of the world’s first subsea power-distribution stations. Once installed, these stations would connect via a single line to a “topside” (maritime parlance for above water) generator, wind turbine, or power plant, and redistribute electricity to underwater equipment. “Our technology is an enabling technology for the subsea factory,” says Bjørn Rasch, head of subsea power for Siemens.

Both projects have been in the works for more than five years. ABB will complete its final round of testing in June and expects to install its first subsea power system in 2020. Siemens tested its version in shallow water in Norway last November and is now talking with clients about putting its first unit in the field. “We’re getting close to where we’re actually deploying this technology in a real project,” Rasch says.

Siemens’s model, which the company calls its Subsea Power Grid, consists of a transformer, a medium-voltage switchgear, and a variable-speed drive. Its distribution voltage is around 30 kilovolts, while its variable-speed drive puts out 6.6 kV. The system can provide electricity to devices with power ratings between 1 and 15 megawatts. The umbilical that hooks it to a generation station also includes an embedded fiber-optic cable so operators can run everything from afar.

One of the hardest parts of building the station, Rasch says, was ensuring it could withstand the high water pressure of the seafloor. Instead of encasing all the equipment in a pressurized chamber, engineers flooded the electronics with a synthetic fluid called Midel. This biodegradable fluid inside the equipment maintains the same pressure as the seawater, which alleviates stress. The fluid also passively cools the device by transferring heat from equipment to the chilly seawater.

Chevron, Eni Norge, Equinor, and ExxonMobile have all worked with Siemens to get the company’s project this far. The next step for both ABB and ­Siemens will be to deliver the first model for installation at an active production site.

Brian Skeels, professor of subsea engineering at the University of Houston and director of emerging technology for the offshore design and consulting firm TechnipFMC, has seen many attempts to “marinize” technologies to work underwater. Dealing with heat is a common stumbling block. If water can’t flow freely around a device, the heat it generates prompts marine life to grow on the equipment, which shortens its life-span. And, Skeels cautions, “what may work in shallow water may not work at deeper depths.”

Both systems are expected to work at depths of up to 3,000 meters and operate for 30 years with minimal maintenance. At the end of their lives, the units can be removed from the seafloor.

A power-distribution center would be just one piece of any future subsea factory—a vision that has captivated the industry for more than a decade. Skeels says the future of subsea processing will depend largely on whether such projects can add more value to the industry than they drain in expense. Investment into subsea processing dried up when oil prices crashed in 2014. Looking ahead, Skeels thinks the technology holds the most potential for remote wells more than 160 kilometers from other facilities.

Hani Elshahawi, digitalization lead for deepwater technologies at Shell, says there are clear benefits to having power readily available on the seafloor. But he doesn’t think subsea factories will supplant all platform activities, or replace any of them in the near future. “It will require decades, in my view,” he says. “We foresee a more gradual and lengthy transition.”

To Rasch at Siemens, though, the industry’s vision of subsea factories does not seem as far out as it once did. “There are many technologies in many companies that are in place or close to being in place,” he says. “This can be realized in the close future, that’s for sure.”

This article appears in the June 2019 print issue as “ABB and Siemens Test Subsea Power Grids.”