Coordinated planning, improved technologies will define ‘grid of the future’

Coordinated planning and improved technologies will help the electric transmission industry develop and maximize “the grid of the future” to use infrastructure more efficiently, taking full advantage of the capacity available, according to three experts who spoke at TransmissionHub’s TransForum East in Arlington, Va., Dec. 6.

Planning for the grid of the future is taking place at the U.S. Department of Energy (DOE), where a “grid tech team” (GTT) comprised of industry experts, DOE officials, and academics is working to define the future grid and to develop a research and development roadmap for the activities that must take place to make that grid a reality.

The grid of the future will have energy and information going from the utility to the consumer and from the consumer to the utility, said Jay Caspary, a senior policy advisor to the GTT on loan from his role as technical director of transmission development at Southwest Power Pool (SPP).

“We’re seeing consumers being empowered, and we expect them to drive the market, to drive the grid and what it needs to do, much more than they have in the past,” Caspary said.

In addition, he said the design of the grid must be “holistic, from the bulk power system all the way down to the end users to facilitate a two-way flow of information and energy.”

Four discrete areas must work together: generation, transmission, distribution, and the end users with their various devices and appliances. “Those are four different spaces with very different rules, very different standards, and very little connectivity between them,” Caspary said.

The GTT, he said, is working to bridge the gaps between those groups to make the future grid more cohesive and efficient.

New technologies

New and improved technologies are also expected to enhance the efficiency of the grid of the future.

Advanced conductor technology will enable utilities to increase transmission capacity by reconductoring existing transmission lines – a faster, easier, and less expensive process than building new lines.

An advance in conductor technology that is expected to make reconductoring more appealing is aluminum conductor, composite core (ACCC) conductor. Dave Bryant, director of technology at CTC Global and who designed ACCC conductor said it can be a smart component of the smart grid.

“Conductors haven’t changed much in over 100 years,” Bryant said. “They’re conductive aluminum strands reinforced by a steel wire. These wires have limitations.”

By contrast to the round strands of conventional aluminum conductor in steel-reinforced (ACSR) cable, ACCC conductor uses conductive aluminum strands that are trapezoidal in shape, providing more of the surface area that conducts electricity than the round strands of conventional conductor.

In addition to having a higher conductive capacity than ACSR cable, their construction also limits conductor sag, which can be critical in ensuring the reliability of the grid.

ACSR conductor is on the left and ACCC conductor is on the right in the accompanying photo at right.

“While inaccurate telemetry data, computer problems, and communications triggered the event, it was ultimately sagging conductors that caused the cascading outages” of the 2003 Northeast blackout in the United States, as well as a similar event in India in July of this year, Bryant said.

In addition, ACSR conductor is limited in temperature to 100 degrees Celsius, because higher temperatures will anneal the aluminum, resulting in a significant loss of strength. That temperature limitation means the baseline for ACSR conductor is approximately 900 to 1,000 amperes. Pushing more current through the line will result in substantial sag, Bryant said.

Over the past several years, conductors have been developed that will accommodate higher temperatures, but will still sag when higher temperatures are reached. That characteristic limits their use to rights-of-way (ROW) where drooping conductors will not cause a problem, Bryant said.

In addition, higher temperatures mean greater line losses.

“About 3% to 4% of all the energy generated is lost via transmission” under normal operating conditions, Bryant said. 

A test conducted by BC Hydro at Kinectrics Lab in Canada showed that, at 1,600 amps of current, ACCC conductor ran 60 to 80 degrees Celsius cooler than other types of conductors of the same diameter and weight. “That’s a huge reduction in line losses,” Bryant said.

In fact, over a hypothetical 60-mile stretch of 230-kV transmission line with a 1,000-amp peak load operated at 53% of its capacity, the difference in line losses between an ACSR conductor and an ACCC conductor would save 20,000 MWh of energy per year. At $50 per MWh, the savings would total $1m per year for the life of the line, Bryant said.

The savings will also result in savings on the generation side. Because more of the energy generated will be available to serve load, generators will not have to generate megawatts that will simply be lost, he said.

“There’s really nothing stupid about using a conductor that can carry twice the capacity of a conventional conductor, reduce line losses by 25% to 40%, and give us reliability capabilities that have only been experienced in aerospace and other infrastructure projects thus far,” Bryant said. “We need to exploit those technologies.”

He also said, “All of this reminds us that it’s cheaper to save a megawatt than it is to produce a megawatt.”

While reconductoring with high-tech wire can increase the capacities of transmission paths, there are also technologies that will enable utilities to maximize the capacity of existing conductors.

“The transmission grid is one of the most blindly operated portions of the utility system,” Tom Cleaver, director of technical sales for The Valley Group, said. “Once it’s out there, we don’t know what’s going on.”

The Valley Group, a Nexans company, markets dynamic line rating (DLR) technology across North America.

Conductor capacity is usually expressed as a fixed number, determined by applying a conservative scenario of high temperatures, no wind, bright sunshine, and no cooling influences on the conductor. Once that number is established, it remains static for the life of the line. 

By contrast, Cleaver said the reality is that the capacity of a given conductor varies with the ambient conditions. Employing DLR technology could result in an immediate increase in available transmission capability.

Tracking and fully utilizing the system’s varying capacity could make it possible to more quickly integrate new generation resources such as gas and renewables, which can be built relatively quickly, than the current paradigm of constructing new transmission resources that can take 10 years or more to permit, design and build.

“Maybe using [the existing system more efficiently] helps bridge that gap,” Cleaver said. “Maybe that helps get us to where we want to go, especially in the short term while we’re planning out … the big stuff that’s going to be in place in 2018 or 2020.”

Dynamic line rating, while not broadly deployed, has been recognized as part of the grid of the future.

“It’s important that FERC and DOE have recognized [DLR] as one of the eight key smart grid metrics, but the only one on the transmission part of the grid,” he said. 

That, Cleaver said, must change.

“We’re not using the [system] efficiently,” he said. “A small puff of wind, a little bit of cloud cover, a little bit colder temperature; all that capacity is there. There is a ton of capacity available on the grid right now that can be reached with a small amount of intelligence and technology.”