New cable design alleviates flaws in superconducting wires

When current flows through a wire, its path is not always perfect. Tiny defects in the wire mean the current must travel a more circuitous route, a problem for engineers and manufacturers seeking reliable equipment.

Through a partnership with industry, researchers from the FAMU-FSU College of Engineering, the Center for Advanced Power Systems at Florida State University and the National High Magnetic Field Laboratory supported the development of a design using multiple strands of superconducting tape to create a cable, minimizing the risk of failure due to faulty points in a wire. When current encounters a fault in one wire, it switches to a neighboring wire to continue moving.

The research, published in Superconductor Science and Technologyhelps solve engineering and manufacturing challenges for manufacturers and could lead to more efficient and less expensive wires for electric motors and many other superconducting coil applications.

“By partnering with Advanced Conductor Technologies, not only are we supporting the development of a new and innovative idea, but we also have a means to quickly scale the technology into applications,” said co-author Sastry Pamidi, interim director of the Center for Advanced Power Systems and chair of the Department of Electrical and Computer Engineering.

“The research we are doing directly translates into low-cost superconducting wire and mitigates equipment failures due to conductor defects.”

How it works

Through previous work with Colorado-based Advanced Conductor Technologies, or ACT, Pamidi’s team supported the development of a superconducting wire technology called Conductor on Round Core (CORC) wire, which served as the basis for off-the-shelf superconducting coils that rely on helium gas for cooling instead of liquid nitrogen. This change gives engineers greater design flexibility because helium remains in the gas phase over a wider temperature range than other media.

CORC wires are made by winding strips of multiple superconducting tapes into a spiral shape. Instead of soldering the strips together, they rely on pressure between the strips to allow electricity to flow from one to the other. This keeps the wire flexible and strong under tension.

If faults are randomly distributed in a wire, it is unlikely that they will cluster in the same location in a cable. In a process called current sharing, current flows from one wire to another when it encounters a fault. This allows manufacturers to use more of the wire they make, minimizing waste and costs.

Create through collaboration

The research is the latest result of the partnership between FSU researchers and private industry. Previous work has brought together CAPS and ACT teachers. This project also included New York-based SuperPower Inc., a manufacturer of second-generation high-temperature superconductor tapes.

FSU researchers first collaborated with ACT through a U.S. Small Business Administration program called Small Business Innovation Research and Small Business Technology Transfer, or SBIR/STTR.

“We don’t do research just for the sake of doing research,” Pamidi said. “It makes an impact. Our work helps companies develop products. Without us, these companies can’t do this work, because we bring scientific expertise and cutting-edge research facilities that directly benefit companies and help them advance their manufacturing processes.”

Collaboration brings benefits to all parties that would not otherwise be available. Participating companies can benefit from world-class engineering expertise and facilities to help them solve difficult engineering problems.

“Florida State University’s expertise and scientific infrastructure have been essential to the development of CORC superconducting cables and wires at Advanced Conductor Technologies since they were first introduced as a commercial product by my company in 2014,” said Danko van der Laan, president and CEO of Advanced Conductor Technologies.

“Our collaboration with FSU, which has lasted for approximately fifteen years, has allowed us to resolve many technical challenges that would have prevented our cables from becoming a successful commercial solution for applications such as fusion, particle accelerators and energy applications.

Why it matters

Superconducting wires have many applications: electric motors and generators, electric aircraft, ships, medical equipment, fusion power plants, artificial intelligence data centers, power transmission lines, high energy physics experimental facilities, etc.

Anywhere engineers want to move electricity, superconducting wires can move it without losses, enabling more efficient machines and magnetic systems, including magnetic levitation used in high-speed trains.

But making superconducting wires is challenging. The manufacturing process inevitably introduces some defects into the yarn. The traditional solution to this problem was to solder multiple parts together to create a long, defect-free length of wire.

Combining wires into cables, as in the solution optimized by the FSU, ACT and SuperPower partnership, is a way to benefit from the benefits of superconducting wires at a lower cost.

“We are very happy to see the result of this work,” said Yifei Zhang, vice president of research and development at SuperPower.

“Thanks to the unique structure of CORC and the way the wires in this work were manufactured, the project successfully demonstrated that spools made with VIC wires, wires considered defective, performed equivalently to spools made with near-perfect wires. This result may change the way wire production yield is calculated, leading to a significant reduction in wire cost.”

The first superconductors required extremely low temperatures, close to absolute zero, to operate. Pamidi and other CAPS researchers are developing new technologies for high-temperature superconducting wires that can carry current without resistance at temperatures as high as 77 kelvins, making simpler and more affordable applications for the technology possible.