New cable design research supports U.S. Navy quest for all-electric ship

Engineering researchers develop expertise in helium gas-cooled superconducting power devices useful for naval applications

When Peter Cheetham first arrived at the Center for Advanced Power Systems (CAPS) as a graduate student four years ago, there was a problem that needed a solution. Researchers at the center were working on a million-dollar grant from the U.S. Office of Naval Research to design a power system for an all-electric ship—something that hadn’t yet been done. 

One of the U.S. Navy’s requirements was to use helium gas-cooled superconducting cables to transmit the ship’s electric power to its systems. Current cables were significantly lighter and more compact than traditional copper cables, but they were not able to provide the medium voltage range needed for the job. 

Cheetham was a doctoral candidate at the time and worked with graduate and faculty researchers on the project including Sastry Pamidi, Ph.D., Lukas Graber, Ph.D., Chul Kim, Ph.D. and  Chanyeao Park, Ph.D. Through a partnership with Georgia Tech, the group was studying gases and their electrical properties related to superconductors. 

The group discovered that when helium is used as a cryogen for a superconductor cable, it is the gas that restricts the voltage rating of the cable. By mixing a small amount of gas to the helium, they improved the electrical properties of the helium as a cyrogen. However, this gas blend required a new cable design.

Pamidi with students in lab
Sastry Pamidi, Ph.D., working with students in the CAPS cryogenics lab. Pamidi is professor and chair of the FAMU-FSU College of Engineering Department of Electrical & Computer Engineering. PHOTO: M Wallheiser/FAMU-FSU Engineering

“We tried different gas mixtures using the typical superconducting cable design,” Cheetham said. “We mixed gases like hydrogen and nitrogen to helium and we were able to increase the voltage rating but it was still not enough. Then we tried using a new cable design with the gas blends and found a significant increase in voltage levels with this new process. We are currently trying to optimize the design and look at variations to address this problem.”

The new cable design is known as a superconducting gas-insulated transmission line (S-GIL). While it was developed for helium-cooled power cables (HTS), it can be adapted to other gas mixtures. The novelty of the S-GIL is that it removes the solid electrical insulation from the superconducting cable and utilizes the helium gas mixture. In this way, it acts as both the coolant and insulation for the superconducting cable. The team is now looking at ways to utilize this design for different cable configurations. The new S-GIL design offered an 80-200 percent improvement depending on the gas mixture used. 

Pamidi, the Associate Director of the CAPS and a professor at the FAMU-FSU College of Engineering talked about the research the group was working on. Pamidi’s lab is the only cryogenic facility in the United States studying high voltage engineering. Of those labs, they are the only facility whose research involves very low temperature. 

“When we started this investigation, we did experiments and also modeling studies to understand the properties of gases at cryogenic temperatures,” Pamidi said. ”We collaborated with the Georgia Institute of Technology and jointly published over 20 papers on different elements of these gases. We are the experts in this area in the U.S. and we have developed an international reputation, that’s why companies come to us. We have the facilities and expertise in this area.”

Pamidi’s group has achieved success from the educational front as well. Two undergraduate researchers on the team, Cheetham (Florida State University) and Chanyeop Park (Georgia Tech) earned their doctorates. The two were co-advised by Graber of Georgia Tech and Pamidi. 

“This is a true collaboration,” Pamidi said. “Georgia Tech does most of the modeling work and we do the experimental work. The collaboration started when a researcher in my group went to Georgia Tech to take a faculty position there. We continued working together presenting our work in international journals and conferences.”

Now that the project has finished at a basic research level, the group continues to optimize the design of the S-GIL line and their work with gas mixtures. The applications for their research extend beyond naval applications to electric aircraft and trains. 

The success of this project demonstrates how discoveries found during fundamental research can be developed at the next level. From the original discovery, new topics of related interest continue to arise, including understanding the electrical insulation properties of gases at cryogenic temperatures.