Prospects brighten for future superconductor power cables

New research from the National Institute of Standards and Technology (NIST) suggests that next-generation, high-temperature superconductor (HTS) wire can withstand more mechanical strain than originally thought. As a result, superconductor power cables employing this future wire may be used for transmission grid applications. Projected to become available in three to four years, the advanced superconductor wire (known in the industry as second generation HTS wire) is expected to cost less than the HTS wire used in today’s superconductor power cables. The NIST research is described in the Nov. 17 issue of Applied Physics Letters.

Superconductor power cables can carry three to five times the power of conventional copper cables. Compact, underground superconductor cables can be used to expand capacity and direct power flows at strategic points on the electric power grid and can be used in city centers where there is enormous demand, but little space under the streets for additional copper cables. One important challenge in using this next-generation HTS wire in such applications is the need for sufficient strength and resiliency to withstand the stretching and bending that occurs during power cable fabrication and installation.

Using superconductor ceramic coatings on metallic substrates fabricated by American Superconductor Corp. and Oak Ridge National Laboratory, the NIST researchers tested the material’s electromechanical properties. According to lead author Najib Cheggour, they found that these advanced wires could stretch almost twice as much as previously believed without any cracking of the superconductor coating and with almost no loss in the coating’s ability to carry electricity.

Moreover, the NIST team found that strain-induced degradation of the superconductors’ ability to carry electricity is reversible up to a certain critical strain value. That is, the materials return to their original condition once the strain is relieved. The strain tolerance of this future HTS wire was found to be high enough for even the most demanding electric utility applications. The discovered reversible strain effect also opens new opportunities for better understanding of the mechanisms governing the conduction of electricity in this class of superconductors.