Electric Power Applications of Superconductivity WILLIAM V. HASSENZAHL, MEMBER, IEEE, DREW W. HAZELTON, BRIAN K. JOHNSON, MEMBER, IEEE, PETER KOMAREK, MATHIAS NOE, AND CHANDRA T. REIS, MEMBER, IEEE Invited Paper The development of superconducting systems for electric power is driven by the promise of improved efficiency, smaller size, and reduced weight as compared to existing technologies and by the possibility of new applications. Superconducting power compo- nents can also contribute to improved power quality and increased system reliability. This paper addresses historical developments and technology status of four superconducting power applica- tions: cables, superconducting magnetic energy storage (SMES), fault-current limiters, and transformers. Today, SMES is the only fully functional superconducting system and it has seen only limited use at grid power levels. A few model or demonstration units exist for each of the other three applications. Superconductivity faces several hurdles on the path to widespread use. Perhaps the most important is the need for operating voltages of 100 kV or more. Though progress in this and other areas has been rapid, con- siderable development is needed before superconducting devices perform reliably in the utility environment. As a result, today, most initial installations are aimed at niche applications and will be installed where space is limited, where power demands are in- creasing over existing corridors, and/or where initial development costs can be offset by enhanced power grid performance. Keywords—Cryogenics, electric power, fault-current limiters (FCLs), high-temperature superconductivity (HTS), power cables, superconducting magnetic energy storage (SMES), superconduc- tivity, transformers. I. BACKGROUND It is instructive to provide a simple description of an electric power system before exploring how superconduc- tivity might contribute to its performance. Though there are Manuscript received December 1, 2003; revised April 29, 2004. W. V. Hassenzahl is with Advanced Energy Analysis, Piedmont, CA 94611 USA (e-mail: advenergy1@aol.com). D. W. Hazelton and C. T. Reis are with SuperPower, Inc., Schenectady, NY 12304 USA (e-mail: dhazelton@igc.com; creis@igc.com). B. K. Johnson is with the Department of Electrical Engineering, University of Idaho, Moscow, ID 83844-1023 USA (e-mail: bjohnson@ece.uidaho.edu). P. Komarek and M. Noe are with the Forschungszentrum Karlsruhe, In- stitute for Technical Physics, Eggenstein-Leopoldshafen 76344, Germany (e-mail: peter.komarek@itp.fzk.de; mathias.noe@itp.fzk.de). Digital Object Identifier 10.1109/JPROC.2004.833674 several important exceptions, electricity is produced by a generator, converted to an appropriately high voltage by a transformer, carried by a transmission line over long dis- tances, transformed to a voltage that is appropriate for local distribution systems, carried to a local load by a distribution line or cable, and finally used for a variety of purposes. Along the path, there are various elements, controls, and feedback systems that ensure the near-continuous operation of the power grid, even under upset conditions that may be short- or long-lived. In principle, most of the conventional components of an electric power system could be replaced by a superconducting equivalent. However, the tremendous developments that have occurred over the past century—as a large fraction of the world has been electrified—have led to conventional components that are effective and simple. These attributes combined with large-scale production deliver low costs and provide a significant barrier to the introduction of any new technology. Electricity as we use it is not available in a natural form. It must be converted from some other source. By tracing the path of the energy, it is clear that only a fraction of the ini- tial energy is converted to electricity and that an even smaller fraction is delivered to the consumer. Most electricity is pro- duced by converting heat to rotary mechanical motion that powers a three-phase electrical generator. Generators are typ- ically 95% efficient or better in carrying out this conversion. Without going into details, Table 1 shows a range of effi- ciencies in the production of electricity. The systems that require conversion of thermal energy to mechanical energy and then to electrical energy are subject to thermodynamic limits (Carnot efficiency [1]) related to the upper and lower temperatures of fluids in the turbine systems. Hydroelectric power looks very good in this comparison, so it is no surprise that Europe and the United States use almost all the water resources available to produce electricity. Many developing countries are building dams for power production. Wind and solar will eventually become important sources of electricity 0018-9219/04$20.00 © 2004 IEEE PROCEEDINGS OF THE IEEE, VOL. 92, NO. 10, OCTOBER 2004 1655