It has long been advocated that large-scale SMES can only be economical with earth (or warm) support; that is, with the Lorentz forces transmitted to the earth through cold-towarm support members. This conclusion was based on assumptions pertaining to the specific conductor and coil design. This paper shows that for certain design concepts, the reverse is true, and more economical systems can be built when using self-support (cold) instead of the earth to react the Lorentz loads. By using a cable-in-conduit conductor, and by combining structural and protection functions in a single aluminum member, it is possible to make a self-supported coil more economical than its earth-supported counterpart.
~TRODUCTION
Designs for SMES systems have been under development for years as a means for providing efficient electric energy storage. Potential applications have ranged from small systems, similar in size to current laboratory magnets, to provide frequency or power quality control, to massive systems designed for diurnal load leveling capable of storing several thousand megawatt-hours. While smaller devices have been designed to be self-supporting, it has long been advocated that large-scale SMES can only be economical with earth (or warm) support. This belief was incorporated to engineering demonstration units, which were required to prove earth-support schemes [ 1 ]. However, recent design advances and the corresponding cost studies have shown that the self-supported approach can be more economical than its earth-supported counterpart for coils storing up to 1000 MWh and more. The realization that all SMES applications in the foreseeable future would be better served by the self-supporting design has a profound impact on the technology demonstration program. Larger SMES units can be demonstrated through the construction of a continuuna of smaller self-supported units. This paper describes the SMES design developed by Bechtel/Martin Marietta (formerly General Dynamics) as part of the Engineering Test Model (ETM) Risk Reduction program. * Work sponsored by the Defense Nuclear Agency under contract DNA001-92-C-0065.