Scaling Law of Stray Fields from SMES Coil Configurations as Functions of Stored Energy and Maximum Magnetic Field

The recent developments of superconducting magnet technology allow us to construct a small and medium-scale SMES (Superconducting Magnetic Energy Storage System), which would be effectively used for electric power management and quality control because of its high convergence efficiency and its simultaneously quick response of real and reactive power. Since a SMES of this kind should be situated in a power substation or near a demand site, a stray field from superconducting coils restricts its use. The stray field outside a solenoid is analyzed by a series of Legendre polynomials; therefore the results are applied to various coil configurations. We derived the stray fields from various SMES configurations as a function of Rp, where Rp is distance from the coil. In this paper we analyzed the stray fields from single solenoid coil and toroidal coil arrangements, as functions of stored energy E and maximum magnetic field Bm, which are the main parameters of superconducting coil. The stray field from the single solenoid coil configuration decreases as E/Bm, and that from the toroidal coil configuration decreases as (E(n+2)/Bm(2n+1))1/3, where n is the number of coils.