Toroidal-type shielding coil systems for the power system control SMES

SMES systems for applications of power system control, such as power line stabilization and compensation of power fluctuation, attract interest recently. In these applications, the use of low-loss type conductors as strand cables are necessary to reduce AC losses accompanied with rapid changes of magnetic fields; however, it brings some difficulties of high cost and low mechanical strength of the superconducting coil. To solve the above problems, the shielding coil system, which is composed of a main superconducting coil and a normal shielding coil connected in parallel, were proposed. In the shielding coil system, the fluctuated current at energy input and output is diverted to the shielding coil and only the constant current flows in the main superconducting coil. In this paper, we propose a new shielding coil system of toroidal arrangement, which has low stray magnetic fields in ambient areas. Results of the optimization of coil configurations in the toroidal shielding system are presented. Besides the toroidal systems of the circular elementary coil, those of D-shaped elementary coils, which have lower electromagnetic stress than circular one, are also studied.