Study of Application Possibility on Shielding Coil System for Power System Control SMES

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To reduce the fluctuated current and field in a superconducting coil of the SMES system for power system control such as compensation of power fluctuation and stabilizations of frequency and voltage, feasibility of a shielding coil system, which is composed of a main superconducting coil and a normal shielding coil connected in parallel was studied.Use of a toroidal type shielding coil system was proposed in this study. This type of a coil system had an advantage of low stray fields in ambient space. Fundamental electromagnetic characteristics such as superconductor quantity, fluctuated fields from the shielding coil on the superconducting one and normal loss were studied. As a result, the optimum configuration for a practical scale SMES was obtained. It is also confirmed that the superconductor quantities and the system radius of the shielding coil system were comparable to the usual type one.The compensation for the voltage decent in the normal shielding coil was studied. To verify the operation of the voltage compensator, an experimental shielding coil system, which was composed of coaxial solenoid type coils, that is, a main superconducting coil, a shielding coil and a pair of collection shielding coils. The experimental shielding coil system had the same inductance conditions as the practical scale SMES mentioned above. The voltage compensator was composed of a bridge type converter and the control system. For various current patterns of the SMES system, the resistance of the normal shielding coil and performance of the system were studied. Results showed that the voltage compensator worked properly and the fluctuation of the superconducting coil current was almost suppressed.Electromagnetic forces on the coils were also studied by the finite element method. Results showed that stress in the coils were enough low even in the practical scale SMES.