No abstract

No abstract

Force-Balanced Coil (FBC) is a helically wound toroidal coil. The FBC can minimize working stresses by selecting an optimal number of poloidal turns. In order to demonstrate the validity of the FBC concept for high field superconducting magnets, a 7-T Force-Balanced Coil (7-T FBC) was designed. The 7-T FBC will have 270-kJ stored magnetic energy with a major radius of 0.20 m at maximum magnetic field of 7.0 T. This coil is a hand-made coil using NbTi superconductor. The 7-T FBC is designed within an allowable radius whose maximum working stress within an allowable stress of the stabilizer of NbTi strand. Then the winding of the 7-T FBC will be carried out without reinforcing materials for NbTi strand. The experiments will be conducted with pool boiling liquid helium cooling.Index Terms-Electromagnetic force, helical coil, high field magnets, NbTi, SMES, the virial theorem.

Force-Balanced Coil (FBC) is a helically wound toroidal coil that can minimize the required mass of its structure by selecting an optimal number of poloidal turns per toroidal turn. A 7-T Force-Balanced Coil (7-T FBC) was designed in order to demonstrate the feasibility of the FBC concept for high field superconducting magnets. The 7-T FBC with an outer diameter of 0.53 m will have 270-kJ stored magnetic energy at maximum magnetic field of 7.0 T. This coil is a hand-made coil using NbTi superconductor. The maximum working stress of the 7-T FBC is lower than the elastic limit of the Cu matrix so that the 7-T FBC can be excited up to the rated magnetic field of 7.0 T without reinforcing materials for the NbTi strand. The winding form is made of aluminum alloy and slots are cut on its surface with the shape of the helical winding with a numerically controlled (NC) lathe. The experiments will be conducted with pool boiling liquid helium cooling in order to measure the quench properties of the 7-T FBC and evaluate the working stresses in the helical windings.Index Terms-Electromagnetic force, helical coil, high field magnets, NbTi, the virial theorem.

The objective of this work is to discuss the concept of back‐to‐back interconnection systems with energy storage, especially with a Superconducting Magnetic Energy Storage (SMES) incorporated into a back‐to‐back DC link. In this case, each converter of the back‐to‐back system is used as a power conditioning system for the SMES coils. Since the AC–DC converter can be designed independently of the frequency of the power system, a two‐way switch is connected to the AC side of each converter. This two‐way switch can select the interconnected power systems. By using the two‐way switches, this system can provide the stored energy in the SMES system to each interconnected power system through two AC–DC converters. For instance, lower‐cost power of each power network can be stored through two converters during the off‐peak hours and made available for dispatch to each power network during periods of demand peak. Then this system increases the reliability of electric power networks and enables the economical operations depending on the power demand. This paper describes the unique operations of the back‐to‐back interconnection with SMES and discuses the optimal SMES configuration for a 300‐MW‐class back‐to‐back interconnection. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(2): 37–43, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20482