Studies on deformation and mechanical loss of a superconducting coil caused by electromagnetic force

It is crucial to identify mechanical behaviors when developing a practical large-scale SMES (superconducting magnetic energy storage) featuring high reliability and high efficiency. A FEM (finite element method) simulation model was developed to display the nonlinear mechanical deformation of a modified D-shaped elemental coil with a Rutherford type conductor in a 1 kWh/1 MW practical SMES. The model uses nonlinear mechanical characteristics of a conductor measured by bending test. The conductor's nonlinear mechanical characteristics are roughly explained by the frictional slip between two layers in the conductor. This paper describes two types of slip models between the conductor and the coil spacer, taking into account FEM simulation models, and examines the detailed mechanical behaviors of the coil. Analytical results on the nonlinear deformation and mechanical loss of the coil were compared to those actually measured in a 1 kWh SMES test. The FEM results almost coincided with the mechanical deformations of the coil measured in the test.