Experimental and Numerical Analysis on the Inductances of Multi-Layer Superconducting Helical Windings

Equivalent circuits are a versatile approach for electromagnetic modelling of superconductors applications, as they allow to easily include full-scale devices in complex electric grid circuits and to investigate their mutual interaction. However, they rely on the correct definition and estimation of the equivalent circuit parameters. In particular, the inductance can be a critical parameter, especially for AC applications or when fast-transients are required. Nowadays, the estimation of self- and mutual-inductances between helically-wound components (as in superconducting coils or cables) is performed with different analytic formulae or numerical methods. Verifying the reliability of a given approach is not a simple task. This work proposes and validates a numerical model for estimating the self- and mutual-inductances of helical windings realized with High Temperature Superconducting (HTS) tapes. The model is based on the combined use of numerical and analytical methods, consisting of numerically integrating over the whole tape volume the analytical partial mutual-inductances between straight tape segments. The tool allows to get equivalent parameters for both single and multiple tapes' windings connected in series and in parallel. The model is adopted for an HTS coil, composed by three windings, and supplied with AC currents. A novel sample holder allows the coil to be designed and realized to supply each winding individually. Then, multiple tests are carried out by putting in series the single windings realizing inductive or anti-inductive combinations. The tool is validated by comparing both the numerical voltage profiles with those acquired during tests and the inductances estimated from the measurements with those resulting from the model.