Shielding current analysis by current-vector-potential method: Application to HTS film with multiply-connected structure

• The virtual voltage method is an accurate method for an HTS film with cracks.
• If any part of a crack is just below a coil, the inductive method will be inaccurate.
• A crack detection method is proposed on the basis of the inductive method.
• Both shape and position of a crack in an HTS film can be accurately determined.

The performance of the virtual voltage method is compared with that of the conventional method in which integral forms of Faraday’s law along crack surfaces are treated as natural boundary conditions. As a result, it is found that there is a significant difference between numerical solutions by the two methods. In this sense, not the conventional method but the virtual voltage method should be employed to the shielding current analysis in a high-temperature superconducting film with cracks. By means of the virtual voltage method, the influence of a crack on the inductive method is investigated numerically. The results of computations show that, if the threshold current changes remarkably from its ambient value, a part of a crack is contained in the projection of the field-generating coil onto the film surface. Furthermore, the applicability of the inductive method to the crack detection is investigated numerically.