Calculation of AC losses in HTS stacks and coils for large scale applications

Nowadays, research is performed on designing motors, generators, and magnets that would take advantage of the high magnetic field achieved by HTS coils. Although these devices are designed so that their HTS elements do not experience AC fields, hysteretic losses are expected during transient operation.

Calculating these losses is fundamental for performance evaluation and design. In many cases, this boils down to computing AC losses in stacks of tapes that are subjected to transport current and/or applied magnetic field. In this work, we present a homogenization method to model a stack of HTS tapes.

The idea is to find an anisotropic bulk equivalent for the stack of tapes: “washing out” the geometric internal features of the stack while keeping its overall electromagnetic behavior. Our work extends the anisotropic bulk model originally presented by Clem et al. and later refined by Prigozhin and Sokolovsky.

We disregard assumptions upon the shape of the critical region and use a power law E-J relationship allowing for overcritical current densities to be considered. This plays an important role when considering transient response of devices or non-harmonic oscillations. The method presented here allowed for a computational speedup factor of up to 2 orders of magnitude when compared to full 2-D simulations taking into account the actual structure of the stacks without compromising accuracy.