Losses in HTS carrying AC transport currents in AC external magnetic fields

Any high-temperature superconductor (HTS) that is developed for power applications will have an optimal working point in temperature (T), magnetic field (B), and transport current (I), when the cost of both the conductor and the AC losses are considered. To optimize the use of an HTS in a specific application, there is a need for design tools based on models of the AC losses. The models can be of the form P-ac = P-ac(T, B, I, f), where f is the frequency. In this paper we present a semi-empirical model and apply it to experimental results of AC losses measured on a multifilamentary Bi-2223 tape produced for DC applications. The model is based on the Bean critical state model and it accounts for the combined action of an AC transport current and an AC magnetic field applied parallel to the face of the tape. To measure the losses we used a calorimetric apparatus in which T, B, I, and f can be varied independently of each other.