Any high-temperature superconductor (HTS) that is developed for power appli
cations will have an optimal working point in temperature (T), magnetic fie
ld (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 a
pplication, there is a need for design tools based on models of the AC loss
es. The models can be of the form P-ac = P-ac(T, B, I, f), where f is the f
requency. In this paper we present a semi-empirical model and apply it to e
xperimental results of AC losses measured on a multifilamentary Bi-2223 tap
e produced for DC applications. The model is based on the Bean critical sta
te 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 meas
ure the losses we used a calorimetric apparatus in which T, B, I, and f can
be varied independently of each other.