The power cables in underground transmission lines consist of a conductor, an insulator, and a metallic sheath.
The metallic sheath serves to protect the cable from external physical impacts. When a large fault current is
applied to the transmission line owing to an accident, the metallic sheath prevents the fault current from penetrating
into the transmission-line current and thus enhances the reliability of the transmission line. However,
owing to the alternating current flowing through the conductor, an eddy current is generated in the sheath and
a loss occurs. Thus, the overall transmission efficiency is reduced. In this paper, an eddy current loss in a metallic
sheath was analyzed using an analytical method, and the results thus obtained were verified by comparing
them with those obtained using the finite element method. In addition, a design was proposed for reducing the
eddy current loss.