PURPOSE: To avoid excess temperature rize caused by the local concentration of the current by arranging a plurality of conductor segments each of which has different resistivity in parallel in a section.

CONSTITUTION: A circular arc shape conductor 4 with a limited width is divided into three radially equal parts and each part is made of a material which has different resistivity and is arranged from inside to outside according to the magnitude of the resistivity. These three circular arcs have an identical width and a uniform thickness so that the current dencity is proportional to the current of the DC voltage applied to a feeder part. If the resistivity of the materials is selected suitably, the temperature rise of the inside circular arc and the outside circular arc is approximately the same. The resistivity of other central arc can be adjusted in the same theory. With this constitution, the excess temperature rise due to the local concentration of the current or leakage.