Eddy-current losses in a semi-infinite solid due to a nearby alternating current

IN many engineering structures one is confronted with the problem of eddy-current losses in conducting solids due to nearby alternating currents. In electric machines such as motors, generators, and transformers, the machine parts exposed to variable fields are made up of laminations so as to break up the eddy-current paths and avoid losses. Yet, in parts of these machines, solid metallic structures do occur which are exposed to alternating fields and which it is impossible to laminate. Among these are end plates of rotors and stators in the field of the end turns, and transformer tanks in the field of current leads. Similarly, in buildings of reinforced steel construction, heavy current leads may cause eddy-current losses in the steel girders. Finally, eddy currents may be excited in sea water or in the earth, either under conditions of zero-phase short-circuit currents in power lines or when alternating currents are provided with ground leads. In problems of interference between power and telephone lines, the distribution of eddy currents and their effect on the interference factors are of interest.