Progress in oil-filled cables and their accessories

After recalling the genesis and growth of the oil-filled cable system of power transmission, and touching upon its reliability as proved by 30 years of service experience, the paper dwells in more detail on recent developments. Improvements in insulating and screening materials and in manufacturing techniques, especially that of precision lapping have warranted higher design stresses. The resulting increased consistency of performance has justified closer design limits. The importance is emphasized of balanced development of both a.c. and impulse performance of high-voltage cable and accessories. Significant reductions in dimensions of oil-filled cable accessories have been effected without reduction in performance level, and the introduction of epoxy-resin castings has permitted a new approach to the design of certain of these accessories. A development of considerable moment is the increase in permissible operating temperatures, which gives oil-filled cable systems overload capacity commensurate with that of the transformers with which they are frequently associated. Long-term investigations have shown that, with suitable materials and laying conditions, operation for very long periods at conductor temperatures up to 110° C is permissible.