Abstract :
ASSUMING that satisfactory 66-kv cable could be obtained, the Commonwealth Edison Company, Chicago, Ill., in 1926 adopted a new system plan1 which included 66-kv underground lines of 60,000-kva carrying capacity that practically constituted a bus extending across the city and sectionalized at the generating stations. The record of failures on this cable, which began shortly after it was placed in operation late in 1926, gave unmistakable evidence (Fig. 1) that this assumption was not entirely warranted; and, further, that there were some marked differences in the quality of the insulation furnished by the different manufacturers. There resulted a great impetus to the investigations2,3 on cable for lower operating voltages that had been in progress in Chicago for several years.
