The Inductive Coordination of Common-Neutral Power Distribution Systems and Telephone Circuits

P R I O R to about 1915, delta-connected 2300-volt, three-phase, primary circuits were used extensively for the distribution of electric current. While some distribution networks throughout the country still operate in this manner, the marked increase in load densities, starting about 1915, often made the retention of the 2300-volt delta system impracticable. In a few instances the development of the particular network was at a point where it was feasible to change from the 2300-volt delta to a 4600-volt delta arrangement but in other cases the existing equipment represented too great an investment for a complete change of this character. From studies of various methods of caring for the augmented load densities it was found that the existing equipment could largely be saved and the capacity of the distributing networks substantially increased by converting them to a 2300/4000-volt, star-connected, four-wire primary system. By about 1925 this system had extended to most of the larger cities and most power companies had found it economical for use in at least some parts of their territories. In using the 2300-volt equipment on the 4000-volt, four-wire system it was necessary to stabilize the neutral conductor in some way. Most of the four-wire systems had the neutral conductor grounded at the * Published in Electrical Engineering, January, 1937. f Mr. J. O ' R . Coleman, joint author of this paper, is an engineer on the staff of the Edison Electric Institute, New York City. 76