General light and power supply of Chicago

The development of a distribution system is largely determined by the load density and Us rate of change. The following is a discussion of these factors and their influence on the Chicago distribution system: The d-c. system which supplies the central part of the city includes an area of about one sq. mi. in which the load is expected to reach 200,000 kw. in 20 years. This would economically require substation supply of about 10 substations of 25,000 kw. each. Surrounding the small d-c. area the general light and power supply over the city is by means of 60-cycle, 4,000-volt circuits, except for the larger industrial loads which are supplied from 12,000-volt lines. The load density of the greater part of the 4,000-volt system is about 4,000 kv-a. per square mile, and the economical supply would be from 7,000 kv-a. remote controlled substations spaced about 1.3 miles. The maximum density of load on this system is 10,000 kv-a. which would require 10,000-kv-a. substations. Calculations indicate that, with increasing load densities, the economy of this intermediate distribution voltage disappears, and in the ultimate development higher distribution voltages are necessary.