Utility generating stations, supplying electricity to Chicago's streetcars and elevated trains.

In the early 1900's, Commonwealth Edison began furnishing Chicago with what at the time, was a modern network of coal fired generating stations. Prior to then, generating stations had reciprocating units, using piston technology similar to traditional steam locomotives. But the new generating stations constructed at the time instead used steam turbines, which proved to be more efficient. And Commonwealth Edison was then in a better position, to be a practical alternative over the electric railways generating their own power.

Converting From AC To DC

From the large centralized generating stations, electricity is best transmitted at high voltage alternating current to substations in neighborhoods throughout Chicago. And then transformed and converted to the 600 volts direct current used by Chicago's streetcars and elevated trains.


As of 1908, public transportation accounted for 65 percent of the electricity usage. The electric railways used direct current (DC), which at the time was converted from alternating current (AC) using rotary converters located at the substations. And lower frequency AC was best suited for the rotary converters. These generating stations supplied 25 hertz AC to the substations, transmitted at 9,000 volts. Or 20,000 volts to the more distant substations, supplied by the Fisk station. These more distant substations were the three serving Calumet & South Chicago Railway, and the Calvary substation in Evanston.

In addition, these and newer generating stations supplied 60 hertz AC to the substations, transmitted at 12,000 volts. This 60 hertz AC electricity is now of course standard, including for residences. And in 1964, Commonwealth Edison began phasing out the availability of the 25 hertz AC. And the remaining CTA rotary converters were replaced with more modern rectifiers.

The generating capacity of these stations was expanded over the years. Most notably with the pioneering Fisk station, whose original generator units were 5,000 kilowatts each. But those units were soon replaced with newer 12,000 kilowatt units.

1111 W. Cermak Rd.
Opened 1903
10 units 12,000 kilowatts each/total 120,000 kilowatts

25th St. and Quarry St.
Opened 1908
6 units 14,000 kilowatts each/total 84,000 kilowatts

Roscoe Ave. and California Ave.
Opened 1912
10 units 20,000 kilowatts/total 200,000 kilowatts

As of 1921, Commonwealth Edison still supplied more electricity at 25 hertz than 60 hertz. But as of 1929, public transportation's share of electricity usage had declined to 25 percent, with increased typical consumer use of 60 hertz electricity.


All stations supplied strictly 60 hertz electricity.

100th St. and Commercial Ave.
Opened 1921

3501 S. Pulaski Rd.
Opened 1924

State Line and Lake Michigan, Hammond IN
Opened 1929

Fisk generating station, as viewed from CTA's Orange Line.

Commonwealth Edison was controlled by Samuel Insull. And at the time, Commonwealth Edison only served the city of Chicago. Although in outlying northern Illinois, many of the electric utilities were also controlled by Insull. In 1932, Insull resigned from control of all of his companies. The electric companies outside Chicago eventually became Public Service Co. of Northern Illinois, which was absorbed by Commonwealth Edison in 1953. And as a regional electric utility operating in Illinois, Commonwealth Edison became an early major user of nuclear energy, with all nuclear generating stations constructed outside the populated areas of Chicago.

And within Chicago, the coal fired stations were gradually phased out. In 2012, the last three remaining stations (Fisk, Crawford, State Line) were all closed.

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