Friday, October 6, 2017

Lost/ComEd Northwestern Generating Station

(Satellite, it was on both sides of California between Addison and Roscoe)

I knew about the Fisk Generating Station because it was an early one built by ComEd, and Samuel Insull pushed General Electric to build a turbine that was significantly bigger than any they had built so far (5000hp). The fact that it is still standing is another reason I know about it. ComEd built their fourth plant about 6 miles northwest of downtown.

1910 rendering showing option for second generating plant. Illustration from "Central Station Electric Service: its Commercial Development and Economic Significance as Set Forth in the Public Addresses of Samuel Insull", from RailwayPreservation
Only the left (south) half of the planned complex was built. It had three units, each with a 20,000hp turbine. The north part of the property appears to have been used for an office building that still exists (street view).

1938 Aerial Photo from ILHAP

Electric Railroad

Near the lower-left corner of the  above 1938 photo, we see an overpass over Elston Avenue. This is the beginning of a double-track elevated railroad that ComEd built west to the C&NW railroad. It was an electrified railroad that used 500v DC (600v according to another source). It had a yard on the west side to store incoming coal and equipment cars and outbound ash cars. It "took its own medicine" by buying its DC electricity from the nearby Chicago Railways power plant. [RailwayPreservation-Railroad] 60-ton locomotive #4 is preserved at the Illinois Railway Museum.

1938 Aerial Photo from ILHAP

Abandoned RR Map

Excitation Current

Each of the 20,000 hp units are standalone with their 10 boilers, turbine/generator, condenser and transformers except for the excitation current. The current has triple redundancy. The primary source is a turbine-driven exciter of 300-kw capacity. The secondary source is motor driven with a 200-kw capacity. And the tertiary source is a storage battery that can supply 140 kw for one hour. [RailwayPrservation-Station]

Steam Piston Driven Auxiliaries

The condenser of each unit is fed by a 36-in centrifugal pump, which is driven at 120 rpm by a 20-in x 30-in Corliss engine. The pump can circulate 40,000 gallons of cooling water per minute against a 20-ft head. The water is drawn from the North Branch and discharged 450 ft. downstream. I normally would not bother to discuss a pump, but note that in a plant full of General Electric equipment they are using a 19th Century era piston driven steam engine. Of course, this engine does have a lot of steam power available with 10 boilers generating steam for the primary turbine.
The turbine is mounted vertically with the generator on top. The end of the shaft holding almost 100 tons of rotating mass rests on an oil bearing. The oil is supplied "under a pressure of 1200 lb. per square inch by a pair of duplex double-acting steam driven pumps, 12-in x 3-in x 18-in of 30-gallon capacity." [RailwayPrservation-Station]

High-Voltage Testing

A very important part of the auxiliary electrical equipment is the high-voltage testing set. It consists of a 200-hp, 220v, three-phase motor with compensator starter, driving a 500kva, 300v, three-phase generator with a 12-kw exciter and a 500kva transformer for raising the voltage to 20,0000, 40,000 or 60,000. There is also a bank of three resistors, each of 5.4 ohms resistance and 1012 amp capacity, and three variable-resistance shunts. The testing set is used for locating cable faults [RailwayPrservation-Station]
Two things caught my eye. Were the piston-driven steam engines needed for the pumps because they required more than 200hp? The voltages are low by today's standards, but this 1912 plant was delivering just 9,000v from the regular transformers. It also raises the question of how do you locate cable faults with voltages up to almost 7 times the designed voltage? Increase the voltage until the problem area melts and then the problem becomes obvious?

Terry Pawelko posted   [Riverview Park]
I loved the Shoots
Christine Opalecky Commonwealth Edison generating Station in background
It is interesting how the size and number of smokestacks changes over the years.


  1. About High Voltage cable testing. I used an old TAKK test set when I worked for GE. I would test in 2 to 5 KV steps and read the leakage current. If current too high, I would stop the test before damaging the cable, the customer could still use the cable but plan to replace it. I rescued the test set when GE closed our shop in 94. Here is a link to it in operation

  2. interesting plant with it's short line railroad.