Commonwealth Edison’s (ComEd) ambitious effort -- the West Loop project -- to bring 345-kV bulk power into Chicago’s central business district to improve reliability has reached its 95 percent completion milestone. The project installs the additional bulk power capacity, much of it underground, to serve Chicago’s growing load requirements, while converting the electric transmission system from a “hub and spoke” design to a network model, by providing central Chicago substations multiple sources of supply. The required completion date is June 1, 2008. According to Bruce Whiteway, Program Manager, “We will finish ahead of that date and under budget.”

The project consists of new equipment at 11 of ComEd’s substations, and two new 345-kV transmission lines. One line is approximately 10 miles in length and connects the ComEd Crawford Substation on the near south side (see diagram) to the new 345-kV substation at West Loop on the north side. A second 345-kV line, approximately 3 miles in length, connects West Loop to the existing Taylor Substation. Approximately 8 miles of the new 345-kV lines are installed underground in trenches in city streets and in a tunnel under the Chicago River. West Loop Substation is located on Goose Island, an industrial area in the north fork of the Chicago River. Tunnels 55 ft below the surface enable the transmission lines entering West Loop to pass beneath the Chicago River.

Whiteway explained, “The circuit distance from Taylor to West Loop is about 3 miles and that portion is entirely underground. Of the 10 miles from Crawford to West Loop, approximately 5 miles is underground; the first portion is overhead. For about the last 3 miles into West Loop, the circuits are co-located in the same trench. While the co-located circuits run in the same trench, we put the cable joints in separate vaults as an added reliability feature.”

Overhead construction included about 3 miles on existing overhead transmission poles and 1.6 miles of new construction on 27 monopoles on concrete caisson foundations.

The 345-kV solid-dielectric cables used for underground transmission are comprised of cross-linked polyethylene (XLPE) insulation and 1600 mm square cooper conductor supplied by Prysmian Cables & Systems. Whiteway said, “The cable is installed in a duct package. We create a matrix of PVC duct in a concrete protective casing buried under city streets. In some places such as under highways and railroads, in addition to under the river, we had to tunnel or push pipe casings to install the cable.”

Major challenges for the utility and its contractors on this job, according to Whiteway included installing cables in the city streets, tunneling under the Chicago River, and installing two huge autotransformers at the West Loop Substation. “With the excellent cooperation and support from the City of Chicago, the street installations went in without complaint,” Whiteway said. The autotransformers were shipped from The Netherlands, where they were manufactured, to the Port of Burns Harbor, Indiana –at the southern end of Lake Michigan. From, there they traveled by barge through Lake Michigan and into the Chicago River to Goose Island where they were offloaded onto a special vehicle for transport to the substation.

Contractors for the project included Kenny Construction Co. as prime contractor and tunneling contractor; Sargent & Lundy, LLC was the primary engineer; HBK Engineering, LLC designed the duct packages and handled the permitting; MJ Electric was the subcontractor for overhead transmission construction and substation electrical work. Cable supply, installation and testing was done by Prysmian.

Other major suppliers were SMIT (transformers at West Loop), Siemens (345 kV gas-insulated switchgear at West Loop), Mitsubishi (gas-insulated switchgear at Taylor), and Trench (345 kV air-core inductors at Calumet).