STATE STREET SUBSTATION
OWNER: Commonwealth Edison
The State Street substation project was the second project to grow out of Commonwealth Edison's ten year optimization plan to add capacity to their Transmission and Distribution system in Chicago to accommodate future growth in energy consumption in a congested urban setting.
State Street was built on the site of an existing parking lot located in a residential/light commercial neighborhood 14 blocks south of downtown Chicago. A city rapid transit elevated train line formed the eastern boundary of the site and operated during the entire project. Given the proximity of the elevated train line and the subsurface conditions of land reclaimed from Lake Michigan in the early 1900's, issues of significant dewatering, earth retention and curtailed work hours near the tracks had to be addressed.
Soil conditions at the site allowed for the use of mat slabs for all of the foundations. Up to 8 ft of contaminated soil had to be removed along with approximately 250,000 gal of contaminated subsurface water. This water was collected in tanker trucks and transported for chemical treatment, filtration and discharge.
The site footprint was large enough to accommodate a partially enclosed substation. The 30/40/50-MVA transformers were installed outdoors, while the 138-kV GIS equipment and a 13.2-kV indoor metal-clad switchgear were enclosed in separate buildings. For aesthetic reasons and to address potential issues of noise, safety and site security, the site was surrounded with a decorative precast concrete wall. On the east and west sides, the wall also serves as the back wall for the GIS building. Exterior wall treatments allow the facility to blend with the commercial buildings in the area. The use of precast wall panel developed in conjunction with the supplier, Spancrete, allowed significant cost savings over conventional block walls constructed as the enclosure on other projects.
The EPC project included demolition of the existing parking lot, new facility design and construction, equipment and materials procurement, and installation and testing of operational equipment. The configuration of the 138-kV portion of the substation consists of an eight-breaker 138-kV GIS ring-bus for four lines and four transformers with space provisions for a ninth breaker to serve a fifth 132/13.2-kV transformer.
The configuration of the 13.2-kV substation consists of two rings connected by a normally open ring-tie circuit breaker. Each 13.2-kV ring contains six buses that supply underground feeders and is connected by bus-tie circuit breakers. Each ring is supplied by two 30/40/50-MVA, 132/13.2-kV transformers with the option of being ties to a future fifth 30/40/50-MVA transformer.
Transformer oil containment design at the substation was more conventional in that the containment structures consist essentially of large concrete tubs, or pits, which serve as the mat foundation for the transformers and the exterior precast walls. By combining five separate transformer oil pits to make two large pits, excavation and concrete work was significantly reduced on the project.
To address ventilation issues, the switchgear and GIS buildings were designed for up to 104 degrees Fahrenheit using only outside air for ventilation, with the understanding that during occurrences of severe heat or humidity, this temperature might be exceeded.
A CO2 gas system and a conventional sprinkler system was used for fire protection.
The Kenny scope of services for this project also included all the underground transmission and distribution work. This included open cut excavation in busy Chicago streets. Kenny self performed the construction work and managed the design and the permitting.