Design and Construction in an Urban Environment
Last summer, in the wake of the power outages that crippled the Northeast and Midwest, President Bush issued a “wake-up call” on the antiquated state of the nation's electrical grid, a move eerily reminiscent of the scene that played out in Chicago almost exactly four years earlier. In the summer of 1999, after a month of recurring outages that brought vital parts of the city to its knees, Mayor Richard M. Daley issued an immediate call to action.
The challenge: to construct a comprehensive overhaul of Commonwealth Edison's (ComEd) T&D system to accommodate future growth in energy consumption in a congested urban setting, while ensuring the safety of employees and subcontractors, and providing customers with uninterrupted service during construction. The solution: innovative, flexible and cost-efficient substation design and installation at two new ComEd substations near Chicago's central business district.
After conducting evaluations in the summer and fall of 1999 to identify weak points in the T&D system, ComEd determined that a 138-kV looped system in the Chicago Loop and north side would provide a critical step forward in fulfilling the goals of its overall system reliability program for the city. Among the targets for improving reliability were the addition of the Kingsbury Substation (“Kingsbury”) and the addition of a new State Street Substation (“State Street”). The project team of Kenny Construction Co. (Wheeling, Ill.), Sargent & Lundy (Chicago, Ill.) and M.J. Electric, Inc. (Iron Mountain, Mich.) would complete both substations according to a multi-phase implementation schedule.
The Challenges of an Urban Environment
Construction and electricity generation are high-hazard occupations, particularly in confined urban spaces. For the ComEd project team, safety was the top priority and an integral part of quality control, cost reduction and job efficiency. ComEd tied safety incentives to its contracts, and safety orientations, safe work plans, daily jobsite inspections, fitness-for-duty-testing and ongoing training were required as part of the day-to-day routine. Contractor-initiated training included confined space work, rigging and lifting, flagging and critical lift plans. Root-cause analyses were performed for even the most minor incidents.
At Kingsbury, the substation would be constructed with new, higher-capacity equipment fed from a recently constructed 138-kV gas-insulated substation (GIS) ring-bus located adjacent to the site. The first phase of the program also included building a new State Street substation that also would feature a 138-kV GIS ring-bus fed by 138-kV lines from two separate substations. These two completed projects would provide ComEd with increased capacity, improved reliability and better operating flexibility.
Kingsbury was built on the site of an existing 1920s vintage, five-story warehouse in a residential/light commercial neighborhood a few blocks northwest of downtown Chicago. The site footprint is 110 by 98 ft (34 by 30 m). Because of the small lot size and highly visible urban location, the substation, at 73 ft (22 m) tall, was designed as a fully enclosed substation.
The engineer, procure and construct (EPC) project included demolition of the existing warehouse, new facility design and construction, equipment and materials procurement, and installation and testing of operational equipment. The configuration of the 13.2-kV substation consists of two rings connected by a normally open, ring-tie circuit breaker. The 13.2-kV rings each contain six buses that supply underground feeders and which are connected by bus-tie circuit breakers. Two 30/40/50-MVA, 132/13.2-kV transformers with load-tap changers supply each ring.
The Kingsbury site is bound on the west by an existing six-story warehouse that area hotels use to store wine, on the north by Ohio Street, on the east by a newly constructed 132-kV GIS building and on the south by an alley. A key focus of the project team was to help maintain ComEd's customer relationships by fully addressing a range of issues, from aesthetics to noise to potential vibrations that might disturb the stored wine.
At State Street, the substation 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 ran during the entire project. The existing parking lot sat on land that had been reclaimed from Lake Michigan in the early 1900s. Given the proximity of the elevated train line and the subsurface conditions of the reclaimed land, the team needed to address issues such as significant dewatering and earth retention. The team also contended with curtailed work hours near the tracks during heavy train traffic at rush hour.
At about 300 by 113 ft (91 by 34 m), the site footprint was large enough to accommodate a partially enclosed substation. The 30/40/50-MVA transformers were installed outdoors, while 138-kV GIS equipment and 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 team decided to surround the entire site with a pre-cast concrete wall. On the east and west sides, the wall also serves as the back wall for the switchgear building and the front wall for the GIS building. Exterior wall treatments allow the facility to blend with the other commercial buildings in the area.
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 tied to a future fifth 30/40/50-MVA transformer.
Design and Construction Challenges
Although the two projects share some design similarities, the Kingsbury and State Street project designs are quite different. The most obvious difference is that Kingsbury is a fully enclosed substation while State Street is partially enclosed; as such, the Kingsbury project required a ventilation system capable of moving large volumes of air for transformer cooling, while the State Street project avoided this challenge because the transformers are located outdoors.
A major design issue involved the foundations at both substations:
Kingsbury
The site's soil conditions and foundation loading indicated that a floating slab foundation would be inadequate for this building. Piles, stone column foundations or augured caissons would be required. However, given the vibration sensitivity of the wine storage facility west of the site, driving piles was ruled out. It should be noted here that in most urban areas, lengthy and complex permitting processes can challenge any infrastructure project schedule. Although the city understood the need for the new T&D system and actively worked with the team to obtain needed permits, bottlenecks still occurred.
For example, the city required foundation permits but was less familiar with stone column foundations than with other alternatives. The team, anticipating difficulty in obtaining permits for stone column foundations at Kingsbury, opted instead to use augured caissons. The permitting process also required that at least two soil borings be taken in the center area of the new building site. This typically is done after completing demolition but was hampered in this case by an existing warehouse at the site that had yet to be removed. Given a tight project schedule and the time anticipated obtaining a permit, the team moved to have soil borings taken in the warehouse basement before demolition.
State Street
Soil conditions at the site allowed for the use of mat slabs for all of the foundations. Up to 8 ft (2 m) 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 existing foundations for the adjacent train tracks were about 5 ft (1.5 m) above excavation and required the team to install an earth retention system to prevent the foundations from sliding into the excavation. As a result, the entire site was fully enclosed by sheeting that required diagonal support struts (rakes) extended into the site. The virtual maze of steel that this created had to be traversed to install the below-grade grounding and conduit packages. The foundation portion of the work was successfully completed thanks to the carefully choreographed and safe actions of the design and construction management team, the excavator and the concrete contractor.
Transformers at both substations proved to be a challenge, both in the areas of oil containment and ventilation:
- Kingsbury
Four 132/13.2-kV 30/40/50-MVA transformers at the location contain about 7900 gal of oil each. In the event of a tank rupture, the oil must be safely contained to minimize the risk of fire and prevent the offsite migration of oil. The transformer foundations, which extended from the cable space up to the building's first floor, were hollow boxes that proved to be ideal for transformer oil containment. This alternative allowed the team to avoid the need for associated drain piping and gain precious space in the cable training area under the first floor of the building.
In the area of transformer ventilation, separate chambers or vaults contained the four 132/13.2-kV transformers inside the building at Kingsbury and posed a cooling issue because transformers typically are designed for outdoor installation. The transformers are conventional 30/40/50-MVA substation transformers except that they were supplied without oil pumps or fans mounted on the radiators. External fans in the building divert or force the airflow for the transformers through the radiators.
State Street
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 pre-cast walls. By combining five separate transformer oil pits to make two large pits, the team was able to significantly reduce excavation and concrete work on the project.
To address ventilation issues, the switchgear and GIS buildings at State Street would be designed for up to 104° F (40°C) using only ventilation and a limited amount of ventilation duct, with the understanding that during occurrences of severe heat or humidity, this temperature might be exceeded.
The importance of fire protection in a dense urban setting is a critical aspect of design and construction:
Kingsbury and State Street
Although the Kingsbury and State Street substations are unmanned facilities, Chicago code mandates fire protection systems in all buildings. All air inlet and outlet wall openings must include three-hour fire-rated, UL-labeled smoke and fire dampers to isolate each fire-protected area. Both substations utilize CO
Finally, a pressing architectural design issue in an urban environment involves aesthetics:
Kingsbury
The architectural details of the new Kingsbury building were carried over from the abutting 138-kV GIS building, and building elevations were treated with brick and block and provided with architecturally pleasing louvers. Upon completion of construction, the Kingsbury and GIS building sites were landscaped to satisfy city permit requirements and unify their appearance.
State Street
Here, too, the city requested that the new substation fit in with the general surroundings. The community, which has seen a recent surge in residential growth, wanted a facility that integrated with the architectural appearance of the neighborhood, and for security reasons, ComEd wanted to avoid the traditional look of a substation. Again, it is worth noting that this process can be time-intensive. In another recent project, the city's aesthetic review and approval process took a full year for all parties to agree on the final “look” of the proposed substation. This should be considered when starting any new building project in an urban area.
Reliability Back Online
The Kingsbury project was awarded in July 2000 and the substation energized in June 2001. The State Street project, awarded in March 2001, saw the substation energized in June 2002. ComEd and members of its project team successfully joined forces to complete the new substations, delivering design, procurement and construction on a fast track and on budget in some extremely confined urban areas.
The team succeeded because of the capable and experienced members of the design and construction team, as well as other elements that were in place from the outset, including:
A strong alliance between ComEd and the contractor/engineer team benefited both parties. Evidence shows that the upgrades, maintenance and new construction are achieving measurable results in improved reliability. These results have helped to foster a long-term alliance partnership that, through ongoing refinements, will continue to ensure reliable energy delivery to ComEd customers.
An unyielding commitment to safety that was further developed through the alliance work. Recently, Kenny Construction Co.'s work as the lead and general contractor on the ComEd project earned it the National Safety Council's 2003 Green Cross for Safety Medal.
The ability to remain flexible. As the substation projects illustrate, the team was able to “roll with the punches,” including some dealt during permitting and demolition, to accommodate changes that are an inevitable part of any complex infrastructure project.
The desire to actively communicate with neighbors at both project locations and respond to their concerns. The team's attention to potential construction noise and the architectural design of the new buildings were key to succeeding with these neighbors and other stakeholders in the city.
The new Kingsbury and State Street substations play an integral role in ComEd's T&D system, delivering reliable power to Chicago's central business district. Each time members of the alliance partnership step to the plate to meet a deadline or go above and beyond what is expected, a giant leap is taken to achieve the ultimate goal of these kinds of T&D projects, which is to earn the confidence and support of electric power customers.
Acknowledgment
The authors wish to acknowledge Edward Crockett, lead electrical engineer, Power Delivery Services, Sargent & Lundy LLC; Mike Rowe, director, Commonwealth Edison Co.; and Jon D. Andrews, principal, Tylk Gustafson Reckers Wilson Andrews, LLC.
Frank Shainauskas, engineer director, Power Delivery Services, Sargent & Lundy LLC, is responsible for the design and engineering of medium-voltage substations for industrial facilities and utilities, and high-voltage and extra-high-voltage switchyards for major fossil- and nuclear-fueled generating stations. Shainauskas directs the formulation and implementation of design criteria, as well as the monitoring and coordination of activities of the various disciplines involved in these transmission and substation projects. He graduated from the Illinois Institute of Technology in 1969 with a BSEE degree.
FShainauskas@SargentLundy.com
Karl Miller, executive manager, Kenny Construction Co., is responsible for all aspects of power work including design, procurement, construction, testing and commissioning of power plant, transmission and distribution projects. Miller initiated development of Kenny's Power Group and manages all group projects, budgets, schedules and client relationships, including that with ComEd. He also initiated the group's safety program, which consistently has performed below national averages in all areas. He graduated from Kansas State University with a BSME degree.
KMiller@KennyConstruction.com
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