MGM Mirage's $9 billion Project CityCenter is redefining the Las Vegas skyline and adding 102 MW of load demand to NV Energy's system. To meet the growing power needs of this project (the largest privately funded construction project in the United States), the utility designed the new Sinatra substation and installed underground and overhead transmission and distribution infrastructure.

Las Vegas-based Nevada Power Co., now doing business as NV Energy, initiated negotiations with MGM Mirage for the new facilities in 2004. Design commenced in 2006, and construction started in June 2007. The project team is wrapping up the multifaceted $100 million project on schedule, on budget and with no injuries. MGM Mirage expects to open its CityCenter late 2009.

Throughout the project, the electricians, linemen and other workers faced many challenges, namely a compact substation footprint and crowded underground infrastructure. By devising efficient work methods and applying innovative ideas, these skilled craftsmen overcame these challenges and successfully supplied power to CityCenter, a city-within-a-city consisting of a casino, hotels, high-rise condominiums, and retail and entertainment district.

Tight Footprint

The 230/138/12-kV substation was developed adjacent to the expanding Las Vegas Strip, where real estate is scarce and expensive. Consequently, the substation was designed to fit on a 1.6-acre site. A normal open-air design would typically require a 10- to 15-acre site, and a gas-insulated design would normally require a 3- to 5-acre site.

The pie-shaped compact footprint presented many challenges, as well. The project was located next to a major interstate and across the street from the massive CityCenter construction site. The project also presented logistical problems for storing materials. The company stored much of the required materials at several nearby substations. Some of the major equipment was received directly from the manufacturer and installed in place.

The crews also used cranes to place equipment on site. On many instances, crews shut down traffic on the adjacent road to place equipment on site. Much of this work occurred at night to avoid obstructing construction and other city traffic.

Crew Coordination

One of the significant challenges that the utility faced was coordinating work with other utilities. Clark County, Nevada, required the company to obtain approval of its design from all other utilities with underground infrastructure within the street. NV Energy does not typically install transmission lines under streets within the Clark County franchise, because the county, at its discretion, may require NV Energy to relocate facilities within the franchise at its own cost. Typically, NV Energy installs its underground transmission within private easements adjacent to the street to avoid these and other permit restrictions.

Another obstacle was coordinating the work of so many craftsmen on a very tight footprint. On average, NV Energy's crews worked alongside 11 other contractors on the 1.6-acre site. At any given time, there were 55 to 70 workers at the Sinatra substation site and an average of 7,000 employees at the nearby CityCenter site.

“Trying to coordinate the simultaneous work of so many posed a substantial challenge,” said Mario Bonaventura, the substation construction foreman. “We've always had various work-proximity issues at other projects, but not to the degree we experienced at the Sinatra substation. Our abilities to safely squeeze so many individuals and varied work activities on such a small site were often pushed to the limits.”

While one crew worked on the substation, other teams focused on constructing the 230-kV and 138-kV transmission lines. The 138-kV line travels three-quarters of a mile under the road adjacent to the substation and directly behind the Monte Carlo, CityCenter and Bellagio hotels. In order to avoid interrupting critical service to the Bellagio Resort and Casino, crews carefully planned and constructed a high-voltage shoe-fly.

Staying Safe

Crews took precaution to address the many safety concerns on the project. One of the earliest activities was to construct bore and receiving pits to accommodate construction of underground transmission and distribution line duct banks under the interstate. These pits were more than 18 ft deep. Workers sloped the sides of the pit to prevent cave-ins and to facilitate access.

To enhance safe night construction of the underground transmission lines within the busy Las Vegas roadways and to minimize traffic disruptions, team members developed and implemented detailed traffic-control plans.

To maintain progress in extreme temperatures as high as 120°F outdoors and 136°F inside certain construction equipment, workers took regular breaks, drank plenty of water and constructed improvised canopies. Workers typically started work at 5:30 a.m. and performed heavy labor during the morning and light labor or labor within air-conditioned facilities during the hot afternoon.

Innovation

Throughout the project, team members applied innovative techniques. Following are a few examples.

Transmission engineers designed overhead dead-end structures consisting of steel monopoles on concrete caisson foundations to accommodate a compact right-of-way. The engineers selected full-length anchor bolts to reduce the diameter of foundations and the volume of the required concrete. One concrete foundation was 11 ft in diameter and more than 37 ft deep. To fabricate anchor bolt cages within tolerance, workers stood them up to tie the vertical rods and horizontal loops of steel rebar. Some anchor bolt cages took about four days to fabricate.

Two of the overhead 230-kV transmission structures were 180 ft above grade. To install hardware and conductor on these tall structures, the contractor had to rent a special bucket truck.

Crews had to construct a 23-ft-deep trench for the 230-kV underground transmission duct banks to avoid an 84-inch critical water pipeline, which is a primary water source for North Las Vegas. The water utility's engineer was concerned that the loose material used for backfill around the water pipeline would slough off into the trench and cause the pipe to fracture. The project team designed and constructed a 41-ft by 23-ft sling and frame structure to support the pipeline throughout construction of the duct bank.

Overhead Lines

The project consisted of overhead and underground transmission and distribution lines. Workers installed 18 double-circuit, 230-kV steel pole structures supporting 12 conductors and two ground wires.

The crew constructed the overhead lines in phases. In 2008, they constructed the 138-kV lines and temporary facilities to loop the Decatur-Mead 230-kV line into the existing Arden 230/138-kV substation. In 2009, crews completed all new permanent construction, including the addition of two new 230-kV breaker-and-a-half bays and the relocation of 11 poles to move six 230-kV line terminations. Crews were required to adjust a number of the line terminations in the field to maintain the schedule and mitigate delays due to the acquisition of permits.

“It looks easy on a piece of paper to take a line and move it an inch or two, but it's much more challenging when you get out into the field,” said Randy Bosche, construction administrator for the overhead transmission line crews.

Crews carefully scheduled the work to coordinate outages and maintain reliable electric service. Outages were not allowed during the summer months due to operational constraints.

Underground Lines

Crews also installed approximately 2 miles of double-circuit 230-kV and three-quarters of a mile of single-circuit 138-kV underground transmission line.

Each 138-kV circuit consisted of three insulated conductors per circuit, and each 230-kV circuit consisted of six insulated conductors per circuit to accommodate the capacity of the line. In total, crews installed approximately 16 miles of insulated conductor.

Constructing the underground duct bank presented several obstacles. In addition to the interstate highway and water pipeline described above, the crews avoided high-pressure natural gas lines, a jet fuel pipeline, fiber-optic cables and sewer lines. As expected, the various utilities did not maintain good records of the location of the facilities, and the duct bank had to be adjusted to accommodate.

“We had to go 23 ft below the road surface to go under the 84-inch water line. One wrong move and we could wash out a major intersection,” said Wayne Creveling, construction administrator for the underground transmission line crews. “Electricity and gas and water are all in the same slot.”

While boring under the interstate, crews encountered caliche. Caliche is an extremely hard rock, often harder than concrete. To complete the bore, workers had to replace three drill bits per day. On one occasion, the auger struck a horizontal shelf of caliche, causing it to deviate substantially below the intended path. Workers had to pull the auger back out of the excavation, backfill and then restart the bore, ensuring the auger maintained the correct path. The duct bank casings came in 40-ft sections, so the crew didn't have much room to get the pipes into the bore pit and under the freeway. The five 48-inch casings were only supposed to take three or four months to install, but it ended up being a nine-month project.

Unique Fire Protection

Another unique aspect of the project was the installation of two large firewalls that surround the 230/138-kV autotransformer. The special firewalls, designed by a former NASA engineer, protect the 138-kV and 230-kV gas-insulated substation equipment (GIS) in the event of a transformer fire. GIS equipment is very compact and the only installation possible for this small space. The panels are removable to enable quick access to repair or replace damaged equipment. The crew only took two weeks to install the firewalls, which was one of the first utility installations of its kind in the U.S.

By working together as a team, the engineers, linemen, electricians and contractors devised and implemented solutions to a myriad of obstacles in the field. Through teamwork and innovation, NV Energy finished the project on time and within budget, which is no easy feat in today's work environment.

SINATRA FACTS

Within 1.6-acre Sinatra substation:

• One Siemens 230/138-kV, 180/240/300//336-MVA autotransformer (45°/55°C rise)
• Four EFACEC 138/13.09-kV, 30/40/50//56-MVA distribution transformers (45°/55°C rise)
• Total of more than 51,000 gal (376,000 lb) of oil in the five transformers
• One 138-kV ABB GIS six-breaker ring
• One 230-kV ABB GIS four-breaker ring
• Eight 138-kV GIS termination precast vaults
• Three 230-kV GIS termination precast vaults
• Two composite firewalls (41 ft by 28 ft [length by height]) and 58 ft by 28 ft
• Four 138-kV Vee switches
• Six 138-kV CT/PT metering units
• Two Powell 12-kV arc-resistant switchgear with 40 12-kV breaker positions (bank, transfer, feeder)
• Four metal-enclosed 12-kV capacitor banks
• Fourteen 12-kV precast vaults
• Thirty relay panels with 87 SEL relays, plus 10 local control cabinets for the associated GIS
• Five 350-ft, 42-inch casings, bored under I-15, took nine months to complete

Overhead and Underground Transmission:

• Miles of 138-kV XLPE-insulated 2000-kcmil underground cable installed: 4.5 miles
• Diameter of 138-kV underground cable: 4.06 inches
• Miles of 230-kV XLPE-insulated 2500-kcmil underground cables installed: 12 miles
• Diameter of 230-kV underground cable: 5 inches
• Total 1.8 million lbs of transmission cable installed
• Average underground transmission depth: 10 ft
• Deepest underground transmission ductbank crossing: 23 ft
• Miles of 230-kV ACSS overhead conductor installed: 9 miles
• Average overhead transmission line easement width: 10 ft
• Average underground transmission easement width: 30 ft
• Average overhead transmission line pole height: 155 ft
• Overhead/underground riser pole height: 105 ft
• Tallest overhead transmission pole height: 190 ft
• Largest deadend pole foundation: 37.5 ft deep by 11 ft wide
• Average overhead tangent pole embedded depth: 25 ft
• Total foundation concrete: 474 cubic yds
  Source: NV Energy

ELECTRIC UTILITY OPERATIONS

The Electric Utility Operations section is designed to help utility field personnel increase productivity and safety on the job. The section, which goes out to 10,000 Transmission & Distribution World readers each month, carries a monthly theme and includes features and departments such as Life Line and Safety Talk.

To make Electric Utility Operations more valuable to our readers, we'd like to hear from you. Do you know of a lineman or foreman who we could profile in Life Line? Do you know of a safety issue we should feature in Safety Talk? Is your utility working on an interesting or challenging project right now? Has your field crew come up with an innovative work practice or invented a faster or easier way to get things done? If so, please contact Amy Fischbach, Electric Utility Operations contributing editor, at afischbach@tdworld.com, 913-385-7725, or 11525 Hemlock, Overland Park, Kansas 66210.