California has a strong appetite for electricity. Its residents increasingly favor a supply produced through renewable resources such as wind. Southern California Edison (SCE) is one of the utilities that leads the pack towards meeting state mandates for renewable sources of power in 2010, having put contracts in place for more than 20% of delivered power to come from renewables. A big part of SCE's effort is the Tehachapi Renewable Transmission Project (TRTP), which will deliver wind power to customers in Southern California.

The Tehachapi wind resource area is in Kern County, north of Los Angeles. The route from the wind farm area to the grid traverses a range of land uses, from urban residential to rural farmland. The terrain varies from flat high desert to rugged mountains. Part of the construction for the TRTP takes place in remote, difficult-to-reach locations within the Angeles National Forest

To construct a 500-kV transmission line in California — and across land managed by the U.S. Forest Service — SCE and its owner's agent, Burns & McDonnell, faced a level of scrutiny not experienced when most existing lines were constructed 20 years ago or more. The environmental measures required to permit and begin construction of this transmission line are a harbinger the electrical transmission industry must be prepared to manage as upgrades to the grid are made in coming decades.

Functionality and Aesthetics

TRTP is a true representation of the form-follows-function design principle. The initial segments of the TRTP, which include approximately 75 miles (120 km) of 500-kV and 10 miles (16 km) of 220-kV lines, required an unconventional approach to overhead transmission line design. The most notable issue was having to account for many environmental factors specific to the region and required by the California Public Utilities Commission (CPUC). Additionally, the varying terrain and weather zones presented numerous line design challenges.

The engineer-procure-construct contractor, PAR Electrical Contractors Inc., partnered with Dashiell Corp. as the design engineer (both companies are owned by Quanta Services Inc.). This partnership allowed straightforward incorporation into the design of the construction methodologies required for the project's varying terrain and weather zones. The owner's agent provided engineering design reviews, field engineering, construction management, quality assurance/quality control, project scheduling, document control and environmental monitoring services.

One challenge was accommodating construction along approximately 14 miles (23 km) of mountainous terrain through the Angeles National Forest. Inaccessible sites and restrictions on work within the forest boundaries meant that foundation installation and lattice tower erection largely had to be completed using helicopters. Tower splice designs were developed that accounted for helicopter load-carrying capacities. Additionally, subsurface investigation reports guided the selection of tower sites, reducing potential slope instability amid rugged terrain and potential landslide zones.

A visual specialist from the CPUC analyzed the project to determine what structure types, colors and finishes would be required to minimize the visual impacts. Lattice steel towers were the primary choice and three colors were used. Where the new line parallels an existing lattice steel structure line, the selected design and color reduce visual complexity.

Tower aesthetics also factored into the selected design, which traverses several of the wind farms. The CPUC visual specialist requested a modified tubular steel-pole design that mimics the form of a modern monopole wind turbine mount. This Y-shaped configuration, developed by Thomas & Betts Inc., meets both aesthetic and loading requirements. This particular line segment also is likely to experience the greatest wind and ice loading, so structural integrity was critical.

Additional Factors

Despite Southern California's reputation as a weather paradise, climatic conditions vary through the diverse geographical areas and the dramatic elevation changes from one end of the project to the other. An intensive meteorological study, ordered by SCE, assisted the utility in designing to ensure future reliability. Data from weather stations in the project area was summarized, including wind speeds and icing conditions. In addition to SCE and General Order 95 loading conditions, 15 separate loading zones were identified, each factoring in wind, ice and wind on ice design loads. In spans where loading zones changed, the more conservative loading scenario was incorporated into the design.

The initial segments of TRTP had to cross numerous extra-high-voltage transmission lines. Reliability is critical through these corridors. One critical crossing, known as Haskell Canyon, was a 2,632-ft (802-m) span crossing a 1,000-kV DC line, four 230-kV lines and two 115-kV lines. Another line section had eight 220-kV crossings over SCE-owned lines, four 220-kV crossings over the FPL Energy-operated Sagebrush line, and two 500-kV crossings. Still another segment crossed 11 220-kV lines and one 1,000-kV DC line.

Subconductor oscillation became an issue during TRTP construction of the initial segments. The phenomenon occurred during periods when moderate to strong steady winds were blowing perpendicular to the line. The wake from one subconductor induced vertical motion in the other subconductor of the same phase bundle, which caused uncontrolled oscillation of the bundle, with peak amplitudes as high as 6 ft (1.8 m). This is most common in smooth areas, unobstructed by trees and other obstacles, but in this instance, it also occurred in mountainous terrain.

A quick design solution prevented potential significant wear or fatigue damage to conductors, spacers, dampers and support hardware. Design engineers stepped subconductors of the horizontal bundle approximately 6 inches (152 mm). This horizontal bundle design modification mitigated the oscillation. A line segment crossing mostly flat terrain was stepped over the entire length of the alignment as a proactive measure.

Making It Happen

For the initial TRTP segments, as many as 15 to 20 biological or environmental monitors were active at one time, conducting clearance surveys before crews could move into a site, monitoring nests and spot-checking crews. The constantly changing environment was challenging, but no shutdowns were required for environmental noncompliance, other than self-imposed measures to ensure the project stayed in compliance with all regulations.

Close coordination with a single point of contact for the U.S. Forest Service allowed efficient resolution of environmental and construction issues related to the Angeles National Forest. During construction, the Forest Service determined daily whether work could proceed the following day and what type of work was allowed. This primarily served to minimize the potential for fires, but it did make construction planning a challenge.

To maximize the construction team's ability to manage the entire TRTP effort, enterprise construction management software, Oracle's Primavera P6 Enterprise Project Portfolio Management and Contract Management suite, was selected for the project. The Burns & McDonnell OneTouchPM geospatial project dashboard also was implemented to enhance that tool set.

Biological observations, including the potential presence of active nests and protected plant species, were tracked in OneTouchPM. Biological monitors collected coordinate locations for observations using a handheld GPS device. The data was aggregated, reviewed and delivered to an analyst, who made the data available on maps and in OneTouchPM.

The Safety Factor

Building transmission lines through rough terrain requires unconventional methods. Part of the construction for the TRTP takes place in remote, difficult-to-reach locations within the Angeles National Forest. Construction of the initial segments had to be done either without building access roads or the roads had to be removed upon completion of construction. That made helicopters the primary mode for bringing equipment, crews and materials to each job site.

Construction safety plans had to factor in the rapidly changing weather and wind in the region. Crews able to get on site for the day had no guarantee of being able to get back out. Sites were stocked with all necessary provisions for overnight stays, including food, equipment and first-aid kits. Crews received survival training to prepare for the threat of sudden weather changes or forest fires. All personnel had to be capable of recognizing and responding to the presence of varied wildlife, including mountain lions and rattlesnakes.

All crews were prepared to handle weather issues, from snow and fog to high winds and dust. High winds, in particular, made it impossible at times for helicopter use. It also was difficult to retrieve crews; on several occasions, they had to hike out of the forest because helicopters were grounded.

The OneTouchPM tool was customized to integrate satellite tracking of crew members. Each crew member was outfitted with a satellite transmitter similar to what hikers use. OneTouchPM interfaces with Google Earth Enterprise software to enable live tracking of each person's location.

Moving Forward

In meeting California's goals for renewable power, SCE is breaking new ground to comply with environmental controls that are unprecedented in the industry. As the electrical transmission industry nationwide moves to upgrade an aging infrastructure and accommodate wind, solar, biomass and other renewable sources, utilities and their partners are likely to see a similar regulatory environment.

Development of programs and procedures to manage the complex planning and execution of these projects will be a challenge for all. Before beginning construction of subsequent segments, SCE evaluated the methods and programs that enabled the first segments to remain in compliance with all regulations.


Don Johnson (donald.johnson@sce.com) is manager of Third-Party Interconnection Projects at Southern California Edison. He was project manager for the initial Tehachapi Renewable Transmission Project segments. He has more than 27 years of diverse project management, engineering and design experience in the transmission, substation and distribution business. Johnson earned a BSEE degree from the University of Alabama and completed the project management certification program from the University of California at Irvine.

Ken Gerling (kgerlin@burnsmcd.com) is an associate project manager at Burns & McDonnell and was the project manager for the initial Tehachapi Renewable Transmission Project segments. He also has worked on major transmission projects for Northeast Utilities, San Diego Gas & Electric and Vermont Electric. His expertise is in project planning, design management and construction management. Gerling has a BSCE degree from the University of Missouri and a master's degree in engineering management from the University of Kansas.

Special Mitigation Measures

Once permitting was complete, but before construction could begin, detailed mitigation, monitoring and compliance plans were required for the Southern California Edison (SCE) Tehachapi Renewable Transmission Project (TRTP). The necessary level of planning required to receive approval to begin construction took nearly nine months for the portion of the line that was outside the Angeles National Forest. Receiving approval to build within the forest took nearly two years.

The mitigation, monitoring and compliance plans demonstrated how the construction teams would manage all aspects of the project, including complying with all California Public Utilities Commission (CPUC) regulations and U.S. Forest Service requirements. Factors considered included sensitive plant species, the protected California condor and migratory bird species.

Plant Species

As is the case in much of California, the Angeles National Forest is home to many sensitive plant species. Construction monitors worked to avoid disturbing the mariposa lily species found in the forest. If the plant was found in the construction zone, it was avoided or transplanted to a safe area.

Construction crews also prevented the migration of weed species onto forest property through vehicles or supplies. All vehicles and equipment were washed and free of seeds and plant materials before being moved into the forest, and temporary soil stockpiles were weeded before being transported to construction sites.

Protecting the Condor

The California condor is a state and federally listed endangered species with habitat in the project area. The condors are curious creatures, attracted to colorful bits of plastic and wire or shiny bolts and nuts, known as microtrash on job sites. If the birds swallow these things, they can interfere with their digestive system. If the birds take the material back to chicks in the nest, the chicks may ingest them. In either case, death is likely.

Microtrash patrols were instituted in tower assembly yards and tower sites to remove all materials that fell to the ground during tower assembly or construction. To further protect the condor in selected canyon crossings, the project team installed swan flight diverters on static wires to make them more visible, helping avoid mid-air collisions with the wire.

Migratory Birds

Nearly all bird species in the United States are protected by one or more federal or state laws, especially the federal Migratory Bird Treaty Act, which prevents the capture or harm of most species. Active nests, defined as a nest with eggs or young on the nest, are included in the scope of the law.

During nesting season, generally mid-February through mid-August, nests are often found on partially erected towers, near tower sites or wire-pulling locations, or on construction equipment. An active nest has the potential to shut down work at a tower site or could cause cranes or wire-pulling equipment to be unusable until the young birds fledge.

For the TRTP, nest surveys performed using both ground and helicopter methods in advance of construction helped identify and deal with nesting birds in the project area. Construction was delayed at times during the nesting season. To mitigate these concerns, site monitors surveyed sites for several days before crews were scheduled to move in, relocating nests that were not yet active. In other cases, construction was halted for weeks until access and work on the sites were cleared with the appropriate agencies.

Companies mentioned:

Burns & McDonnell www.burnsmcd.com

California Public Utilities Commission www.cpuc.ca.gov

Dashiell Corp. dashiell.com

Florida Power & Light Co. www.fpl.com

Oracle www.oracle.com

PAR Electrical Contractors Inc. www.parelectric.com

Quanta Services www.quantaservices.com

Southern California Edison www.sce.com

Thomas & Betts www.tnb.com