Photovoltaic panels soak up the sun’s energy during the daytime while the blades of the wind turbines spin at night, generating clean, green power for the state of California. To transport this renewable energy to Southern California Edison (SCE) customers, the utility recently energized both new and upgraded transmission lines and built substations between eastern Kern County and San Bernardino County.
Through the Tehachapi Renewable Transmission Project (TRTP), SCE is helping California to reach its goal of deriving 33% of its power from renewable energy sources by 2020. SCE linemen worked alongside contractors to build 250 miles of transmission facilities from wind parks in Kern County, south through Los Angeles County and east to the Mira Loma substation in Ontario.
Because of the sheer size of the project, TRTP was divided into 11 segments. The first three segments consist of 83 miles of new transmission lines, and segments four through 11 include 173 miles of new and upgraded transmission lines and new substations. As of mid-June, all of the overhead lines were completed and energized except for the sixth, seventh and eighth segments, which include the construction of a 3.5-mile high-voltage line underground.
When finished, the project will deliver 4,500 MW of wind and solar energy from the Tehachapi Wind Resource Area 75 miles north to downtown Los Angeles, and then through portions of the Antelope Valley, the Angeles National Forest, the San Gabriel Valley and the Western Inland Empire. Originally, the project was scheduled to be in service by December 2013. However, because of a petition to bury a section of overhead line in Chino Hills, the project is still underway as linemen are working on installing the first section of 500-kV line underground in North America and the fourth in the world.
Installing and Upgrading Infrastructure
During the construction of the overhead project, the linemen constructed two 500/220-kV substations and one new 500/220/66-kV substation. In addition, the crews built an overhead transmission line with single- and double-circuit lattice and tubular-steel structures. These structures varied in height from 135 ft to 260 ft, depending upon where they were situated within the transmission corridor and whether or not they had to cross over other transmission facilities, freeways or highways.
For example, over the course of construction, the linemen had to deal with seven transmission crossings on major freeways, including the construction of 240-ft structures along freeway crossings near I-605 and the San Gabriel Freeway. To remove existing conductor and install new wire, the utility also had to shut down another freeway in two different segments 14 different times, and to minimize traffic disruption, the linemen had to work at dawn in the mornings and on weekends.
The linemen also had to work within the existing transmission corridor, which in some cases, was installed as early as the 1920s through 1940s. At that time, the linemen constructed the line through unpopulated areas with no homes. Since then, however, developers have built housing and commercial buildings all the way up to the transmission corridors. As a result, linemen had to work within a confined area close to homes and backyards while upgrading the lower-voltage single-circuit line with a double-circuit line.
Crossing Sensitive Lands
The linemen not only constructed the new transmission structures near freeways, but they also had to cross federally owned and protected lands such as the Antelope National Forest. In this area, the crews had to abide by regulations set forth by the U.S. Forest Service, the Army Corps of Engineers and the California Department of Fish and Wildlife.
As such, they faced environmental restrictions for threatened, sensitive and endangered species. For example, the lakes, waterways and land are home to such animals as red-legged frogs, California coastal gnatcatchers, the least Bell’s vireo and southwestern willow flycatcher, spotted and burrowing owls, hawks, Arroyo toads, southwestern pond turtles, desert tortoise, ground squirrels and newts.
Before the project began, the California Public Utility Commission (CPUC) conducted environmental studies to determine what impact the project would have on the wildlife. For example, if the field crews impacted the coastal sage scrub, the California coastal gnatcatcher’s natural habitat for foraging, then they would need to replant at a ratio of 3-to-1. If the workers disturbed 1 acre of land, then they would need to later plant 3 acres in a protected land reserve area, but the ratios could be much higher depending upon the species and quality of habitat.
Now that the linemen have finished the construction of the overhead line, SCE’s contractor crews are returning to the affected foraging and nesting areas for the protected species and beginning the restoration process. As part of this project, they are replanting shrubs and landscape material to support the native wildlife.
In addition, the linemen had to adapt their schedule around nesting birds. The linemen avoided the nesting periods for the red-tail hawks and eagles during the construction project, and also mitigated hundreds of stream break crossings and natural waterways through specialized mats and the construction of temporary bridges or archways. Each time it rained, they obtained a permit on how to mitigate the natural waterway path before proceeding with construction. During the six-year project, however, California suffered one of the worst droughts in its history, which wasn’t beneficial for the state but did provide some advantages for the project.
Working From the Air
To minimize the impact to the land, SCE relied on a variety of different helicopters on the project to construct the single-circuit line through the Angeles National Forest. Within this area, the linemen removed an existing lower-voltage line and replaced it with a higher-voltage line. Using an Erickson heavy-lift helicopter, the pilots were able to help the linemen construct the upgraded line within the forest, eliminating the need for roads and lessening the impact to the forest.
Within the city limits, the double-circuit towers were too heavy for the helicopter to lift, and the area is too populated for the helicopters to hover during construction. The forest, however, provided an ideal setting for the helicopter construction to reduce the footprint and impact to the forest.
The linemen assembled the single-circuit lattice towers in a laydown area, and then the helicopter transported them to the job site. The linemen then worked underneath the hovering helicopter to connect the pieces and bolt them together.
The helicopter pilots lifted the crews to many of the work locations, including the remote regions within the national forest with no roads or vehicular access. The helicopter pilots also helped transport materials into the work sites, and remove and install new conductor for the single-circuit lattice towers.
Specially trained linemen worked on long lines and off of suspension platforms to work from the helicopter. When necessary, they were dropped off at the top of the towers with full fall-protection harnesses.
Because the line crossed diverse land and remote territory, the linemen had to face challenges such as weather. For example, the crews had to contend with high winds, icy conditions and frigid temperatures in the national forest.
However, some of the most significant challenges involved safety issues. During the project, SCE worked with multiple contractors with small embedded crews. For example, three primary contractors were responsible for overhead structures and the construction of the substations. To ensure that the crews were all trained in the safe and acceptable work procedures, SCE created and trained everyone on the project in a safety, training and validation program.
The workers received specialized training on the construction of the transmission line and the operation of a crane for a high-voltage line. The utility required contractors to validate the workers’ skill sets and trend the safety activity of the crew. SCE offered incentives to the contract crews to report near-misses and problematic areas, which were a good indicator of the potential for future accidents. For example, if the utility discovered that a lot of the crews were dropping tools off their belts, they would try to work with the contractors to develop a new system of essential tools during the climb and bringing other tools up and down as needed.
Also, each work day started with a mandatory tailboard before any worker went to job site. At each job site, they had a job hazard analysis as well as another tailboard to review the work scope, hazards and safety requirements. All the linemen were responsible for signing the job hazard analysis, and if they did not follow the rules or blatantly violated them, they could be removed from the job site.
When working on the project, SCE focused on three primary components: safety, environmental compliance and productivity. By focusing on safely building the structures and lines and following environmental guidelines, the repetition of work brought about productivity and positive results in the utility’s goal of all the workers going home injury-free. In fact, through a focus on safety, SCE and its contractors finished 2014 on the overhead line with a DART rate of .85 over a total of 7 million work hours.
Burying a High-Voltage Line
While the project is nearing completion, one part of the project remains still underway — the conversion of an overhead line to an underground line. Two years ago, linemen constructed 3.7 miles of overhead line, but they had to halt work on this section of the project when the city of Chino Hills filed a petition to modify the scope of the project. The CPUC then evaluated the petition, and after approving it, SCE and its contractors began work on the project and made plans to complete the underground portion of the line by October 2016.
On the underground portion, the linemen faced the daunting challenge of installing a 500-kV underground portion, which measures approximately 3.5 miles. When undergrounding a transmission line, there are typically three options: a tunnel, direct burial or conduit. In the United States, most of the direct burials are done at lower voltages rather than 500 kV, and they are predominately within duct structures. For that reason, SCE spent a significant amount of time evaluating similar projects in South Korea, India, China and the Soviet Union. The utility also looked at installations in Japan, where the engineers have installed high-voltage lines underground in short spaces and in built-in tunnels.
Because the line is high voltage, SCE had to face three main issues: heat, power separation and cost. Specifically, the linemen had to avoid breaches in the power flow and unevenness in the power line while transitioning the overhead line to a high-voltage underground line. To successfully manage this transition, the linemen are constructing transition stations, which transition the power into an underground configuration and bring it back up to an overhead configuration. Also, the substations feature voltage control. As such, they operate, simply put, as oversized surge protectors.
On the underground portion, the linemen are working on 14 different splice vault locations measuring 64 ft by 10 ft by 10 ft. Each vault comes in eight different segments to form a rectangular shape, and over the course of the project, the crews have completed more than 42 of the vaults.
While the construction of the first vault took nearly 11 hours, the field crews can now complete the assembly in just four hours. Through the experience of the crew in rigging the crane and performing the repetitive work, they have fine-tuned the installation process. Each time, it gets easier and better, and they have learned which one to set first, and the best way to rig it and bolt the pieces together.
Connecting to the Grid
In addition to installing the overhead and underground structures, SCE and its contractors also had to construct substations north of the Angeles Forest and the Kern County region. Predominately, the wind collector system collects the power, and then the linemen construct the line to connect at the utility’s substations.
The individual developers are responsible for connecting into the SCE substations. SCE operates transmission and distribution lines, and it also purchases power from these renewable power producers such as wind and solar farms. When the state required all investor-owned utilities to comply with the Renewable Portfolio Standards of 20% renewable energy, The CPUC recognized the need for the construction of new transmission lines to these remote areas to meet these goals.
As a result, the CPUC ordered SCE to construct segment one of TRTP, believing if they built it, they will come, referring to the alternative energy developers. Their prediction came true as the construction of the TRTP began, and the project triggered a flood of interconnection requests. At that point, the project became a major effort for renewable energy to be delivered to the state. Since TRTP began, the state now requires utilities to acquire 33% renewable energy, and it was the first major project to meet these requirements.
Today, California has wind parks throughout the state, in the Tehachapi area as well as Palm Desert and Hot Springs. The state has created renewable energy zones, which are areas with the most likely amount of renewable energy in wind, solar and geothermal energy.
Through the project, SCE is expanding and enhancing the transmission system to maintain reliability and improve access to areas with potential for wind, solar and other forms of renewable power generation.
Sandra Blain ([email protected]) is the principle manager of major projects for Southern California Edison. She has been with the company for 13 years and is responsible for the execution of major transmission and substation projects. She is the first woman in the company’s history to oversee the construction of a major transmission line.
Jim Sheftal ([email protected]) is a senior project manager for Southern California Edison and has been with the company for four years. In this role, he is responsible for the execution of the first 500-kV underground portion of the project. Previously, he was responsible for building or upgrading many of the utility’s substations.
Powering California with Green Energy
Through the Tehachapi Renewable Transmission Project (TRTP) project, Southern California Edison (SCE) is transporting renewable energy to its customers in Los Angeles and beyond. Here are some fast facts about the project.
- The California Public Utilities Commission approved SCE’s application to build segments four through 11 back in 2009.
- When the project is completed, the TRTP project will be capable of delivering 4,500 MW of clean wind-generated energy that can supply approximately 3 million homes at peak output.
- SCE is the nation’s largest purchaser of renewable energy. Four years ago, the utility delivered about 21.1% of its power from wind, solar, biomass, geothermal and small hydro energy suppliers. Today, about 24% of its power is derived from clean energy.
- The TRTP project is the first major transmission project being constructed specifically to access multiple renewable energy generators in a remote renewable-rich resource area. The project is providing the high-voltage transmission infrastructure necessary to interconnect and deliver the renewable energy resources from the Tehachapi Area to SCE customers and the California transmission grid.
- California was the first state to develop large wind farms in the early 1980s, and Tehachapi has become one of the world’s leading wind energy centers.
Source: Southern California Edison