- Fiber Optic Cable Addition
Portland General Electric (PGE) plans to install a fiber optic cable on the Bethel-Round Butte 230-kV circuit. This installation will provide reliable high-speed data between PGE resources. We performed a preliminary design assessment for installation of fiber optic cable on the existing transmission line (Phase 1), followed by a 60 percent design and constructability, permitting and land rights assessments (Phase 2).
The Bethel to Round Butte 230-kV transmission line is 99 miles long, in north central Oregon. It comprises a variety of structure types, including wood H-frames, aluminum lattice guyed masts and lattice steel towers. The line crosses flat terrain, with densely populated communities and farmlands east of Salem. It also crosses mountainous terrain further to the east, including Willamette, Mount Hood and Ochoco National Forest lands as well as the Warm Springs Indian Reservation.
In PGE territory, lightning strikes are not prevalent, so most existing lines have minimal overhead ground wire (OHGW) installed. Due to the absence of OHGW attachments, all-dielectric self-supporting (ADSS) fiber optic cable was considered for the installation. Since ADSS cable does not have metallic components, it can be installed in close proximity to energized conductors. The ADSS cable considered for this project was a high strength 144 fiber cable from AFL, DNA-30317. We collaborated with AFL to provide electrical stress diagrams for the different structure configurations. The diagrams provided recommendations for ADSS placement in relation to the existing electrical conductors.
ADSS cable tends to produce design challenges when installed on existing infrastructure. For this application, the primary challenge was the mechanical ice loading on the ADSS cable, which generates significant sag compared to metallic cables. ADSS cable’s small weight-to-diameter ratio, which is less than metallic cables, causes ADSS cable to blow out faster and further than the existing conductors. Wire-to-wire clearances were unique, due to the numerous static and dynamic weather conditions and also depending on the location of the ADSS in relation to the existing phase conductors.
Our team provided a cost-effective design solution for the ADSS installation considering materials, access, constructability and maintainability.
- Project management
- Detailed engineering
- Material procurement support
- Permitting support
- Construction support
- Install ADSS fiber cable on existing infrastructure in various terrain conditions
- Design to minimize Federal Aviation Administration (FAA) requirements
- Complex design requirements to accommodate ADSS on various structure types
- Design for various static and dynamic wire conditions to meet clearances