Central Lincoln crews transfer the final conductor to the newly built steel structure. The 927 AAAC double-bundle conductor is one of two feeds serving the northern half of the district.
The display screen on the FLIR T400 unexpectedly shifts from a pattern of violet hues to bright white; the infrared camera is aimed at a jumper that runs from a tie switch to the 69-kV bus. The jumper is 1,000-kcmil copper and part of a 35-year-old wire bus infrastructure located in a 60-year-old substation of Central Lincoln People’s Utility District.
The jumper is carrying double its usual load and nearing its capacity, as the only other 69-kV feed at this substation has been de-energized. The temperature of the jumper, while very high, remained fairly steady, so the decision was made to continue the process of swinging the de-energized 69-kV line into its new position. More than half of the utility’s 38,500 customers and its largest industrial customer are receiving their power through the closely monitored jumper.
The Lower Olalla substation, located 7 miles (11 km) east of the Pacific Ocean on Oregon’s central coast, is a 69-kV switching station interconnecting five transmission lines and serving one local power transformer. It is the only power source for two-thirds of Central Lincoln’s load, serving 15 area substations, thousands of customers and a large industrial plant. The substation sits in both a 100-year floodplain and tsunami impact area with a mere 1,000-A capacity, limited
operational flexibility and aging infrastructure, giving cause for safety and reliability concerns. Replacing Central Lincoln’s most critical substation was essential.
Collaboration, Cooperation and Coordination
In spite of its efficient staff size of 130, Central Lincoln has developed the capability for the design and construction of its own substations. The rebuilding of the Lower Olalla substation was the largest project in the utility’s 70-year history and involved more than half of the employees, including civil and electrical engineers, a transmission specialist, a substation crew, operations crews, communications and network specialists, relay technicians, and procurement and warehouse staff.
Planning for the rebuild of the Lower Olalla substation began more than 10 years ago. Early project complexities included the acquisition of land, the close proximity of wetlands and nearby flooding hazards. After land acquisition, mitigation and hazard evaluation, planning began with the preparation of the substation one-line diagram. This was a collaborative process involving design engineers, operations personnel and substation craftsmen. The process also included consideration of land and water constraints, safety, operational flexibility, ongoing maintenance requirements and the necessity of physically isolating the energized portion of the substation from the areas of construction. On completion of the one-line diagram, phased build plans were detailed, all National Electrical Safety Code clearances were confirmed, and a load-flow analysis was conducted to identify and mitigate issues that might halt or hamper the construction process.
The final substation design included a larger control building, eight 69-kV SF6 breakers, a 2,000-A main and auxiliary bus with a bus differential, a capacitor bank and transmission distance relaying using fiber-optic cable. The five-phase, six-month plan included keeping the original substation energized, an outage strategy for the five transmission lines interconnected with the substation and raising the substation from 10 ft (3 m) above the mean sea level (MSL) to a final elevation of 16 ft (4.9 m) above the MSL.
Using computer-aided design (CAD) software, the substation one-line diagram was converted into a 3-D model; a parts list was generated along with design specifications for the steel manufacturers and foundation details for local contractors.
In all, the new substation would have more than 25,000 pieces of fabricated steel, bolts, nuts and washers. The steel structures alone would weigh 132,000 lb (59,874 kg), an construction components would include 2,800 ft (853 m) of 3-inch (7.6-cm) aluminum bus, 520 bus compression fittings, 4,000 lb (1,814 kg) of copper for the ground grid and 19,000 ft (5,791 m) of control cable. In addition, three steel transmission deadend structures would be required outside the substation.
With lead times exceeding six months for the manufacturers and suppliers, it was critical for material quantities and design details to be absolutely perfect.