Sierra Nevada line crews are gearing up for the second half of a large maintenance job that uses a helicopter to replace a total of 610 insulators on 49 dead-end structures in northern California.
“The guys have been doing a great job,” said Foreman III Lineman Brian Adams. “We have had some delays due to weather and mechanical issues and were still able to finish the first half of the job ahead of schedule.”
The insulators are located on structures along 94.27 miles of the Malin-to-Round Mountain 500-kilovolt #1 line between Redding, California, and Malin, Oregon. Each structure contains 12 insulator strings in need of replacement.
“We replace, on average, one structure’s worth of insulators a day,” said Adams. “Desert Southwest and Rocky Mountain crews are also rotating in during the job, which helps a lot.”
The SN helicopter transports the linemen and equipment to the top of the each structure—a technique called human external cargo, or HEC—saving time and energy and reducing the environmental impact of the job.
“There is very rugged, mountainous terrain in the area, and some structures could not be accessed with a bucket truck,” said Adams. “HEC with the helicopter is working out real well. It’s a great tool to have.”
The DSW and RM crews are taking advantage of the opportunity to practice their HEC processes and procedures. SN Pilot Rory Kirkendall is also splitting flight time with DSW Pilot Logan Schuck to help both meet the annual flight-time requirements to maintain their long-line certification and keep pilots rested and alert.
“We have 12-hour days, seven days a week for three weeks at a time,” said Adams. “That is about eight hours of flying, which is a long time for crews and pilots. There was about one hour of travel each way and loading and unloading.”
Crews worked for two three-week periods in April, May and June, replacing 276 insulators on 24 towers. The second half of the project begins Sept. 30 for three weeks in both October and November to complete the remaining 25 structures. A weeklong break between halves allows crews to rest, prepare for the next big section and make any necessary repairs.
Routine inspections uncover weaknesses
The network of 500-kV lines in northern California is critically important to keeping the state energized, especially during hot, summer months.
During routine inspections, SN linemen noticed hairline cracks in the porcelain bells—also called skirts—in the insulators, which were originally installed in 1966.
“We sent 15 sample insulator strings to Bonneville Power Administration to test their insulating and strength properties,” said Adams. “A few from the dead-end structures failed, and the recommendation was to replace them.”
Hairline cracks commonly occur due to varying temperatures affecting the concrete holding the porcelain skirts in place. As the concrete expands in the heat and moisture, and contracts in cold and dry temperatures, the porcelain around the concrete can crack.
The work was originally slated to occur last year, but the California Independent System Operator requested WAPA to delay as another utility needed to work on a different 500-kV line in the Sacramento Valley.
“You can’t have two 500-kV lines out in the Sacramento Valley,” said Adams. “They’re too necessary for energy delivery. The same goes for working in the summer. We couldn’t do the work in July or August when the temperatures are highest due to demand in Southern California.”
Three structures also provide the unique challenge of traversing sensitive spotted-owl habitat. Crews expect the owls will have fledged by the fall.
“This line is important to California all year ‘round,” said Adams. “If we are able to finish early, we want to release it back into service as soon as possible.”