Rebuilding for reliability
As Minnkota’s blink outage efforts wind down, line rebuild projects ramp up.
Nearly 20,000 feet of power line conductor sped off a reel toward the sky during a sunny August morning south of Roseau, Minn.
Minnkota lineworkers were stringing the aluminum wire as part of a complete rebuild of 15 miles of 69-kilovolt (kV) transmission line. Crews disassembled the aging line earlier in the summer before setting and stringing the new wooden structures placed about 350 feet apart.
Line rebuild projects will become a summer routine in upcoming years as Minnkota begins to wind down its blink outage mitigation projects. A multiyear effort, blink mitigation included adding technologies to 1,000 miles of existing lines to limit exposure to momentary outages. While reliability and performance could be improved on some existing lines through blink mitigation, others were identified as needing a full rebuild.
The rebuilds started in 2018 with improvements in the Fargo and Lakota, N.D., areas. Nearly 100 miles of line is scheduled to be rebuilt by 2022.
At a cost of about $5.5 million, the Roseau-area project will provide a large region with better reliability, said John Thompson, project lead. It includes the replacement of a three-mile stretch of 69-kV line from the Malung switch to the Stafford switch and a 12-mile stretch of 69-kV line from Stafford to the Badger substation.
“We’ve been doing a lot of blink mitigation,” Thompson said. “Now these are some of the early projects for total rebuild. It will increase the capacity and reduce the blinks because of the added overhead shield wire for lightning protection.”
At an average height of 60 feet, the new standard 69-kV transmission structure in the Minnkota system is about 20 feet taller than the original structures. In addition to an improved structure design and new conductor, the project will include static wire to protect from lightning strikes.
The line’s original copper wire is being replaced with aluminum wire, which meets Minnkota standards. Overhead copper lines are among the oldest on the Minnkota system and have increased maintenance requirements. All copper conductor on the Minnkota system will be replaced by 2022.
“The copper wire is going to be stored for security as it comes down,” Thompson said. “It will be salvaged based on the weight.”
Minnkota is taking on a large share of the project itself in the Roseau area, with contractors helping with such items as framing of the structures and material handling and kitting. The Minnkota Transmission Department set and installed wire on all the structures.
“We’ve had a few outages up there,” said Braden Nelson, project planner. “It’s time for an upgrade. As blink mitigation winds down and our maintenance is starting to get caught up, we’re hoping to get a few more of these big projects done with our own crews.”
Minnkota also is resetting the Stafford switch during construction, moving it several feet to the west and adding height to the structure to make room for the static wire.
The new conductor was strung with a four-drum puller, which has its own engine that drives the drum. It is equipped with rope used as the pulling line. The line was pulled through the travelers in the sag section and attached to the conductor. The conductor was then pulled in by winding the pulling line back onto the drum.
“We’re putting in larger conductor for more capacity,” Nelson said. “It was an old line that was in pretty tough shape.”
Minnkota’s 69-kV rebuild program utilizes the 69-kV Transmission System Study, which is completed by the Transmission Planning Department every five years.
The study reviews several factors, including the capacity, performance, condition and age of every 69-kV transmission line in Minnkota’s system. The 69-kV rebuild program team annually reviews the proposed projects from the study to recommend the priority order.
Minnkota hopes to rebuild about 20-30 miles of line per year at an annual cost of $6-7 million.
69-kV Rebuild Timeline
2018 – West Fargo-Warren – 2.7 miles
2018 – Lakota-Stump Lake Rebuild – 7.2 miles
2019 – Badger-Stafford-Malung Rebuild – 15 miles
2020 – Hensel-Glasston-Lincoln Rebuild – 21.5 miles
2021 – Mandt-Park River – 5.7 miles
2021 – Williams-Lund – 20.4 miles
2022 – Moranville-Williams – 19.9 miles
2022 – Thief River-Northland – 2.2 miles
Main image: Minnkota crews work on the Malung to Stafford line section. (Kevin Jeffrey/Minnkota)