Work almost finished on replacement undersea power line

The marine work is done and all that remains are the final shoreside connections and testing, and a new undersea power cable between Woronkofski and Vank islands will be ready to carry electricity.

The cable repair barge that pulled up the broken line and laid down 3.5 miles of new cable has left, with the onshore work expected to take until about mid-August, Trey Acteson, chief executive officer of the Southeast Alaska Power Agency, said July 29.

At its deepest, the crossing is about 700 feet, though the broken cable was in water about 300 feet deep, Acteson said.

The line - one of four between the islands - broke in September 2019. The cable moves Tyee Lake hydroelectric power from Wrangell on to Petersburg. Three of the cables are needed to move power, while the fourth is backup.

The new cable, almost twice as thick as the old line, has all three conductors bundled together and can be used on its own to move power, or the three original lines can carry the load, Acteson said, providing strong backup.

Project costs total more than $13 million.

The original cables were installed in 1983. The power agency and its insurer will examine the broken line in hopes of determining what caused its demise, Acteson said.

The agency contracted with Japanese cable company Sumitomo, along with several subcontractors, for manufacturing and installation of the new power line along with removal of the old one that failed, using a remotely operated underwater vehicle for the project.

A 220-foot-long cable barge came up from Vancouver, British Columbia, for the work.

Workers hauled up the 3.5-inch-diameter cable and found it had almost completely broken in one spot, with one remaining strand of the line stretched more than 65 feet.

No wear was visible on the outside of the line, Acteson said.

"Of course, the insurance company is going to do their own investigation and try to make a determination on the root cause of the failure," he said in an interview with Petersburg public radio station KFSK.

"Just simple observation of the ends that were retrieved, it appears that there was a sudden breakage in the cable. Some type of an underwater event triggered that. It could have been sediment, maybe perhaps a cornice of sediment that had built up on top of a ledge there and it cut loose and broke the cable, or something of that nature."

The power agency has borrowed $13 million for the work.

The agency has not raised its wholesale rates to its member communities - Wrangell, Petersburg and Ketchikan - in 23 years, Acteson said, noting that the agency got a very good rate on the borrowed money, paying just 2.5% interest.

Any rate increase to repay the bonds will depend in part on insurance proceeds for the work.

Even without any insurance payments, a wholesale rate hike of less than half a cent per kilowatt hour could cover the bond payments. The agency board will consider the issue at a later date.