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"The rehabilitation of the circuit to Ketron Island was a technically demanding undertaking. Access to the cable ends required island wide power outages. Novinium had the expertise to plan the work to minimize the impact on Tacoma Power and its customers."

Debbie Ruckwardt
Senior Engineer
Tacoma Power

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Tacoma Power Uses Cost-Effective Rejuvenation to Manage 4,800 Feet of Submarine Cable

Some 4,800 feet of submarine cable from Tacoma Power, feeding 14 customers on tiny Ketron Island, was nearing the end of its design life. The utility decided to rejuvenate the underwater line before a fault occurred and has not experienced any faults in the now-guaranteed, rejuvenated cable.

The Company and the Situation

The approximate cable path to Ketron Island is shown in red. Pole terminations on both landfalls provide access to the strands for injection.

Tacoma Power, a division of Tacoma Public Utilities, was created in 1893 when Tacoma, Wash., citizens voted to buy the privately owned Tacoma Light & Water Company. The utility provides electric service to the cities of Tacoma, Fircrest, University Place, Fife, parts of Steilacoom, Lakewood, Ketron Island, and unincorporated Pierce County.

The small Ketron Island community in Washington’s Puget Sound has only 14 year-round residents, but they expect the reliable electric power which Tacoma Power is mandated to provide. Testing of a portion of the 4,800 feet (1,450 meters) of submarine cable feeding the island indicated that the single radial circuit suffered from significant water trees. This finding, along with the age of the cable, indicated reliability should be a growing concern. It was only a matter of time before the first costly underwater repair would be required. The City of Tacoma decided to extend the life of this critical circuit before it failed.

Evaluation Process:

The City had previously received bids to inject this cable, but had not selected a vendor. Novinium submitted a bid that was less than 20 percent of the cost of previous bids and less than 10 percent of the cost of a new cable.

Plastic tubing provides fluid access.
Norm Keitges, Novinium engineering manager, inspecting a fluid-filled tube.
Company
Tacoma Power
Location
Tacoma, WA, USA
Website
Cable Sizes + Length
3-phase, 15 kV, XLPE insulated, 4/0 (107 mm2) conductor, 4,800 feet
Method
Sustained Pressure Rejuvenation (SPR) process with Cablecure® 732 fluid

Solution

Novinium crews injected 4,800 feet of submarine cable with Novinium® Cablecure® 732 fluid.

Results

The utility has not experienced any faults in the rejuvenated line at the time of this publication. “The load on Ketron Island is unlikely to grow appreciably in the coming decades and 40 additional years of reliable service for 10 percent of the cost of replacement are just what we needed,” said Debbie Ruckwardt, senior engineer at Tacoma Power.

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