Cables from South Korea key to innovative solution for underwater crossing to Quadra Island
Stronger cables, accurate placement, help deal with strong tides
Strong tides are so tough on underwater cables that one of our major BC Hydro submarine cables between Campbell River and Quadra Island failed after only just 12 years.
"The strong tidal current changes had played havoc with the existing cables, by moving them back and forth over the abrasive rocky ocean bottom," explains Russell Dobie, a BC Hydro distribution manager who oversaw the Quadra Island submarine cable replacement.
The project was completed in September after new, more resilient, cables were supplied from South Korea.
BC Hydro first dealt with the cable failure by putting the spare cable into service. But video from a remote operated vehicle showed that the other cables were also in bad shape and would need to be replaced.
The challenge was to install cables that would last for at least 30 years in that harsh marine environment. Here's how it got done, on time and on budget.
To ensure the delivery of power to Quadra Island during the project, the BC Hydro team did a temporary upgrade of the existing overhead lines to Quadra Island. Next came careful research and planning into cable types, oceanographic mapping, and installation methods.
The result? New, more robust submarine cables were purchased and installed more accurately, and they're expected to yield a much longer service life than the existing cables.
Cable installation involved a number of firsts
"It was the first distribution submarine cable designed specifically with a higher stability factor to withstand the high tidal currents," says Dobie. "And it was the first distribution submarine cable purchased from LS Cables in South Korea."
The new cable was designed with two layers of galvanized steel wire armour and a lead sheath to give it an increased weight-to-surface area ratio. That improves longevity, but the weight of the cables – 350 tonnes in total – made them difficult to install. The solution was to use a GPS-controlled barge to lay the cable accurately on the bottom of the ocean.
"This was the largest diameter cable that our crews have installed, and it took a lot of planning, some specialized rigging and a lot of manhandling to get it up the terminal pole and into the manhole," said BC Hydro cable foreman Dave Calder.
To minimize exposure of the cables to strong currents on the ocean floor, at depths of up to 90 metres, the new route was chosen after careful surveying and mapping. BC Hydro senior cable engineer Calin Micu worked with Terra Remote Sensing Inc. and Island Tug and Barge with video from a remote operated vehicle to find a route that avoided the most difficult terrain.
Recovery of the old cables and installation of the new cables was planned for mid-September when the weather is typically good and the currents in the passage were at their lowest.
"Mother Nature forced a one-day delay in the cable laying schedule due to strong winds, but other than that everything went as planned," said BC Hydro's John Oliver, who managed the project.