Offshore wind technology gets better every year with more innovative turbine and blade designs. But no matter how well they design a wind turbine, engineers perpetually confront the unique difficulties of exporting electricity back to shore.
Subsea power cables are built with the demands of open ocean in mind. Multiple layers of alloy and fiber strengthen and protect the power-conducting cables inside. In the open ocean, far from ship anchors and fishing nets, deep-sea communication cables can last for decades without a fault.
Power cables installed near dry land have it much tougher because they are so much closer to the ocean surface, where turbulent weather and heavy machinery can cause havoc. Indeed, an article at RenewableEnergyFocus.com estimated that export cable damage surged by 500 percent in the past 12 months.
Survivability is the central concern of cable manufacturing because oceans bring peril with every wave. Typhoons, fishing trawlers, corrosion — it’s always something. Here’s a quick look at the key challenges with power cables that export electricity from offshore wind farms:
Finding the Damage
Occasionally, a ship anchor will snag a cable and snap it in two. This is bad news because it shuts off a revenue source for the offshore wind operator, but it could be much worse.
A pure break location is somewhat easy to track down because engineers can measure the resistance in a length of power cable and calculate with a fair degree of precision where the electricity cuts off. Then it’s a matter of sending a ship to the estimated location of the break, pulling up the broken cables and using splicing gear to reconnect them.
The much more daunting challenge happens when a cable starts developing significant losses in transmission — often because the cable was damaged and exposed to the corrosion of seawater. This kind of damage is less likely to leave telltale hints about its location, which can bog down the pace of attempted repairs.
Windfarm designers have figured out how to build towers and turbines that can withstand gale-force winds and furious storms. Unfortunately, the worst weather may damage even the most well-built cables, which requires ships to locate the problem and try to fix it.
Repair crews cannot do their jobs in storms that toss their giant vessels around like corks. So they have to wait for the weather to calm down. It might take days; it might take months.
It’s not unheard of for a ship to be at sea for three months in pursuit of a single repair if severe storms continually blow it off course. There are only so many ships available, and they can fix only so many damaged cables.
Once a repair ship locates a cable problem, it has to pluck the cable from the ocean floor and pull it up to the surface. If all goes well, this process won’t damage the cable even more.
After the damaged area of cable arrives at the surface, the next step is to recondition the broken areas, rejoin any damaged conductors, then seal the assembly with heavy-duty splicing equipment. The techniques for repairing and rejoining subsea power cables are well understood. But repairs are still hostage to the first two problems: finding the cable fault and waiting out the weather.
This is Why Subsea Cable Accessories Must be the Best of the Best
All these challenges give offshore wind operators plenty to worry about. The accessories that attach and connect their power cables should not be another source of anxiety.
At PMI, we aim to provide the most durable, practical subsea power cable accessories on the market. We’re big believers in the promise of offshore wind and other marine renewable power sources, but we’re also realistic about the depth of the challenges facing the industry.
It may turn out that difficult cable repair jobs are the price we have to pay for offshore renewables. If so, we’ll do our part to make sure those fixes stay fixed.
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