EMF cable survey conducted

Using unique device
Fri, 03/03/2017 - 10:15am
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“The goal (of National Grid) is not to leave a hazard to the public, and leave the cable well-protected.”

That’s what National Grid Engineer David Campilii told The Block Island Times on Tuesday while conducting a survey of the utility’s sea2shore cable at the Fred Benson Town Beach that transmits electricity from the Block Island Wind Farm to, at this point, the mainland. Campilii, along with other representatives from National Grid, were on-island to address the cable’s inadequate burial depth, and associated electromagnetic field concerns.

Campilii said that during the cable installation process in June of 2016, the jet plow, the machine used to forge a six-foot deep trench to install the cable, encountered hard seabed “when it came ashore.” As a result, according to Campilii, the cable was only buried three to four feet beneath the seafloor, about 200 feet off the Town Beach, for a stretch of approximately 80 feet in that location.  

Camipilii, National Grid’s Underground Cable Engineering Specialist, said the Rhode Island Department of Environmental Management and the Coastal Resources Management Council requested that the utility provide an electromagnetic field survey to determine if the cable’s “levels are permissible” in that area. An electromagnetic field is generated by charged electrons (electricity) that are put in motion; delivered through a source such as a power cable, producing an electromagnetic field.

Conducting the survey was University of Rhode Island Oceanography Professor John King, and Swedish engineer Peter Sigray, who created a device called the SEMLA (Swedish Electromagnetic Low-noise Apparatus), which takes readings of electromagnetic fields. (King said the SEMLA is also named after a Swedish cream puff pastry.)

King said that an AC power cable, like National Grid’s sea2shore cable, should not attract large, predatory fish, such as Great White sharks. “It will attract harmless fish, like skates, and dogfish,” he said. Part of our work we will be to determine if the cable is “operating the way it’s supposed to — at a safe level.” 

King, who has worked with the SEMLA for the past two years on surveys, said that “conditions were good,” with minimum surf in the surf zone to take the magnetic readings on Tuesday. However, King also noted that the Block Island Wind Farm, which was not in operation at the time, needs to be operating; sending electricity through the cable to the mainland, in order for the survey to be conducted.

“The wind farm needs to be operating at peak capacity for us to get the proper readings,” said Campilii.

“It’s not unusual on projects like the (wind farm) to encounter issues,” said Campilii, who also installed an undersea cable to Nantucket. “There’s a learning curve. It’s a fairly complex system. So, they’re still adjusting their controls to accommodate how much wind they’re getting, and seeing how their generators interact with our generators.”

Campilii said that National Grid’s focus was “to figure out what to do about the cable.” Due to its shallow burial depth, he said the cable could be exposed during a storm. So, the issue of addressing it is complicated.

To that end, Campilii said the SEMLA would be “pulled across the length of the cable a few times. It has sensors on it that detect the (electromagnetic) field” being emitted from the cable. “We’re going to take readings of the cable every half-mile, or so,” he said. “And we will take extra readings on the 80-feet of cable off the Town Beach.”

As for a solution to the problem, Campilli said National Grid is considering installation of a protective sleeve made of plastic that would be wrapped around the cable at its low burial depth section. Campilii said divers would use water-jets to unearth a trench, and then the protective sleeve would be installed.

“The CRMC said they would be willing to let us put the protective sleeve in place, but don’t necessarily view it as a permanent solution,” said Campilii, noting that the CRMC may require a “monitoring program” for the cable. 

Once the survey is completed, Campilii said that National Grid will be sending its findings to the DEM and CRMC, and then addressing the situation.