Undersea cables monitored for EMFs

Fri, 12/22/2017 - 9:15am
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The University of Rhode Island is keeping an eye on any electromagnetic activity associated with National Grid’s undersea transmission cable.

A team from URI, employing a device called the SEMLA, were deployed at Town Beach to monitor the EMFs on Monday, Dec. 18.

Prof. John King and his crew from URI’s School of Oceanography, were hired by National Grid, which was directed by the Coastal Resources Management Council to conduct EMF monitoring of Grid’s sea2shore cable and Deepwater Wind’s export cable. The 18-mile long sea2shore cable connects the island to the mainland, while the eight-mile long export cable links the wind farm to the island.

The EMF monitoring, conducted while the wind farm was generating energy in winds of about 10 miles per hour, is being done to ensure the cables are operating properly, are protected, and do not pose a hazard to the public. An electromagnetic field is produced when an electrical current, or charge, flows through a source such as a wire, or in this case, the wind farm’s power cables. 

A device called the SEMLA, an acronym for Swedish Electromagnetic Low-noise Apparatus, and invented by Swedish engineer Peter Sigray, is dragged along the sand above where the cables are buried in order to capture the readings. The EMF readings are then sent to a computer for analysis.

The burial of the cable at the Town Beach in June of 2016 is shallower than was anticipated by National Grid and the project’s developer, Deepwater Wind. It presented a problem that National Grid addressed by placing a protective sleeve over an 80-foot segment of the sea2shore cable about 200 feet off the beach. 

King said that in the areas where the cables were buried at a shallow depth the readings could be higher than in places where it was buried the mandated six feet beneath the seabed. “Seasonal erosion” could make burial depth shallow, and cause a higher reading as well, noted King.

“Burial depth is important and has an impact” on the EMF levels, said King. National Grid and Deepwater Wind “did not make project burial depth” in some places, most notably at the Town Beach, where the developer and the utility encountered hard seabed. “The fact that they didn’t make project burial depth is not that critical.” King said the way the cables are constructed prevent them from emitting dangerous EMF levels.

“The EMF fields are not high,” said King. “The cable was modeled at 22 milligauss. We are seeing two to three milligauss with our readings. The highest reading we had last time was 8 milligauss.”

To understand what this means, a milligauss is one-thousandth of a gauss, which is a measurement scale used to measure the strength of an electromagnetic field. 

A study by U.C. Berkeley Professor Bruce A. Buffet in Dec. of 2010 noted that the earth’s magnetic field at its core is 25 gauss, making compass needles align north-south; while a common refrigerator magnet is about 10 gauss.

At the end of June, the CRMC furnished The Times with readings that King and his crew captured earlier in the year, noting that the EMF levels were quite low and safe. King said the results from Monday’s readings will be sent to National Grid first, and then to the Department of Environmental Management and the CRMC, before those two state agencies publish them for public review on their websites.