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August 2014 » Project + Technology Portfolio » Energy
Growing load from resort communities drives replacement of a vintage subsea electric cable to Drummond Island, Mich.
Peter Ebersold
The power cable is installed 20 feet below the low water datum at a depth of 6 feet. Once the cable is beyond 20 feet, the cable is transitioned out and then lays on the bottom of the DeTour Passage

Two subsea electrical cables serve Drummond Island, located at the end of Michigan’s eastern Upper Peninsula. Referred to as the “Gem of the Huron,” and “Michigan’s Ultimate Playground,” the 87,000-acre island is the second largest fresh water island in the nation. It has 150 miles of rugged, scenic shoreline, 133 square miles of forested landscape, and 34 inland lakes. The island has a growing number of resort communities, as well as some full-time residents. It is also home to the Drummond Island Quarry, a major producer of crushed and broken dolomite that is used in manufacturing steel, glass, and paper and as a soil neutralizer for agricultural applications.

The two existing cables — one serving mainly residential dwellings and one serving the quarry — were installed in 1975 and 1989, respectively, and had reached the end of their useful life. When the quarry was operating at full capacity, there was insufficient capacity between the cables in the event of a failure, causing the quarry to partially shut down. While the load at the quarry is not anticipated to grow, Cloverland Electric Cooperative determined that the resort load is likely to increase as older smaller cabins are turned into larger ones, and modern amenities such as air conditioning are added. Cloverland decided to install a new cable that could handle the entire island. The plan was to maintain two circuits. The first would be replaced in 2014, while the sister cable is budgeted for completion in 2017.

Cloverland called on GRP Engineering, Inc., a Michigan-based power utility consulting firm, to handle the first cable replacement project. The firm, which has more than a decade of experience with municipal and rural electricity cooperatives in Michigan, handled initial planning, cost estimates, permitting, and design, as well as installation oversight and startup.

GRP Engineering developed the bid specifications, and the project was bid out “from termination top to termination top.” Kerite was the successful bidder for the subsea cable, offering the lowest price as well as the most experience — more than 100 years providing subsea cable. Kerite is also the only U.S. manufacturer of ethylene-propylene-rubber subsea cable. Kerite’s EPR insulation formula enables its subsea cables to operate in direct contact with water without the need for an impervious lead sheet or asphalt coating. The cable can be covered with individually jacketed steel armor wires for mechanical protection and ease of installation pulling. During the bidding process, Kerite responded to Cloverland’s questions about thermal issues, providing a report with engineering test data to confirm that the cable is good for 340 amps. Kerite used a subcontractor to dig trenches and install the cable.

Coordinating closely with Cloverland on permitting and budgeting, GRP Engineering was responsible for oversight of manufacturing and installation done by Kerite and its subcontractors to ensure everything was done in accordance with the permit. For example, the island’s location in a sensitive environmental area meant a joint permit was required, incorporating separate guidelines from the Michigan Department of Environmental Quality and the U.S. Army Corps of Engineers. Fish spawning was an important issue at the time of the year during which the project was scheduled, and the permit schedule accommodated that concern.

The reel holding the continuous piece of cable weighed 171,000 pounds. After shipment from Connecticut by oversize truck, the reel was loaded onto a barge for the final part of the journey.

The project required 7,465 feet of 28-kilovolt (KV) cable; Kerite provided the full length in one continuous piece of cable — with no splices. The line is currently being operated at 7.2/12.5 KV, and Cloverland will potentially be switching to a 14.4/ 24.9 KV operating voltage. There are three single-phase conductors, each 350 KCM (1,000 circular mils), and a full, uninsulated neutral at 350 KCM. Also included is a 24-count fiber optics cable that Cloverland is using for communications with its substation and motor-operated switches on the island. Spare fibers are being leased out to the island’s high-speed Internet service.

The design called for installing the cable 20 feet below the low water datum at a depth of 6 feet. Once the cable is beyond 20 feet, the cable is transitioned out and then lays on the bottom of the DeTour Passage. Typically, cables are installed 15 feet below the low water datum at a depth of 4 feet, but with this location on the St. Mary’s River, the deeper installation protects the cable from boats, ice, or other objects that might puncture it.

Cable installers float the cable to land at DeTour.

Tricky shipping, smooth installation

The reel holding the continuous piece of cable weighed 171,000 pounds. Kerite used its onsite rail siding and special lifting equipment at its Seymour, Conn., manufacturing plant to place the reel onto a freight truck specially equipped to handle the extra weight. The truck had a larger than standard number of axles and a trailer that sits low to the ground so it can clear most bridges. The vehicle was subject to special permitting and there was a few days delay when New York State did not have troopers available to escort the truck in accordance with that state’s requirements. Because the truck was not permitted to go over the Mackinaw Bridge, the reel was loaded onto a barge in Rogers City, Mich., for the final part of the journey.

The original plan was to pull the cable from the mainland side at DeTour village to the Drummond Island side. However, because of a strong southwest wind, GRP Engineering decided to pull from the Drummond side to the DeTour side.

To protect fish spawning, the project was originally scheduled for completion by Oct. 1. Due to shipping delays, GRP Engineering worked with the MIDEQ to get a brief extension. Weather is a main concern for a project like this, but all went smoothly and the entire project was completed in eight days. The cable is now energized and carrying the quarry load.

Michael McGeehan, president of GRP Engineering, said he was extremely satisfied with the project, which was the company’s first subsea cable assignment. “Kerite did a great job. They were concerned about getting it done properly and on time, and keeping to the schedule to ensure compliance with the permit conditions required by fish spawning concerns,” he said. “Everyone involved made sure the cable would be a success.”(this language is not supported by Hyperlink Helper)

Peter Ebersold is the director of Market and Product Development for the Kerite (www.kerite.com) and Hendrix brands at Marmon Utility.


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