Special underwater trenching sled used for the first time to help bury the new transmission line.

New Jersey, USA  – Jersey Central Power and Light (JCP&L), a subsidiary of FirstEnergy Corp.,  has completed the replacement of an underwater high-voltage transmission line, stretching more than a mile across Barnegat Bay along the Tunney-Mathis Bridges, to enhance electric service reliability to New Jersey's barrier islands.  Dredging operations in recent years are believed to have damaged the underwater transmission line that ran through the area, necessitating its replacement. The new 34.5-kV line is one of four high-voltage power sources serving approximately 30,000 JCP&L customers on the barrier islands.

To bury the line, JCP&L brought in a special underwater trenching sled, marking the first time the technology was used by any FirstEnergy company. The sled used water jets at 150 pounds-per-square-inch pressure to blast a trench about one foot wide and 10 feet deep in which to lay the new power cables. A large barge carried massive reels of armored submarine cable, hydraulic and water pumps, surveillance monitors, control systems, and other gear as it pulled the 12-ton, school bus-sized sled at rates up to 10 feet per minute.

As the sled was pulled along the bottom of the bay, the trench simply collapsed behind it, leaving only a shallow depression marking the location of the line. The 5,800-foot crossing was completed in a matter of days. The new line now safely sits 10 feet below the bay's soft, sandy base. Each of the three cables that make up the line are wrapped with 28 strands of aluminum armor wire, providing robust protection and eliminating the need for a bundled armor casing commonly used in underwater power line projects.

"This project supports our commitment to using new, innovative ways to improve service reliability by utilizing an emerging technology that placed the submarine line in a safer location while also minimizing the work's impact on the bay's fragile ecosystem," said Jim Fakult, president of JCP&L. "The new line helps ensure that our barrier island customers will have the reliable service they need in these peak summer months."

Source: T&D World