- ENGINEERING INFO
- CASE STUDIES
First announced to the public in 2008, Southern Maryland Electric Cooperative’s (SMECO) initiative to reinforce electrical power reliability to its more than 150,000 customer-members includes the addition of 30 miles of 230kV power transmission lines to loop its system. The key element in the plan is the recently completed Patuxent River Crossing, which included the never-before-attempted installation of 4,500-plus feet of uncased conduit bundles via horizontal directional drilling at a depth of 50 feet beneath the 110-foot deep Patuxent River.
Engineering calculations performed by Black & Veatch suggested that a slick bore directional drill installation (no casing or grout) would provide the best solution to deliver power across the river with the least ampacity loss. At that length, however, traditional conduit materials such as solvent welded PVC and HDPE pipe were out of the question. The pipe material challenge was addressed when Black & Veatch selected 8-inch DR14 Fusible PVC® conduit for the two separate five-conduit bundles. In September 2013, Mears Group, Inc. mobilized its drill rig to the site and Underground Solutions, Inc. (UGSI) delivered and began fusing the one-thousand plus fusion joints required for the project.
Each fusion joint required internal de-beading to produce a smooth interior surface for pull-in of the high voltage power cables. In addition, as required by specification, UGSI fusion technicians mandrel-tested, videotaped, and logged each de-beaded joint under the watchful eye of the cable supplier and cable installation contractor. By early October, pullback operations were ready to commence.
As is often the case when pushing the limits of horizontal directional drilling technology, difficult, unknown conditions on pullback created some challenges. Fortunately, understanding the risk involved, SMECO and Black & Veatch had planned for contingencies by designing a five-conduit bundle (including a spare contingency conduit) and planned for the future by including a back-up, five-conduit bundle for a second, future circuit. Torsion of the bundles was suspected in the loss of the contingency conduit, still leaving enough conduits to successfully complete the installation of the first circuit, as well as allowing space for the future circuit.
The end result was successful pull-in of the 230kV XLPE cables in early October 2014, followed by the entire circuit being energized on November 3, 2014. According to Ken Capps, SMECO’s Senior Vice President of Engineering and Operations and Chief Operating Officer: “We faced considerable challenges associated with engineering the river crossing. A year ago, we used horizontal directional drilling technology to bore under the riverbed, and then pulled two bundles of five Fusible PVC® conduits through the boreholes. This was a first for the industry; no previous installations using Fusible PVC® conduit come close to the combined length and complexity of this project.”
|Pipeline Details and Project Summary|
|Project:||Southern Maryland Reliability Project|
|Location:||Solomons Island, Maryland|
|Conduit Length:||4,600 LF per bundle (46,000 LF total)|
|Conduit Size:||8” DR14|
|Owner:||Southern Maryland Electric Cooperative|
|Engineer:||Black & Veatch|
|Contractor:||Mears Group, Inc.|