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115kV to 230kV Transmission Line & Submarine Cable Upgrade Facility Study

115kV to 230kV Transmission Line & Submarine Cable Upgrade Facility Study

Line PV-20 115kV Line

Project Scope:
The purpose of this project was to evaluate the Client’s existing 115kV PV-20 transmission line and underwater cable that interconnects to the neighboring electric company, for an increase in electric load and potential upgrade to 230kV.

Engineering Activities:
In the first phase of the project, Realtime evaluated the overhead transmission line in its present condition for maximum electric load without clearance violations. Realtime further evaluated the line for 10% and 25% increases in electric load, over the current voltage rating, as a projection of short term and long term growth requirements.

The available line capacity was determined not sufficient at electric load that yielded no clearance violations. The maximum conductor rating was then evaluated and NESC clearance violations were identified. Although the existing conductor was sufficient for short term growth projections of 10% given the clearance issues were corrected, the conductor capacity was not sufficient for a 25% load increase. Realtime determined the required conductor size to meet the long term growth need and developed the scope, cost and schedule for the reconductoring the PV-20 Line at 115kV.

Subsequently, the submarine cables that crossed (1.5) miles of Lake Champlain that connects the Client and electric company were evaluated for maximum capacity and remaining life span. The submarine portion of the line met the short term growth need of 10% but the cable was close to the end of its useful life span. Realtime determined the required cable size to meet the long term growth need and developed the scope, cost, and schedule for replacing the submarine cable at both the 115kV and 230kV levels.

The transmission line and substations on either end were also evaluated for an upgrade to 230kV using the long term growth parameter of 25% and Realtime developed the scope, cost, and schedule for an upgrade of the entire line to 230kV.

Project Highlights:
Facilities analysis for increased electric load; Line upgrade options were evaluated using Phase-Raisers, re-tensioning conductor, reframing structures, reconductor options, etc.; Cost comparisons of multiple and alternate options were completed; Life cycle assessment of the existing submarine cable and determination of replacement cost and installation of the underwater cable were accurately scoped for budgeting purposes.