400kV Full Line Tension (FLT) Gantry
Project Brief
National Grid (NG) had initially commissioned LSTC to conduct a feasibility study and outline design for a generic steel lattice full line tension (FLT) gantry. Subsequently, LSTC has been instructed to undertake further detailed design and produce construction drawings. As part of an initiative to improve visual impact, NG aims to use this design on numerous Major Instructure Development (MID) projects, with the possibility of a generic design for other projects.
Our Approach
LSTC developed an outline and detailed design structure to carry the heaviest conductor system of triple 700mm2 AAAC Araucaria conductors. Two different designs were provided, 26m and 22m widths, to offer the maximum flexibility for different phasing arrangements to suit all 400kV tower suits. Various exercises were undertaken to identify the optimum design to suit different phasing arrangements.
Challenges
- To design and detail this structure, we had to maintain non-standard internal clearances to NG standards under a long span of 265m and maintain 30° maximum angle of entry for the phase conductor.
- The height of the FLT gantry was also restricted to the substation standards.
- Providing flexibility for conductor attachment catering for two conductor systems, i.e. 3 x 700mm2 AAAC Araucaria conductor and 2 x 850mm2 AAAC Redwood.
- The overall footprint was also smaller than expected for this type of structure.
Project Outcome / Deliverables
- This project was completed on time and within the budget, with National Grid initially deploying this structure on the Hinkley project.
- An FLT gantry structure is hugely cost-effective compared to other tubular-type gantries available.
