Statnett has been performing voltage upgrade on the existing 300 kV overhead transmission lines with duplex line configuration. In addition to the voltage upgrade, the OHTL's thermal capacity was upgraded.
The project's objective
Statnett, the system operator in the Norwegian energy system, has over 4500 km of 300 kV OHTL in its central grid. The long-term plans are to voltage upgrade those to 420 kV to increase the transmission capacity. Of these 4500 km, 1500 km already have a duplex line configuration which can be upgraded without replacing the conductors or tower structures.
Since 2009, EFLA has assisted Statnett with planning, development of design processes and tools, modelling, and selection of measures and solutions, in addition to preparing design and tender documentation for about 920 km of OHTL. The scope of the work has spanned over fifteen OHTLs and included rerouting them into most of the new 420 kV substations:
- Nedre Røssåga-Namsskogan-Tunnsjødal / Namsos-Tunnsjødal / Namsos-Ogndal-Verdal-Klæbu
- Tonstad-Feda-Kristiansand-Arendal-Bamble / Solhom-Honna-Arendal
- Aura-Vågåmo / Vang-Minne / Lyse-Førre-Saurdal-Liastøl
Environmental issues
Statnett was responsible for planning, construction license application and tendering. EFLA provided support during these phases. The voltage upgrade project is both very cost effective and environmentally friendly, as the capacity increase results in better use of the existing structures with minimal measures.
EFLA's role
- Development of design processes and procedures (design guidelines)
- Development of program routines for special checks
- Modelling of existing OHTL and verification of data
- Line calculations and controlling electrical clearances
- Surveying of critical terrain points for ground clearances
- Design of solutions to achieve higher insulation levels
- Calculation of electromagnetic fields and audible noise
- Electromechanical design of insulation strings and hardware for the voltage upgrade
- Design of reinforcements to towers and foundations
- Preparation of tender documentation and assistance with procurement of materials
- Assistance during construction and completion of as-built documentation
- Additional operations related to maintenance of the lines, for example installation of aircraft warning spheres
The project's long term benefit
The voltage upgrade strengthens Statnetts grid and increases the transmission reliability between North and South in Norway.
Review of EFLA'S performance
- From Statnett
"We are very pleased. EFLA has good competence and delivers good quality and has good professional insight. We are also very pleased with the response to more informal inquiries."
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