The current values of radial ice accretion defined in BS EN 50341-2-9:2017 are regarded as conservative with little basis in modern Meteorological science, especially as applied in the North of Scotland. Application of these values may lead to overdesign of overhead lines being designed and constructed to enable the energy system transition.
This project will develop a new ice accretion model and integrate it with existing global Numerical Weather Prediction (NWP) models with high granularity topological and orographical parameters. It will thereafter use this composite model with extreme value analysis techniques to derive new values for radial ice accretion, which reflect modern meteorological practice.
The new values will be compared with BS EN 50341-2-9:2017 to assess the potential benefits of adopting a new design practice.
Benefits
OHL design is a complex process with widely varying inputs. Benefits and construction costs will therefore vary by project, so assumptions have been used for the purposes of this CBA as follows;
For wood pole OHL, the benefits of reduced ice loading would result in increased span.
• Raw construction cost / km = £0.3m
• Average span with existing ice loads = 80m
• Estimated average span with new ice loads = 95m
• Estimated potential cost savings /km (60% of construction cost * reduced number of structures) = £0.03m
• Estimated potential cost savings on contracted pre design wood pole OHLs 54.5km = £1.55m
For steel OHL, the benefits of reduced ice loading would primarily result in lighter structures and foundations, but only where the wind and ice weather case results in higher transverse loads than the wind weather case. Benefits and construction costs vary widely by project, so assumptions have been used as follows;
• Raw foundation and structure construction cost / km = £0.7m
• Approximate reduction in structural loads when maximum design load is wind rather than wind & ice = 25%
• Estimated potential cost savings /km (50% of construction cost * .75) = £0.09m
• Estimated potential cost savings on contracted pre-design steel OHLs 27km applied to 10% of structures = £0.24m
Subject to these assumptions, a reduction in ice accretion could result in benefits of up to £1.8m if applied to the currently contracted pre-design OHL projects in the SSEN Transmission area. Further benefits would then be realised by future projects.
Learnings
Outcomes
The outcomes to date have shown that new learning has been developed as part of the project. A detailed technical report of the findings is available; however, this is not suitable for inclusion within this progress report, due to its size and format. This report can be made available to relevant network licensees.
Lessons Learnt
Adopting the new Ice Map values for structures will require deviation from the current British Standard (BS EN 50341-2-9) and therefore this BS will need to be updated to accommodate the new findings. The review cycle for the BS does not align with the requirements of SSEN Transmission based projects and this will mean the Ice Mapping project outputs cannot be employed immediately to generate benefits for the industry and consumer.
Following discussion and assessment with SSEN Transmission Technical Authority it has been agreed that the Ice Mapping values can be employed for ice conductor clearance calculations providing significant value. The methodology generated by this innovation project can be adapted to other network licensees for their geographical area.
The project has identified the challenges of deviation from the current BS standards in particular where the review cycles for standards may not align with the implementation objectives of the project outputs. Further detail is provided in section 10.
