Overhead line (OHL) foundation condition is difficult to assess without costly and disruptive excavation. Based on existing knowledge or previous data, non-intrusive techniques can be used and have been available for many years but are inadequately researched/developed for use in OHL foundations to base refurbishment and replacement decisions upon. The proposed solution will carry out the development, testing, and trial of a new method with an aim to achieve a reliable non-intrusive foundation assessment.
Benefits
This project has the potential to provide benefits for all Transmission network overhead line foundations and is likely to also be entirely relevant to distribution networks. The benefits are expected to be:
• Reduction of foundation intrusive exploration expenditure.
• Reduction of foundation upgrade works, with cost and time savings, and safety improvements through reducing construction works. This reduction will be justified through a better, more evidence-based understanding of residual risks, allowing policy adjustments to be made.
• Better ability to predict higher-risk foundations reducing the chance of future foundation-related incidents.
• Improve health and safety by removing damage to OHL/towers during foundation upgrades, hence, reducing the probability of risk events.
• Environmental impact – Reduction in materials and concrete required during foundation upgrades and reduction in access works.
An existing 132kV OHL with 193 towers of which 72 initial proposed foundation upgrades was examined to assess potential benefits for a single case.
Cost Benefit Analysis
The CBA Model is based on some assumptions below:
• The CBA model incorporates the project cost as part of the development cost.
• Due to the uncertainty and low level of TRL, an assumption that this project has a 40% probability of success has been made to estimate the low-level benefits.
• The capitalisation rate is 90% which is based on the current versus non-current cost.
• The number of foundation upgrades required will reduce by 40% when intrusive and non-intrusive testing method are employed.
• In the current approach, the percentage of foundations tested intrusively is 5% to 10% per line, and this rate is factored into the base case for this analysis.
• 50% of total foundations are tested non-intrusively, and 2% of total foundations are tested intrusively to validate non-intrusive findings. This approach is considered as a preferable option.
Summary of Benefits
Preferable option: Combining both non-intrusive and intrusive foundation testing.
• For a single case, the estimated saving is £1.4m discounted in 2018 real price. The benefit of this project will realise in 2029.
• For scaled benefits, it is estimated £2.3m discounted in 2018 real price. For £1 spending in this project, it can return £1 in cost saving by T3 or £5.9 through the lifetime of all eligible projects. (Annualised ROI: 15.2%).
• Due to uncertainty of this technology, the probability of success for this project is assumed to be 40%, which leads to the low benefits estimated at £915k in 2018 real price for the scaled benefits.
• In addition to a potential saving in CAPEX, there are also social impacts and other savings due to risk reduction. The total risk benefit saving is estimated at £132k.
Breakeven point analysis:
• For a single case, this innovation will need to achieve at least an 8% reduction in the number of foundation upgrades or 6 towers to break even and be considered a feasible investment.
• If not accounting for the development cost, this innovation project will reach break-even point if it can reduce 1 foundation upgrade compared to the initial number of foundation upgrade proposed in a single case.
