Direct Insulation Real-Time Temperature (DIRT)
| Funding mechanism | Network Innovation Allowance (NIA) |
|---|---|
| Duration | Sep 2025 - Mar 2026 |
| Estimated expenditure | £136,175 |
| Research area | Optimised assets and practices |
Ground conditions have a crucial part to play in how we use our underground cables. When calculating how much load an underground cable can carry, we use assumed environmental values, such as ground temperature and moisture content, to ensure cables do not exceed their designed thermal limits.
The DIRT project will investigate the accuracy of historical environmental assumptions used today whilst identifying areas of opportunity to both optimise and protect existing future assets.
Problem(s)
Underground cables are designed to operate at their maximum efficiency up to a maximum core temperature. The maximum core temperature is limited by the maximum conductor temperature specified by the cable manufacture/IEC. Due to network design, high voltage (HV)/low voltage (LV) networks are at greater vulnerability to thermal exceedances and run hotter than extra-high voltage (EHV) when normal running arrangements are considered.
Using cable rating software, thermal limits/cable ratings are calculated using the maximum core temperature and other environmental factors such as soil temperature and soil resistivity. However, these ratings on distribution networks are calculated using assumed potentially inaccurate environmental values as both real time climatic and conductor temperature data is currently unavailable, also significantly varying throughout a cable route. Cable calculations assume that specific backfill materials are used with specified specifications, however, in reality these assumptions are not a true representation of real-world environments.
When considerations are made to the variance in assumed environmental factors due to location, climate, installation type, backfill material and changing load profiles, there is potential that maximum calculated load ratings (used for network design/operation) may not align with actual experienced conductor temperatures. During periods of high or exceeded load, it is unknown what real time conductor temperatures are. Desktop assumptions that ignore external environmental factors could be over cautious masking hidden network capacity headroom. Alternatively current desktop calculation could miss contributing factors resulting in cables exceeding thermal ratings resulting in both asset damage/reduced asset life and reduced network reliability. For this reason, greater visibility and increased real time data of underground assets is required for an updated approach to cable ratings.
Load profiles are a defining factor in cyclic cable ratings commonly used on distribution networks. DSO research has identified that current load profiles may be redundant by 2035. If cable ratings are to move away from cyclic ratings to sustained ratings, periods of cooling would no longer be available further highlighting the need for thermal data to support cable rating review.
It is possible that in some scenarios maximum calculated conductor temperatures are not reached during periods of maximum demand due to lagging thermal properties and other environmental factors. This has previously been evidenced through international desk-based research projects; however, real-world evidence is required to achieve the confidence to inform rating methodology change to identify capacity headroom opportunities.
Method(s)
To address the problems described above, the project DIRT aims to find solutions to validate the accuracy of real-world cable ratings though the use of monitoring technology. The data collected will then be used to support rating methodology updates leading to areas of both opportunity and identified network vulnerability.
The initial value stream of the DIRT project will be a feasibility study, deep diving existing underground cable rating methodology, industry standards, ground data considerations, existing literature and existing available monitoring technologies.
The output of the initial feasibility study will provide an initial cost benefit analysis alongside a recommendation report advising next steps and proposed follow-on value streams.
Following a successful feasibility stage, follow-on value streams will explore the development and implementation of selected temperature monitoring technologies through both test/real-world network trials. Captured data will then be analysed against existing methodologies with outputs providing recommendations for next steps.
It is expected that a data driven approach to cable ratings will allow for release of “locked-in” network capacity increasing network headroom, thus reducing the requirement for network reinforcement and the use of larger/more costly cables. Conversely, captured thermal data may also highlight areas of thermal vulnerability that would have otherwise remained undetected (fault rates/asset aging). Learnings will also support potential benefits in other areas such as post fault cable ratings and losses.
Following successfully installation and wider roll-out of monitoring technologies further value streams will look to further utilise captured thermal data. Following successful outcomes value streams will explore the development and deployment of dynamic underground cable ratings and explore learnings to support climate change adaptation pathways.
Throughout the project we seek to use knowledge drops to support and expand existing innovation projects.
Scope
Throughout RIIO ED2, NGED are forecast to spend £784m on load related expenditure. This total includes the replacement of underground (UG) cables.
The SILVERSMITH Network Study Result report showed that by 2033, 5% of LV feeders will experience thermal constraints. By 2050, this will increase to approximately 22%. Thermal constraints will become the dominant network constraint type. Significant levels of interventions and, therefore, investment will be required to alleviate thermal constraints, particularly during the 2034-2040 and 2041-2050 timeframes. Such constraints could have significant impact on the customer and net zero targets.
By 2050, it is estimated that a total of approximately 44,220 LV underground feeders on the NGED network will be impacted by thermal constraints. Conventional reinforcement of these feeders would result in significant cost and disruption to customers. Assuming an average feeder length of 300m and a cost of £100/m, overall replacement using current cable rating calculations and replacement methodology would cost c.£1.3b. This challenge is not unique to NGED, proving a future challenge to other UK DNOs.
The scope of the DIRT project begins by conducting a feasibility study to explore available temperature monitoring technologies, installation techniques, data accuracy, and the practicality of deploying such solutions in both new and existing cable installations. Additionally, a review of existing studies will be carried out, an assessment of thermal data requirements, and the identification the most viable approach to improve understanding of cable temperatures and ratings via an indicative cost benefit analysis.
The feasibility study aims to identify and highlight potential opportunities to be gained from the implementation of real-time underground cable temperature monitoring solutions to optimise and realise true network capacity, improve system reliability, and, most of all, reduce future reinforcement costs. By updating and informing industry approach to cable rating methodology and validating with real time thermal data, costly forecast network intervention volumes could be significantly reduced. This would benefit both the customer due to improving value for money and accelerate the road to net zero.
The study will also provide insights into how future climate impacts can be managed through improved monitoring and support the development of potential climate change adaptation pathways.