Project Summary
The primary focus of REVISE is revisiting the current methodology for assigning overhead line ratings. The calculation process uses historical environmental data captured in the 1980s that is applied uniformly across the UK disregarding local/regional climate variations. The existing transmission network is increasingly constrained by system capacity limits exacerbated by rapidly increasing renewable integration. Improving understanding of line ratings, using latest generation high-resolution weather topographic data combined with the latest techniques for system modelling, will allow for improved targeted investment to ensure we meet demand for the connection of new renewables to the network, and deliver a secure energy system.
Innovation Justification
The current methodology used to calculate OHL ratings is over 40 years old and reliant on data from a single test site in southern England. REVISE is seeking to modernise the methodology using the latest accepted practice and build a process/tool enabling OHL ratings to be based on regional environmental data. This has the potential to unlock additional capacity in OHLs in northern England, Wales, and Scotland without the need for physical modification. This increased capacity, assumed for now to be between 2-5%, could reduce/remove constraint or eliminate the need for upgrades resulting in a faster, more cost-effective network transformation.
The Discovery Phase identified core challenges that require innovative thinking and practices to overcome:
- The meteorological data needed to calculate ratings is atypical, complex, and contrary to what is often studied (i.e. most interest is in high windspeeds, not low windspeeds). Innovative thinking, processing, and validation is required to enable the use of current meteorological data to produce realistic OHL ratings.
- Identifying the critical combination of environmental parameters to give a statistically safe OHL rating, whilst also being flexible enough to allow for innovative products/practices used elsewhere in the world, such as conductor coatings or day and night ratings, will require extensive simulations and assessment. The current methodology ignored or oversimplified certain parameters to negate the need for this research and is subsequently inflexible.
- The current methodology, TGN26, is not fully defined, with key aspects not recorded. The industry relies on a spreadsheet to produce the ratings without an understanding of key calculations and their justification. An innovative statistical review of post-fault occurrence across GB transmission is required to address this gap.
- Changing climate has never been considered in the rating methodology and guidance for future changes/updates to the methodology to react to climate change will need to be created.
The innovative, risky, and collaborative nature of this Project means it cannot be funded through BaU activities as it requires input from all TOs and ESO to deliver. The complexities of incorporating the latest generation of high-resolution weather topographic data, with the latest techniques for system modelling and resolving the missing steps used by the current methodology requires significant experimentation to generate a practical approach. Finally, whilst REVISE could have national-level benefits, the benefits for an individual TO are much harder to define and thus justify the investment. The SIF fund is wholly appropriate for this Project as it brings together industry and academia, representing the entire network.
Readiness Levels
The TRL of revising line capacity ratings using environmental data accurate to a line’s location is 9, as this is already BaU. However, the innovative aspect of this Project is harnessing this proven technology and pairing it with the latest generation high-resolution weather topographic data combined with the latest techniques for system modelling to implement the solution within GB.
Through engagement with key stakeholders at Discovery, IRL2 was achieved. This will be built upon in Alpha through further engagement with all three TOs and ESO and Energyline’s objective to ensure that the methodology is usable, and implementation is possible. The cost-benefit analysis will be further developed pushing the CRL to 4.
Counterfactual Solutions
The total cost of managing power flow constraints on the GB transmission system in 22/23 was £1.1billion (£740m on SSEN-T network). Failure to implement an update to the current methodology will result in continued, potential underutilisation of capacity in parts of the network and increased risk in other areas, along with retaining a barrier to innovative products such as novel conductors and conductor finishes.
Impacts and Benefits
Current Position
REVISE offers quantifiable benefits, including potential savings from wind constraint costs and associated indirect carbon savings due to increased renewable energy transfer through the network.
Financial - future reductions in the cost of operating the network
By 2025, total UK constraint costs are expected to peak at around £1billion to £2.5billion a year which is ultimately paid by consumers. The total cost of managing power flow constraints on the GB transmission system in 2022/23 was £1.1billion (£740million on SSEN Transmission network).
The potential cumulative discounted net financial benefit of rolling out REVISE across the whole of GB is estimated as £28million at the end of 2031, reaching £227million by the end of 2050 (lifetime). These are the estimated benefits from the potential reduction of constraints. We estimated the potential benefits up to 2050 to be aligned with the offshore wind curtailment data published in the Future Energy Scenarios (FES) “Leading the Way” by National Grid ESO.
REVISE could also reduce connection costs by allowing smaller, wood pole lines, 132kV circuits, etc., and less costly overhead lines to be viable for many new connection schemes. This benefit will be quantified when data on new suitable projects is available, through CBA development at Alpha. Further consideration will also be given to connected equipment, such as cables and switch gear, and the potential impact this may have on costs.
Environmental - carbon reduction – indirect CO2 savings per annum
Assuming with REVISE, the line rating limitation of current transmission lines will be increased by 2% to 5% enabling more renewable energy to be transferred and reducing wind curtailment by up to 5%, we estimated the environmental benefits of this project. Offshore wind curtailment from 2026 to 2050 is projected in FES "Leading the way".
Carbon savings regarding reductions of carbon intensity of power grid are included as indirect carbon savings. The cumulative indirect carbon emissions saving is estimated at 140k tCO2e with a carbon value £34 million by 2050.
Other qualitative benefits include:
- Alleviating the constraint on renewable generation reduces the partial reliance on fossil fuels used to offset the difference.
- Circuit rating increase can be achieved with no physical works and the associated embedded carbon involved.
- May enable smaller renewable schemes to connect without the need to wait for further infrastructure works, helping to progress the connection queue.
- May remove the need to upgrade/replace circuits following a connection request.
New to market - processes
The Project focusses on the implementation of an updated methodology for calculating OHL ratings into BaU deployment. This will replace the existing methodology (TGN26) that was developed in the 1980s and utilises data captured in one UK location (Leatherhead) over 40 years ago. The revision of updated input parameters to the rating calculations, as well as potential changes to seasonal periods and the potential adoption of a new regionalised approach, will be rolled out across the GB network.
Others that are not SIF-specific
REVISE will offer the opportunity to improve the reliability and safety of the network. Firstly, by identifying circuits that, using the current rating methodology, are at risk of exceeding their safe operating temperature, and thus may put the public and network at risk. Secondly, increasing the post-fault rating of circuits enabling the network to recover demand more quickly in the event of a fault; compared to having to wait for a circuit under outage to be reinstated.
Overall, REVISE will lead to a more flexible and adaptable network.
The cost-benefit analysis will evolve during the Alpha Phase as we move into Beta Phase planning.
