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Reference Number NIA2_NGET0023
Title Cable Alternative Cooling Technologies for Underground Systems (CACTUS)
Status Started
Energy Categories Other Power and Storage Technologies(Electricity transmission and distribution) 100%;
Research Types Applied Research and Development 100%
Science and Technology Fields ENGINEERING AND TECHNOLOGY (Electrical and Electronic Engineering) 100%
UKERC Cross Cutting Characterisation Not Cross-cutting 100%
Principal Investigator Project Contact
No email address given
National Grid Electricity Transmission
Award Type Network Innovation Allowance
Funding Source Ofgem
Start Date 01 July 2022
End Date 30 June 2024
Duration ENA months
Total Grant Value £517,000
Industrial Sectors Power
Region London
Programme Network Innovation Allowance
Investigators Principal Investigator Project Contact , National Grid Electricity Transmission (100.000%)
  Industrial Collaborator Project Contact , National Grid Electricity Transmission (0.000%)
Web Site
Objectives The first stage of the project will investigate the use of established technologies, such as chilling inlet air, which are nevertheless novel for cable tunnel applications. A cable circuit in the area of Greater London has been identified as an ideal candidate for these investigations as, with improved cooling systems, it may be possible to avoid the installation of an additional cable circuit, and instead uprate existing infrastructure. Subsequently more exotic techniques, such as liquid nitrogen cooling systems, will be considered. Understanding the practical implication of such systems, including health and safety, CAPEX and OPEX estimates, and site footprint is of paramount importance.This project will develop purpose-built FEA models to investigate the cooling methods. Some experiments would also be carried out to investigate the possible thermal and mechanical complications.Data Quality Statement (DQS):​The project will be delivered under the NIA framework in line with OFGEM, ENA and NGET internal policy. Data produced as part of this project will be subject to quality assurance to ensure that the information produced with each deliverable is accurate to the best of our knowledge and sources of information are appropriately documented. All deliverables and project outputs will be stored on our internal sharepoint platform ensuring access control, backup and version management. Deliverables will be shared with other network licensees through following channels:o Closedown reports on the Smarter Networks Portal.Measurement Quality Statement (MQS): ​The methodology used in this project will be subject to suppliers own quality assurance regime. Quality assurance processes and the source of data, measurement processes and equipment as well as data processing will be clearly documented and verifiable. The measurements, designs and economic assessments will also be clearly documented in the relevant deliverables and final project report and will be made available for review.In line with the ENAs ENIP document, the risk rating is scored 6 = Low.TRL Steps = 1 (2 TRL steps)Cost = 2 (£500,000 - £1m)Suppliers = 1 (1 supplier)Data Assumption = 2 (Assumptions known but will be defined within project) The project is scoped into 5 work streams (WSs). WS1: Identification of case study site(s) and collation of datasets including experimental samplesThe initial work stream will comprise data gathering required for the simulation investigations. To construct the FEA model geometries, technical drawings of the tunnels, including relevant dimensions and locations of headhouses and risers will be required, in addition to cable design information. Relevant material properties will be taken from the IEC standards or using National Grids existing design values where appropriate. To validate the FEA models, coincident measured datasets of load and DTS temperatures will be required. Analysis of such datasets will be undertaken, including whether additional measurements are required to ensure confidence in the simulation findings. Care will be taken to map recorded fibre data to position data along the tunnel route. As part of this work stream, the project team would also seek to source cable samples from National Grid that are comparable to those used in the case study tunnel(s).WS2: Development of FEA cable tunnel thermal model for existing cooling technologiesUsing data collected in WS1, a fully three-dimensional model geometry of the case study(potentially a selected cable circuit in the area of Greater London) will be constructed. Temperature will be calculated by coupling a thermal model to a computational fluid dynamics simulation of tunnel air, including the consideration of naturally and forced cooling mechanisms as appropriate. Existing models developed for NGET projects, in particular “Ratings of Cables In Tunnels (RoCIT)” will be used as a starting point. These models will be validated using DTS and load data collected in WS1 to provide confidence.Once the models have been validated, the implications of chilling inlet/outlet air into the tunnel on cable ratings will be investigated. Both continuous and dynamic calculations will be employed, and the cooling system requirements to produce a given rating will be determined. The models will also allow the thermal and mechanical stresses within the cable to be calculated. These may be more than those experienced typically, due to the higher thermal gradients within the cable caused by the lower tunnel temperatures.WS3: Experimental investigations into cable system performance in novel thermal environmentsThis work stream will run in parallel with WS2 and WS4 and will determine the impact of the alternative cooling technologies on cable performance. At rated load, under typical installation conditions, the temperature difference between the cable conductor and sheath may be 10 - 15°C. However, if significantly higher loads are applied, combined by lower cable surface temperatures, the temperature gradients across the insulation may be significantly larger, potentially exceeding 90ºC. A series of experimental investigations will determine whether electrical, mechanical or thermal performance of insulation material is compromised due to these thermal stresses. Conditions for these experiments will be specified using the outputs of WS2. It is proposed to utilise the cable samples sourced in WS1 for such investigations. Combined mechanical and thermal testings will be carried out, followed by forensic investigations into the samples. Measurements of key dielectric and mechanical properties will be undertaken. Specifically: tensile strength prior to and after thermal cycling; investigation of the morphology prior to and after thermal cycling; dielectric permittivity and loss factor prior to and after thermal cycling.WS4: Development of FEA cable tunnel model for liquid nitrogen cooling systemsHaving developed simulation models utilising established cooling technologies in WS2, this work stream will investigate the impact of more exotic liquid nitrogen systems. Liquid nitrogen has a boiling temperature of 77 K and is used both as a coolant and an electrical insulator for superconducting high voltage systems. The application of a liquid nitrogen cooling system to traditional cable systems, e.g. 400kV three phase XLPE, has yet to be attempted.Simulation based investigations would initially assess the impact of chilling the inlet air into the tunnel, and the required system specifications to achieve this. Following this, the thermal impact of a cooling pipe installed within the tunnel will be examined. Finally, the influence of regularly misting nitrogen into the tunnel, causing warmer exhaust air to be removed due to the rapid thermal expansion, on cable temperatures will be quantified.WS5: Recommendations to National GridThe final work stream will combine findings from across the project into a report outlining recommendations to National Grid including an assessment of the practical implications of different cooling solutions, with a road map to implementation. Consideration will be given to health and safety, financial expenditure estimates, and site footprint. It is intended to collaborate with NGET staff in the production of this document to ensure that the recommendations provided can be utilised by NGET effectively, including the identification of any remaining unknowns or risks. The objective of this project is to assess the feasibilities of the aforementioned alternative cooling methods for underground transmission system. The key aspects are:Build accurate FEA models that can reproduce the thermal environment in an underground cable tunnelFind out to what extent can the cable ratings be increased by employing the alternative cooling methodsFind out the thermal and mechanical conditions that the cable will experience due to the use of alternative cooling methods and the possible consequences of such conditionsFind out the possible health and safety implications from the alternative cooling methods
Abstract The power flow capacity of high voltage cables is limited by heat dissipation. Cable installed within tunnels are often a thermally limiting section of circuits due to the relatively poor heat transfer through the air surrounding the cables. When reinforcement is required, this can necessitate the construction of additional tunnels which are highly costly. This project will investigate, through bespoke FEA simulations and targeted experiments, the capability of alternative cooling methods to enhance cable ratings in tunnels. The first stage of the project will investigate the use of established technologies, such as chilling inlet air, which are nevertheless novel for cable tunnel applications. Subsequently more exotic techniques, such as liquid nitrogen cooling systems, will be considered.
Publications (none)
Final Report (none)
Added to Database 14/10/22