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| Reference Number | NIA2_NGET0061 | |
| Title | Tunnel power cables earthing, safety and protection under electromagnetic transient voltages and currents (TunCab) | |
| 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 May 2024 | |
| End Date | 31 March 2026 | |
| Duration | ENA months | |
| Total Grant Value | £456,000 | |
| 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 | https://smarter.energynetworks.org/projects/NIA2_NGET0061 |
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| Objectives | Work has been done on the safety aspects of cable circuits, and CIGRE TB801 contains some possible generic arrangements. However, the specific configuration in modern cables circuits in tunnels introduces new challenges for safety and integrity of the circuits under fault conditions.In this project we propose to address the following:Review NSI5 and CIGRE TB801 working methods: This is to evaluate applicable aspects of the document to the modern cable tunnel options. Also, explore any previous work for critical evaluation. This will allow improved models to study the new configurations.Earthing studies and induced voltage evaluations will be carried out and comparison with similar studies will be undertaken.We will seek to extend the results of the preliminary studies by means of CDEGS simulations of the induced effects in cable sheaths under different earthing configurations in both steady-state and transient conditions. Models will incorporate phase transposition arrangements as specified in the modern tunnel layout design drawings. Electromagnetic transient ~(EMT) modelling of cable circuit conductors and their earthing system.A full electromagnetic transient model of the cable tunnel circuit, cable sheaths and Sheath Voltage Limiters (SVLs) is necessary for the evaluation of the transient induced voltages. This work will build a detailed EMT model of the cable in tunnel circuits using LPT2 as an example, Model behaviour will be benchmarked against the steady-state studies and expanded to include lightning and switching transiens propagation in the energised circuit.Using the developed CDEGS and EMTP system models, the impact of adding or removing the NSI5-mandated equipotential mat on induced voltages at the work area may be quantified. The removal of equipotential mats requires consideration of capacitive currents and electromagnetic transient cases that can only be fully studied in a suitable EMT package. The result of this study may enable insulated working to be undertaken outside of the current NSI5 guidance.We will also investigate the consequence of the systematic removal of sheath voltage limiters from the tunnels. SVLs are specified to limit differential voltages under an insulated working regime and are in the designs specified for installation at 2 in every 3 cable jointing bays. This study will investigate the systematic removal of SVLs and its impact on induced voltages in the transient and fault conditions previously investigated. An initial review of NSI5 and CIGRE TB 801 suggests earthed working by creating a local equipotential zone using earthing mats may work (a temporary earth is required instead of a permanent earth). Detailed EMT studies are required to confirm all scenarios under normal operation and fault conditions. In addition, there may be no need for SVLs (Sheath Voltage Limiter) since there is no earthing point in the tunnels. The project aims to:review current knowledge and build on current recommendations of NSI5, CIGRE TB801, IEC 60617 and 60417develop a model for transient studies and SVL requirements in cables circuits in tunnelsdevelop electromagnetic models of cable circuits in tunnels develop earthing system models for earthing performance develop evaluation techniques for new mitigation options for SVL use and earth farms. | |
| Abstract | LPT2 will comprise 30km of cable tunnels stretching from Wimbledon in south-west London to Crayford in south-east London. When de-energising a circuit for maintenance the absence of earth bars in the tunnels removes the possibility for locally-earthed safe working, being the preferred method under NSI5. It has been determined separately that earth rods installed in the tunnel present an inadequate control measure, installation of rods through tunnel walls is undesirable for reasons of wayleave, hydrostatic pressure and corrosion. This project seeks to evaluate the alternative working methods for implementation on LPT2 by June 2025, in the first instance in preparation for energising Hurst-Newcross cct 2. Further detailed investigations will be carried out to consider various scenarios. Furthermore, magnetic field exposure will need to be determined and ensure that that they are within the allowed limits. | |
| Data | No related datasets |
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| Projects | No related projects |
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| Publications | No related publications |
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| Added to Database | 02/10/24 | |
