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Projects: Projects for Investigator
Reference Number NIA_NPG_009
Title Development of Oil-filled Cable Additive
Status Completed
Energy Categories Other Power and Storage Technologies(Electricity transmission and distribution) 100%;
Research Types Applied Research and Development 100%
Science and Technology Fields PHYSICAL SCIENCES AND MATHEMATICS (Chemistry) 25%;
PHYSICAL SCIENCES AND MATHEMATICS (Metallurgy and Materials) 25%;
ENGINEERING AND TECHNOLOGY (Electrical and Electronic Engineering) 25%;
ENGINEERING AND TECHNOLOGY (Mechanical, Aeronautical and Manufacturing Engineering) 25%;
UKERC Cross Cutting Characterisation Not Cross-cutting 100%
Principal Investigator Project Contact
No email address given
Northern Powergrid
Award Type Network Innovation Allowance
Funding Source Ofgem
Start Date 01 March 2016
End Date 01 June 2017
Duration 15 months
Total Grant Value £180,000
Industrial Sectors Power
Region Yorkshire & Humberside
Programme Network Innovation Allowance
Investigators Principal Investigator Project Contact , Northern Powergrid (99.999%)
  Other Investigator Project Contact , UK Power Networks (0.001%)
Web Site http://www.smarternetworks.org/project/NIA_NPG_009
  • Construction and commissioning of the laboratory fluid leak containment rig.
  • Evaluation of the properties of the modified self-repair fluids that support containment.
  • Design and costing of the fluid filled cable test rig with the cable requirements of the supporting DNOs fed back into the design.
  • Selection of the cable test rig host and establishing a costing for the hosting of the technology.
  • Define the development activities to enhance repair and containment function for Evaluation of materials produced using the assessment methods already reported in Stage 2.
  • Accelerate the design, costing and location of the FFC cable test rig in preparation for an accelerated follow-up project.
  • Prime the low pressure FFC fluid producers in the UK to provide purified fluids in volumes suitable for the cable test rig and FFC circuit trials.
  • Stage gate review to decide whether the project can still deliver benefit to customers and to determine the required follow-up work. 

The success for this low TRL project is the delivery of the objectives detailed above and a confirmed decision as to whether to continue the project into a further development phase as a separate follow-up activity.

Abstract All major GB electricity utilities have fluid filled cable circuits on their distribution networks. These are mostly of the low pressure fluid filled type, typically designed to operate at 3 - 5 bar pressure with short term peaking pressures up to 8 bar. Over time these cables may begin to leak cable fluid and subsequently the cable pressure may drop and the cable insulation system (fluid impregnated paper or paper-polypropylene laminate) may eventually fail. In some cases the leaks may also cause environmental contamination that is of concern to the network operator, to the public and importantly the Environment Agency who could enforce the closure of cable circuits or impose limits on their operation.

The causes of leaks can be categorised as follows:

  • Third party damage leading to rupture of the metallic sheath (the most common cause)
  • Ageing/corrosion of metallic sheaths due to thermal and mechanical stress or possibly vibrations
  • Changes in the thermal resistance of the soil surrounding the cable
  • Corrosion of contacts in pressure gauges leading to faulty alarm function
  • Degradation of terminations
  • Influence of cable construction on ageing

Further reduced reliability has been associated with:

  • Exceeding the normal design life of the order of 30 to 40 years - many of the oil/fluid filled cable circuits in operation are in this position
  • A significant reduction in the skills of repairers and poor quality repairs
  • A significant decrease in maintenance on fluid filled systems due to pressure on operating budgets
  • The increasing difficulty of sourcing spares

These aspects have resulted in an uncertain outlook for the future reliability of fluid filled cables. However there are still many of these circuits in operation, and the challenge remains to improve the condition and reliability of existing cable circuits, to reduce failures and outages, and to significantly reduce the associated liability costs of outage and environmental pollution. There is an urgent and on-going need in the GB electricity distribution network to prevent and treat cable fluid leaks to improve the reliability of fluid filled cables and to reduce environmental damage that often accompanies oil leakage. However, it is important that the methods used to achieve this fit into a low-maintenance strategy and where possible are self-managing without the need for detection, location-finding and manual repair. For land based cables deployed underground in backfill, in cable trough installations or deployed in cable ways in tunnels and other civil constructions, damage may occur at the time of installation and also during operation when third parties carry out civil repairs. Damage may also occur through cable ageing and stressing. Once cable leakages have been detected,locating the sourceof the leak is a difficult process. In-situ cable self-repair is seen as invaluable as damage may be localised and non-obvious from inspection of the cable during operation and may appear many years after installation. In many cases it may not be possible to inspect the cable in inaccessible environments. The project seeks to address this challenge by utilising new developments in self-repairing polymers, resins and reactive chemical technologies for fluid systems that are potentially capable of providing a repair function for a variety of cable sheath defects and damage types that may occur. The uniqueness relates to the use of the fluid medium to affect the repair when key reactions are triggered by the presence of a leak and exposure of the fluid to the ambient conditions around the cable. This project is being undertaken in a series of self-contained stages. The first three of these have already been completed under IFI. The method as a whole has to be taken in the context of this previous work which is described below to provide that context.

Stage 1 - Completed under the IFI Critical review and selection of potential repair technologies with account of the damages/ leaks to be repaired, and the sourcing of the component compounds and design of test rigs - to include consultations with EDF R&D.

Stage 2 - Completed under the IFI First level scoping assessment of synthesised and formulated self-repair technologies to assess their ability to function in cable-like environments when subjected to damage and use these findings to select candidates for more detailed evaluation.

Stage 3 - Completed under the IFI Second level evaluation of the best candidate repair technologies from Stage 2 with recommendations on which technologies to move to cable testing in stage 4.

Stage 4 - This project :

  • Component sourcing and construction of the fluid containment rig for lab assessment of containment.  Operation of the containment rig to assess different fluid blends.
  • Operation of the rig to investigate fluid containment in relation to backfill and soil type and self-repair fluid type.
  • Evaluate the properties of modified self-repair fluids to support containment.
  • Carry out cable test rig design and costing to accelerate phase two.
  • Consult with the DNOs on the type and details of FF cables to be tested in Phase 2.  Select the location to host the cable test rig and establish a costing for its operation.
  • Define the development activities to refine the self-repair fluids to enhance leak repair and the containment of fluids to the vicinity of the cable circuit.
  • Prime the UK’s leading suppliers of low pressure cable fluids to supply purified fluids for the cable test rigs and cable trials in advance of network deployment.
  • Review the project and determine whether it still hasthe potential to deliver benefitsto customers.


Note : Project Documents may be available via the ENA Smarter Networks Portal using the Website link above

Publications (none)
Final Report (none)
Added to Database 09/08/18