5.5. Operation And Maintenance

  1. Although the Proposed Development will not be permanently staffed during operation, access will be required to the Proposed Development for potential operation and maintenance activities 24 hours per day, 365 days per year.
  2. The frequency of visits to the onshore substation will be approximately four times per month to inspect the equipment as necessary. Each visit will require at least two personnel (in a van or car). For scheduled maintenance, it is anticipated that 6 visits would be required per year, requiring up to 30 personnel. Additional visits would be required for faults.
  3. Annual checks, on foot, will be required along the onshore cable corridor during operation. Access would normally be along the agreed onshore cable corridor. In the unlikely event that there is any failure of onshore cables, a fault finder with test gear would locate the fault along the onshore cable corridor section. Once located, the area around the fault would be excavated and the fault repaired. If the onshore cable cannot be repaired, a new length of onshore cable would be inserted and jointed to replace the failed section.
  4. The most common failure mode in onshore cables is due to external mechanical damage (e.g. diggers and spades) which can be avoided by marking the locations of onshore cables on service maps. The likelihood of a breakdown in insulation due to other problems is very low, particularly for onshore cables installed in ducts such as the proposed onshore cables. In the unlikely event of a failure, the cable will be replaced between joint bays so to minimise any disturbance and only in the very unlikely event of catastrophic failure will the cable require to be accessed at the point of failure between joint bays.
  5. Planting trees and other deep-rooted vegetation over the onshore cables or within 3 m of the onshore cable trench will be restricted, to prevent encroachment by vegetation.
  6. Onshore substation security will likely comprise of CCTV, access control systems and security fencing. Permanent lighting at the substation will also be installed to aide security and facilitate safe access during hours of darkness.  

5.6. Decommissioning

  1. After the lifetime of the Project (35 years from final commissioning of the wind turbines), the Proposed Development is likely to remain in situ as part of the functioning transmission network. The decommissioning plan and any associated decommissioning activities will be subject to consultation and approval by the ELC.
  2. If the onshore cable is removed, the area required for removal activities is expected be no more than the area required for construction activities.
  3. The design life of the Project is 35 years. For the purposes of the current consenting framework and as a basis for the EIA, a high-level decommissioning approach based on the current technological and regulatory framework is outlined below. The eventual decommissioning of the OnTW will consider the latest technological developments, legislation and environmental requirements at the time that the work is due to be carried out.

Cable Decommissioning

  1. At present it is industry standard to leave onshore export cables in-situ and the assessment has been undertaken on that basis. At the time of decommissioning a decision will be made, based on industry best practice and legislative guidance, as to the need to remove cables and in ground equipment. Should they be left in-situ contingency plans will be developed to ensure that appropriate actions are taken should any of the redundant cables become exposed.
  2. If cable removal is required this will be achieved by excavation. Typically 6 m or more of land is required on each side of the cable route to accommodate the excavation equipment. Excavators will be used to remove the overlying soil and retrieve the cables which will then be rewound onto drums. Cranes may be needed to lift loaded cable drums onto transport vehicles. After a complete cable length has been removed, the trench will be back filled with the excavated material. At a road crossing the road will be resurfaced.
  3. Where burial conditions allow cables may be pulled out. This may involve a partial excavation of the trench. If protective tiles have been used then these will also be removed. Any hard core and sand below the cable will be left in the trench as part of the backfill. Following cable removal the trench will be backfilled and the surface reinstated in keeping with the condition before the decommissioning works.
  4. All supervisory control and data acquisition (SCADA) cables, fibre optics and other control cables will also be removed during power cable excavation.  Cables which run in ducts, tunnels or other means of crossing obstacles will be removed. The ducts, tunnels or similar will be removed if appropriate and as agreed. In some cases where there may be a risk of settlement or subsidence, the ducts will be left in situ. In such cases, the ducts or tunnels will be sealed at each end to prevent unauthorised third party access. Warning signage will be used and the ducts reburied as appropriate. In some cases ducts may be backfilled with an inert material to provide lateral strength and prevent access by any third party.

 

Joint Bay Decommissioning

  1. The need to remove the export cable joint bays will be determined at the time of decommissioning.
  2. If removal is required, the joint bays will be excavated and fully removed. The removed material will be broken up in situ and disposed of appropriately. The resulting pits will then be backfilled and the surface reinstated in keeping with the local environment.

Substation Decommissioning

  1. At the end of its operational life the onshore substation may be decommissioned or it may be modified to allow for ongoing use.
  2. To decommission the onshore substation, all electric plant will be removed from its foundations and transported to a facility for processing for reuse, recycling or disposal. The foundations will be either cut back and covered or pulled out and disposed of and any pits backfilled with earth, if required. Any residual contamination will be treated to the required standard. The surrounding fencing, the control building and any other building on site will be demolished and all materials disposed of. The access tracks will be removed and land restored as far as practicable.

Braidwood Burn Cable Culvert Decommissioning

  1. At the end of its operational life the cables and/or associated structure at Braidwood Burn may be partially removed, fully removed or left in situ. At the time of decommissioning a decision will be made, based on industry best practice and legislative guidance, as to the need to remove the cables (including in ground equipment) and/or the structure.
  2. Should the infrastructure be left in-situ, contingency plans will be developed to ensure that appropriate actions are taken should any of the redundant cables become exposed. An assessment of the structure would also be undertaken to establish any ongoing examination and maintenance regime. This may be a continuation of that already in place during the operational phase.
  3. If cable removal (including ducting and associated in ground equipment) is required this will be achieved by excavation. This would require enabling works, similar to those outlined in the construction period, followed by earthworks excavation to cable / duct level. Cables and ducting would then be cut and removed – the cable would be rewound onto drums, and the ducting disposed of. Cranes may be needed to lift loaded cable drums onto transport vehicles.  Next, the remaining earthworks, scour protection, structure headwalls, structure, and structure foundations would be removed. All earthworks, structures and electrical materials will be removed from site and transported to a processing facility for reuse, recycling or disposal, unless suitable measures were agreed for use elsewhere. Following complete removal from site, regrading of embankments and any associated re-planting will be completed. For further detail on cable ducting excavation please see above text on Cable Decommissioning.

 

5.7. References

 

Cathie, 2019. Cable Landfall Feasibility Study.

Cathie, 2019. Landfall Feasibility Addendum.

Cathie, 2019. Onshore Geotechnical and Geo-environmental Desk Study.

Cathie, 2019. Onshore Geotechnical and Geo-environmental Desk Study

Scottish Environment Protection Agency, 2010. Engineering in the Water Environment: Good Practice Guide. River Crossings. Available at: https://www.sepa.org.uk/regulations/water/engineering/engineering-guidance/

Scottish Government, 1997. Town and Country Planning (Scotland) Act 1997

Scottish Government, 2011. The Water Environment (Controlled Activities) (Scotland) Regulations 2011 (as amended)

 

[1] Number of trenches reduced from landfall to onshore substation due to change in voltage level and constraints along the route.