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Pentir - Dolgarrog - St Aspah - Connah's Quay
Main Contractor
Project Length

The 132kV AC Line is a double circuit route that runs from Dolgarrog to Connahs Quay. The Northern Circuit comes through into Holywell, Kinmel Bay, and Colwyn Bay and connects to the AD (Pentir) Line just outside Dolgarrog at Tower AC192A.

The route has a circuit length of 97.29km and comprises 174 PL16 specification towers. Built-in 1952, it is over seventy years old, with only minor modifications in 1963 and 1969, with further modernisation taking place between Towers AC101B, AC121R, and AC124 in 2007. This latter modification was due to the connection of the offshore wind farm near Kinmel Bay, whereby the installation of poplar phase conductors and OPGW Earth wire took place. The recent refurbishment project saw the replacement of the Lynx 175mm² ACSR Phasewire with new Poplar 200mm² AAAC conductor and the Horse 70mm² ACSR earth wire with 36 fibre Horse equivalent OPGW.

Scope of works

Keltbray undertook tower steelwork condition assessments, with a corresponding detailed report, along with the replacement of:

  • All identified corroded, damaged, or missing steel members that are NGC category five or above.
  • All phase conductors and earth-wire between towers AC06 – AC54 – AC301 – AC302, including down-leads at tower AC302 on to ground anchors at Holywell substation on 1 circuit.
  • All phase conductors and earth wire between Holywell Substation AC302 – AC101, including down leads on both circuits on AC101 at St Asaph Substation.
  • All phase conductors and earth wire between towers AC124 – AC193, including downleads on AC193 on to the concrete gantries at Dolgarrog Substation.

Additional works include:

  • Installation of ducted fibre optic system and associated fibre to ODF cabinets at Connahs Quay, St Asaph, Holywell and Dolgarrog substation ends.
  • Restoration and reinstatement of foundations as necessary.
  • Installation and removal of all necessary access/egress roads and work areas.

Challenges and Solutions

There were many challenges during the refurbishment project, including pulling the conductor over:

  • Network Rail Infrastructure
  • A55 Dual Carriageway
  • Various Roads
  • Live 11kV and 33kV Distribution Circuits
  • SSSI and Watercourses
  • Housing Estates, Golf Courses, and Caravan Parks

Keltbray also had to pull the conductor under a 400kV National Grid Transmission Circuit.

The planning, development, and approvement of a Safe System of work enabled works to be safe, efficient, and to a high standard. The use of our own Aerial Catenary Support System (ACSS) was critical in providing a temporary protection system while replacing the conductor over the highways, electrified railway lines, power lines, private houses, and waterways. It also assisted in meeting our outage deadlines.

Twenty-seven 11kV and twelve 33kV Distribution outages (pole lines) were necessary for the AC Line. Twenty of the 11kV outages were the result of the installation and removal of the scaffolding nets. The remaining seven of the 11kv Distribution outages were for the deployment of the ACSS on the bottom phase conductor due to an electrical infringement of the ACSS equipment passing over a live 11kV pole line. These seven Distribution outages were taken and returned over one day periods due to customer demand. This requirement meant the ACSS had to be deployed and secured in the relevant span on the 132kV line, with the new conductor pulled in the section being worked on and safely secured with the new equipment. Allowing the 11kV to be re-energised in the same working day and without disruption to the customer.

Wiring works began at the start of March 2020 and progressed in conjunction with the programme schedule. However, when the Covid-19 pandemic arose, Keltbray, classed as part of the countries infrastructure and critical key workers, reacted swiftly to implement a strategy to protect the health and safety of our staff. Subsequently, Keltbray’s Management Team revised all policies and procedures, including the Risk Assessment and Method Statement (RAMS), travel, and accommodation, which posed significant challenges and implications. Completely new working methods were the result, such as the entire AC Line workforce continuing to support, but working away from their home and families for long periods. As always, our staff maintained their professionalism and effectively  operated with a positive attitude throughout the crisis.

Environmental challenges include obtaining several licences from Natural Resource Wales (NRW), including Badger, Doormouse, Great Crested Newt (GCN), and breeding birds. To further mitigate risks associated with habitats and Sites of Special Scientific Interest (SSSI), a dedicated ECoW was on site to supervise the works. The production of constraint maps following relevant stakeholders’ advice was distributed to each member of the working party, inclusive of designated access/egress, specific routes, and a ‘traffic light’ methodology highlighting constraints within the vicinity.

Archaeological constraints included three registered historic landscapes, which pass close to numerous heritage assets, including the remains of a neolithic chambered tomb near Dolgarrog, along with bronze age burial mounds. The baseline assessment took into consideration all known archaeological assets extending to 250m on either side of the AC line, in addition to any potential access and egress routes. The assessment identified a total of 59 designated assets, including 37 historic hedgerows.

The Keltbray site team produced a mitigation strategy to avoid or reduce any adverse impacts that might result from the proposed scheme on the cultural heritage resource. Avoidance by careful planning, design, and demarcation of sensitive assets was the successful strategy Keltbray undertook.

As large parts of the AC route passed through numerous woodland, arable fields, equestrian centres, and caravan parks, etc., advance discussions and negotiations took place with landowners. The advance negotiations by our specialist team of experienced wayleave officers ensured that the correct access and egress agreements were in place throughout the line and dealt with any landowner concerns. They were highly effective, managing all safety considerations.

In total, circa 6710 temporary trackway panels were necessary on the project, providing essential access to both the towers and also to install Equipotential Zones (EPZ) at puller/tensioner sites. EPZ provides a safe zone for operatives and equipment, protecting them from any potential flashover between the conductor set out and the opposite live circuit.

Installation of stone roads enabled safe and efficient access to towers positioned in environmentally challenging locations.

Other sections of the route were through various private residential areas. Taking due cognisance of maintaining access where possible, the protection of public safety was a high priority, which resulted in some unavoidable road and path closures and diversions, all managed in liaison with the relevant stakeholders. All Traffic Management requirements and arrangements were in accordance with the code of practice for the Roads and Street Acts 1991.

Throughout the project, Keltbray has utilised a specialist scaffolding sub-contractor to provide protective scaffold structures offering asset protection during all wiring activities. Each design was specific for the site location, with further protection by a design risk assessment, calculations, construction drawings, and a Scaffold Guard Detail Form (line clearance document).

In total, 61 scaffold structures were designed and erected to provide the utmost protection while also minimising disruption.

Additional challenges, such as inclimate weather and mountainous rural terrain, were overcome by ensuring the provision of correct Personal Protection Equipment and well-equipped welfare units.

High Voltage Equipment Installed

  • 285.2 – The total amount of conductor, including OPGW (Optical Ground Wire) installed on the AC Route during this outage period equated to 285.2 kilometres (177.2 miles). This is the equivalent of travelling in a straight line from the AC Route offices (Hendre Bach, Flintshire) to Keltbray offices (Esher, London)
  • 32 – Tension Towers (3,528 – 125KN Tension Glass Insulators and Fittings).
  • 108 – Suspension Towers (7,216 – 80KN Suspension Glass Insulators and Fittings).
  • 8 – Suspended Tension Towers (Bottom Phase on Suspension Towers re-designed to Tension Towers for archiving electrical ground clearance).