SSEN Transmission and its principle contractor, Balfour Beatty, has successfully completed, on time, the challenging upgrade of the existing Fort Augustus to Fort William overhead transmission line.
Bringing to a close two years of hard work, the project team has upgraded one of the north of Scotland’s longest serving power lines and by doubling its capacity, provided additional capacity to accommodate the growth in renewable electricity in the area, supporting the transition to net zero emissions.
The 44Km line was originally built in the 1950’s following the passing of the Hydro Act, which revolutionised and industrialised the north of Scotland by bring power to the glens. After nearly 70 years’ service the project team needed to determine the best way to upgrade the line while minimising the impact to the local communities surrounding it. The location of the line, which crosses public roads, railway lines and the Caledonian Canal, following steep terrain throughout its route, added to the challenges that the team would need to be creative to overcome.
Firstly, would a completely new line need to be built? Looking at the towers, they reviewed if the current towers were in a good enough condition to be retained. This would remove the need for a new line to be built and a new route for the line found, decreasing the level of construction impact on the local community. Innovation was the key, the existing conductor was changed to an ACCC conductor which is made using special aluminium wrapped around a carbon composite core, the change means the conductor will be twice as strong as the steel, 70% lighter and able to carry twice the amount of power. By using this technology and strengthening the existing towers only 5 of the 156 towers would need to be replaced, retaining 97% of the towers, sustainability at its best.
Secondly how could this work be done whilst maintaining the security of supply to the customers? A very detailed and extensive Emergency Return to Service plan was put in place to restore supplies to customers in the event of a fault occurring on the network while this work was in progress. This included automation of remote switching points, temporary generation, staff on continuous standby and practical timed exercises on training rigs. Special working methods had to be employed to allow the conductors on one side of the tower to be changed whilst the other side remained live at 132,000 volts, this was essential as this line is the sole source of supply to the customers in this area.
Next, how to reach the towers to carry out the work with minimal environmental impact. The steep sides of the glen the line runs through made access difficult and would mean new access tracks would have to be built to complete the works. In some locations the side slopes were so steep specially built sets of stairs were installed to allow access up the hillside to the towers, then once the work was complete moved on to the next section.
Where the line crossed the A82, local roads and the canal, netting was placed under the wires on scaffolding to protect the areas below. Where scaffolding couldn’t be used, another innovation was the use of Catenary Support System (CSS) over the Caledonian Canal and A82 & A87, this is where a motorised tug pulls the new conductor and rollers along the old conductor between towers. This was a massive win, as it meant that no road closures or closure of the canal would be required, keeping the local community, tourists and road users moving.
Lead Project Manager Pat Howe said:
“I am immensely proud with what we have been able to achieve as a team during this project. At the outset of the project we couldn’t have imagined we would have been able to retain so much of the existing infrastructure as well as doubling the capacity of the line.
Our first priority is always to safely deliver a robust, efficient and reliable network to our customers in the most sustainable way. In delivering this essential service, we have demonstrated that this is achievable, even on a project that contained as many challenges as this one. Our team has worked closely with the local community throughout the project, being awarded an Excellent in the Considerate Constructors Scheme, raising over £8000 for local charities, including the Scottish Air Ambulance, Lochaber Hope and the Highland Hospice.
This project has embraced safety, innovation and sustainability, whilst striving to have a positive impact on the communities we have had the privilege of working in. We have set a high standard of how future projects should be delivered. “