Electric avenues

Jon Lawson

Scotland’s first new power conductor in almost 30 years goes live

Scottish Power Energy Networks announced in January the successful installation and energisation of the first new live electricity conductor in Scotland in almost three decades.

Using a 3M aluminium conductor composite reinforced (ACCR), the 275kV single conductor doubles the available power capacity without making major changes to the existing electricity network between Coylton and Mark Hill in South Ayrshire.

Via a subsea cable, the ACCR conductor enables Scottish Power to bring power from its local offshore wind generation plant.

The project is part of Scottish Power’s RIIO targets, which included a forecast of 2.5GW generation connected to the network by 2021, a target that at 4.9GW has already been exceeded.

Using the ACCR, Scottish Power can meet its baseline shared use infrastructure (BSHE) target of 1,073MVA by the end of 2016.

The project involved close collaboration between Scottish Power Energy Networks, contractor Balfour Beatty and 3M and was completed in just three months, against the predicted timescale of eight months, despite the challenges of a remote, difficult terrain and a particularly wet Scottish summer.

“Using ACCR meant that we could double the ampacity using the existing tower infrastructure and manage sag resulting from higher temperatures caused by increased power. This approach removed the need to carry out extensive new infrastructure developing, so the impact on the local community and environment has been minimised and without the delays that civil engineering permissions and rights-of-way would traditionally involve,” says Richard Wylie, lead design engineer, Overhead Lines, Scottish Power Energy Networks. “Although this was new territory for Scotland and relatively new in the UK overall, we had confidence in ACCR because it is a proven technology with many reference customers worldwide.”

The alternative would have been to build new infrastructure, because the thermal increase of installing larger conductors would have been inadvisable and uneconomical on the existing towers.  The anticipated current ratings for ACCR conductor at 275kV are between 3382-3878A.  The conductor is also reportedly much quieter than other conductor technologies, according to Scottish Power.

Simple and fast installation

Collaboration between Scottish Power Energy Networks, Balfour Beatty and 3M was critical to the project’s success.

Wylie explains: “Advance planning contributed to on-site efficiency and speed of project completion, including making sure that the installers were familiar with the technology long before they were on-site, so they were not learning on the job and any concerns had already been addressed. For instance, it became clear that some aspects of the installation process needed to be amended to suit Scottish Power’s specifications, such as designing longer installation platforms, something we were able to do in advance.”

There was no problem with the installation, the techniques are mainly the same as for other products, with just a few changes in the process.

The installation team was happy to work with ACCR; one installer reported he completed an electrical joint in just 30 minutes.

ACCR was introduced commercially in 2005 and is now installed on six continents. Because its light weight and low sag properties often enable line upgrades without the need to construct larger towers or expand rights of way, the conductor has found widespread use wherever tower replacement is difficult or uneconomical, including crowded urban settings and environmentally sensitive locations, such as river crossings and estuaries.

Extensive testing demonstrated that the conductor retains its integrity after exposure to temperatures even higher than the rated continuous operating temperature of 210˚C and the emergency operating temperature of 240˚C. It has the durability and longevity of traditional steel core conductors, even when operated continuously at high temperatures.

The conductor’s strength and durability result from its core, composed of aluminium oxide (alumina) fibres embedded in high-purity aluminium, using a specialised process.

The constituent materials can withstand high temperatures without appreciable loss in strength. Also, since the technology is based on aluminium, it has the corrosion resistance typically associated with all-aluminium conductors.  

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