SSEN Transmission’s winter preparation

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A blog by Dave McKay, Director of Asset Management & Operations

As Christmas trees have gone up in homes, tree felling helps keep our electricity network safe from extreme weather – with native species replacing trees removed

People can rest assured that SSEN Transmission has gone the extra mile to prepare for whatever the winter weather throws at us – ensuring security of electricity supply, with the continued flow of home-grown, clean green power across the country.

SSEN Transmission is responsible for the electricity transmission network in the north of Scotland, maintaining and investing in the high voltage 132kV, 220kV, 275kV and 400kV electricity transmission network. This network consists of overhead lines on wooden poles or steel towers, underground and subsea cables, and electricity substations. It extends over a quarter of the UK’s land mass, crossing some of its most challenging terrain, where winter weather can also be particularly severe.

Reliable Energy

The first priority of the business is to provide a safe and reliable supply of electricity to our communities. Thia is done by taking the electricity from generators and transporting it at high voltages over long distances through the transmission network for onwards distribution to homes and businesses in villages, towns and cities.

In our recent Business Plan for investment in the grid, submitted to Ofgem in December and covering the period April 2026 to March 2031, SSEN Transmission set out our three goals:

  • Reliable Energy, with an ambition for zero interruptions in electricity supply to homes and businesses due to the north of Scotland transmission network.
  • Clean Power, with the north of Scotland transmission network having the capability to meet 20% of GB demand for clean power.
  • Our Legacy, to drive investments in the energy transition that delivers transformative lasting benefits for local communities, the economy and nature.

Preparing properly for winter is a crucial element in the achievement of Reliable Energy.

Compared to the infrastructure which fulfils onwards distribution, faults on the transmission network are rare – but if they happen could impact tens or even hundreds of thousands of people, with winter weather increasing the risk.

To mitigate this risk and deliver security of supply, the Transmission business undertakes year-round work which is stepped up in advance of winter.

SSEN Transmission’s performance in numbers

The National Electricity Transmission System Performance Report provides the statistics to demonstrate a strong record of delivery by SSEN Transmission.

The Overall Reliability of Supply for the transmission system in the north of Scotland during 2023/24 was 99.998518%.

And among the three Transmission Owners in Great Britain, SSEN Transmission has the best performance in terms of system availability.

System availability is reduced whenever a circuit is taken out of operation for either planned purposes or following a fault. Planned outages are required for system construction and new user connections, in addition to the maintenance necessary to retain a high level of system reliability to ensure that licence standards of security are met.

In 2023/24, SSEN Transmission achieved Annual System Availability of 95.82% in the north of Scotland.

Tree felling – and replacement with native species

One element of SSEN Transmission’s resilience activity is a programme, ongoing since 2017, to remove trees close to transmission infrastructure. So far, more than 90 per cent of spans – the overhead lines in between pylons – are now fully resilient to falling trees.

There is also a biodiversity gain from this programme, as the trees felled are typically non-native commercial forestry, and are replaced with tree-planting away from the lines with species that are native to the north of Scotland.

Other key aspects of SSEN Transmission’s winter preparation include:

  • Inspection of critical overhead lines and substations are enhanced in the run-up to and during winter, with more than nine in 10 inspections of lines now done by drone or helicopter.

  • Most annual maintenance is completed by the end of October, leaving the network more robust throughout the winter months, with non-essential maintenance paused during the festive period.

  • Business continuity plans have been reviewed, and simulation exercises for different scenarios conducted during this year.

  • Specialist plant and equipment including 4x4 vehicles and helicopters are available to support our teams should any emergency situation arise.

  • Staff rotas are in place to ensure we have critical cover throughout the year. The number of staff on these rotas are increased during holiday periods or ahead of any severe weather, enabling the business to respond to any emergency events.