"In the past we’ve had problems with programme timings. With Balfour Beatty taking this approach, we beat the programmed installation rate and by the time we came to jointing we were 2 weeks ahead of schedule.”
Scott Sadler, Project Manager, National Grid
Much of the electrical network infrastructure in use throughout the UK has reached the end of its life, jeopardising service resilience and requiring extensive and costly maintenance. The Croydon Tunnel project, which connects two electricity substations in London, was proposed to ensure the capital’s energy network had the capacity to support future growth with minimum reliance on disruptive overhead lines. Balfour Beatty was awarded the cable installation contract to install 31km of 400kV cable along the 11km stretch of tunnel in 2006.
With old systems representing major obstacles in terms of safety and efficiency – over 30 operatives would previously be required to physically ‘pull’ the cable into tunnels – the installation demanded an innovative approach. The Balfour Beatty team developed a new mechanised method of cable installation, based on a technology used on another of the company’s projects, the Woodhead Tunnel.
Being used for the first time in a purpose-built HV cable tunnel environment, the Tunnel Cable Machine (TCM) delivered significant safety, efficiency and quality improvements for the Croydon project. The machine was developed with a modular design, allowing it to be used in the restrictive environment of the tunnel.
The TCM allowed a cable pull of 1.2km – the longest cable length ever pulled in the UK and Europe and reduced overall timescales for the cable installation by 33%. The mechanised process also greatly improved quality and safety; and, most importantly, there were zero lost time safety incidents during the installation.
The TCM has been a remarkable success on the Croydon Tunnel project and is expected to produce even greater efficiencies on future projects both in the UK and around the world.
Key facts and figures
Number of lost time safety incidents
Longest ever cable pull in Europe, achieved on this project
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