On 7th February, the Prince of Wales and The Duchess of Cornwall visited National Grid’s London Power Tunnels (LPT) project to celebrate delivery of the £1bn project on time and under budget. The Prince descended to visit the tunnels while the Duchess visited a substation and viewed one of the tunnel access shafts.
During the seven-year LPT project, National Grid invested in 32 km of tunnels to house 200 km of cables over 10 circuits that now carry up to 20 percent of London’s electricity. The tunnels house National Grid’s transmission cables as well as the local electricity network’s distribution cables.
Building the tunnels means that National Grid has enabled straightforward access to maintain and upgrade the network without digging up roads and disrupting residents and businesses.
ABB played an important role in the project by delivering major upgrades at St John’s Wood substation, which distributes power to Kensington, Chelsea and Westminster. It also built a brand new substation at Kensal Green in West London, which is equipped to provide traction power for Crossrail.
General Manager for Utility Substations Jon Downs attended National Grid’s celebration and said: “It has been a pleasure to support National Grid in its drive to re-wire London for the 21st century and to mark the project’s successful completion. GIS technology has been vital in helping National Grid pack performance onto compact sites. The project highlights ABB’s in-depth knowledge of St John’s Wood substation, as well as our ability to deliver new substations on brownfield sites.”
Kensal Green substation
Building the brand new 400 kV Kensal Green substation in west London was a major achievement as the site presented challenges that had their roots in the Victorian period.
The site was previously a Victorian gasworks and had been contaminated by the waste products from the coking process that produced town gas in the 1800s. There were pockets of cyanide, arsenic, coal tar, asbestos and carcinogenic compounds. Land remediation was therefore the first priority, with the construction team working in hazmat suits and a full-time scientist testing soil before it could be moved off site for treatment.
Another early task was replacing the existing time-served retaining wall to build a brand new boundary wall four metres high and 400 mm thick to contain the foundations for the heavy substation infrastructure. However, before demolition or construction, a specialist waste company had to be called in to eliminate a colony of Japanese knotweed. This plant species was introduced to botanical gardens in the UK in the 1840s and is so invasive that it can destroy concrete foundations and can be classified as controlled waste.
Other Victorian influences on the project arose from its location. Being sandwiched between the Great Western Railway and a canal, the site was compact and access was restricted to a single point.
In addition, the site is visible from the nearby Kensal Green cemetery, which is the resting place of Isambard Kingdom Brunel and other prominent Victorians. As a result, the London Borough of Kensington and Chelsea’s planning conditions required that special architectural features be added to the GIS, control and tunnel access buildings.
Equipping a new substation
As well as housing nine circuits to connect with substations at St John’s Wood, Willesden and Wimbledon, the new substation is a bulk supply point for Crossrail and is equipped with two supergrid transformer feeder circuits for the railway.
ABB scope included design, engineering, construction and commissioning of the substation. It supplied transformers, 420 kV ELK GIS, cabling and control equipment, as well as SMOS Light (Structure Mounted Outdoor Switchgear Light) for Balfour Beatty to install for Crossrail’s feeder substation.
St John’s Wood substation
The LPT project is ABB’s latest at St John’s Wood, where it has delivered projects and upgrades since 1999. The substation provides power to areas of central London including Kensington and Chelsea and Westminster. It is notable for being one of the most compact and complex on the grid and, although it operates at 400 kV, the site’s switchgear is rated at 550 kV, the highest in the UK.
During the LPT project, ABB created seven new circuits, including two for both Kensal Green and Highbury, one for Willesden and two shunt reactor circuits.
ABB took a phased approach, starting with installation of new gas-insulated busbars (GIB) in phase one. This was followed by highly complex installation of a new GIS bus section circuit breaker in the second phase and then installation of transformers, gas insulated switchgear and additional GIB, as well as high-voltage cabling and protection and control equipment in the final phase.
With the site being relatively compact, ABB’s engineers created 3D models and animated video to guide the site team during key phases of installation. In addition, a shunt reactor was delivered to the site with the unusual addition of a self-propelled trailer so that it could be manoeuvred into its enclosure and rotated through 90˚.