Onshore cable route construction update - May 2018
The new onshore substation is located in Burstall, near Bramford. We have constructed the main access road and two cable crossing structures, to give access to site for all the building materials and electrical equipment required.
Above: Construction works at the new onshore substation, near Bramford
Construction of the main substation buildings is also well underway. These will house some of the High Voltage electrical equipment used to convert the electricity into a suitable form for transfer into the National Grid. The electrical equipment installation begins in May 2018 and will continue for the rest of 2018.
Onshore cable route
The onshore cable route is 37km long and runs from Bawdsey, under the River Deben and around the north of Ipswich to the new onshore substation.
The main construction work is divided into packages and includes open cut works, Horizontal Direct Drilling (HDD) and cable installation. As work on a package is completed in one area, the contractor delivering the package will demobilise from that area, move along the construction corridor and set up in the next location.
Open cut works
The majority of the onshore cable route runs through farmland and will be installed by digging a trench and laying ducts to house the cables. The cables will then be pulled through at a later date. When excavation works reach a crossing point on the public highway, a short-term road closure and diversion will be implemented. Please see our Road and Public Right of Way closure section for the latest information on current and future closures.
Open cut works are progressing and most of the ducts for East Anglia ONE and the future East Anglia THREE have been laid from Claydon, through the countryside north of Akenham, Witnesham and Tuddenham to the Bealings.
Ducts still need to be laid under Cockfield Hall Lane, off the B1077 Westerfield Road, under Holly Lane (Little Bealings), through some land to the north of Tuddenham St Martin and to traverse some water courses. The contractor also needs to undertake some drainage works in the area. Most of the workforce associated with the package has relocated to other areas along the cable route, including Little Blakenham, Waldringfield and Bawdsey.
Horizontal Direct Drilling (HDD)
Occasionally the cable route must go under a major transport network or natural obstacle, where it is not possible to use open trench methods. In these locations the ducting will be installed using Horizontal Direct Drilling (HDD) or auger bore techniques. HDD is a trenchless method, used to install ducts beneath the ground, through which the power cables for East Anglia ONE will later be pulled.
HDD requires two working areas either side of the drill:
- The rig side, where the drill rig is located and where the drill commences.
- The pipe side, from which to exit the drill. A pipe (ducting for the cable) is then pulled back through the drilled hole.
The drill under the River Deben was completed earlier in the year using a 250 Ton rig. The rig drilled approximately 700m under the River Deben from Falkenham, exiting at Ramsholt.
The pilot drill included a drill bit on the end followed by a gyro steering tool manually operated on the rig side. The hole was established by jetting drilling fluid down through the drill and out through nozzles in the drill bit. The drilling fluid mixed with the loosening material and was transported back through the drilled hole to the surface. Sections of ‘drill rod’ were added to the back of the pilot drill to protect the integrity of the hole as it bored further under the River Deben.
Above: Rig side pilot drill, west of the River Deben.
After breaking the surface on the pipe side, the drill bit was replaced by a larger rotating reamer, which was sent back along the same path to widen the bored hole. As sections of drill rod were removed on the drill side as the reamer approached, they were added behind the reamer on the pipe side to protect the integrity of the hole.
Finally, the pre-fabricated pipes for the cable ducts which had been laid along the ground at Ramsholt were pulled back through the drilled hole.
Above: River Deben Drill, pipe side at Ramsholt, February 2018. The pre-fabricated pipes were pulled back through the holes drilled under the river.
Our cable installation contractor will shortly commence pulling the EA ONE power cables through the pre-installed cable ducts. The cables will be installed in sections and will be joined together every 2km at a Joint bay. Construction of the joint bays has commenced.
Delivery of the cables on large drums will involve the use of abnormal load vehicles. Once delivery is made to a Construction Compound, onward delivery to the construction area will be made along our temporary haul road within the construction corridor.
The pre-construction phase involved fencing off the construction corridor and building the haul road. Ongoing maintenance works related to this package will occasionally be required.
Once construction of the onshore substation and cable route are concluded and connected to the off-shore windfarm, testing and commissioning will take place. On completion, the stockpiles of earth can be returned, the haul road and other temporary measures will be removed and the land reinstated.
East Anglia ONE is expected to be fully operational in 2020.