Medway Cable Tunnel Project – National Grid/Balfour Beatty (Electricity Alliance East)

Scope: there are two tunnels which run parallel under the Medway River approximately 1.7km long and approximately 2.8m in diameter between Horseshoe Point (on the Isle of Grain) and Chetney Marshes in Kent. The aim of the project was to provide sufficient ventilation to cool the cable tunnel to maintain the oil filled cable within the operating temperatures with the cables being operated at high loads. The project included two very large acoustic enclosures, each more than 8m tall and housing two 8.5-tonne fans. Also included in our contract were the massive-section high-pressure ductwork systems and supporting steelwork, plus all the control and pressure relief dampers. The ductwork ranged in size from 5.8m by 3.2m to 4m by 1m rectangular and the material seleted was galvanised steel to  BS EN ISO 1461 with a 6mm thickness due to the high pressures involved and that the ductwork is located externally. At full duty, each system is capable of delivering 58m3/s of air at 7,500Pa on a duty/standby basis. Pressure transients were managed by the control of the system, for example all the dampers would have to be open prior to the fans starting, after the fans are called to stop the dampers would remain open for a set period of time, the ramp rates for the fans were set to ensure that the pressure didn't increase too quickly. If a damper failed and came off the open limit switch the fan would stop. 

Scheme Value: £5,000,000 - tunnel ventilation fans with associated attenuation systems and ductwork access doors, trough ventilation fans ductwork and attenuators, trough covers, tunnel and trough fan VSD's electrical distribution panels, 11kV transformers and switchgear, DTS system, control system and minor M&E works.

Design, Project Management, Site Supervision and Commissioning Value £600,000

Duration: Contract Start September 2009 - Finish March 2011

Medway Fan Enclosures and               Attenuation  

Medway Ductwork                          

Medway Fan Factory Acceptance Test                

Millennium Cable Tunnel Project – Clancy Docwra

Tunnel Ventilation Systems were contracted to design, supply and install the Millennium Cable Tunnel Ventilation System. The Millennium Cable Tunnel runs from West Ham to the O2 (Greenwich). The ventilation system included the electrical control panel and variable speed drives, instrumentation, fans, ductwork, attenuators and acoustic enclosure. The ductwork ranged in size from 2.5m by 1.5m rectangular to 800mm diameter, galvanised steel to BS EN ISO 1461 as the ductwork is located externally. The fans are capable of providing 15m3/s of air at 2865Pa. Pressure transients were managed by the control of the system, for example the ramp rates for the fans were set to ensure that the pressure didn't increase too quickly. The differential pressure across the fan is measured which will cause the fan to trip on excessively high or low pressures.

Value: £175,000

Duration: Contract Start November 2012 – Finish July 2013


Millenium tunnel acoustic enclosure / panels

Croydon Cable Tunnel Project – Morgan Sindall    

Scope: the Croydon Cable Tunnel is part of National Grid’s ongoing investment programme to upgrade the national electricity transmission network. A new 10km by 4.2m diameter tunnel was constructed to house 400KV cables connecting existing electricity substations at Beddington, near Croydon and Rowdown in the London Borough of Bromley. An ADIT ventilation system was provided. The ADIT is a spur tunnel which under the main project failed to be ventilated correctly, TVS were tasked with correctly balancing the airflows in the main tunnel and to ventilate the ADIT.  The ventilation system included the electrical control panel, fans, electrically actuated dampers, ductwork and attenuators. The ductwork ranged in size from 500mm diameter to 800mm by 200mm rectangular, galvanised steel ductwork to DW 144 was installed within the head house shaft and tunnel. The ventilation system is capable of delivering 1.5m3/s of air at 600Pa. Pressure transients did not need to be addressed at the low pressures that the system is capable of delivering.

Value: £90,000

Duration: Contract Start May 2012 – Finish September 2013

Croydon shaft - ductwork