While third rail and other low-level current collection systems add a lot of equipment to the surface rail, the general approach to electrification around the world involves the adoption of overhead traction systems. In the UK, early designs tended to be relatively low-voltage installations, and decoupling from surrounding structures was not a major challenge.
However, technical advances resulting from the need for higher speeds and higher loads have pushed the industry towards overhead high-voltage (OLE) equipment, which required much larger clearances. The initial higher-voltage installations now accepted quite conservative active equipment permits, and thus the early stages of electrification of the main line on the west coast required significant reconstruction of the bridges. The media brought to life images of exploding bridges and clever solutions to new prefabricated arches were presented.
British Railways – as it was then – realized that the emerging costs of further electrification were at stake and undertook a very significant development effort. This resulted in the design protocols being modified to extend the early work to complete the Euston–Birmingham route.
lower voltage
The first clearances were announced at a conference organized in 1960 by the Department of Mechanical Engineers and the consent of the Director of the Railway Inspection was obtained to conduct experiments to determine the minimum dimensions of safety clearances. As presented at the subsequent electrification conference in 1966, revised electrical permits were approved by the Minister for Transport in August 1962. This enabled the electrification of the Midland region of London to be completed at 25 kV and gained the advantage of adopting the new dimensions. for all national programmes.
At the dawn of modern times, probing questions began to be asked about the cost of electrification, and in addition to the costs of installation and equipment, the need for free space was carefully studied. One solution was to use a lower voltage and instead of the nominal 25 kV standard, devices were installed to provide traction power at 6.25 kV, an approach used on the Great Eastern Lines and in Scotland for projects in the suburbs of Glasgow.
The London, Tilbury and Southend lines were also equipped in this way; the 6.25 kV section ran from Fenchurch Street to beyond Barking, with changes to the Upminster and Tilbury lines, along with the section between Chalkwell and Shoeburyness. The remainder was 25 kV and the 6.25 kV sections were converted to 25 kV in the early 1980s.
However, this seemingly attractive design introduced unintended complications, most notably the use of dual-voltage capability in rolling stock and requirements for switching devices.
Therefore, the search for the possibility of installing aviation devices with smaller distances from stationary infrastructure was continued. Electrification of the East Coast Main Line was done at a cost acceptable to the government, and electrification progressed for a while; however, it has slowed down significantly in the era of privatization and the division of British Rail into infrastructure and other parts.
Finally, prompted by the need to take the environment more fully into account, electrification has resumed, albeit under tight cost controls. As the challenges of electrification costs and green light increased for the Great Western and Midland main line proposals, as well as projects such as the 'power tower', more attention was paid to finding solutions to reduce electricity costs. free space. vigor. As described elsewhere, electrification costs have come under even greater scrutiny, and the situation has been exacerbated by the cancellation of much of the proposed work.
filling the gap
However, the industry was determined to show that costs could be controlled, and the opportunity arose to show how they were made under the Greater Western Electrification Program (GWEP). Recent projects have shown that construction work (particularly bridge reconstructions) can account for about a third of the cost.
An example is the Cardiff Junction Bridge, the main diagonal junction between the Cardiff and Merthyr lines and the South Wales Main Line. Initial plans to rebuild the bridge were estimated at around £40 million. Alternative proposals included lowering the track, rebuilding the culvert and pumping water out of the canal around Cardiff city centre, which was estimated at around £20 million. Both solutions would be very burdensome for passengers and the costs would jeopardize the feasibility of continuing electrification west to Cardiff Central Station, just 400 meters away.
The challenge was taken up by a group consisting of Andromeda Engineering of Speke (Liverpool), GLS Coatings, Great Western Railway, Network Rail (infrastructure projects, engineering and safety engineering (STE) and Wales & Western Route), Pace Networks, Siemens Mobility and the High Voltage Laboratory at the University of Southampton (UoS).
Andromeda Engineering, the designers of GWEP OLE for Cardiff and Network Rail (Wales and West), contacted Network Rail (STE) to propose an alternative design, initially in the form of a proof of concept to avoid further program review. A steering group was created to bring together all decision makers and focus on achieving the developed solution.
The STE project identified state-of-the-art equipment from Europe that could help meet this challenge. This includes:
Bonomi insulated bridge arms, supplied by Pace Networks,
Siemens 25 kV surge arresters complete with arrester status monitor (ACM) by Siemens
electrically insulating coating from GLS Coatings (GLS 100R), which was previously used by Network Rail for signaling power.
Making sure
The solution identified the benefits of using the latest insulating coating technology to provide the bridge's electrical insulation layer to support the limited electrical space. It was the first such proposal for a new electrification. Surge arresters were included in the design to safely control potential transient overvoltages on the bridge without the need for additional clearance.
The suppliers have agreed to submit their equipment to high-voltage electrical tests designed by Network Rail (STE) and the University of Southampton.
The surge suppressor from Siemens is the latest development. Mounted on bridges or tunnels, they significantly reduce the effects of overvoltages caused, for example, by a lightning strike. They were recently installed on Danish railways to reduce static electrical distances from 270 mm to 150 mm.
Tests in the UoS High Voltage Laboratory included combinations of components from different suppliers to determine the optimal layout. Each has been tested in dry and wet conditions, with a mix of contaminants added to contaminate all insulating surfaces to make testing as realistic as possible.
They achieved much better results than expected. When all the equipment was used together as a system, a minimum gap of just 20mm proved to be sufficient to prevent electric shock in wet and contaminated environments. However, even that wasn't enough to power OLE under the bridge. It has been proposed to install the contact wire at a reduced height.
Standard deviation
In its proof-of-concept project, Andromeda confirmed that in the event of a deviation from the minimum OLE cable height requirements of the RSSB standard, a design can be developed that connects to the railway line near the bridge. Network Rail (STE), UoS and GWR have developed additional high voltage tests covering the minimum required electrical gap between the OLE and the roof of trains of various widths. These tests confirmed that a surge suppressor attached to the OLE provides additional benefits and only 70 mm is needed to prevent flashover between the OLE and the top of the rail vehicles.
To gain confidence in the design, Network Rail (Scotland) agreed to conduct a field trial which involved gradually lowering a steel plate covered with GLS100R closer to the OLE. In this way, a metal bridge was simulated and the concept was demonstrated on a working railway. This gave Network Rail (Wales and West) confidence that they could proceed with and accept the replacement of the bridge lining. GWR provided further assistance by working with its suppliers to confirm that the pantographs could be satisfactorily operated below the downstream and supported Network Rail by providing the necessary rerouting to the RSSB.
work together
Adopting a collaborative approach to innovation exploitation, risk management and decision-making was key to ensuring broad stakeholder support for an unconventional proposal. Along with the acceptance of the solution, the key to the success of the project was Andromeda Engineering's commitment to positive stakeholder management, so that everyone was satisfied at every stage of the work.
The meeting of the Strategy Steering Group and the Implementation Working Group ensured a top-down approach to facilitate cooperation. The groups met regularly to discuss key areas, making sure there were clear and concise deliverables for implementation. This approach has also achieved considerable efficiencies and has demonstrated what can be achieved when industry partners come together for a common purpose.
Estimates suggest that this approach has generated significant cost savings as well as avoiding significant rail disruption and reducing program risk. The total development and installation cost was less than £1 million, representing a return of 95%. In December 2019, OLE power was turned on under the bridge. There have been no skips so far and the build has been working perfectly. Despite the low cable height, the route remains free for all track widths typical of rail vehicles.
The importance of the project was recognized by Andromeda Engineering, which in 2018 became the winner of the Rail Industry Innovation Award and a finalist in the "Driving Efficiency" category at the Rail Partnership Awards in the same year.
The voltage controlled clearance (VCC) concept has been adopted in future electrification projects including TransPennine and Scotland. In total, it is estimated that VCC could save over £100 million. It will therefore play a key role in making electrification more efficient and helping to decarbonise railways.
