In issue 140 (June 2016) of Rail Engineer, Colin Carr wrote about the work being undertaken on the Great Western route in the Severn Tunnel to allow for electrification. Mention was made in that article of the preparation for conductor beam installation in the tunnel by Furrer+Frey, working alongside the Alstom, Babcock and Costain joint venture ABC Electrification.
Conductor beams have been used in tunnels in the UK before but, to find out more about this latest system, Rail Engineer visited the London office of Furrer+Frey to meet Ankur Saxena, project engineering manager for the company.
Although the London office has been open since 2013, Furrer+Frey is still a Swiss company so the discussion used pan-European terminology rather than British.
This included the phrase ‘Overhead Contact System’ (OCS) and, as a part of that system, what has traditionally been known as the catenary wire is now the ‘Messenger Wire’.
Nevertheless, the company has also ensured it has familiarity with UK standards and practices where these are part of National Technical Rules. Experience with the recent Great Eastern electrification upgrade, where the catenary (sorry – OCS) is being upgraded to Great Eastern Furrer+Frey (GEFF), reinforced this.
Furrer+Frey has been creating overhead line solutions for decades. Formed in 1923 by two friends, Emil Furrer and Arnold Frey, the company has always been conscious that there is more to customer service than just technical expertise – successful design also involves listening to those customers and working closely with them.
This philosophy drove the company, at the beginning of the 1980s, to develop an alternative to the conventional overhead contact line.
Design investigation was underway for the electrification of some very restricted gauge Swiss rail tunnels and a new approach was needed. The outcome was the Furrer+Frey Rigid Overhead Conductor-rail System (ROCS). The first prototype installation was in Munich in 1984 and, following this early experience, the system became more-or-less standard for existing tunnels in mainland Europe.
Since then, more recent installations have included sites in markets as far away as China.
Compared with other, more traditional, contact systems, the philosophy is reasonably new, but an analysis of the advantages put forward make interesting reading. Ankur offered a list of plus points for the system such as:
Allowing smaller tunnel cross- sections for new construction;
» Allowing electrification of tunnels and terminals originally built for steam or diesel traction;
» Significantly larger conductor cross section; allowing additional feeders to be avoided;
» Greater fire resistance than a traditional wired Overhead Contact System;
» High operational reliability requiring little maintenance regardless of the operating voltage;
» Faster installation.
History tends to suggest that these types of conductor might not be suitable for high-speed railways, but operational experience has proved that the system performs reliably at up to 250 km/h, at which speed it is also TSI compliant.
In the UK
The Severn tunnel will be subject to 160km/h train speeds, as will Patchway, while Box Tunnel will be set at 225km/h design speeds.
As higher linespeed installations multiply in the United Kingdom, F+F is assisting Network Rail in developing standards for the conductor rail on
its own infrastructure. Although maintenance should avoid dewirements, there is no doubt that, if problems occur, it is the pantograph on the train that will be dislodged, not the ROCS.
Higher wear tolerances may also be accepted as the contact wire is not in tension. In addition, Ankur pointed out that the ‘Overhead Drop Zone’ could be regarded as much more restricted as the risk of conductors dropping across the route is almost nil, and very restricted laterally.
Reviewing the rigid conductor system in the United Kingdom, one is reminded that it has been around for quite a long time but in relatively low-key, low-speed installations. The system has proved ideal for lifting, swinging and other moving bridges and was, in fact, installed in the very early 1980s as a solution to providing an overhead conductor across Trowse swing bridge in Norwich, East Anglia. Rigid conductors have also found favour for moving bridges in the USA and Canada.
A development of the rigid contact system is the retractable conductor rail used in depots where safe roof access to rolling stock is needed – a UK installation of some significance was the Temple Mills Eurostar depot.
As the system has become more familiar and experience has been gained, the design of the conductor- rail profile has developed. Special design characteristics have been incorporated and contact wire of between 100 and 161mm2 may be accommodated.
Finally, a range of assembly aids has been developed including drilling and lifting equipment and devices for inserting contact wire. There are section insulators and neutral sections, and a bespoke transition arrangement allows for a robust interface with conventional wired OCS.
The system is also flexible in application for different voltages, rated at up to 50kV AC and performing admirably up to 3kV DC. 120mm2 copper/silver contact wire has been chosen for Great Western.
Testing in Leicestershire
That last fact brought the discussion around to Great Western electrification, within which the system is receiving its main exposure to UK main line high-speed use, although it has also been used in the Mound and Haymarket tunnels at Edinburgh.
For the Great Western project, significant research and testing was required and advantage was taken of the railway test site at Old Dalby, near Melton Mowbray in Leicestershire.
Much of the original Advanced Passenger Train high-speed feasibility research, with its associated electrification equipment, took place there and the site has the advantage of being insulated from the operating railway. So the Old Dalby site has a long history of involvement in system testing and includes the 1.2km Stanton tunnel, just the place to allow designers to judge the suitability of the system for the Great Western tunnels, particularly Severn, Box and Patchway.
What emerged was the UK’s first high speed Rigid Overhead Conductor Rail System, designed and supplied by Furrer+Frey for line speeds up to 225km/h and which will be used, at Old Dalby, for testing the IEP trains for Great Western and East Coast main lines.
Particular features of the ROCS, as fitted to Stanton tunnel, include:
» Drilling using the F+F drilling rig to the precise measurements important for high speed systems; » F+F generation-4 conductor rail;
» Transition bar for smooth interface between conventional OCS and ROCS;
» State of the art expansion joints to accommodate movements due to temperature variations;
» Stainless steel components for good performance in corrosive environments;
» Special protection cover for areas with water ingress.
The installation is now providing valuable lessons for design in the active railway environment as well as effective feedback on the rolling stock/infrastructure interface during vehicle testing. Of particular note is that most previous high-speed installations have been on slab track whereas, for Great Western, the novelty lies in the application to ballasted track.
So far, the indications are that the application is successful and effective. The installation has enabled the modelling of the interaction between train and conductor that facilitates design in a production situation. That modelling is being supported by infrastructure data from Network Rail and train data from Hitachi. Based on that, modelling the requirement for track to match conductor geometry still remains a maintenance need but, by the nature of the system, much less access is required – a tremendous advantage on today’s busy railway with restricted access such as in tunnels.
The system has been rewarded with the presentation of a certificate from the Institution of Engineering and Technology for their innovation award; Ankur himself receiving an award from the Network Certification Body as project manager of the year. Rail Media was also pleased to make an award to him – project manager of the year at last year’s RailStaff Awards.
Moving on to the GW
Following the experience at Old Dalby, F+F now finds itself working in full production with ABC on Great Western electrification, with particular responsibility for the conductor in the tunnels on the route.
Compared with Stanton tunnel, the Great Western route presents even greater challenges, and not just because the tunnels are longer.
The Severn tunnel bore is actually smaller than the Stanton test site tunnel while Patchway and Box tunnels are even tighter. The Severn tunnel is also exceedingly wet and the conductor bar design has been modified with drainage arrangements to allow for that wetness and the avoidance of bimetallic electrolytic action between the support bar and the copper contact wire. A form of plastic screening has also been developed to protect the insulator while, as previously mentioned, the stainless steel construction resists the corrosive effects of the site.
Further applications of the ROCS system have been made. On other railways, it is quite common for the rigid conductor to be used under bridges, although this has not been the case in the United Kingdom so far.
At Patchway, however, there are two tunnels with a short length of open track between them and, to avoid transition from ROCS to wire to ROCS in a very short distance, a length of F+F conductor will be installed on relatively conventional outdoor OCS structures.
The rigid system still gives performance similar to a traditional one and thus stagger is introduced. However, rather than the straight sections between supports seen in wired OCS, the stagger may be in the form of a gentle sinusoidal wave. Similarly, the system may be effectively set up for compliant vertical curves with fine adjustment in the style of conductor support. Ankur summed up the system as very flexible horizontally, very rigid vertically!
Overall it seems that the ROCS system will become more familiar in the UK, with installations already being designed and considered for further works in Scotland such as the Queen Street tunnels in Glasgow and sites at Falkirk High and Winchburgh. As further electrification takes place, in tunnels and under bridges with limited clearance, rigid overhead systems will become even more commonplace.