Renewal of 25 kV overhead wires, coupled with the world's first autotransformer feeding of a four-track main line, will enable Virgin's Pendolino tilting trains to slash journey times and double frequency from May 2005. Richard Hope explains how it is being done mainly during overnight possessions

JUST A YEAR ago, on November 12, a contract with a potential value of £430m was awarded by Railtrack to an 'alliance' formed by Balfour Beatty Rail Projects Ltd, GT Railway Maintenance Ltd and WS Atkins Rail Ltd. Railtrack is itself a member of this OLE & Distribution Alliance.

Their contribution to the £5·8bn West Coast Route Modernisation project is to upgrade a total of 2 220 track-km of overhead line equipment (OLE) on Britain's most important trunk route, mainly to cope with higher speeds. They will also introduce new power feeding arrangements between London and Crewe, enabling Virgin to double the frequency of its inter-city trains.

Preparatory work started last April, and will be in full swing by the first quarter of 2001. The first objective, covered by the Phase 1 contract, is to increase the maximum speed from the present limit of 177 km/h on key segments of the WCML network to 200 km/h by May 2002, when 29 of the 53 Pendolino tilting trainsets ordered from Alstom by Virgin Trains should be in service.

In May 2005, the Pendolinos should be able to run at 225 km/h on the Fast pair of tracks for most of the 254 km between London Euston and Crewe. It is this section, together with the associated Slow tracks on this mainly four-track route, which is being changed over from booster transformers to autotransformer feeding at 25-0-25 kV so as to approximately double the power available.

Forty years old

British Railways decided to adopt 25 kV 50Hz in the mid-1950s as a result of successful trials in France. WCML electrification commenced in 1957, working south from Manchester and Liverpool. The first electric trains reached London Euston in November 1965, and the loop through Birmingham and the West Midlands was completed early in 1967. The compound catenary used was designated Mark I.

It had been the intention to continue electrification north from Weaver Junction to Glasgow, where suburban lines were also being electrified, but the economics were challenged. Only when costs were reduced through the development of much lighter Mark III catenary was the go-ahead given in 1970, with completion in 1974. The WCML link from Carstairs to Edinburgh followed in 1990.

Despite the fact that most Mark I OLE (and the power distribution system) is around 40 years old, Alliance Project Director John Dunwoodie describes its condition as 'surprisingly good'. In a lot of areas, wear of the contact wire is under half the permitted maximum of 25% of the cross-section, although there can be corrosion around the dropper clips. Wear of the catenary wire over supporting pulleys has generally been dealt with by splicing in new wire.

The galvanised OLE structures have been painted from time to time and have not deteriorated. However, some of them will have to be reinforced to withstand the higher wire tension required for 200 or 225 km/h running. For the same reason, all of the Mark I contact wire will be renewed wherever speeds are to be raised above 177 km/h. None of the Mark III wire is to be replaced, even on 200 km/h sections.

Where speeds remain at or below this speed, as on the Slow lines that extend for much of the way between London and Crewe including the Northampton loop, the OLE will remain basically unchanged. Also in this category is Wolverhampton - Stafford, which will be used by Virgin's diesel powered Voyagers at 200 km/h but is not a core route for Pendolinos. Dunwoodie explains that the policy is to carry out component replacement wherever the remaining life is deemed to be less than 10 years.

Speed upgrades

From May 2002, Pendolino operation at 185 to 200 km/h is required, except where signalling, alignment or pathing difficulties make this impractical. The principal exceptions are a ceiling of 193 km/h in Scotland and 185 km/h on the route through Stoke-on-Trent taken by Manchester trains, as well as on the branch to Liverpool. There are shorter sections, mainly on the approaches to major cities, where speeds remain at or below 177 km/h.

In addition, between Crewe and Willesden, 8 km from Euston, a further upgrade to 225 km/h is required three years later. It would obviously make no sense to upgrade Euston - Crewe twice, so most of the wire renewal for 225 km/h will have to be completed within the next 30 months. Provision will be made for increasing the wire tension during the following three years. While five additional switching stations are needed, the major power upgrade can come later because Virgin will not be introducing its final WCML service frequencies until 2005.

To achieve either of these higher speeds, the auxiliary wire will be removed from Mark I OLE at the same time as the contact wire and all the droppers are renewed. The catenary wire will not be replaced, even at 225 km/h, because there are no dynamic changes. This simplifies the upgrade, because unlike the contact and auxiliary wires, the catenary wire passes over rather than under the portal structures typically used on four-track sections.

The cross-section of the hard-drawn copper-silver contact wire will be increased from 105 to 120mm2 in order to accommodate the rise in tension from 10 to 14 kN. This will also offset the loss of conductivity in the former auxiliary wire.

Another important modification that applies to Mark III as well as Mark I OLE is replacement of the cantilevered registration arms - this is already in progress north of Weaver Junction. The new, lighter assembly using aluminium tube and polymeric insulators has a haunched profile, which allows the pantograph greater uplift. The contact wire stagger will be reduced to minimise the risk of dewiring.

At the same time as the contact wire is renewed, its gradient will be reprofiled on the approaches to bridges and tunnels to improve current collection and eliminate hard spots. Fortunately, electrical clearances specified in the early days of 25 kV were more generous than is considered necessary today, so the uplift permitted beneath structures can be increased. A new design of support inside tunnels has been produced and 415 of these will be installed. The planned reduction in level crossings on core routes will also help to maintain a level contact wire.

A total of 1128 new or replacement structures are required for the upgrade. This does not include the near-total OLE renewal recently completed on the approaches to Euston, where the track layout was remodelled last summer.

One major requirement for additional structures arises from the need for longer overlaps where 225 km/h operation is planned. This is where the pantograph switches from one tension length to the next. This will normally require the insertion of two additional portal structures, together with tie anchors, pulleys and balance weights, for each tension length; that is, at intervals of 1200 to 1600m.

Neutral sections, where a change of phase occurs, also have to be replaced to cope with 225 km/h. A new design is being supplied by Jacques Galland, based on those used by SNCF for high-speed lines.

Design and installation

Survey and detailed design of the work required at thousands of locations is a major task in its own right, which has taxed the resources of Alliance members. In addition to three design offices in the UK, it proved necessary to farm out some OLE structure design to WS Atkins' established facility at Sharjah in the United Arab Emirates, using 64 personnel employed by Rites of India.

Wherever soil conditions permit, foundations consist of tubular piles 610mm in diameter and about 4m long, with a flexible cap on which the mast can be aligned and bolted. Otherwise, foundations must be excavated and concreted in the conventional way.

Windhoff is supplying the Alliance from Germany with three trains based on the CargoSprinter, with cabs at each end and modular wagons in between. One will undertake piling and mast erection; the other two will replace the contact wire and retrieve the auxiliary wire over a complete tension length during a single possession of 5 h. In addition, a concrete mixing train has been made up using existing road/rail vehicles.

Each new wiring train costs £3·3m and consists of four powered cars, three hydraulic elevating platforms, and equipment for installing or recovering wire. The 200m long train travels to site at 100 km/h, where it splits into five sections (Table I).

As with other aspects of West Coast Route Modernisation, intensive use is being made of road/rail vehicles for replacing registration arm assemblies, and extending overlaps after the additional portal structures have been erected - both of which require high level platforms. Up to 140 temporary access points are being created, where 25m long 'level crossings' made from Holdfast rubber panels allow the vehicle to be driven on to the line as soon as a possession is confirmed, but while the OLE is still energised, and moved quickly to the work site. Alliance members have already ordered 41 of these vehicles costing £6·9m: 33 from SRS in Sweden, and eight from Harsco Track Technologies (formerly Permaquip) in Britain. The working platforms are 1·6m wide and 2·5m long, extendable to 4·5m. The maximum lateral outreach from the centreline of the track on which the vehicle is standing, without outriggers, is 5·2m. All motions of the platform, and of the vehicle along the track, can be controlled from the platform.

Both the Windhoff wiring trains and the road/rail vehicles are fitted with earthing pantographs. These allow manual earthing arrangements at 400m intervals to be dispensed with, thus saving time during an isolation.

Power upgrade

Although the power feeding arrangements installed 40 years ago were not expected to cope with the demand experienced on the WCML today, for the most part the equipment is coping well. Russell Adams, Railtrack's Head of Electrification Delivery for the WCRM project, says that some booster transformers are operating close to their rated power, and are at the limit when emergency feeding arrangements become necessary because a feeder station has been lost, for example.

The 225 km/h timetable being introduced in 2005 would take the normal load over the booster transformer limits between Euston and Rugby, and for this reason the decision was taken to convert the Euston - Crewe line (including the Northampton loop) to autotransformer feeding. This will almost double the power available for traction, leaving a substantial margin for future growth.

Work has already started on the installation of pairs of grid transformers with 25-0-25 kV output, mostly alongside existing feeder stations, at five locations approximately 50 km apart. The associated switchgear will be capable of connecting the output either to the existing catenary with its booster transformers at 25 kV, or to newly installed 25 kV feeders in antiphase with the catenary at 50 kV.

For 200 km/h operation of an enhanced service in 2002, the existing booster transformer system will be strengthened by creating five extra switching stations. Over the following three years, autotransformers will be installed at 23 sites together with switchgear and the anti-phase feeders. Each site will have two ATs.

Then, under possession, the booster transformers and return conductors between a 50 kV feeder station and the mid-point switching point (about 30 km) will be disconnected and recovered, and AT feeding will be brought into use.

Up to now, AT feeding has been applied largely to new high speed lines with double track. WCML is the first multi-track route with mixed traffic to be supplied in this way.

Elsewhere on the WCML network, Adams sees the power supply 'not undergoing a major upgrade', although there will be some replacement of booster transformers. 'The capacity that already exists is sufficient, but where reinforcement is necessary, the new "platform" will be designed to accommodate both BT and AT feeding.'

Table I. The Windhoff wiring trains split into five sections to perform these tasks

Stage Equipment Operation Comments

1 MPV unit and flatbed- Releases old droppers and Existing catenary wire is mounted recovery equipment recovers existing auxiliary and not renewed by this train. contact wires onto cable drums under nominal tension

2 Two long hydraulic platforms Removes old droppers from the A low-silhouette vehicle mounted on flatbeds existing catenary and installs new capable of hauling rolling droppers ready to support the stock up to 120 tonnes pulls new contact wire these units along the track

3 MPV unit and flatbed-mounted New contact wire is installed tensioning unit complete with under full tension and clipped new contact wire drums into the new support and registration equipment

4 MPV unit and long flatbed- Installation of new droppers and mounted platform any midspan equipment

5 MPV unit with hydraulic platform Measure and record at varying Independent of the plus a Windhoff-manufactured speeds the height and stagger of preceding stages HZ80 overhead catenary the new wire along with the measurement system track cant

  • CAPTION: Above: Re-wiring work in full swing during the 19-day Proof House Junction blockade on the approaches to Birmingham in August
  • CAPTION: Scissors-lift platforms are used to install OLE on the realigned fast tracks at Proof House Junction
  • CAPTION: The rewiring trains supplied by Windhoff are based on the German CargoSprinter, with a cab at each end (below). Modular intermediate wagons include a scissors-lift platform for Stage 2 works (centre) and a cable drum wagon with contact wire tensioner for Stage 3 (below left)
  • CAPTION: The Harsco and SRS/Volvo road-rail vehicles are all equipped with earthing pantographs to simplify the procedure for electrical isolation

Catenary upgrade will introduce 225 km/h on UK tracks

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Ya han comenzado las obras de un proyecto de cinco años con un presupuesto de 430 millones de libras cuyo propósito es sustituir o reacondicionar la catenaria sobre una longitud de vías de 2220 km y la puesta en servicio del primer autotransformador del mundo de 25-0-25 kV alimentando a una línea principal de cuatro vías. Esto permitir a los trenes basculantes Pendolino de Virgin reducir dr sticamente los tiempos de viaje y doblar su frecuencia desde mayo de 2005 en la línea principal de la Costa Oeste de Railtrack que une London con Birmingham, Manchester, Liverpool, Glasgow y Edinburgh. Richard Hope explica cómo se est efectuando esta mejora principalmente con vehículos biviales durante breves ocupaciones de vía