Talk – Tuesday 20th September 2016 ‘Modern UK Tramways’
Ian Wetherall RCEA
In principle the description is intended to cover those tramways constructed post 1960 and will therefore exclude pre-war municipal tramways operating up to their closure in the late 1950’s .
In the UK, a RAILWAY usually operates on a fenced right of way (with no street running).
LIGHT RAILWAYS are built to operate at lower speeds with lower crashworthiness, for example, Tyne and Wear Metro and Docklands Light Railway. In neither case is there any street running.
The Tyne and Wear Metro (shown opposite) shares track with Network Rail lines to Sunderland. Because the Metro trains were built to light rail standards, the results from an accidental collision with a Network Rail train on the shared tracks in and near Sunderland would be catastrophic.
As well as the Metro cars being equipped with an automatic warning system (AWS), the shared tracks are operated on a double block system. This means that both Network Rail and Metro trains are separated by an unoccupied section and are thus protected by two red (stop) signals.
1500V dc was chosen because there was no street running. The higher voltage allows the system to require fewer substations and the train currents are approximately 50% of that needed to supply trams on a 750V system.
Docklands Light Railway (shown opposite) operates at 750V dc on third rail conductor rail system utilising a shrouded bottom contact system which minimises the risk of accidental contact with the “live rail”.
A TRAIN-TRAM is basically a train adapted to be compatible with and run on a tramway for part of its route. There are no Train-Trams operating or proposed in the UK.
A TRAM-TRAIN is basically a tram adapted to be compatible with and run on a conventional railway for part of its route. Currently there is only one Tram-Train project under way in the UK.
New Tram-Trains are being built to operate over Network Rail tracks from Meadowhall (part of the Sheffield Supertram system) to Rotherham. The section of Network Rail over which dual running will operate will be electrified as a 750V DC OHL system.
The modern tramways in the UK all incorporate some street running and are driven on “Line of Sight” principles.
At major intersections with roads or at tramway junctions simplified signalling is in use.
At road intersections, the trams are usually given priority over road traffic. The tram priority is initiated either by the tram driver or more usually by the tramway control system detecting the approaching tram.
On the street sections additional signals are provided which apply to the trams only. Although ordinary road signals are provided at junctions these do not apply to the trams.
Line of Sight running has no fixed signals. Tram speed is regulated by fixed speed markers which limit tram speed to that at which the tram can stop short of any visible obstruction. Maximum speed is usually 80kph (50mph) although the proposed tram-train will probably operate at higher speeds on NR tracks. When running on public roads the tram speeds are limited to that of normal road traffic.
Blackpool opened in 1885. The only pre-war system still in operation, now fully modernised with a fleet of new trams operating between Starr Gate and Fleetwood. In the summer peak season the modern fleet is supplemented by vintage trams to give a higher frequency service.
Proposals for extending the tramway to Blackpool North Station are under consideration.
Operates on 600V dc OHL system, normal service trams utilise pantograph current collection as this allows one man operation. Many vintage trams still use trolley pole collection. Blackpool is the only UK modern tramway to operate double deck trams.
Manchester was the first UK modern tramway to be commissioned in 1992, running over ex BR routes to Bury and Altringham with street running in central Manchester. Unique in the UK in adopting high platforms at the stations. The first trams were built by Ansoldo-Breda in Italy. After 22 years in service, the last Ansoldo T68 tram was withdrawn in February 2014.
A new fleet of 120 Bombardier M5000 trams entered service from 2008 to 2014. Now operates 7 routes over 57miles of track. Unlike the other new UK tramways, the Metrolink trams can operate as multiple units in a 2 x 2 formation.
Birmingham Metro opened in 1999. It had only one route, from Wolverhampton to Birmingham Snow Hill. This has recently been extended to Birmingham New Street and in Wolverhampton the tramway will be extended to a new bus/train/tram interchange in the town centre. Plans exist to extend the system across Birmingham City Centre to Moor Street and Curzon Street and to the Airport via Digbeth. Parts of this extension may be operated under battery power to avoid installation of wires in the City Centre .
Nottingham Express Transit (NET) opened in 2004 operating a single route from Nottingham to Hucknall. Since 2014 NET has operated 2 routes, both passing through the City centre, Clifton to Phoenix Park and Chilwell to Hucknall. NET has two tram fleets, delivered to match the expansion of the network. The first 15 trams were Incentro AT6/5s built by Bombardier. By 2014 a further batch of 20 Alstom Citadis 302 trams were delivered to match the expanding network.
Sheffield Supertram opened in stages in 1994/5. Three major routes radiate from the city centre to Meadowhall, Middlewood and Halfway opened in 2004, minor branches also operate to Malin Bridge and Herdings Park.
Work is currently under way to extend the tramway from Meadowhall to Rotherham over Network Rail tracks. Sheffield Supertram is operated by a fleet of 24 Siemens- Duewag trams.
A further 7 Vossloh Citylink Class 399 tram-trains, are being delivered to operate the extension to Rotherham. Only these 7 Class 399 tram-trains will be allowed to operate on the Network Rail route to Rotherham from Meadowhall.
Initially these 7 trams will operate on the existing Supertram routes until the extension to Rotheram has been commissioned. The Class 399 trains will be equipped with AWS and will be more robustly built than the existing trams. The NR route to Rotherham will be electrified on the overhead system at 750V dc.
After a disastrous overrun on both costs and construction time, the Edinburgh tram system, from the Airport to York Place near Waverley station, finally opened in 2014 having taken 6 years to build. Original plans would have extended the tramway to Leith via two routes, possibly in a complete loop. As a result of disorganised project management, Edinburgh finds itself the owner of 27 new trams to operate a service which only requires 17 trams. There were hopes that Croydon Tramlink would be able to purchase them at a bargain price, but the trams were significantly different and Croydon looked elsewhere.
CroydonTramlinkopenedin2000,withroutesfromCentralCroydontoWimbledon,NewBeckenham, ElmersEnd and New Addington. Now generally referred to as Tramlink the original consortia was bought out for £98m in 2008 and is now part of TfL.
Tramlink is one of the busiest of the modern street running tramways, carrying over 27m passengers / annum, a figure only exceeded by the two light rail systems, Tyne and Wear Metro and the DLR, and Manchester Metrolink, with much larger systems.
No extensions to the start-up system have been constructed but an additional platform has been provided at Wimbledon and stretches of single line have been doubled on the Wimbledon route. These works have enabled Tramlink to increase thetramfrequencyandcapacitytodealwiththeeverrisingdemand. TheadditionalplatformatWimbledonhasbeen constructed in the same manner as the Overground platforms at Clapham Junction, that is with one platform set back to allow a second tram to pass the first and gain access to the additional platform.
The original fleet on start-up comprised 24 Bombardier CR4000 trams of which 22 were required for service.
To match rising demand and overcrowding a further 10 Variobahn trams (shown opposite) have been purchased from Stadler.
All the modern tramways are electrified on the overhead line system at 750V dc.
The trams use inverters to change to a variable frequency 3 phase supply which is connected to squirrel cage motors. This arrangement allows the motors to be used for both driving and braking as well as regenerating power back into the overhead line.
There are 13 substations on the Tramlink system which are remotely controlled from the depot at Therapia Lane.
The substations are typically supplied at 6.6kV or 11kV from local electricity company systems. None of the modern tramways generate their own power. The substations first transform the incoming high voltage supply to approximately 800V before rectifying this to 750V dc.
Current Collection – Most pre-war tramways used a trolley pole to collect the power from the overhead line. Today, almost without exception, modern tramways use a pantograph to collect the power. Blackpool still uses trolley pole collection on some of its vintage trams.
Where it is considered desirable to avoid overhead equipment in environmentally sensitive areas, various solutions have been used to eliminate the “unsightly” overhead equipment.
A number of tramways adopted the conduit system either for their whole network or just for inner city areas. In the conduit system, a conductor bar was located in a covered trench situated between the running rails. The tram was equipped with a vertical “plough” which ran through a slot in the roadway. In London the conduit system was used extensively in the centre and in the outer suburbs the tram changed over to trolley collection.
In Bordeaux, the French have installed a version of the conduit system, using a multi-section switched conductor rail which is only energised when covered completely by the trams.
This system costs about 4 times that of the equivalent conventional overhead line.
Earthing & Bonding Because DC currents are particularly corrosive, every effort is made to avoid deliberate or inadvertent connections between traction negative and earth. The running rails, which form the return current path between the trams and the substations, are not connected to earth. The system is earthy, because of the large number of high resistance leakage paths between the running rails, sleepers and ballast etc.
Outside the street running sections, no special precautions are taken. On the street running sections there is a “current collection mat” located between the rails and the reinforcing bars of the slab track. This mat is connected back to the substation, and supposedly collects any stray currents leaving the running rails.
The return currents in the running rails create a resistance voltage drop between the trams and the supplying substations. Close to the tram, the rails are at a higher potential than earth and near the substation the rail voltages will be lower than earth. Under normal conditions these rail – earth voltages are quite low, typically between +/-5V.
Legally the rail to earth voltage should not exceed about +/-45V under normal conditions, rising to +/-50V under fault conditions.
The Depot at Therapia Lane contains equipment which has to be connected to earth, such as the wheel lathe and other power tools. A separate rectifier is provided which gives the overhead line within the depot an earthed 750V DC supply.
Insulated joints are provided in the OHL and running rails to separate the earthed and un-earthed systems. The depot contains a 2 track workshop with a wheel lathe, bogie drop, high level access walkway and lifting jacks as well as a tram washer and berthing roads for the 30 tram fleet.
The Wheel Lathe is designed to re-profile the tram wheel tyres without removing the bogies from the tram.
The lifting jacks simultaneously lift all the cars of a tram together which avoids the problems associated with un-doing and re-connecting the couplings between the individual cars.
Ian Wetherell.
