Third rail
We have the largest third rail network in the world, powering electric trains, and it’s mostly found on tracks in the South East of England.
When we talk about the third rail, we mean the live rail which provides electric power to a train through a conductor placed alongside the rails.
This network carries over one third of all national passenger weekday trains. It’s capable of supporting very frequent services of up to 12 carriages, running at up to 100mph. An impressive 84% of all lines in Network Rail’s Southern Region are already electrified. As a result the Southern Region has the lowest percentage of diesel passenger services running in the UK.
The history of third rail
The third rail system was first used on underground and metro systems from around 1900, with the main line electrification of what became Southern Region commencing in 1915. Between 1915 and today, the strategic decision to invest in electrification resulted the network we have today. Each extension brings significant passenger benefits, reduction in journey time and economic benefits. As a result this significantly grows the number of passengers using the trains and the number of trains running on the network.
To begin with, steam services were replaced with electric services. But since the replacement of steam in the mid 1960’s, electrification extensions or infill projects have replaced diesel services with electric services.
How third rail works
The trains pick up electrical energy using metal blocks (“shoegear”) which make contact with and slide along the top of the conductor rail. The conductor rail is made of a special conductive steel.
The conductor rail is located adjacent to the running rails of the track. It’s raised slightly on insulators to support it and make sure it stays in the right place. Conductor rail ramps are used at the start and finish of each length of conductor rail to raise and lower the shoegear of the train. This enables smooth transition of the shoegear with the conductor rail. Gaps in the conductor rail may exist between adjacent lengths of conductor rail, or where conductor rail cannot be installed. For example, at level crossings.
The conductor rail is supplied with direct current (DC) electricity from lineside substations located between 1 and 6 miles apart. This depends on the intensity of the train service. The substations are supplied from our own high voltage alternating current (AC) supply system (normally 33kV) which distributes the power from National Grid or electricity company supply points to our substations.
We manage this system to provide a resilient supply and can normally switch to resupply substations in the event of a fault or loss of a supply point. Each substation then converts the supply from high voltage AC to 750V DC.
The conductor rail is divided into a number of electrical sections with circuit breakers at each end. This is so we can remotely operate and switch off or switch on each electrical section as required. Electrical section is supplied with power at both ends of the section. This improves the efficiency and reliability of the supply to the trains. The distance between substations can be increased by installing a Track Paralleling Hut (TP Hut) between substations. TP huts do not provide an input of power to the conductor rail, they’re used to improve the efficiency of the supply. They also have remotely operated circuit breakers for switching the conductor rail on and off.
Modern trains on the third rail network can generate power back into the conductor rail when they brake. This converts movement energy back into electrical energy, provided another train is taking load in a reasonable distance from the braking train (most likely nearer to London). This increases the efficiency of the system.
You vs. Train campaign
The You vs. Train campaign, run by Network Rail and the British Transport Police, is targeting teenagers to hammer home the dangers present on the railway. Whether obvious like a train, or hidden like the electric current in the third rail or trackside facilities.
The only way to avoid these dangers is to never step foot on the railway in the first place.
Research shows that in particular a large proportion of young people remain unaware of its potentially fatal dangers. The third rail is probably one of the most difficult dangers to see. It looks just like an ordinary rail, but it carries 750 volts – easily enough to kill you.
The system is designed to deliver an electrical supply to move trains. But if you touch or fall on the conductor rail your body will conduct the electricity to a level which is sufficient to give an electric shock that can kill you or give you severe burns. You may not be able to move away from the incident further injuring you.
Keeping the workforce safe
Network Rail has a clear safety vision: Everyone home safe every day. Conductor rail safety is designed around our staff, who are trained to work on track. The conductor rail is assumed to be always live unless safety documents have been issued stating where it is safe to work.
Safety of the workforce has been transformed with the Safer Smarter Isolation programme. Remotely operated switches are being installed to switch off part of an electrical section to replace devices fitted to the conductor rail.
Additionally, to protect people further, rather than having to fit portable devices (short circuit straps) on the track, people can now operate fixed equipment (negative short circuit devices) located off the track in a position of safety. This significantly reduces safety risk from trains and electricity to the staff.
Staff can also use approved shields designed to cover all sides of the conductor rail. This protects from a live conductor rail under certain circumstances
Third rail system into the future
The conductor rail system is a very simple but capable system supporting the requirements of the train service. A high percentage of the Southern network is already electrified. So it can be more cost efficient to extend this system, rather than install other electrification systems. Electrification is a way of decarbonising the railway service. This is done by replacing diesel trains with electric trains.
There are a number of options being looked at to suit the different types of in-fill extension opportunities. Each will be investigated, and the most feasible and viable option identified.
These options include full third rail system installation, hybrid third rail electrification and train battery solution. This is a pure train battery option and overhead line installation. All options will be looked at to see what is technically feasible and will provide the lowest whole life cost solution.
We’re working with our regulator, the Office of Rail and Road (ORR), to look at new third rail electrification designs. Part of that work is to have a clear business case and the safety justification assessment to support the option selected.
The high voltage distribution system also lends itself to inputs of power from renewable energy sources. These include solar or wind power, which will help the UK further decarbonise the electrical supply system. As a trial, and on a small scale, we were the first railway to feed our third rail traction supplies from a solar panel system. We’re working up larger scale renewable projects using the lessons learnt from the trial.
We’re also trialling DC energy storage solutions. This is to see if they can provide efficient capture of regenerative braking energy in those areas that would otherwise be lost. This improves system efficiency. It’ll also support the electrification system during the peak loading which would reduce the peak loading on the power system. And be used to help support running more or longer trains.
We’re always driving innovation to deliver new products. These are to either give a safety, reliability or cost advantage. And to use new technology to predict and prevent failures of components within the overall system.