Simone Bruckner, managing director of power resistor manufacturer Cressall, explains how rail transport can help lower emissions in the transport industry.
The International Energy Agency (IEA) estimates that passenger and freight transport activity will more than double by 2050. Railway transport provides an efficient solution to meet growing transport demand, while electrification offers a way to meet expectations with minimal environmental impact.
The transport sector is responsible for around a quarter of greenhouse gas emissions in Europe and is the main cause of higher levels of air pollution in cities. Increasing reliance on rail transport for short passenger journeys, freight and international travel can help the industry take a significant step towards reducing these levels. While we’re already beginning to electrify, this must continue to roll out on a greater scale.
On the right track
Rail transport is already more efficient than individual road vehicles when it comes to moving a large amount of people. The high passenger occupancy of trains means that CO2 emissions per passenger are significantly reduced. In addition, fewer cars on the road also reduces localised congestion and pollution levels.
However, the daily commute isn’t alone in being able to benefit from these carbon reductions. According to Eurostar, travelling from London to Paris by train instead of by plane can cut CO2 emissions by up to 90%.
For those in the UK, there are numerous international destinations available by rail, including a direct Eurostar service from London to Amsterdam. The journey takes just four hours and its environmental impact is considerably lower than the same trip by air.
Passengers aren’t the only ones who can benefit from a lower carbon footprint by letting the train take the strain, however. Significant CO2 reductions can also be demonstrated by transferring freight transport from roads to railways. Each tonne of freight transported by train rather than heavy goods vehicle decreases emissions by 7%, and removes up to 76 lorries from the road.
The ticket to carbon free
While already widely viewed as an eco-friendly option, technology developments in hydrogen electric, battery electric and overhead electric trains have the potential to cut rail travel emissions even further.
Around 40% of UK railways are already electrified, but Network Rail’s recent Traction Decarbonisation Network Strategy recommends installing an additional 11,700 km of track with overhead lines for electric trains. This is in addition to allocating a further 900 km of track for hydrogen electric trains and 400 km for battery electric trains, which have rechargeable onboard batteries and therefore do not require overhead cables.
Electric trains using overhead cables will be the leading solution to making rail transport more environmentally friendly, with hydrogen and battery electric trains providing support where overhead cables cannot be installed.
Overhead electric trains should be prioritised as they boast a higher efficiency than hydrogen electric, and can be around 35% cheaper. They are also more convenient to operate than battery electric trains, where the battery adds weight, requires frequent charging and replacement every seven years.
The safety and reliability of the electric railway system is dependent on the power quality of the train power supply system. Power issues such as overvoltages and harmonics can damage equipment and therefore disrupt the rail transport system. Therefore, the management of the electrical power must be carefully considered in mass-scale electrification of railways.
Resistors for railways
Overvoltages in the power supply commonly stem from lightning strikes or switching operations, but their effects can be avoidable. Soft and hard crowbar resistors can be used in traction power supply circuits to deal with the consequences of transient or longer lasting over-voltage conditions.
A soft crowbar resistor is pulsed to dissipate transient over-voltages, but if these become worse or prolonged, the main breakers are opened and the system is short-circuited through the hard crowbar to absorb the stored energy.
To prevent surges and unwanted harmonics entering the rail power supply, capacitor/inductor filter circuits are used to decouple the traction power supply from the drives. Here resistors are used to limit inrush currents to the capacitors during charging and to safely discharge them when required.
High speed trains require a large amount of energy to brake, and often disk brakes alone are unsuitable because of high wear rates with resulting maintenance and replacement costs. Many electric trains now use the electric traction motor as a generator to slow the vehicle.
Where possible, the generated electrical power is fed back into the supply line to be used by other trains elsewhere on the network in a process known as regenerative braking. However, when there are no other trains available to use the regenerated power, the excess is safely dissipated by brake resistors mounted on the train itself or at fixed track-side locations.
As the demand for freight and passenger transport grows, electrifying the railways and extending their use will be key in delivering a high performance service with minimal environmental impact.
