Railway electrification

While diesel locomotives burn petroleum products, electricity can be generated from diverse sources, including renewable energy.

The landlocked Swiss confederation which almost completely lacks oil or coal deposits but has plentiful hydropower electrified its network in part in reaction to supply issues during both World Wars.

Today, many countries have extensive electrified railway networks with 375000 km of standard lines in the world, including China, India, Japan, France, Germany, and the United Kingdom.

Electrification is seen as a more sustainable and environmentally friendly alternative to diesel or steam power and is an important part of many countries' transportation infrastructure.

In the United Kingdom, 1,500 V DC was used in 1954 for the Woodhead trans-Pennine route (now closed); the system used regenerative braking, allowing for transfer of energy between climbing and descending trains on the steep approaches to the tunnel.

It was formerly used by the Milwaukee Road from Harlowton, Montana, to Seattle, across the Continental Divide and including extensive branch and loop lines in Montana, and by the Delaware, Lackawanna and Western Railroad (now New Jersey Transit, converted to 25 kV AC) in the United States, and the Kolkata suburban railway (Bardhaman Main Line) in India, before it was converted to 25 kV 50 Hz.

[citation needed] Increasing availability of high-voltage semiconductors may allow the use of higher and more efficient DC voltages that heretofore have only been practical with AC.

[16]: 6–7  UIC conducted a case study for the conversion of the Bordeaux-Hendaye railway line (France), currently electrified at 1.5 kV DC, to 9 kV DC and found that the conversion would allow to use less bulky overhead wires (saving €20 million per 100 route-km) and lower the losses (saving 2 GWh per year per 100 route-km; equalling about €150,000 p.a.).

This scheme was introduced because of the problems of return currents, intended to be carried by the earthed (grounded) running rail, flowing through the iron tunnel linings instead.

The problem was exacerbated because the return current also had a tendency to flow through nearby iron pipes forming the water and gas mains.

Some of these, particularly Victorian mains that predated London's underground railways, were not constructed to carry currents and had no adequate electrical bonding between pipe segments.

While part of the SkyTrain network, the Canada Line does not use this system and instead uses more traditional motors attached to the wheels and third-rail electrification.

Thus both systems are faced with the same task: converting and transporting high-voltage AC from the power grid to low-voltage DC in the locomotive.

[28] However, the higher voltages used in many AC electrification systems reduce transmission losses over longer distances, allowing for fewer substations or more powerful locomotives to be used.

Also, the energy used to blow air to cool transformers, power electronics (including rectifiers), and other conversion hardware must be accounted for.

Lowering the current reduces the ohmic losses and allows for less bulky, lighter overhead line equipment and more spacing between traction substations, while maintaining power capacity of the system.

The standard-frequency AC system may introduce imbalance to the supply grid, requiring careful planning and design (as at each substation power is drawn from two out of three phases).

For passenger operation it is possible to provide enough power with diesel engines (see e.g. 'ICE TD') but, at higher speeds, this proves costly and impractical.

The high power of electric locomotives also gives them the ability to pull freight at higher speed over gradients; in mixed traffic conditions this increases capacity when the time between trains can be decreased.

The higher power of electric locomotives and an electrification can also be a cheaper alternative to a new and less steep railway if train weights are to be increased on a system.

Therefore, most long-distance lines in developing or sparsely populated countries are not electrified due to relatively low frequency of trains.

This is mostly an issue for long-distance trips, but many lines come to be dominated by through traffic from long-haul freight trains (usually running coal, ore, or containers to or from ports).

Newly electrified lines often show a "sparks effect", whereby electrification in passenger rail systems leads to significant jumps in patronage / revenue.

[36] The reasons may include electric trains being seen as more modern and attractive to ride,[37][38] faster, quieter and smoother service,[36] and the fact that electrification often goes hand in hand with a general infrastructure and rolling stock overhaul / replacement, which leads to better service quality (in a way that theoretically could also be achieved by doing similar upgrades yet without electrification).

The overhead wires make the service "visible" even in no bus is running and the existence of the infrastructure gives some long-term expectations of the line being in operation.

Due to the height restriction imposed by the overhead wires, double-stacked container trains have been traditionally difficult and rare to operate under electrified lines.

However, this limitation is being overcome by railways in India, China and African countries by laying new tracks with increased catenary height.

Such installations are in the Western Dedicated Freight Corridor in India where the wire height is at 7.45 m (24.4 ft) to accommodate double-stack container trains without the need of well-wagons.

The percentage then continues falling in order with Laos, Montenegro, India, Belgium, Georgia, South Korea, Netherlands, and Japan, with all others being less than 75% electrified.

A number of countries have zero electrified railways, instead relying on diesel multiple units, locomotive hauled services and many alternate forms of transport.