With the increasing performance and service life of traction batteries (i.e. electric powered batteries), interesting possibilities open up for the operation of various heavy vehicles. In addition to the well-known buses, partial trolleybuses, forklifts and self-propelled automatic vehicles (AGVs), hybrid locomotives are also appearing more and more. The following article summarises how traction batteries can help economically and operationally with locomotives. In doing so, it will focus on the domestic environment, which seeks not to fall behind ongoing developments abroad.
First, something about railroad and electric traction
On the railways, locomotives can be encountered towing (possibly pushing) non-motorised passenger or freight cars, and also motorised passenger cars or units – thus in short these are, self-propelled passenger cars. Locomotives in line service carry complete trains, shunting locomotives manipulate carriages in the station, the depot or on the sidings (rail links connecting various enterprises). The propulsion of locomotives or motor cars and units is provided by a diesel engine or an electric motor (heavy engine locomotives also use so-called electric power transmission, where the internal combustion engine produces electricity and driving electric motors on the chassis – this is due to efficient traction management).
The electrification of the line, including stations, requires a massive investment and the maintenance of the traction (overhead contact line) is an operating cost source. On the other hand, the operation of electric trains themselves, i.e. electric traction (from the Latin word traher – tow), is considerably cheaper compared to diesel traction. Also, electric trains do not produce harmful emissions locally.
It’s not difficult to deduce where the biggest challenge for electric power will be: First, it is traffic on medium-frequency secondary lines — large enough to significantly burden the environment with diesel traction, yet not large enough to pay to invest in line electrification. Secondly, it is a shift in stations for which, for some reason, electric locomotives powered by a trolley cannot be used.
Hybrid power abroad
This challenge creates an opportunity for the use of electric hybrid locomotives and units with battery-powered energy storage. These can combine either an electric drive powered from a trolley and a battery (such as an extended-range tram or trolleybus) or a diesel drive powered from a battery.
Both solutions can already be found abroad: An example of the first solution is the Flirt Akku electric units from Stadler, which are prepared for operation in Schleswig-Holstein, Germany. An example of the second solution are diesel-battery shunting locomotives on siding operations in various parts of Germany.
Situation in the Czech Republic
The use of electric hybrid drives on railways in the Czech Republic today is mainly focused on the area of station shifts. This has one important ecological aspect: Stations and other facilities where shunting diesel locomotives are in operation are very often located in the middle of cities. The operation of these locomotives, often obsolete, here represents an unpleasant burden for the population in the form of air pollution and noise.
Let’s first describe a few facts that characterise the operation of locomotives in this service. In terms of the cost of operation, it can be stated that the cost of operating an electric locomotive is about half to a third compared to the operation of a diesel locomotive. The high operating costs of diesel are also due to the fact that, in addition to the price of energy, given the need to provide compressed air and the impossibility of frequent repeat launches, it is customary in the depot for diesel locomotive engines to run all day. And this is even if the actual work of the locomotive is less than half the total time. The remaining time the locomotive is standing, the diesel is operating in idle mode, which significantly increases the operating costs of fuel and lubricants and significantly reduces the life of the diesel locomotive. In addition, it releases exhaust emissions and causes much noise.
It would only seem logical to use electric locomotives powered by a trolley. However, not all lines are electrified – about a third of the approximately 10,000 km of lines in the Czech Republic are electrified. And even on these lines, there are places where overhead lines cannot be installed for operational, economic or safety reasons — such as cargo stations, transfer yards, industrial plant trails, depots, wash stations, etc.
Hybrid Drive Types and their Uses
As mentioned above, a hybrid locomotive can be of two types. The first is a diesel-battery hybrid (DBH), the second is a power supply combination from the traction (overhead) line and from the battery, abbreviated to traction-battery hybrid (TBH). Both variations have their greater or lesser economic and operational advantages. In general, it is clear that both variants improve operation.
In both types, the advantage is the possibility of collecting energy during braking and its subsequent use for starting the locomotive. When braking with an electrodynamic brake (EDB), there is so-called recuperation, when the electric motor acts as a generator and produces electricity. If it is not used, it will be uselessly converted into heat in the brake resistors and radiated into the surrounding environment. A different situation is where this electricity can be stored in batteries on the locomotive. The total energy losses of the hybrid locomotive are then very small. In addition, not only fuel is saved, but also wheelsets and brake calipers.
Diesel battery hybrid
This hybrid combination can save up to 50% of fuel thanks to the battery. The power of a diesel is usually less than the power of an electric drive, so the battery is also used to cover power peaks, for example during acceleration. The presence of a diesel engine makes such a locomotive completely independent of the external power supply (trolley).
DBH can go the way of modernising old locomotives or producing new ones. The Czech company CZ LOKO deals with these types of hybrid locomotives.
There are plans in the Czech Republic to modernise old electric locomotives. This includes a complete regeneration of the chassis, replacement or refurbishment of electronic components, the addition of a battery with a capacity for the required range (20, 50 or more km) and other modifications. A locomotive modified in this way, which has already been written off for a long time, will have its technical service life extended by thirty years. As a result, rail operators can significantly save on investment and operating costs. The Pilsen company DI-ELCOM is working on this project.
The battery is always charged when the locomotive is under the trolley, so there are no downtimes and no one has to worry about the battery.
As can be seen, the development of battery technologies makes it possible to save on financial resources and the environment. In the case of locomotives, battery technology helps to significantly reduce operating costs. Nor is it negligible that, for example, one type of locomotive capable of providing all manipulations will suffice for depot operations. If locomotive operators calculate all the pros and cons, then a hybrid locomotive is an advantageous choice.
Jakub Eliáš – nano power a.s. and the editorial staff of Smartcityvpraxi.cz
Illustrative photo © archive of the Smartcityvpraxi.cz editorial staff