June 16, 2016

Raising the Baar for battery-powered trains

Written by  Ankur Saxena
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Furrer and Frey has developed a static recharging station for battery-powered trains, which it is targeting for low-capacity lines currently reliant on diesel traction, as product engineering manager Ankur Saxena explains.

WHILE railways strive to benefit from the improved performance offered by electrification, diesel traction remains common on rural and low-capacity branch lines where there is a poor business case for installing overhead or third rail traction.

Onboard batteries present an alternative source of environmentally-friendly traction. Yet limited battery life means they have typically been used in conjunction with rather instead of conventional traction systems.

RailBaarFurrer and Frey and Opbrid are attempting to bridge this gap to increase the reliability and feasibility of battery-powered rail vehicles by adapting technology already in use in the bus sector. Specifically, RailBaar is a high-power overhead automatic electric charging station for battery-powered electric trains. The system expands the scope and range of battery-powered trains, with RailBaar designed primarily for one to three-car trains and as an alternative to DMUs.

RailBaar is based on Furrer and Frey and Opbrid's BusBaar, which has been used on buses since 2010, and is helping to reduce fuel and energy consumption. For example, in Gothenburg it has helped Volvo to reduce fuel consumption by 81% and overall energy consumption by 61% on the three buses using the system which is installed at two locations on the network.

Like the bus solution, RailBaar utilises a platform side station concept, which is substantially less expensive and more versatile than existing overhead electrification structures. The RailBaar charging station consists of a post to which the RailBaar is attached. Affixed to this stainless steel mechanism is the inverted aluminium pantograph which is fitted with copper conductors. These are connected to a power source via cables and have a flexible design, ranging from thin collectors for low-power charging, to wide collectors for a high power charge. The pantograph is stored in a protective hood and can be lowered to the height of any train or raised to a suitable safe height when not charging.

The train roof is subsequently equipped with four-contact fixed in-line current collectors. To operate, the inverted pantograph lowers to make contact with the collectors to enable charging to take place, although only the inner two connectors are live, and only when the train is at the station. In addition the physical geometry of the system ensures that the correct contact is always made to prevent overheating, sparks or welding during high-power charging. A special insulating cover on the train roof also removes any electrocution risk at platforms as well as preventing snow and ice accumulation.

The initial RailBaar concept is typically based on 750V dc, although an ac version is under development along with a version with only two collector strips. The system has a capacity of up to 800kWH to provide rapid charging and to allow trains to receive a top-up charge when waiting at the platform. It can take 10-30 minutes for a full charge depending on the battery size - a 120kW battery is fully charged in 10-12 minutes - the number of coaches and the charger capacity, while a top up charge can take 1-3 minutes.

All of the system's moving parts are contained within the protective hood, meaning that RailBaar can be mounted on a wide variety of supports, allowing designers the freedom to visually blend the system into the station concourse. The supporting post also accommodates the charger, again minimising the size and visual impact of the structure.

Run all day

With the RailBaar rapid charging station installed, a battery-powered electric train can run all day with only a few minutes of charging required at intermediary charging stations. It is also possible to recover braking energy in the accumulators, and accelerate away from the station under grid power, further saving energy. In addition, by eliminating diesel engines or electric traction equipment, the weight of the train is dramatically reduced, improving performance and capacity.

The technology also offers substantial potential savings compared with conventional 25kV electrification. The estimated cost of installing the mechanical and battery infrastructure along with two RailBaar charging stations on a prospective 20km installation is around a sixth of the similar cost of installing overhead electrification, excluding signalling and rolling stock upgrades, which are expected to be similar in both cases.

The project is currently in the concept phase, with discussions underway with both infrastructure managers and rolling stock suppliers about potential main line trials. Furrer and Frey's only rail-based implementation so far is in China on the 20.3km Huai'an light rail line, which opened in February. The line is entirely catenary-free and utilises battery-powered LRVs supplied by CRRC Zhuzhou which recharge at stations. Furrer and Frey supplied the mechanical part of the charging infrastructure, and is eyeing further opportunities in this as well as the main line sector.

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