Rail Industry Focus

01.04.13

From one track to another

Source: Rail Technology Magazine March/April 2013

Formula 1 engineers are used to developing high-end bespoke components and systems to improve the performance of their team’s drivers. But increasingly, technology developed for the sport is having an impact in the very different fi eld of public transport, most recently with a partnership between Alstom and Williams to develop a specialised energy storage flywheel system for trams. RTM spoke to Damien Scott, general manager of the Williams Technology Centre in Qatar.

Making better use of otherwise wasted energy is an obvious benefit for the light rail sector.

Engineers at Williams Hybrid Power developed a new kind of flywheel energy storage for the 2009 Williams F1 car, since introduced into applications such as London buses and the Le Mans winning Audi R18 e-tron quattro.

But it is now finding a rail application too, with the company entering into an exclusive arrangement with Alstom to develop a solution based on the technology for its Citadis tram type.

It will offer fuel savings and emissions reductions by harvesting the energy that is normally lost as heat when braking and turning it into additional power. It is ideally suited to trams because of their stop-start nature and high mass, the companies say.

Core principle

Damien Scott, general manager of the Williams Technology Centre in Qatar, told RTM more about the technology, and a variant static trackside system for metros.

He explained that the reason the technology is so unique is the composite material used in its construction.

He said: “The primary innovation is that it uses the magnetic composite as part of the rota. The core principle is that it’s an electro-mechanical flywheel, so it stores energy in the kinetic motion of the flywheel, which accelerates or decelerates by using effectively an electric motor. It allows you to store electricity and when you want it returned, the system works like a generator.

“The use of carbon fi bre allows you to spin the flywheel at incredibly high speeds – it has the tensile capability to get up to 35,000 or even 45,000 RPM – and that increases the amount of energy you can store.

“Our core innovation is magnetic loaded composite (MLC) – the inclusion of a very small magnetic particle in the composite rota itself. We then fl ash-magnetise that to get the permanent magnet pattern we need, which forms part of the electric motor generator. The key advantage of that is you don’t get any eddy current.

A carbon fibre flywheel tends to get damaged if temperatures exceed 100 - 110C degrees, meaning you can’t cycle it continuously. For example, if you’re using a UPS, you could pulse discharge and the flywheel would heat up, and you’d need to leave it for an hour or so to cool down. The MLC moves that heating component in the rota, so we can continuously charge and discharge. That opens up a whole host of possible applications for rapid high-power energy cycling.”

Inherently safe

Scott continued: “The other advantage is that your rota, the key spinning element, is then wholly composite, so in the event of a failure precipitated by any one of a number of different causes, you don’t have to ‘contain’ large metallic components.”

Imagine a steel flywheel, or one with large permanent magnets – if that were to fail for any reason, it has components spinning around at sometimes multiples of the speed of sound, so containing that safely is a challenge.

The technology is “superior in a number of ways” to chemical batteries, Scott said. Although it is too early to list the specific tram networks likely to benefit from rolling stock equipped with the MLC flywheels, Nottingham is due to take delivery of 22 Alstom Citadis trams soon as part of its tram upgrade, so could be one to watch.

ALST 46753-MedRes-ALS124 VB 1272

Retrofit vs new build solutions

Scott told us: “Alstom is very interested in on-board energy storage for tram systems in general. The OEMs we supply, because of the life of the capital stock of the equipment they supply, tend to see both retrofit and new build offerings as being quite attractive.

“Retrofit provides its own challenges, as you’ve got to integrate it with an existing system that wasn’t necessarily designed for on-board inclusion of energy storage. Depending on the weight of the tram, you’re looking at one or two units per tram, largely determined by the overall energy equations of what they’re trying to optimise versus the additional packaging requirement and the additional mass.

“The key principle is that when the tram needs to come to a stop, if its drive motors have been run in reverse as generators and the overhead line cannot accept the power that has been generated, it has to be burnt-off locally in resistor banks. Therefore what we can do is increase the fraction that’s captured, and then re-introduce when the tram accelerates from stop again.

“The other interesting thing that can be done is self-rescue, for example if power is lost or if the tram network is designed with gaps in the power supply – at intersections, for example, overhead catenary is quite unsightly and you can design the system so trams move on their own power across those short gaps.

“That also helps in the event that you lose all power and you have to get the tram away from shared public roads or to the nearest safe place for the passengers to alight.”

Culture gap

Obviously F1 engineering and railway engineering have different ways of working and different priorities.

Scott said: “Rail engineers would say that F1 engineers are very good at making very high performance things and can do that very quickly – the problem is, the rail sector would say, it tends to be hideously expensive and only needs to last for two hours on a Sunday!

“But rail needs everything to be cheap as possible and to last for 20 years – so how are you going to reconcile the two?

“That’s been a really interesting journey – where we take our skills in rapid incremental improvement and prototype engineering and refocus on optimising for cost and for life.

“You couldn’t think of two more different sectors than the rail industry and Formula 1 – that’s a really interesting aspect of this business diversification.”

Trackside technology

It is the static, trackside version of the system that is the focus of the Williams Technology Centre in Qatar.

The stationary variant is much higher power, offers much more energy storage and is designed to operate trackside in underground metro systems and to be interfaced into the electrical infrastructure.

“It allows a metro to increase quite substantially the fraction of kinetic energy that’s recovered in a braking event,” Scott said, while also meaning the rolling stock isn’t carrying any extra weight.

“In a rush hour situation at a metro station when you’ve got trains coming in every twothree minutes, they’re dumping a signifi cant amount of electricity through a braking event.

“Often what happens is that if it can’t go anywhere – to another train on the same electrically isolated segment of track – that electricity will be burnt off in resistor banks or the friction brakes will take over. That leads to more dust and heat in the tunnel.”

He said there would be “good potential” for London Underground to make use of the system, and said it could help with the major engineering challenge of cooling the deep Tube lines. But he admitted that it is a “very challenging” infrastructure.

He said: “One way we could potentially help an installation like LU is if, for example, they wanted to put a higher frequency of train service over a particular segment of the network, or they wanted to introduce new heavier rolling stock with a higher power demand, they have to do one of two things.

“Either they have to upgrade the traction power capabilities – and that means new traction power substations and civils works and the connectivity that goes with that – or introduce localised energy storage, which can top up the power requirement when that heavier train or trains at a higher frequency go over the line.”

The Doha metro, due to open in around three years time – which Scott called “one of the most ambitious projects in the world at the moment” – is looking at using such wayside technology across its four lines and 300km route length and 98 stations.

Scott said: “What QRail [Qatar Railways Company] is proposing to do, in terms of the number of stations and amount of track in that timescale has never been done before. It’s quite an exciting project, and our intention and the trajectory is very much to work closely with them to use the technology in a new build for the first time.”

Tell us what you think – have your say below, or email us directly at opinion@railtechnologymagazine.com

(F1 image: AP Photo / David J Phillip)

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