Battery benefits

Is this the answer to powering our future trains ?

THREE years ago, when I heard that Bombardier was running the Class 379 battery train demonstrator in public at Manningtree, I had to go for a trip to see for myself, as I was sceptical about the proposition.

But that trip turned out to be an almost magical experience. I was also lucky enough to sit beside a Bombardier engineer monitoring the train on a laptop. The look on his face said it all!

I am a retired Control and Electrical Engineer who has spent the past 50 years looking at the mathematics of all types of systems - in engineering, finance, project management and research. The Manningtree experience set me thinking hard about battery trains, and their mathematics and possibilities.

I hadn’t known about the counter-intuitive property of running vehicles with steel wheels on steel rails - as the mass of the train increases, the rolling resistance decreases! This enables Class 59 locomotives to haul massive stone trains from the Mendips to London.

But it also means that the weight of a battery on a train is only a penalty under acceleration.

I have never seen a published figure for the kinetic energy of a train, but here’s the calculation for a full nine-car Class 345 train, which (according to the internet) has eight motored cars.

I estimate that the mass of the train with 1,500 x 80kg passengers is just short of 450 metric tonnes. Suppose the train is travelling at the full speed of 145kph (90mph) - this would give the kinetic energy of the train as 102 kilowatthours.

Bombardier makes a Primove 50 battery for trams with a capacity of 49 kilowatt-hours, and which weighs under a tonne. A number of these or similar batteries would make storing the energy generated under braking a very practical proposition.

Why not put such a battery under each motored car? This would give 400 kilowatthours, which is more than enough storage. It would also distribute the weight and put the batteries close to the traction motors, which would probably keep electrical losses to a minimum.

Could Crossrail have been designed around trains which handle their own regenerative braking in batteries? It would have the following benefits:

Trains would have an emergency power source in the batteries that could be sized to be sufficient to move the train to the next station or safe evacuation point, in the case of a complete 25kV AC power failure.

The 25kV AC supply would not have to handle the reverse currents of regenerative braking.

The trains would reuse up to perhaps 80% of the train’s kinetic energy at each stop.

Only top-up power would need to be provided along the route, so the power needs of the railway would be reduced.

The energy efficiency and battery-braking would mean less heat would be generated in the tunnels. Would this mean lower cooling needs for stations and trains?

It has been disclosed that the 25kV AC is supplied to the tunnels at the ends. So how simple is the Aventra-only Crossrail compared with a traditional railway, which has to accommodate all possible types of electric train?

Another rail line is also being designed and built in London that will be used only by Aventras… the Barking Riverside extension of the Gospel Oak-Barking Line.

I have read all of the published Transport for London documents about this extension and although electric trains are mentioned, electrification is not!

The extension is only a mile of new track. Trains could leave the electrified c2c line with full batteries, and it would not be difficult to go to Barking Riverside and back on stored power. Benefits would include:

Less visual and audible intrusion of the new railway.

Simpler track and station design.

It might be easier to keep the railway at a safe distance from all the highvoltage electricity lines in the area that bring power to London. A possibly safer and more reliable railway in extreme weather. Costs would be saved. These two examples show that adding batteries to a train gives design and cost advantages when building new railways.

There is also the article in RAIL 850, which describes the proposed 125mph Aventra-based bi-mode from Bombardier.

I’m not sure how low noise levels and the claimed 125mph on both diesel and electric power are achieved. But I am certain that batteries and a very sophisticated control system on the train are at the heart of the design.

The power requirements in a high-speed cruise with an efficient and aerodynamic train could be surprisingly low, and able to be met by battery power which would be topped up as required by well-insulated diesel generators.

Stopping would not be a problem, as the regenerative braking would charge the batteries. The biggest problem will be accelerating the train after a stop.

So why not electrify through and either side of stations, where the 125mph trains stop? It doesn’t need to be 25kV AC overhead, but it could be shielded 750V DC third rail that is only activated when a train is present and needs power.

In the future, batteries will have a very positive effect on how we build our trains and railways.

“I was lucky enough to sit beside a Bombardier engineer monitoring the train on a laptop. The look on his face said it all!”