The Mathematics Of Fast-Charging Battery Trains Using Third-Rail Electrification
In Vivarail Unveils Fast Charging System For Class 230 Battery Trains, I talked about how Vivarail are proposing to fast-charge their Class 230 trains.
- The trains are fitted with special high-capacity third rail shoes.
- Third-rail electrification is laid in stations.
- The third rail is powered by a bank of bstteries, that are trickle-charged from the mains or perhaps even solar power.
- When the train connects to the rail, the rail is made live and a fast transfer takes place between third-rail and train.
So how much electricity could be passed to a train during a stop?
The most powerful locomotive in the UK, that can use 750 VDC third-rail electrification is a Class 92 locomotive.
According to Wikipedia, it can produce a power output of 4 MW or 4,000 kW, when working on third-rail electrification.
This means, that in an hour, four thousand kWh will be transferred to the train using conventional third-rail electrification.
Or in a minute 66.7 kWh can be transferred.
In Vivarail’s system, because they are transferring energy between batteries, enormous currents can be passed.
To illustrate how batteries can can deliver enormous currents here’s a video of a guy using two car batteries to weld things together.
These currents are possible because batteries have a low impedance and when the battery on the train is connected to the battery bank on the station, the two batteries will equalise their power.
If we take the example of the Class 92 locomotive and conventional electrification, this would be able to transfer 200 kWh in three minutes or 400 kWh in six minutes.
But I believe that battery-to-battery transfers could be at a much higher current
Thus in a typical one or two minute stop in a station, upwards of 200 kWh could be transferred to the train.
On this page of their web-site, Vivarail say this.
Due to the high currents required for the train Vivarail uses a carbon ceramic shoe able to withstand the heat generated in the process – without this shoe the charge time would make operational running unfeasible.
The devil is always in the details! From what I’ve seen and heard about the company, that would fit!
The Anonymous Widower 
I think the problem may be stated in your proposal – the shoes could weld to the third rail if the train is not moving – the current is over 5kA
Comment by R. Mark Clayton | July 12, 2019 |
Vivarail have released this and say that it’s patented. Perhaps the patent concerns the materials used!
Vivarail must have some clever protection in the design, because if they didn’t the Chinese and the Russians would pinch it, whether it was patented or not! Remember too, that the Class 92 locomotive draws 4MWh or 200 kWh in three minutes on conventional third-rail with 1960s technology.
Comment by AnonW | July 12, 2019 |
Indeed, but a Class 92 is either moving, or is going to move as soon as it draws the current, ensuring a sliding contact between the shoes and the third rails. If the train is stationary and drawing this much current then they will weld – a bit like this: –
https://www.progressrail.com/en/infrastructure/railwelding.html
only about 300A
Comment by R. Mark Clayton | July 15, 2019
It just shows how much current you can get through a humble shoe. Incidentally, this morning, I was looking at the shoe gear on a Class 710 train. Looks like a big redesign compared to an Electrostar.
Comment by AnonW | July 15, 2019
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[…] In The Mathematics Of Fast-Charging Battery Trains Using Third-Rail Electrification, I showed how a third-rail-based fast charging sstem, like that proposed by Vivarail could transfer several hundred kWh to the batteries of a train stopped in the station, for a few minutes. […]
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