Scottish Electrification: Stock

[Philip Phlopp]

DC rapid charging appears to be inevitable for exactly those difficult cases you've identified.

DC rapid charging is complicated to implement - there are too many stations fully electrified with 25kV AC OLE for a DC only charging strategy to work on a number of routes. There will need to be 25kV AC OLE involved, partially because the use of 25kV AC OLE will enable battery charging whilst an IPEMU is operating on 25kV AC from OLE, reducing the need for DC rapid charging, and partially because where 25kV AC OLE is already installed limits where you can site a DC rapid charging station. Glasgow Queen Street, for example, is out. It's all 25kV AC OLE already.

West Highland Line stock, for example, have 46 miles of OLE (Craigendoran-Glasgow Queen Street-Craigendoran) to ensure the battery pack is fully charged for the next run to Oban/Fort William and Mallaig. If it's limited to an IPEMU converted from DMU with no 25kV AC OLE capability, it would need to have more than 50 miles of range to get from Helensburgh Upper to Glasgow Queen Street and back to Helensburgh Upper, as there's no where after Craigendoran that you can situate a DC rapid charger.

The WHL example is a good example, not only because we're looking at ScotRail future stock, but also it's a situation repeated at a number of stations, go IPEMU with only DC charging and it really limits charging options - Thames Valley branches, Northern services. If you're running in and out of Paddington, where do you charge ? If you're running in and out of Liverpool Lime Street, Manchester Airport, Piccadilly or Victoria, where do you charge ?

That then leads down a headache inducing option of sections of third rail for battery charging (the assumption here is that manually connecting rolling stock to a power source is out on both a safety and a time basis) and I can promise you, S&T will find you and will kill you, if you start talking about things like third rail at stations like London Paddington, Glasgow Queen Street or Manchester Victoria. S&T murdering people brings in another potential problem - I've no real idea what S&T and the signalling system manufacturers will need to do to prove DC rapid chargers are safe to use with our existing signalling kit - DC rapid charging doesn't necessarily work at voltages or currents signalling kit has been designed for previously.

 

[NotATrainspott]

DC rapid charging is complicated to implement - there are too many stations fully electrified with 25kV AC OLE for a DC only charging strategy to work on a number of routes. There will need to be 25kV AC OLE involved, partially because the use of 25kV AC OLE will enable battery charging whilst an IPEMU is operating on 25kV AC from OLE, reducing the need for DC rapid charging, and partially because where 25kV AC OLE is already installed limits where you can site a DC rapid charging station. Glasgow Queen Street, for example, is out. It's all 25kV AC OLE already.

West Highland Line stock, for example, have 46 miles of OLE (Craigendoran-Glasgow Queen Street-Craigendoran) to ensure the battery pack is fully charged for the next run to Oban/Fort William and Mallaig. If it's limited to an IPEMU converted from DMU with no 25kV AC OLE capability, it would need to have more than 50 miles of range to get from Helensburgh Upper to Glasgow Queen Street and back to Helensburgh Upper, as there's no where after Craigendoran that you can situate a DC rapid charger.

The WHL example is a good example, not only because we're looking at ScotRail future stock, but also it's a situation repeated at a number of stations, go IPEMU with only DC charging and it really limits charging options - Thames Valley branches, Northern services. If you're running in and out of Paddington, where do you charge ? If you're running in and out of Liverpool Lime Street, Manchester Airport, Piccadilly or Victoria, where do you charge ?

That then leads down a headache inducing option of sections of third rail for battery charging (the assumption here is that manually connecting rolling stock to a power source is out on both a safety and a time basis) and I can promise you, S&T will find you and will kill you, if you start talking about things like third rail at stations like London Paddington, Glasgow Queen Street or Manchester Victoria. S&T murdering people brings in another potential problem - I've no real idea what S&T and the signalling system manufacturers will need to do to prove DC rapid chargers are safe to use with our existing signalling kit - DC rapid charging doesn't necessarily work at voltages or currents signalling kit has been designed for previously.

I think you misunderstood me. All new IPEMUs will come with 25kV AC capability. What I'm proposing is that the optimum system for the WHL would be to fit sections of HV DC solid conductor bar at important stations on that section of otherwise-unelectrified line, where the trains could charge up again. Under 25kV AC the train pantograph would feed into the transformer and other traction electronics as normal, including a DC supply to charge up the batteries. Under the HV DC charging sections the pantograph would feed directly into the battery charging circuitry. Between Craigendoran, Queen Street and Craigendoran again a WHL train would be on 25kV AC power for traction and charging the battery. Going northwards at Craigendoran, the battery would be full and allow the train to make it to the first charging stop - probably at Crianlarich. There'd be similar DC charging sections at Oban, Fort William and Mallaig, as well as any other intermediate stops where it is deemed necessary.

The reason is that it is perfectly fine to charge from the 25kV AC network where that exists, but it is not sensible to use 25kV AC for charging stops powered by static batteries. That's because the losses and costs involved in turning battery DC into 25kV AC and then back into battery DC would be noticeable, but there'd be little benefit. 'Discontinuous electrification' seems to mean providing wires on certain sections of line on the basis that trains would take power from it while moving. The DC network would only cover the area where trains would stop. It'd probably be conductor bar because trains would stop completely before raising and then lowering their pantographs to charge up. You'd only have enough conductor bar to cover the few metres where you can ever reasonably expect a pantograph to go. On the WHL stations that would probably mean covering the entire station loop, in case we have future DC charging locomotives which might hang slightly off the end of the platform.

The point of the green lines on the TS map is that they believe there are lines in Scotland which will never have a realistic chance of electrification through standard-ish 25kV AC. Given that they're suggesting 25kV AC to Tain, I think it's clear there's a fairly high bar on that assessment. The DC charging idea would provide a permanent solution for electrifying these stretches. The 25kV network can be used on all other lines, even if discontinuous to begin with.

It's possible that on certain routes, it may make sense to retrofit modern DMUs with battery technology even if it won't be easy to install a pantograph. This is essentially what the D-Train proposal has turned into. Whether that means a special section of third rail, or some sort of automated arm to plug in a charging connector, I don't know.