I am not an engineer but I would assume that with a more complicated design / elements to the traction, the more prone to failures it is. It’s simple probability. Having a battery-powered option is going to involve a set of mechanism between the battery and the motor and a switch between getting power from overhead electrical lines and the battery, for instance, which is not needed / much simpler in a pure EMU train, and that mechanism has its chance to fail in addition to the components common to them and the EMUs. So theoretically a BEMU should be less reliable than a simple EMU, assuming other things being constant.
I think engineering side has been resolved - 800’s do switch between modes quite well, that is once under the wires driver selects electric mode and it takes less than a minute ( may be 20sec ) to switch . Same the other way .
Where did I say it would be worse? Any failure between Oxford and Didcot causes an almighty mess, due to the frequency of trains. As opposed to the consequences of a battery set failing on the Henley branch, for example.
Installation of 25kv overhead there is a no brainer, both to eliminate lots of Turbo milage and allow IETs to keep their diesel engines off all the way between Oxford and Paddington, and as a step on the way to getting an electrified route (albeit needing dual-current traction) between Birmingham and the South Coast for passsengers and freight.
Battery electric units are a great idea for the GWR local services on the Thames Valley branches and to Gatwick and to Basingstoke (pending 25kv wiring between there and Reading as well) but not when existing GWR emus could perfectly well take over the Oxford-Didcot stopping duties the instant overhead wires are installed - and reinstate direct trains between Oxford and the stations between Didcot and Reading - without any need to install charging kit for battery units.
I was talking about what happens should a battery set fail/break down. Nothing to do with possible range on battery power.
I can see how BEMU’s could replace Turbos between Didcot and Oxford without electrification of Oxford , in short to medium term.
All 387’s (Paddington to Didcot terminators) or traction that may be replacement of thereof in the future, would have to have battery packs fitted allowing to get from Didcot to Oxford and back to Didcot + lets say 2 hours of hotel power for the dwell times in the sidings .
That would also apply to 800’s with diesel engines removed for Paddington - Oxford fasts.
Batteries could be charged on the move as for majority of time trains would run under wires (plus dwell times at intermediate stations especially Paddington ) .
Charging on the move would remove need for charging these units at Oxford if staying less than , lets say, 2 hours.
For the trains that stay longer than 2 hours at Oxford, there are 2 solutions or combination of both to keep batteries charged:
- shore supply installed ( perhaps 2 lines in Down Sidings and 2 lines in Up Sidings ) , where trains staying over 2 hours but remaining in traffic would be plugged in.
Shote supply may be useful EWR units if they were to be stabled at Oxford too ( happy to be corrected).
or
- auxing off the units to preserve batteries charge .
Of course full electrification will be needed if “electrical spine” is ever to be achieved but before that , I think , pure electric units could be used between Padd and Oxford ( may be even Banbury ) .
Anything beyond Oxford on North Cotswold line will need bi-modes of course .
