DC bimode options

[Meerkat]

To avoid clogging up specific TOC/route threads I thought I would start a specific one (please merge if I messed up searching for a previous thread again!)
What are the options for DC bimodes? Discounting 230s as they aren’t mainline.
769s are the only current option....and they don’t work so far!
Can Bombardier mash up Aventra with a bit of Turbostar experience?
Can Hitachi merge their 80x/395/385 expertise?
Can either of them do it quickly?!

How many do Southern need/want for Uckfield and Ashford-Hastings if EMR take away the 171s?
Very similar requirement for Reading-Gatwick, but that would presumably mean Porterbrook would have to be lessor as they would lose the 769 deal.
Once you had the basic product would producing a faster end door version for the Waterloo-Exeter line be simple?

If they were significantly reducing diesel use and built in England it would be good PR for the DfT.....

 

[swt_passenger]

All other aspects being equal, such as carriage numbers and vehicle length, a modern DC powered EMU ought to have more room underneath to add batteries compared to the same design of EMU’s AC powered variant.

Using as an example an AC 379, let’s assume the battery pack is connected in to the DC link between the transformer rectifier and the traction package, then exactly the same would surely be possible on a dual voltage AC/DC 377/2. Then if you lost the transformer/rectifier as on a DC only EMU you now have even more space (and weight allowance) for batteries.

I still have huge doubts about battery supporting normal performance for significant lengths of routes, but that’s been discussed often before. I mean, has anyone ever seen the detailed results of the 379 trial?

 

[Terry Tait]

How about a flirt style power car that could be marshalled between two 377/375/450?
Could such a thing be built?

 

[Meerkat]

The flirt power car shares articulated bogies with the adjacent carriages. Too short for its own bogies and a four wheel version would presumably have interesting stability.

 

[adamedwards]

Power pack Pacer? !

 

[paul1609]

All other aspects being equal, such as carriage numbers and vehicle length, a modern DC powered EMU ought to have more room underneath to add batteries compared to the same design of EMU’s AC powered variant.

Using as an example an AC 379, let’s assume the battery pack is connected in to the DC link between the transformer rectifier and the traction package, then exactly the same would surely be possible on a dual voltage AC/DC 377/2. Then if you lost the transformer/rectifier as on a DC only EMU you now have even more space (and weight allowance) for batteries.

I still have huge doubts about battery supporting normal performance for significant lengths of routes, but that’s been discussed often before. I mean, has anyone ever seen the detailed results of the 379 trial?

Southern/Network Rail from discussions with them at Marshlink Action group Meetings have looked in to the feasibility of using a DC version of the 379 battery emu for both the Uckfield and marshlink lines.
The discussion came about as a way to maintain the service as an Ashford to Brighton service rather than the current service which has been cut back to Eastbourne but still has summer capacity issues.
For reasons to do with the power supply a dc version of the 379 would not be able to charge its batteries as fast as the ac version and because of this it would not be possible for a unit to meet the previous Ashford to Brighton timetable diagrams it would just run out of charge during the day. It would be possible to achieve it if a unit did a Brighton to Ashford round trip followed by a return trip to Seaford.
However the Uckfield Line was basically a non starter because of the distance of Hurst Green to Uckfield and return and as rolling stock for the 2 lines are tied together it effective meant the investigations weren't taken any further.
Im still of the opinion that the best bet for Marshlink would be AC electricfication from Ashford to Ore utilising spare capacity in HS1/ Ashford Station and the use of ac/dc emus given that your only going to talking a maximum of 3 emus in the ac section at any one time.

 

[Bald Rick]

Southern/Network Rail from discussions with them at Marshlink Action group Meetings have looked in to the feasibility of using a DC version of the 379 battery emu for both the Uckfield and marshlink lines.
The discussion came about as a way to maintain the service as an Ashford to Brighton service rather than the current service which has been cut back to Eastbourne but still has summer capacity issues.
For reasons to do with the power supply a dc version of the 379 would not be able to charge its batteries as fast as the ac version and because of this it would not be possible for a unit to meet the previous Ashford to Brighton timetable diagrams it would just run out of charge during the day. It would be possible to achieve it if a unit did a Brighton to Ashford round trip followed by a return trip to Seaford.
However the Uckfield Line was basically a non starter because of the distance of Hurst Green to Uckfield and return and as rolling stock for the 2 lines are tied together it effective meant the investigations weren't taken any further.
Im still of the opinion that the best bet for Marshlink would be AC electricfication from Ashford to Ore utilising spare capacity in HS1/ Ashford Station and the use of ac/dc emus given that your only going to talking a maximum of 3 emus in the ac section at any one time.

I guess that was a few years ago.

Battery technology has moved on. D.C. Battery hybrids that can do Ashford - Hastings (Eastbourne) and the Uckfield Line are now well within the realms of possibility. I’d be surprised if some weren’t in service within 5 years.

Note that D.C. only electrostars have several tonnes of concrete in place of the AC version transformers...

 

[edwin_m]

Due to the limitations of the power supply, dual voltage capable units have poorer performance in DC mode - they have to limit the maximum current they draw to avoid overheating of the infrastructure. A battery unit would be similarly limited, and if using some of that current to charge the batteries it would therefore have poorer performance than an equivalent non-battery train, even if the two were the same weight. The batteries might also need longer to charge than on an AC unit. This isn't ideal for an intensively-used route such as Croydon to London, although it would probably still be better than the 171s they might replace on that route. It probably wouldn't matter on Marshlink though.

One solution might be to beef up the traction supply on the routes the battery units use when in third rail mode, so the traction current limitation could be made less severe (possibly with some form of geofencing to allow different limits on different routes). However this may already have been done to the maximum extent possible on some routes. There's also the possibility of ordering a batch of Aventras or other newer designs that are a bit lighter than Electrostars, so might be able to achieve the same performance using less current for traction and therefore be able to charge the batteries while remaining within the current limit.

 

[Bald Rick]

Due to the limitations of the power supply, dual voltage capable units have poorer performance in DC mode - they have to limit the maximum current they draw to avoid overheating of the infrastructure. A battery unit would be similarly limited, and if using some of that current to charge the batteries it would therefore have poorer performance than an equivalent non-battery train, even if the two were the same weight. The batteries might also need longer to charge than on an AC unit. This isn't ideal for an intensively-used route such as Croydon to London, although it would probably still be better than the 171s they might replace on that route. It probably wouldn't matter on Marshlink though.

One solution might be to beef up the traction supply on the routes the battery units use when in third rail mode, so the traction current limitation could be made less severe (possibly with some form of geofencing to allow different limits on different routes). However this may already have been done to the maximum extent possible on some routes. There's also the possibility of ordering a batch of Aventras or other newer designs that are a bit lighter than Electrostars, so might be able to achieve the same performance using less current for traction and therefore be able to charge the batteries while remaining within the current limit.

All fair points. But...

The amount of time most modern D.C. EMUs spend on full power is surprisingly small. For the rest of the time a D.C. hybrid is ‘on the juice’ it can be charging. That includes drawing full power from the 3rd rail whilst it is coasting, stationary or braking, in the latter case regenerating into the batteries concurrently.

It is possible that some locations may need beefing up of substation power - typically stations where a few trains will be charging for a while concurrently. But it’s usually a lot cheaper to add capacity to an existing substation site than to build a new one on a non-electrified route.

Similalry, it should be possible to have isolated islands of con rail to help boost the battery, eg at some stations. With appropriate precautions (eg shielding / enhanced anti trespass measures / the con rail only being live when a train is in section), I think this will meet the ORRs test of reasonableness. Alternatively, have a short section of OLE, and use a standard pantograph. (Clearly more power to charge would be available if it was AC, however that then needs a transformer on the train which adds a lot of weight that could be batteries. Perhaps a higher voltage D.C.?)

And these islands don’t need to have an N-1 capability; if they are switched out for any reason then some operational measures can be applied.

Batteries also bring the prospect of taking the units off the leash in critical areas, ie whilst the current draw from the con rail may be limited, they can have a boost off the battery to enable better acceleration. This could be helpful in areas of high service frequency where station reoccupation / junction margins are critical. (The battery could then be recharged from braking and/or less power critical parts of the network).

As I said above, I’d be surprised if the two GTR diesel lines aren’t using Battery hybrids within 5 years. And I can see the North Downs following suit.

It’s a really interesting subject.

 

[edwin_m]

All fair points. But...

The amount of time most modern D.C. EMUs spend on full power is surprisingly small. For the rest of the time a D.C. hybrid is ‘on the juice’ it can be charging. That includes drawing full power from the 3rd rail whilst it is coasting, stationary or braking, in the latter case regenerating into the batteries concurrently.

It is possible that some locations may need beefing up of substation power - typically stations where a few trains will be charging for a while concurrently. But it’s usually a lot cheaper to add capacity to an existing substation site than to build a new one on a non-electrified route.

Similalry, it should be possible to have isolated islands of con rail to help boost the battery, eg at some stations. With appropriate precautions (eg shielding / enhanced anti trespass measures / the con rail only being live when a train is in section), I think this will meet the ORRs test of reasonableness. Alternatively, have a short section of OLE, and use a standard pantograph. (Clearly more power to charge would be available if it was AC, however that then needs a transformer on the train which adds a lot of weight that could be batteries. Perhaps a higher voltage D.C.?)

And these islands don’t need to have an N-1 capability; if they are switched out for any reason then some operational measures can be applied.

Batteries also bring the prospect of taking the units off the leash in critical areas, ie whilst the current draw from the con rail may be limited, they can have a boost off the battery to enable better acceleration. This could be helpful in areas of high service frequency where station reoccupation / junction margins are critical. (The battery could then be recharged from braking and/or less power critical parts of the network).

As I said above, I’d be surprised if the two GTR diesel lines aren’t using Battery hybrids within 5 years. And I can see the North Downs following suit.

It’s a really interesting subject.

Indeed it is and there are lots of good possibilities here. I guess the main issue is the sensitivity of the supply system - and also the sensitivity of the people responsible for it - to extra power being needed. I get the impression the current limiting was essentially to mimic the consumption of the old slam-door units because everyone knew the system mostly worked at that time but nobody really knew what would happen if it was asked to deliver more power. If this is still the attitude then things like drawing current when coasting would be ruled out. But if some more detailed and dependable analysis is possible then there could be scope to move the boundaries a bit, along with perhaps some selective upgrades as you suggest.

 

[Taunton]

Battery technology has moved on. D.C. Battery hybrids that can do Ashford - Hastings (Eastbourne) and the Uckfield Line are now well within the realms of possibility. I’d be surprised if some weren’t in service within 5 years.

I wonder if it has moved on. 60 years ago, 1950s, an adapted 2-car former dmu was fitted out as a battery unit and ran on the Aberdeen-Ballater line, 43 miles (more than Ashford-Hastings), except it was substantially uphill westbound. It ran on an opposite diagram to a diesel unit which had the same timings. It was charged overnight, and also during daytime layovers at Aberdeen station where charging equipment was installed.

It ran for about four years, without any of the lengthy commissioning that seems to plague modern units, but eventually interest seems to have been lost in the trial. However it carried on with other random work, over about 25 years, and surprisingly made it through to preservation, still battery powered. The batteries were old traditional lead-acid ones, but it worked. The project was in conjunction with the local hydro-electricity board.

https://railcar.co.uk/type/battery-multiple-unit/summary

Germany (both east and west) built hundreds of battery-powered railbuses for branch lines at the same time. Those all seem to have gone, though they lasted a full life.

 

[RichJF]

My personal opinion is that the class 387 will be fitted with batteries and used on both lines. Based on the 379 tech but put into 387s because of their already in place 3rd rail capability. I also think a short section of 3rd rail (same length as the platform) may be installed at Uckfield to charge the units while they wait to return to London.

Then the 387s can run as EMUs on the 3rd rail & charge when not on the non-electrified sections.

 

[AM9]

Indeed it is and there are lots of good possibilities here. I guess the main issue is the sensitivity of the supply system - and also the sensitivity of the people responsible for it - to extra power being needed. I get the impression the current limiting was essentially to mimic the consumption of the old slam-door units because everyone knew the system mostly worked at that time but nobody really knew what would happen if it was asked to deliver more power. If this is still the attitude then things like drawing current when coasting would be ruled out. But if some more detailed and dependable analysis is possible then there could be scope to move the boundaries a bit, along with perhaps some selective upgrades as you suggest.

The SRPSU (Southern Region Power Supply Upgrade) was started when the characteristics of new trains, (specifically Electrostars and Desiros) as a plan to allow the maximum current for a 4-car train to be lifted from the EE507 era's 1500A. It involved considerable upgrades to existing substations, high voltage feeder locations, many lengths of DC cable upgrades and eight new 33kV feeds from National Grid.
Like so many major capital projects timescales slipped and costs rose. Some of the planned work was deferred which would in effect force new trains to stay limited to the lower maximum power levels.
What we have now with almost all trains running 3 phase ac induction motors, is fleets running at 50-60% of their acceleration capability. The supply limitations now include the basic shortcoming of LV DC , i.e. the local resistance of track and conductor rails, cabling and switchgear. To run a modern 12-car EMU at full performance requires 4500A to 6000A, which given the 10000A practical maximum draw, can require one feed per 2 trains even allowing for some diversity, and that also complicates the distribution of regen. current.

 

[Taunton]

... a plan to allow the maximum current for a 4-car train to be lifted from the EE507 era's 1500A. It involved considerable upgrades to existing substations, high voltage feeder locations, many lengths of DC cable upgrades and eight new 33kV feeds from National Grid ... Some of the planned work was deferred which would in effect force new trains to stay limited to the lower maximum power levels.
What we have now with almost all trains running 3 phase ac induction motors, is fleets running at 50-60% of their acceleration capability. The supply limitations now include the basic shortcoming of LV DC , i.e. the local resistance of track and conductor rails, cabling and switchgear. To run a modern 12-car EMU at full performance requires 4500A to 6000A, which given the 10000A practical maximum draw, can require one feed per 2 trains even allowing for some diversity, and that also complicates the distribution of regen. current.

Maybe I haven't quite got this, but if a traditional 4-car drew 1,500A then a 12-car is 4,500A, which seems to be much the same as the modern "at full performance 4,500A to 6,000A", and yet they are then artificially throttled back to 50% of this. Now the Southern has been running full 12-car sets since the 1930s, and at Clapham etc you have always been able to see maybe half a dozen of these running at once, and just a block apart, so how is the 10,000A current limit per electrical section now an issue.

It also reads that the new trains were ordered without thought of the power supply side, then a lot was spent on upgrading the power supply to supposedly sort this out, and yet still things have to be throttled back, after that expenditure.

 

[edwin_m]

Maybe I haven't quite got this, but if a traditional 4-car drew 1,500A then a 12-car is 4,500A, which seems to be much the same as the modern "at full performance 4,500A to 6,000A", and yet they are then artificially throttled back to 50% of this. Now the Southern has been running full 12-car sets since the 1930s, and at Clapham etc you have always been able to see maybe half a dozen of these running at once, and just a block apart, so how is the 10,000A current limit per electrical section now an issue.

It also reads that the new trains were ordered without thought of the power supply side, then a lot was spent on upgrading the power supply to supposedly sort this out, and yet still things have to be throttled back, after that expenditure.

Part of the issue is that the characteristics of the DC motor means that the current draw drops off at higher speeds. An AC motor and the associated electronics, when not throttled, can accelerate better at higher speeds but draws that much more current while doing so.

 

[paul1609]

I guess that was a few years ago.

Battery technology has moved on. D.C. Battery hybrids that can do Ashford - Hastings (Eastbourne) and the Uckfield Line are now well within the realms of possibility. I’d be surprised if some weren’t in service within 5 years.

Note that D.C. only electrostars have several tonnes of concrete in place of the AC version transformers...

The discussion would have been just over 2 years ago. I was under the impression that the issue was with battery charging rather than the battery technology or capacity, in that the charging rate would be limited by the capacity of the dc train bus, shoe gear and the power supply to the track. As the current standard timetable only has 14 min turnaround at Ashford and 6 mins at Eastbourne there is no time for layover charging without using extra units and the current truncated route is roughly 50% electrified in terms of time on the standard timetable. Ill be impressed if Marshlink is Battery Hybrid in 5 years time.

 

[MarkyT]

The discussion would have been just over 2 years ago. I was under the impression that the issue was with battery charging rather than the battery technology or capacity, in that the charging rate would be limited by the capacity of the dc train bus, shoe gear and the power supply to the track. As the current standard timetable only has 14 min turnaround at Ashford and 6 mins at Eastbourne there is no time for layover charging without using extra units and the current truncated route is roughly 50% electrified in terms of time on the standard timetable. Ill be impressed if Marshlink is Battery Hybrid in 5 years time.

A greater proportion of the route would be electrified if the trains were re-extended back to Brighton, hence giving more time to charge en route. If the HS1 - Marshlink through working to Hastings or Eastbourne ever happen, battery equipped AT300 derivatives might be able to charge (en route or while laying over) from OHLE as well as the third rail where these exist.

 

[Bald Rick]

As the current standard timetable only has 14 min turnaround at Ashford and 6 mins at Eastbourne there is no time for layover charging without using extra units

The current timetable. Not the future timetable. Besides, there’s 20 mins layover charging plus the 1h20 in each cycle the unit is on the juice (for which it would be drawing full power for rather less than half that). Even with the current timetable, in a 3hr cycle, it would have at least an hour charging at full power, another hour or more charging at lower than full power, and a fair bit of regen in the mix too. More than enough.