DART+ (DART Expansion)

There's only marginal advantage, for a very high cost, in replacing a 1500 V DC system with 3000 V. It won't happen.

The only realistic alternative was to switch DART to 25 kV AC to match what will most likely eventually be used on the longer distance network, but even that poses insurmountable problems. The first problem is that it makes the DART trains slightly heavier and slightly more expensive. Plus you have the cost of replacing the current OHLE. The bigger issue would be operational, though: you'd have to completely close the DART lines to do that voltage change, and because existing DART stock can't use AC, it immediately becomes obsolete, reducing your capacity and resilience overnight.

Basically, 1500 V has the advantage of incumbency, so as the electric local network expands, it will use that voltage. Higher voltage is still better for long distance use, but that doesn't prevent inter-city trains running on 1500 V lines: these trains are all available in dual-system versions that allows them to operate on 25 kV or 1500 V: we're not the only country to have different line voltages; actually, having all lines in a county on the same electrification system is the exception, not the rule.

DC lines over 3000 V are a very new development (the electronics needed to efficiently produce DC at this voltage did not exist until the 1980s). They might be an option here, especially as mainline electrification isn't happening soon, but again, operational concerns are against such a choice.

That's because we would still need to interoperate with NIR, which is likely to follow UK practice and use 25 kV AC. If we decided to use HVDC, say 11 kV, for long distance services, then Connolly-Belfast trains would end up being "special" again as they'd need to support three voltages: 1500 VDC, 11kV DC and 25 kV AC. In pure technical terms this is not an issue, but we're only now getting away from the need to have special stock for Belfast (when both sides adopt ETCS): it'd be a shame to have to go back to that situation.

I'd imagine the Cork fleet will basically be the Belfast fleet with a different seat mix, unclear if the contract includes a broad framework order option to save hassle with tendering again, assuming the fleet works out.

Standardisation between commuter and IC trains isn’t that desirable, as they have very different patterns of use. It's much better to standardise equipment based on role: i.e., have one type of intercity EMU and one type of commuter EMU per generation. That way, stock can be added or moved from place to place easily.

It would be better for CACR to be 1.5 kV DC, as that would allow for common commuter stock (the Alstom X'Trapolis DART trains at 1500 V DC) everywhere in the country. Basically, your suggestion of using extra framework purchases, but without the need for modifications.

DC is better suited to a railway that has trains stopping and starting regularly - note how nearly all of the world's metros run on DC, even those built in the late 20th century. The use of DC means that the trains are a little lighter, more space efficient, cheaper and less complex than if they were using AC (AC trains need transformers on board to reduce the line voltage down to something the traction motors can use). The disadvantage is that the lower voltage means that more substations are required for a given length of track, but this is an acceptable compromise on small-area networks - it also increases the resilience of the network, as a single substation fail won't black out a huge section of the network.

Inter-city trains will be converted to dual-voltage once there's any electrified mainline for them to run on, but there are sections of track shared by intercity and commuter services: CACR includes the Mallow-Kent mainline, so that will need to be electrified too, and probably before the main Cork-Dublin line. Your choice is between making commuter trains dual voltage, or intercity trains dual voltage (ripping out the DC network and making the whole country AC is a non-starter), and the cost savings are in keeping the commuter trains as simple as possible - they do the most trips, and unlike intercity units, they don't cruise, so can't use momentum to compensate for higher weight.

Incidentally, 1500 V DC trains operate at up to 250 km/h in France; in an Irish context, where we're targeting 200km/h and not aiming beyond 250 km/h ever, there's no speed penalty with using 1500 V DC. (Anything above 250km/h needs higher voltages, which until very recently has meant using AC).

It may even make sense for all of the final approaches to stations to be electrified at 1500 V DC, as that would allow any of the tracks to be used by both “DART” and Inter-city stock.

I think goingnowhere was referring to Cork’s intercity fleet, not commuter.

With regards to enterprise traction, “The next generation Enterprise trains were initially described as tri-modes, but Railway Gazette International understands that they will primarily be electro-diesel multiple-units, fitted with small traction batteries to reduce emissions at stations and depots. The trains will remain largely dependent on their diesel powerpacks in the early years, pending a firm decision on how or whether to electrify more of the route between the two cities.”

https://www.railwaygazette.com/passenger/dublin-belfast-boost-in-irish-timetable-recast/66799.article

Going to be interesting to see what speed (if any) they can change from OHLE <> diesel at. Putting pantographs up at speed isn't the safest thing to do.

Yes, but if delivered before OHLE reaches Drogheda, the transition would be Malahide.

Not sure there's as many entitled lawyers to throw JRs in against DART+ North, but nothing can be trusted here.

If BEMUs are doing the job between Malahide and Drogheda, why would you go to the cost of electrifying at 1.5kV DC? Surely it'd be better just going with 25kV AC and doing Malahide - Belfast in one go.

I was thinking that services north of Malahide would be operated using 25kV AC stock. It is probably more appropriate for that type of outer commuter service. The logic behind using 1.5kV DC is allowing for DARTification but doing that with BEMUs probably negate much of that logic now.

Regarding electrifying being cheaper in the long run, would that also apply to 1.5kV DC over such a distance? The batteries would take us well into the 2030s, really should be electrifying all Malahide - Belfast in one go at that stage.

The RO is one thing but it remains to be seen if that actually happens. The BEMUs make it very easy for the government to put that part of DART+ Coastal North on the long finger (other aspects of it have to happen to facilitate increase in services).

I didn't say anything about not electrifying the line so not sure why you are talking about the cost of the batteries over the next 40 years. My point is that electrification doesn't necessarily have to be to 1.5kV DC. If going with that, probably best to continue it all the way to Belfast and not needing Enterprise trains compatible with 25kV AC.

new carriages and signalling will increase capacity. The carriages have started arriving and the signalling has been installed on the existing Dart line.

Punctuality should (in theory) improve with the new signalling but it'll still be Irish Rail running the system and I don't have much confidence in them. I got the Dart yesterday and the morning train was 10 minutes late and the evening train 15 minutes late. This is after they rolled back their timetable changes to "improve punctuality". Meanwhile on the northside some people were trapped on stationary trains for up to an hour due to a signalling failure.

Why would we try to force NIR to install any 1500 V DC systems? There are no 1500 V mainlines at all in the UK (Tyne and Wear Metro is the only railway of any kind to use it), and NIR has always relied heavily on engineering guidance from other UK operators.

The decision to use 1.5kV DC in the Republic is because we have a significant investment in 1500 V rail that we would lose completely if we changed. From. NIR's point of view, deliberately starting a two system network is stupid.

Also, using 1500V means building a substation every 6-8 km. That's acceptable in a populated area where you've got towns (and stations) at the same kind of distances from each other, but it's not true north of Drogheda. For 25 kV the spacing is over 30 km, which is much more suited to a railway through a more rural area.

Even if we wanted to, we could not "force" NI to install 1500V DC. They have decided in peinciple to go 25kv AC, when the oppostunity arises. The real question is will the DC-AC changeover be at Drogheda or Dundalk (i.e the border). AFAIK, you can change from one system to the other while on the move, as elsewhere in Europe.

The only possible aspect that would 'force' 1500v on NI is if they wanted to electrify their own commuter lines and wanted to go DC, they 'might' choose 1500v so they could borrow DART stock for flexibility and the intercity could use 1500v as specced.

Drogheda is the logical switchover point, nowhere else makes a lick of sense

See my reply above. My point is the Dublin - Belfast line should be considered and either do the whole lot in one voltage or maximise the distance of 25kV AC. Going with 1.5kV DC for one third and 25kV AC for two thirds doesn’t make much sense, particularly as 1.5kV DC is more appropriate for much of the 25kV AC section.