Cross-border review of rail network officially launched

Please keep sectarian politics out of this discussion. If the “cross border rail” you’re referring to is the suggested Mullingar-Portadown link, then it’s actually the NI section that is more likely to go ahead without the “south” rather than the other way around. Portadown-Armagh is a much more viable proposition than Mullingar-Cavan, let alone Mullingar-Clones.

Hmmm, yes, that's exactly what the Irish tender says. I was wondering where I got the idea that was more than “nice to have”, then I see that on the UK side, the tender notice ( Enterprise Fleet Replacement Project [Notice] ) it says something slightly different:

Initial traction power will be Internal Combustion Engine (ICE) Battery Electric (using the existing 1.5 kV DC OHLE) with the train designed to transition to a net zero carbon operation during its life by the removal of the diesel power generation for replacement with dual OHLE power supply equipment.

Note the additional word “Battery”, and that 1500 V operation was considered a baseline requirement. That said, I believe the Irish notice on etenders is the definitive one, as IÉ seem to be running the tendering.

I agree that future mainline electrification will be 25 kV AC, but in order to run on OHLE into Dublin on the Northern Line, the Enterprise trains will have to be capable of 1500 V DC operation too.

I expect that all other inter-city electric stock in the Republic will be dual OHLE because otherwise the fleet will be split between “into Connolly” (AC and DC) and “into Heuston” (AC only) sets, as only Heuston will have a dedicated inter-city tracks that could be electrified at 25 kV AC; all approaches to Connolly are going to be 1500 V DC after DART+. That kind of split creates operational problems where none should really exist, so my own thoughts are that in addition to all stock being dual OHLE, the Greater Dublin Area will also be exclusively 1500 V on all tracks so that any OHLE train can be routed anywhere around Dublin under its own power.

One quirk about the Enterprise call for tenders is that the top speed is requested as “minimum 180 km/h”, while the long-term plan for this line is 200 km/h within the lifetime of these trains. Fortunately, most manufacturers’ products fall into categories with maximum speeds of 160, 200 or 250 km/h, so we’ll probably end up with a 200 km/h trainset anyway.

Pretty much that.

Theoretically, the 1500 V DC DART trains could be adapted to be dual voltage too, but this makes each one more expensive and also a little less efficient. Those differences add up when you’ve got so many DART trains, running so many journeys every day, so in practice I’d expect that they won’t do this, and instead any “far commuter” services to be run using dual-voltage EMUs that work at 25 kV outside the “DART area” and 1500 V inside.

Making longer-distance trains dual-voltage has the same penalty as making DARTs dual voltage, but those trains make fewer journeys, don’t stop and start as often and are generally heavier anyway, so the additional “cost” is outweighed by the benefit of being able to run on both OHLE systems.

Having to deal with two electrification systems is down to history: back in the late 1970s, DART was specified as 1500 V DC, not 25 kV AC - both were an option at the time, but 1500 V had some very clear cost advantages for an urban railway with the technology of the time. As there’s so little electrified rail in Ireland, the possibility of replacing the existing DART 1500 V system with 25 kV AC was considered during the early stages of DART+, but it was ruled out because it would have nearly doubled the cost of the electrification project, and worse, it would have needed the current DART service to shut down entirely for months while the existing line was swapped over.

Basically, adding extra a small extra cost to every long-distance train for the next century or so was cheaper than the enormous cost and disruption of ripping out the current DART and re-electrifying it as 25 kV.

Ireland will not be unique in having to use dual mode trains, as there’s several countries in Europe that have two electrification systems within their borders, and of course, rail travel between countries with different systems is commonplace:

The reason supporting two voltage standards isn’t such a big deal is because modern trains use AC induction motors, where the speed of the motor is determined by the frequency of the voltage applied to it. That means that no matter what’s on the overhead line, you’ll need electronics in the train to convert it into something useful: whether you provide two converters or one doesn’t change things hugely. Modern signalling systems have protocols for handling OHLE voltage changes safely.

25 kV at 50 Hz is the preferred system for new rail electrification across the EU, which is why it’s the most likely for us to adopt for mainline use.

North of Drogheda will be 25kV as is the plan with west of Hazelhatch so a dual powered fleet is needed.

The internal DC bus on most modern trains is around 1500v so dual voltage is fairly straightforward

The Drogheda to border section is a great candidate for the first rollout of 25kv AC with enterprise planned to be multi-modal. Means the service isn't dependent on the electrification being in place which mitigates against risk. They should start asap.

Translink already has their feasibility study and outline business case for Belfast to the Border.

In addition to this, would 1.5kV DC also struggle with the power needed for higher speeds? It is a limitation AISRR mentions, although I am not sure to what extend 1.5kV DC would actually affect top speeds.