Transport Infrastructure projects planning status - see post #2 for latest info.

You'd have to assume that by the time all the 3 new DART+ lines and Metrolink are ready to be turned on 'energised' that the above noted proposed ESB transmission line improvements in the Dublin region will be in place to accommodate them.

Not sure though what could be done if there was insufficient capacity, as the extension of the existing 1500V DC system of the DART was picked it seems as it was the simplest, most straightforward and familiar system to use - and seamless extension of existing obviously (for DART), and reduced clearance issues of new line and existing line's wires to structures above (see the DART+ project report below).

Annex-5-1-DART-Expansion-Rail-Electrification-Assessment.pdf

I'm not sure up, or down-powering DART to 3000 V DC or 750 V DC respectively would ameliorate capacity issues from the ESB national transmission grid onto the new DART lines, and would anyway require some/ a few alterations to all the DART sets equipment (especially if going up to 3kV DART).

Alternatively (!) I'm not sure if a change to 25 kV AC for new DART lines would help ESB transmission matters, or make them worse? But 25kV AC was ruled out in the above voltage comparisons document and would probably require new plans and permissions for 1 or 2x 25 kV AC large substations.

For the rest of the country, if there really was a future rail electrification and national grid capacity issue, what rail system would offer the least problems for integration?…

And at least there is the benefit of a clean slate of not having a legacy national rail electrified system to work onto.

According to the press coverage of the 30th anniversary of the service, the current DART operation uses the same amount of electricity “as 6000 homes”. Average domestic electricity use is generally assumed to be 4200 kWh (=4.2 MWh), so the current DART network uses somewhere around 25 GWh of electricity (6000 “homes” x 4.2 MWh each = 25,200 MWh = 25.2 GWh). That’s certainly a “lot” of electricity, but not in the grand scheme of things: it’s less than 0.1% of the total electricity demand in Ireland in 2024, which was 30 Terawatt-hours (30,000,000 MWh).

ESB doesn’t supply that as DC. The DART+ substations are fed with AC at “up to 110 kV” (which most likely means 38 kV or 110 kV, as those are the HV connections ESB Networks offers to customers). At the DART substation, this supply is transformed (voltage lowered) and rectified (turning AC to DC) before sending it onto the train overhead lines. Both of these processes involve some loss (rectification more than transformation).

For an AC train system, the rectification step is not necessary, so loss is lower at the substation… but AC trains are less efficient than DC… except where they aren’t. And that’s the problem: it’s a complex question to answer, because so much depends on the kind of service being run, and what’s already in place.

DC is good for dense urban lines with lots of trains operating at the same time, because it allows for simpler, lighter trains, which is why almost all metros use DC; AC systems do better over long distances because they tend to operate at higher voltages than established DC systems, and there are fewer trains, so the higher complexity needed in those trains isn’t significant (it’s important to realise that voltage is the only thing that determines how far apart you need your substations - 10 kV AC and 10 kV DC have the same loss per kilometre).

Thanks for the info.

I think swapping the DART network over to 25 kV AC operation was ruled out pretty early in the DART+ process. It wasn’t just the cost of re-electrifying the only electrified track in the country, the change would also have created a huge operational headache: changing to AC would instantly obsolete all of the existing DART rolling-stock, and so it would have meant turning off the entire DART for weeks or months while the change was made, then hoping that all the new rolling stock worked when the thing was switched back on.

Incidentally, it’s worth mentioning that “25 kV” doesn’t mean exactly 25 kV: trains designed for “25 kV AC” will work with any AC supply between 19 and 27.5 kV (that’s the steady voltage range, and it excludes transient drops and surges), which is why you see it used even in countries whose transmission networks don’t operate at a handy multiple of 25 kV.

Internally, the trains use induction motors, whose speed depends on the frequency of the AC power that’s fed to them. The source frequency is fixed at 50 Hz (our grid supply frequency), so the train’s driving electronics needs to do a version of that same AC-DC-AC trick to provide fine-grained speed control. That process makes the actual AC source voltage less important than it used to be.

Sorry, should have been clearer that only the first paragraph was replying to you, about how much energy DART uses.

The DC comment is just a habit. I used to write a lot of technical specifications and I learned to never assume that someone else reading what I write will also know what's "patently obvious" to me.. or you. Sorry that it seemed like I was being condescending.. it wasn't the intention.