Older generation French locomotives

[OVS Flatbottom]

In 1980 the 1500V DC electrification system was indeed technically obsolete.

There might be two reasons, though :

1) if the line to electrify has long underground urban sections - at that time it was still feared that 25 kV AC electrification in tunnels below urban areas might induce unacceptable levels of electromagnetic perturbations. This was still feared when SNCF did RER E underground 25 kV electrification between Magenta and Haussmann Saint Lazare. All other underground lines before that were 1500 V.

2) AC substations take power between two phases of the power grid and therefore create a large non symmetrical load. The power grid must be extremely solid in order to accept that. Possibly Ireland, which is not a very industrial country, does not have a very solid power grid, capable of that. This problem is often encountered when electrifying railway lines in third world countries (I do not pretend that Ireland is third world, just that the absence of heavy industry might be a reason for a weaker power grid). This has even been a concern when first substations for high speed lines have been powered up in France. DC rectifiers in substations pull power from the 3 phases and thus generate a symmetrical load, much easier to handle by the power grid.

Both of those reasons are plausible (there were going to be tunnel sections in later phases of DART - though wasn't Picc-Vic in Manchester already being proposed as 25kV in the early 1970s? - and there was indeed concern about the implications of the full network for the power grid, although I think it was more about generating capacity than anything else).

Having said that, I believe the original Dublin Rail Rapid Transit Study in 1975 recommended third rail. 25 kV mainline electrification was already seen as a possibility in Ireland at the time, but this system was rejected for DART by the consultants on what seemed like fairly flimsy grounds - basically that the weight of on-train transformers was excessive. (By this time 25 kV had been operating satisfactorily on similar services in Glasgow for more than a decade, and I'm fairly sure the choice for Picc-Vic had been made before the DRRTS was completed.) The perception that DC gave better acceleration with the technology then available may also have been a factor.

The decision in favour of third rail was partly because it could coexist with 25 kV overhead (as used to be the case on parts of the North London line) in the event that that system was chosen for mainline electrification. Side- or bottom-contact third rail systems were rejected because it was felt they would impinge on the mainline loading gauge. I believe the switch to 1500 V overhead came in the later detailed design stages (when the prospect of mainline electrification had receded) and was motivated by issues with trespass and flooding, which made third rail less desirable. It's surprising that 25 kV wasn't reconsidered at this stage, although perhaps the clearance issues mentioned by @Gloster were a factor.

Note that I'm basing this on my memories of reading the DRRTS and on what I think was a series of papers published by the Irish Railway Record Society around the time of the original electrification in 1984. There was a comparison of 1500 V and 25 kV done for the current DART extension programme, which can be read at https://www.dartplus.ie/getattachme...Expansion-Rail-Electrification-Assessment.pdf; this gives a somewhat different account (page 18 of the PDF), but I think it conflates the DRRTS with the decisions taken in the subsequent design work.

In relation to the current programme, the assumption seems to be that it'll be at 1500 V; however, future mainline electrification is assumed to be 25 kV. I think the assumption is that 25 kV could be brought right into Heuston by electrifying the fast lines on that system and the slow ones on 1500 V, but any 25 kV electrification of the Dublin-Belfast line will require dual-voltage stock because Malahide-Drogheda is being done at 1500 V; in fact, anything that goes north of Islandbridge Junction will need a 1500 V capability.

 

[mike57]

No one has mentioned the LBSCR 6.6kV 25Hz electification during the 1910 period, it got swamped by the 650v DC third rail system from the LSWR, but prior to WW1 LBSCR had inteneded to electrify to Brighton using this system, which was why they chose it over the third rail option, but WW1 intervened and the rest is history. Had this system extended then overhead electrification would have probably developed more quickly in the UK and third rail would have been restricted to urban areas.

 

[Taunton]

No one has mentioned the LBSCR 6.6kV 25Hz electification during the 1910 period, it got swamped by the 650v DC third rail system from the LSWR, but prior to WW1 LBSCR had inteneded to electrify to Brighton using this system, which was why they chose it over the third rail option, but WW1 intervened and the rest is history. Had this system extended then overhead electrification would have probably developed more quickly in the UK and third rail would have been restricted to urban areas.

It was the same as the Lancaster-Heysham system, and I believe for both the equipment came from Siemens in Germany. It was still being installed on the LBSC in 1914 when this supply route was of course broken. Come 1918, then the 1923 Grouping, and it would have been seen as quite inappropriate to use a German supplier to supplant a home-developed system.

 

[Sir Felix Pole]

In France, the original Tours 'by-pass' part of the LGV Atlantique was electrified at 1500V DC when opened in 1990, but has now been replaced by the new LGV Sud Europe Atlantique section. The propensity of dual-voltage stock and the general lack of investment in the classic main lines means there is little incentive to convert 1500V DC to 25kV AC, but something will have to be done soon. The equipment of the old Bordeaux main-line (electrified in 1938) is fast approaching life-expiry, and some of the OHLE on various Midi lines in the SW had to be hurriedly replaced in recent years after a number of high-profile failures.

 

[Taunton]

Well you just buy replacement 1500V equipment. Compared to 25kV it's actually fairly straightforward, having the transformers and rectifiers in a nice trackside building instead of squashed under the vehicle frame, and there are the full range of manufacturers. The only reason the overhead is life-expired is because, like the GEML recently, it's old.

Gerry Fiennes, in I Tried to Run a Railway, was obviously annoyed with the BR Board who decided to replace his, quite new at the time, utterly reliable GE line 1500V DC system with AC, which came with all sorts of engineering challenges and failures, some notably serious.

 

[randyrippley]

The voltage is incidental to AC development, what was the advance was using the 50Hz frequency from the public supply, to avoid having to have independent switching stations or mechanical rotary converters. The pioneer UK 50Hz installation, Lancaster to Heysham, is sometimes misquoted as 25kV, which it wasn't, it was originally 6.6kV at 25Hz with its own power station, which was as far as had been practical to go when installed (Germany etc use 16.6Hz). The R&D was changing this to 50Hz; the voltage was by the by, and just kept the same to avoid changing insulators and clearances.

It's interesting to read that while the original 1908 equipment on the Heysham line is quoted as 99.6% availability after delivery, the 50Hz experimental units 50 years later brought a range of technical issues, something often paralleled on systems which installed 1500V initially and later changed to the new wonder 25kV Electrification Pioneers (visit-gloucestershire.co.uk)

Just to add to this
The original installation used the Midland's own power station at Heysham, built to power the winches and cranes at the harbour. No National Grid or public power utility at the time. As I understand it, Heysham was the first port in the world to be totally electrically powered. (Note this was a coal-fired power station, nothing to do with nuclear).
The second installation used the town electricity supply from NORWEB, generated at the Caton Road power station half a mile from Green Ayre. The point was to see if railways could be powered from the national commercial supply. The Caton Rd power station was originally built to power the WWI National Projectile Factory shell-packing plant on Caton Rd