Economically? It depends on many factors (amount of locomotives ordered, etc.). Currently, many last-mile solutions are provided, up to 500 or 700 KW in diesel mode, and there is the (VERY) expensive ALP-45DP as another example.
It is expected that the first large scale dual-power locomotives from Vossloh will start being delivered in UK and in South Africa. The South Africa version will offer both 2.8 MW in diesel and 4 MW in electric mode (practically double the diesel mode, since electrics are rated at the rail, and diesels are rated at the generator input).
The trick is to uncouple the “producers” (catenary, third shoe, diesel-generator, etc.) from the “consumers” (traction motors, train heating, blowers, etc.). This is usually done by using an intermediate DC bus (typically around 1200-1500 Volts), which takes input from the producers, and inverters convert this to suitable currents and voltages. That is done anyway on single-phase electric locomotives, which take single-phase electricity and convert it to DC, then (via inverters) convert that to 3-phase AC for traction motors, etc.
Thanks for an explanation N.F. In Europe, having 4 different main overhead electricity voltages I see this done many times while the train is rolling simply lowering their pantograph before the brake and raising another that suits the voltage there. Obviously this intermediate bus would be much better alternative. Espeacially since many more types of pantographs are actually needed than the existing voltages would make you think. With intermediate automatic bus it would more or less be a question of using the right pantograph for a section of line.
Do I interpret the bus usage right that locomotives would benefit from it?
In the picture one of the multivoltage SBB early TRAXX locomotives, class Re482 in Muttenz, Switzerland in the weather we are now expecting!
Well, you need four ‘producers’ for converting the four different catenary voltages to the intermediate DC link (I think that there are now only two transformers, one AC and one DC for that job, both working with multiple voltages and -in the case of AC- frequencies).
Note also that the four pantographs are used due to different sizes - alpine routes have less wide pantographs than the other countries (I think the continental Europe has 1950mm width, while Alpine routes use 1450mm). Also, some routes want copper contact strips (usually DC routes), hence the need for four pantographs for pan-European locomotives.
Look also at this sample video, where a ‘last mile’ electric locomotive prototype pulls freight when the electric supply failed:
ahem, dc transformers are non-existant. If you want to raise dc voltage, you convert the power to ac and then back to dc, whether you do the voltage conversion with transformers or electronically. If the multi-use locomotive is going to use 750V DC third-rail power, then economics suggests the dc rail for all power input also be 750volts. But the ac can be anything reasonable, with going above 25,000V on the catenary might mean flashover and general insulation problems.
Currently, the only modern USA equipment designed for both dc and ac operation are the MN New Haven line mu’s. The last locomotives were the EP-5 “Jets.” None of the New Haven’s passenger locomotives were desigined for 60Hz AC, only for 25Hz AC.
ahem, dc transformers are non-existant. If you want to raise dc voltage, you convert the power to ac And as we said in the Navy in Electrical and Electronics Prep School, “Don’t sweat AC Battery Week!”
A little more video with details of this rather interesting class:
Amusing to watch them tinker with those touchscreen UIs at nearly arm’s length as the locomotive is moving … and does that little repurposed rear-vision camera show the track that is hidden from view when the driver is seated?
Not quite true in the sense you mean. It is quite possible to build a switch-mode dc-dc converter with power FETs and SiC Schottky diodes that will handle high voltage, and run it at as high frequency as your electronic noise tolerance allows. Note that this does not involve inductive coupling as in a transformer, and does not involve “AC” conversion in the normal sense. In my opinion, if you wanted to take third-rail power (at 600 to 750 VDC) and transvert it for compatibility with a usual-suspect AC locomotive’s DC link, this is a technology I would consider. The ‘conventional’ alternative would be to invert the third-rail DC to either powerline or alternator AC (depending perhaps on whether the locomotive were operating on catenary or diesel power) with the effective frequency information derived from that of the catenary or alternator source.
An “AC battery” is relatively simple to gin up… with two ‘batteries’ or cells and some circuitry … if there was ever a purpose for the thing in locomotive power transmission. There really isn’t; the electricity going to the motors has to be modulated anyway, and if you want science fiction it would be passive transversion from one frequency of AC to a precise, and variable, other frequency not necessarily a harmonic of the first. (Which is what an “AC battery” drive to locomotive AC traction motors would involve, even before considering issues of polyphase motor connections…)
A preconsideration for using high technology is actual need for advanced aspects of the technology. You may have seen the old sailplaners’ joke about the titanium yaw string for hypersonic flight. AC batteries would be more than a little like that…
Such locomotives have long existed in the USA, starting with a group of New York Central units built in the late 1920’s. The EMD FL9’s, built for New Haven around 1959, were also equipped with third-rail shoes and pantographs. The current bi-mode ALP45DP’s as used by NJ Transit and AMT could easily be equipped to run on third rail as well. In France, there are two series of modern diesel-electric railcars capable of working as straight-electrics (on two different currents/voltages) which could also run off third rail if required.
Show me a NYC motor with AC catenary supply. Show me a NYC tripower with an AC transformer. (Cleveland motors, to my knowledge, didn’t have third-rail shoes; the P motors lost their pans when they came to NYC)
We’ve discussed the ‘pantographs’ on FL9s in some detail; they were DC only and ran on elevated rail sections, not wire. The important correction to what you implied: FL9s were never equipped to run off the catenary. While New Haven had locomotives with both AC pans and third-rail shoes (the EP-5s that were recently mentioned) and diesel trains with third-rail (the lightweight trains that were recently mentioned) they never had one with diesel power, AC pantographs, and third-rail shoes all at once. The ALP45s could easily be fitted with third-rail shoes, as was recently mentioned, but none of them are presently so equipped and it is not particularly likely that they will be … for reasons that were recently mentioned.
Remember that a large part of this three-power discussion involves where a locomotive would need compatibility with these three types of power. Basically that’s limited to the New York City area in the United States … and the market even for dual-modes with a defined high-speed capability is sharply limited.
Dave Klepper has discussed a number of potential services that could use a tri-mode locomotive (one of them being a renewal of service from the New Haven line into GCT or NYP with the same trainsets and locomotives) but the practical market for such a service hasn’t emerged sufficiently to justify the capital expense.
Transformer-less boost converters were made with thyristors (SCR’s) in the 1960’s, s an example, the propulsion electronics for the BART trains acted as buck converters for normal propusion and boost converters for regeneration.
One advantage of using transformers for DC-DC conversion is to get galvanic isolation. For locomotives, this would allow use of something similar to a ground relay on the traction circuit on diesel-electric with DC motors.
For power levels used in locomotives, device choice is limited to GTO thyristors or silicon IGBT’s. SiC FET’s aren’t quite there yet as far as current ratings for commercially available packaging Cree’s top line SiC FET module is rated at 1200V/300A. Maximum switching speed for these devices at 800V/300A appears to be around 50 kHz, with the limit set by the module’s heat dissipation rating. The higher switching frequency possible with SiC FET’s should allow for outpt filtering of the inverter, which should not require the use of inverter grade motors.
I do not remember the exact details, but in Europe locomotives have different transformers for AC or DC operation off the catenary (if my memory is correct, DC transformers are heavier than the AC ones).
Note that the catenary DC voltages typically encountered on European mainlines are 1500 and 3000 Volts (plus an amount of variation).
I do not know the details of wiring and related sub-systems for multi-system locomotives which can ‘consume’ both DC and AC voltages, but the weight difference is approximately three to four tonnes for the MS edition. You could ask Bombardier and Siemens for more details.
These are not touch screens (see the buttons around each screen? These buttons control the user interface). The 3-4 screens cab arrangement is becoming the European standard.
The cameras are installed on coupler height (and there is a small light nearby), so the train driver can do easier switching without running from one cab to the other (only PESA has done this, so far).
There are also many locomotives in Europe sporting backward-looking cameras (usually high and near the cab doors), so you can watch the train trailing the locomotive while running. If you see various European cab rides, you might be able to see this in operation (if you want me to find one for you, tell me).
Some of the inverters used on European electric locomotives run directly off the 3kV DC catenary and use that as the DC link voltage when running off AC. By using an “inverter” instead of diodes for converting AC to DC, the locomotive has closer to a sin wave curent draw from the overhead and alo allows for regenerative braking.
The French were using 1500V for the DC link to enable running off of 1500V DC catenary as well as AC.
but an electronic dc stepup of stepdown of voltage still is not really a transfomer which is defined by its use of inductive coupling, and square waves used in such stepup and stepdown can certainly be considered ac, just not sine-wave ac. Similarly, the batteries used to store and regenerae ac are still dc batteries, with the ac resultng from educated switching and/or simple rectification on charging.
I think the market does exist for the through services mentioned, and they would make for more efficient use of Penn Sta. and open up employment opportunities. The LIRR has already expressed a desire to run to Riverdale, and stops serving Lincoln Center and the Columbia U. complex could simplify commutes for many. The idea has been tested and works with the ballgame New Haven - Secaucus NJT-equipped specials. It will be far more feasible when all catenary in the WAshington - Boston area is 60Hz, since MN New Haven div. mus don’t like 25Hz. Now if they had only kept the washboards! Perhaps also the original M-2s?
