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During the entire fair, "Emma", a 87-year-old small two-axle stram loco restored in working order, was shuttling back and forth on the steep access tracks of the exhibition grounds.



*Lunatic*, n.
One whose delusions are out of fashion.

by DoDo on Sun Sep 30th, 2012 at 03:57:13 PM EST
During my travel, I shot photos of all the vehicles which would have been a good illustration for the story on open access competition in the Czech Republic in the diary Rail policy updates.

First, the train of the second private competitor, Leo Express (currently in testing), was exhibited at the InnoTrans. It is a member of Swiss maker Stadler's FLIRT family, with comfortable interior (which gives me doubts regarding whether they can cut out a big enough market share to even be profitable).

I met a train of the first private competitor, RegioJet, in Prague main station. The train is cheaper (used-refurbished Austrian coaches and used Czechoslovak locos re-imported from an Italian regional railway), and they go for low-budget passengers, which would be a good thing save for the side effects. I wonder how'D they survive a recession economically, though. I saw they are utilising the locos in freight service, too.

The incumbent, state railways CD, operates Pendolino tilting trains (photographed through the train window leaving Prague main station):

There are also the international EuroCity trains, including mine (consisting of a loco of Slovakia's ŽSR and 15-20-years-old coaches of Hungarys MÁV-START), wich were to get newer CD trains but are now to be replaced by services ending in Prague:

Those new CD trains were to be hauled by CD's new Class 380, a type made by Škoda with the same specifications as the best West European electric locos, but problems in commissioning restricts them to domestic services as on the photo below. (The future Prague-Vienna-Graz services which CD will run in cooperation with Austria's ÖBB will use Austrian locos instead, which are already approved to cross the border and indeed reach Prague.)



*Lunatic*, n.
One whose delusions are out of fashion.

by DoDo on Sun Sep 30th, 2012 at 03:57:59 PM EST
[ Parent ]
There was one innovation recently reported in Railway Gazette and also shown at InnoTrans which I deemed pretty significant, but too technical and 'under-the-hood' to discuss in the main diary – but I hope the more technically minded will take interest.

Under AC power supply, the electrical system of a modern electric locomotive has the following four basic elements:

  1. the transformer (supplying a higher-frequency AC with a more manageable lower voltage and creating galvanic isolation),
  2. the rectifier (a group of semi-conductors that turn the AC into DC),
  3. the inverter (another group of semi-conductors to turn DC into a variable voltage, variable frequency [VVVF] AC, necessary to regulate output),
  4. induction motors.

Note that 2 and 3 are often in the same box, called the converter; and during braking, their roles are exchanged.

Of these, the part most resistant to size reduction is the transformer: for a defined input frequency and maximum power, its mass and size is pretty much a given. (For example, when Siemens developed a triple-voltage and slightly smaller cross-section variant of its standard 6.4 MW dual-voltage loco, it had to save mass and space on the transformer, reducing power to 6 MW.) Higher frequency means smaller mass. (For example, the first Thalys trains, which had transformers optimised for North France's 50 Hz system, had a limited top speed under 16.7 Hz in Germany.)

Swiss electronics giant is now trialling a new solution that reduces transformer size: ahead of the transformer, there is a second converter, one in which the high voltage is dealt with by switching the semiconductors in series. This converter supplies constant voltage constant frequency AC power, but of increased frequency, to a small medium-frequency transformer. ABB claims that this solution actually creates a better waveform (said differently, less harmonics that disturb other systems), significantly increasing converter efficiency.

The prototype under trial since February is built into a Swiss shunting locomotive, but ABB envisages its primary use as underfloor equipment in EMUs. I think it will be useful to further improve electric locos, too: the weight saved could be used to combine multi-voltage electronics and a last-mile diesel engine (not possible presently), or install a more powerful last-mile diesel engine (those in the first generation prototypes discussed in the diary range between 180-230 kW), or, in combination with permanent magnet electric motors, further boost maximum power (and thus acceleration at higher speeds).

*Lunatic*, n.
One whose delusions are out of fashion.

by DoDo on Sun Sep 30th, 2012 at 03:58:59 PM EST
[ Parent ]
This is standard practice for domestic power supplies now, the 'switch mode power supply' and even some larger power supplies in factories.  I've always wondered whether there was much benefit to the 16.7Hz supply given the larger amount of magnetic material required.

The better waveform thing is probably a reference to power factor correction, which can be added fairly easily to switch mode supplies.

by njh on Sun Sep 30th, 2012 at 09:43:29 PM EST
[ Parent ]
The low frequency of the 16.7 Hz (pre-1995: 16⅔ Hz) power supply is historical baggage: it was meant to prevent sparks on the commutators of early brushed universal motors. However, having a separate railway power supply system does have its benefits: the whole railway grid can be of the same phase, with no need for phase breaks in the catenary. (Rail passengers can notice phase breaks on multiple units with underfloor motors – motor noise stops – or most air-conditioned vehicles – ventilation stops.)

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Tue Oct 2nd, 2012 at 05:10:19 AM EST
[ Parent ]
I don't understand the bit about the phase changes not being required?  Why is it different for a separate supply compared with a grid supply?
by njh on Wed Oct 3rd, 2012 at 02:34:45 AM EST
[ Parent ]
Power supply from large plants and high-voltage lines in the public grid are three-phase, and substations for the supply of the 25 kV/50 Hz grid can connect to either of the phases, and are actually connected to different phases on purpose so that there is a balanced load. In contrast, the 16.7 Hz railway supply system is single-phase.

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Wed Oct 3rd, 2012 at 04:25:13 AM EST
[ Parent ]
sure, but that has nothing to do with 16.7 vs 50.  The railway could choose to use a single phase at 50Hz.
by njh on Wed Oct 3rd, 2012 at 09:57:34 AM EST
[ Parent ]
I wrote about the benefit of a separate railway system after giving the indeed separate, historical reason for 16.7 Hz. The deeper connection is that (1) the idea of a separate railway grid didn't arose because people foresaw its benefits but because the historical need for 16.7 Hz necessitated it, (2) connection to the public grid (with resulting savings in infrastructure investment for the railway) was the main selling point of the 50 ÍHz system at the time of its introduction. If we started today and we'd have a government willing to start major public investment with a long-term view on security of supply (rather than a short-term view on budget cuts), a 50 Hz or 100 Hz single-phase sytem would obviously make more sense, but we already have thousands of locomotives and substations (and power lines) not compatible with that.

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Wed Oct 3rd, 2012 at 12:37:50 PM EST
[ Parent ]
Ok, that makes sense, thanks.  high voltage DC might make more sense today, say 50kV.  DC would avoid the transmission line phase shifts and would have the built in cathodic protection we discussed a while ago.  Of course then you need dc-dc converters everywhere, which is still not quite more economical than transformers for large amounts of power.
by njh on Thu Oct 4th, 2012 at 11:45:17 AM EST
[ Parent ]
By the way: the main innovation in the ABB system with two converters and a medium-frequency transformer is that the first converter deals with an input voltage that is too much for a single semi-conductor. I know little of the inside of home appliances, so I ask: do series-switched semi-conductors with sub-230 V limits appear in them?

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Thu Oct 4th, 2012 at 11:18:15 AM EST
[ Parent ]
No, it's easy to get a single device rated to up to 6kV, here's a transistor rated to 1200V: http://www.suntekstore.com/goods-14005831-igbt_power_transistor_fga25n120_1200v_313w.html
and here's a 6.3kV 7500A monster for train motors:
http://www.infineon.com/dgdl/DS_FZ750R65KE3_2_3.PDF?folderId=db3a304412b407950112b4095b0601e3&fi leId=db3a304325afd6e00126461fd3936974

More typically consumer switchmodes would be 400V mosfets, remember that the peak voltage of 230VRMS is 230*sqrt(2)V = 325V and then you have some overhead to keep the transistor in a safe operating region.  These aren't stacked in the package because then they would become very hard to insulate and need more fancy gate drive circuits:  When you series stack you need an isolated drive for each gate, which in HVDC land usually means a laser through optic fibre onto a mini PV, or a tall transformer.

This is a well known approach (being used for 50 years or more), but I guess this is the first time that the economics have favoured this approach on trains (rather than just a big transformer).  I predict it will become the standard approach within a decade just like switchmodes have replaced transformers for almost all consumer equipment today.

by njh on Thu Oct 4th, 2012 at 12:10:04 PM EST
[ Parent ]
No, it's easy to get a single device rated to up to 6kV

But we are speaking about 15 kV resp. 25 kV here.

*Lunatic*, n.
One whose delusions are out of fashion.

by DoDo on Thu Oct 4th, 2012 at 02:14:57 PM EST
[ Parent ]
Ah, a proper loco

keep to the Fen Causeway
by Helen (lareinagal at yahoo dot co dot uk) on Sun Sep 30th, 2012 at 05:03:14 PM EST
[ Parent ]
I thought you'd say that :-)

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Sun Sep 30th, 2012 at 05:13:11 PM EST
[ Parent ]
Yea, well someone has to say the truth. Buzz-boxes and paraffin cans just aren't as interesting

keep to the Fen Causeway
by Helen (lareinagal at yahoo dot co dot uk) on Sun Sep 30th, 2012 at 05:30:06 PM EST
[ Parent ]

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