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Old April 24th, 2017, 11:43 PM   #61
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In any case, the relatively linear staggered profile of the fourth derivative of movement (eg derivative of acceleration) 0layd a significant role on the fact the average human feels much more comfortable on a train than a bus starting or stopping
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Old April 25th, 2017, 12:21 AM   #62
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Compared to what? Because in reality they aren't: The latest generation TGV power cars as used for the POS and 2N2 models 'only' have a 4640 kW power rating per car, whilst there are several current locomotive models with a 6400 kW power rating.

In fact realise that on a German Neubaustrecke with a 250 km/h limit an ICE2 would have a hard time beating a Railjet, given that most German cities aren't that far apart. A Railjet would accelerate much faster to it's 230 km/h top speed, helped by it's 6400 kW, whereas the ICE2's 4200 kW will need more distance to get to 250 km/h.
Technically speaking the railjet is just an upgraded ICE2 trainset ... reusing the good old 1216/1116 of course.
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Old April 25th, 2017, 06:56 PM   #63
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With the common in Europe 22,5t maximum axle load pretty much any modern electric loco can reach the maximum possible tractive effort of around 75 kN per axle, regardless of it's maximum speed. A German class 101 or a Taurus is just as happy pulling a passenger train at 200+ km/h as it is pulling a 'heavy' freight train at 80 km/h. A German class 145 can be used for passenger trains.
What about the 75kN per axle if to consider max tractive effort vs continuous? It is confusing. For example, for how long time can it be used; for acceleration from 0 to 230km/h Yes? And for hauling a 3000t freight train up from a steep slope for 20 minutes, rather Not?
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Old April 25th, 2017, 07:02 PM   #64
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1.2m/s2 in regular operation could be tolerated in long distance trains
2.5m/s2 is the usual value considered acceptable for emergency braking ... wich in urban transit is put into effect in daily basis in many systems (especially in light rail/tramway usage) so I put it there.
Wow 1.2m/s2 seems to be quite rapid for long distance trains. I thought for long distance 0.6m/s2 and suburban 0.8m/s2

But which value should be considered for keep the timetable under worst scenario, I mean when the conditions are very bad e.t.c leaves/mist on railhead, 0.5m/s2 or 0.4m/s2 maybe?
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Old April 25th, 2017, 08:29 PM   #65
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What about the 75kN per axle if to consider max tractive effort vs continuous? It is confusing. For example, for how long time can it be used; for acceleration from 0 to 230km/h Yes? And for hauling a 3000t freight train up from a steep slope for 20 minutes, rather Not?
Those 75 kN per axle are available up to the point where maximum power is reached. For most modern locos that would be at around 60 km/h. From that point on power would remain constant and therefore tractive effort would drop with the increasing speed. As I calculated earlier to 25 kN per axle @ 230 km/h for a Taurus, for instance.

An electric loco is only limited by a maximum current and its cooling capacity. As long as the transformer oil (for AC locos), electronics and motors don't get to hot they could theoretically keep on going indefinitely. Most published figures are in fact continuous ratings. Some locos can even deliver more than that for shorter period of time.

Examples:
Siemens ES64U2: 7 MW for 5 minutes, 6.4 MW continuous.
German class 103: 12 MW for short periods, 7.78 MW hourly and 7.44 MW continuously

You wouldn't want to pull a 3000t train up a steep slope with a single loco. When operating at the edges of the performance envelope any loss of traction would bring the train to a halt very quick. It would also be very slow, which may not be practical if you're running only a few minutes ahead of the next high speed passenger train.
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Old April 26th, 2017, 02:41 PM   #66
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Originally Posted by M-NL View Post
Those 75 kN per axle are available up to the point where maximum power is reached. For most modern locos that would be at around 60 km/h. From that point on power would remain constant and therefore tractive effort would drop with the increasing speed. As I calculated earlier to 25 kN per axle @ 230 km/h for a Taurus, for instance.
Yes I got it, expressed myself wrong

As my education is IT, my physics is not the best...
I wrote a piece of code for calculate acceleration 0-230km/h, some drag is added

Vectron + 6 viaggio-comfort coaches
tare + conventional load 426,1 tons
starting tractive effort 300kN
distance for acceleration it gave: 10,4km

Vectron + 4 viaggio-comfort coaches
tare + conventional load 312,9 tons
starting tractive effort limited to 250,3kN
distance for acceleration it gave: 7,4km
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Old May 2nd, 2017, 12:36 AM   #67
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Wow 1.2m/s2 seems to be quite rapid for long distance trains. I thought for long distance 0.6m/s2 and suburban 0.8m/s2

But which value should be considered for keep the timetable under worst scenario, I mean when the conditions are very bad e.t.c leaves/mist on railhead, 0.5m/s2 or 0.4m/s2 maybe?
I'm talking about braking and not acceleration of course. One would need a very different technology to achieve those accelerations all the way up to 320km/h ... nowadays we get sluggish HST trains precisely because they only get one speed/shift ... if they aplied mechanical/hidraulic speed shifting we could have greater (theoretic) accelerations available.


But I prefer another aproach to very high speed ... conventional rails leading onto MAGLEV HSR corridors where the wheels simply lift hidraulically from the floor above a certain speed. And gone be the HSR hardware ...
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