Should it be More Expensive To Travel By Train Rather Than Car

mikey72

robt wrote: »

I have been very bored over the last hour.

Remember this is electric trains only, and I have excluded Eurostar, carriages which are hauled by locomotives, and anything under construction.

Out of 1936 electric trains, 985 have regen brakes which is around 51%.
Out of 7727 electric train carriages (not locomotive hauled carriages), 4282 have regen brakes, which is around 55% (showing a trend that newer trains are longer).

Obviously neither of those are a 'small' percentage.

The brakes would normally return between 16% and 21% of the power the train consumes back into the power system for other trains to use, thus less power is sent into the rail network from the national grid.

What has this got to do with the original post? Nothing. But some people commented on it.

I think you brought it up.
The only regen brakes that contribute anything worth having are on the engine wheels, connected to the train engine. Only the ac systems can put anything back into the system, dc can only be used by a train close by on the same section of track, and they where still trialling some areas last year.
So it's not overly green yet, and emissions are still high.

robt_2

mikey72 wrote: »

I think you brought it up.
The only regen brakes that contribute anything worth having are on the engine wheels, connected to the train engine. Only the ac systems can put anything back into the system, dc can only be used by a train close by on the same section of track, and they where still trialling some areas last year.
So it's not overly green yet, and emissions are still high.

You asked for figures. You got them. Show me some figures that show I am wrong.

I put effort into the post - the least you can do is prove me wrong if you are trying to disagree (which you didn't do directly - you just tried to rubbish what I said by bring up a moot point (below) and talking about last year).

DC regen is only in the Southern region where there will almost always be another train nearby.

mikey72

I was simply pointing out that a lot of the electricity recovered by regenerative brakes was not actually used for anything, just disipated into heating resistors under the train.
More a way of saving on wear on train brakes, then any great green issue.
Figures also give southern rail a fleet of 300 trains, and operating 2100 trains each day.

robt_2

mikey72 wrote: »

I was simply pointing out that a lot of the electricity recovered by regenerative brakes was not actually used for anything, just disipated into heating resistors under the train. More a way of saving on wear on train brakes, then any great green issue.

That is exactly what regen brakes avoid as much as possible, and what normal brakes do.

Figures also give southern rail a fleet of 300 trains, and operating 2100 trains each day.

I'm not entirely sure why you have said this? It doesn't have anything to do with what I have said?

mikey72

robt wrote: »

That is exactly what regen brakes avoid as much as possible, and what normal brakes do.



I'm not entirely sure why you have said this? It doesn't have anything to do with what I have said?

No, normal brakes produce heat by friction, regen brakes produce elctricty by using the engine as a dynamo, so the electricity has to be used somewhere, so it passes through giant resistance windings, that produce heat. Main saving is in friction pads. Not green.

You wanted figures.

robt_2

mikey72 wrote: »

No, normal brakes produce heat by friction, regen brakes produce elctricty by using the engine as a dynamo, so the electricity has to be used somewhere, so it passes through giant resistance windings, that produce heat. Main saving is in friction pads. Not green.

You wanted figures.

Figures that are relevant to something yes. The ones you gave haven't contradicted a single thing I have said.

You are mistaken about regen brakes - even Wikipedia will show you are wrong.

During braking, the motor is changed to a generator. This generator is producing electricity. The electricity created is fed back into the 3rd rail/overhead line under normal circumstances (and obviously some heat is given off).

I'm not actually convinced you know what you are talking about?

thescouselander

Aren't we getting dynamic brakes mixed up with regenerative brakes here? Regenerative brakes do put electricity back into the grid.


robt - thanks for the info, I thought it was interesting at least.

robt_2

thescouselander wrote: »

Aren't we getting dynamic brakes mixed up with regenerative brakes here? Regenerative brakes do put electricity back into the grid.


robt - thanks for the info, I thought it was interesting at least.

Yes - I think he is mixing them up/combining the two.

It is nice that they were appreciated - thank you.

mikey72

robt wrote: »

Figures that are relevant to something yes. The ones you gave haven't contradicted a single thing I have said.

You are mistaken about regen brakes - even Wikipedia will show you are wrong.

During braking, the motor is changed to a generator. This generator is producing electricity. The electricity created is fed back into the 3rd rail/overhead line under normal circumstances (and obviously some heat is given off).

I'm not actually convinced you know what you are talking about?

Don't believe eveything you read on wikipedia.

I am saying that the full regenerative braking system, quite rightly a green system, is in fact being misused by many train operators, who actually are using the system as a dynamic braking system, either internally, or externally to the train, It is improving, but could be done faster, and would give better efficiency, and cost savings, and should, (but probably won't) bring the cost of rail travel down.
It is on your wikipedia, but I've found a reasonable explanation.


Rheostatic Braking
The major drawback with the regenerative braking system is that the line is not always able to accept the regenerated current. Some railways had substations fitted with giant resistors to absorb regenerated current not used by trains but this was a complex and not always reliable solution. As each train already had resistors, it was a logical step to use these to dispose of the generated current. The result was rheostatic braking. When the driver calls for brake, the power circuit connections to the motors are changed from their power configuration to a brake configuration and the resistors inserted into the motor circuit. As the motor generated energy is dispersed in the resistors and the train speed slows, the resistors are switched out in steps, just as they are during acceleration. Rheostatic braking on a DC motored train can be continued down to less than 20 mph when the friction brakes are used to bring the train to a stop.
Before the advent of power electronics, there were some attempts to combine the two forms of what we now call "dynamic braking" so that the generated current would go to the power supply overhead line or third rail if it could be absorbed by other trains but diverted to on-board resistors if not.
In the case of diesel-electric locomotives, dynamic braking is restricted to the rheostatic type. Racks of resistors can often be seen on the roofs of heavy-haul locomotives for which dynamic braking is a big advantage on long downhill grades where speed must be maintained at a restricted level for long periods.

robt_2

I'm quite aware of how both technologies work, I work with them every single day. I was pointing out that it is so elementary that it is something readily available on Wikipedia.

My figures were quite clear in that it differentiated between what does and what doesn't use regen brakes. Maybe I could have phrased it better to what does and what doesn't use regen brakes if available.

Incidentally, the post was for interest only, it was not being used as an argument that it would bring down fares . We all know it won't do that. Just as 'eco driving' on diesel stock won't.