A quick question about regenerative braking

[GingerSte]

I've just been reading about regenerative braking on Wikipedia (just through interest), including its potential and limitations.

According to the article, approximately 17% savings on energy can be acheived. I realise that the technology is in it's infancy, but are there any ways this can be improved? Does this vastly improve the case for electrification? Would newly electrified railways give better figures (assuming that the electrification would be designed to allow regenerative braking, rather than having to be retrofitted)? Are there any good papers/articles that you could point me to?

Also (and this is going to be controversial on a railway forum), could this technology be applied to buses by means of OHLE? I know it's harking back to the good old days of trolleybuses! I imagine it wouldn't be suitable for all routes, but would be suitable for things like major radial routes out of large cities. Battery powered buses could travel under the wires for the major parts and branch off onto smaller roads. I realise, though, that buses already use some of regenerative braking technology already (except for the OHLE part).

I was just wondering. It just seems like a good way to reduce our energy requirements.

 

[John Webb]

Regenerative braking has been around for many years, particularly in places with many hills, such as Switzerland!

Regarding trolley-buses, I asked the question when I was riding on one as as young teenager - there was a technician travelling on the same trolley-bus who explained that it was possible to do it, but switching into regenerative mode would cause a sudden deceleration sharper than a sudden brake application and would upset the passengers.

 

[WatcherZero]

yes you can double its efficiency to around 40% if instead of returning it to the wires the trains have internal batteries, but that adds weight and cost.

 

[CosherB]

The old Manchester - Sheffield 1500VDC locos on the erstwhile Woodhead route had it back in the 1950s. It is much simpler with DC of course, though modern electronics makes it entirely possible with AC (where the phase has to be matched).

 

[wheel tapper]

regen braking in modern day electrostar units only works when there are more then one unit in the same section. If no other unit is in the same section then no regen braking will take place just dynamic braking. modern electrostars use brake blending using regen, dynamic and friction braking.

 

[swt_passenger]

regen braking in modern day electrostar units only works when there are more then one unit in the same section. If no other unit is in the same section then no regen braking will take place just dynamic braking. modern electrostars use brake blending using regen, dynamic and friction braking.

Your point is perfectly valid for DC Electrostars, but on AC they do the other thing...
--- old post above --- --- new post below ---

yes you can double its efficiency to around 40% if instead of returning it to the wires the trains have internal batteries, but that adds weight and cost.

Very dependent on the stopping pattern though. A suburban train spending as much time braking as accelerating will give completely different regen ratio to a Euston - Glasgow service. That's what brings the average right down.

 

[wheel tapper]

this is exactly what happens on ac units as for dc unit dynamic braking works by turning the traction motors into generators the voltage is then dumped across resisters the same happens for ac unit in dynamic braking but when the unit is in regen mode the voltage is passed back through the transformer and up to the oh.
to try and simplify things a bit on modern ac eletrostars 25kv oh picked up goes to transformer then is converted to dc then is converted to three phase ac for the traction motors. during dynamic and regen braking the motor now becomes and generator the three phases are converted back to dc in dynamic this is dumped across a resistor during regan the dc voltage is converted to ac goes to the transformer then is passed back to the oh if the voltage falls below 25kv. older stock ie 313 the traction motors are dc therefore they do not have regen braking during there dynamic braking a small reversing voltage is applied to the field winding of the traction motor therefore trying to reverse the motor will slow it down but the drivers don't like it because it doesn't really work that well.

 

[DaveNewcastle]

According to the article, approximately 17% savings on energy can be acheived.

yes you can double its efficiency to around 40%

We need to be careful to compare like for like.
No matter how EFFICIENT the regenerative breaking (and energy storeage and transmission) systems, that can never do more than reduce the TOTAL POWER requirement of a vehicle by a small amount.
As long as the greatest requirements for energy are in overcoming aerodynamic resistance, inertia, accelleration and climbing gradients (and ignoring all auxilliary power requirements), then any energy captured from braking can only be produced from decelleration. And the energy derived from decelleration isn't going to produce any more than is required for accelleration (on average).

As swt_passenger rightly points out:
Best results come from frequent start/stop journeys where the energy of each stop can be re-used in the corresponding start.
Same for hilliy journeys where fall-energy can be used to assist climbs.
Worst results from long non-stop fast journeys on level ground when nearly all the energy is required to overcome air resistance and hardly any is produced from breaking. Even a hypothetically 100% efficent regen system on such a journey will provide virtually no overall saving.

 

[WatcherZero]

Your thinking too much about it, its 40% of a trains kinetic energy recovered while braking, doesnt matter how much it stops or starts.

 

[theblackwatch]

As a reminder to people, please post in a way which is consistent with "normal writing" to ensure it is easy for people to read and understand - huge sentences with no punctuation are not easy to follow. Thanks.

 

[jopsuk]

Regenerative braking has been around for many years, particularly in places with many hills, such as Switzerland!

Regarding trolley-buses, I asked the question when I was riding on one as as young teenager - there was a technician travelling on the same trolley-bus who explained that it was possible to do it, but switching into regenerative mode would cause a sudden deceleration sharper than a sudden brake application and would upset the passengers.

With modern electronic control this should be far less of a problem- after all, even F1 cars were using regen braking last year (and will be next) there was apparently a slight change in the way car slowed as they went onto mechanical brakes (they had/will have relatively small capacity in the KERS) but that's in an extreme vehicle- in a bus it should be less noticeable.

 

[John Webb]

With modern electronic control this should be far less of a problem- after all, even F1 cars were using regen braking last year (and will be next) there was apparently a slight change in the way car slowed as they went onto mechanical brakes (they had/will have relatively small capacity in the KERS) but that's in an extreme vehicle- in a bus it should be less noticeable.

I quite agree, but I was talking about some time in probably 1958 or early 1959 on a 696 trolleybus heading from Welling towards Woolwich not long before they were replaced with RT buses. I'd heard about transistors but it was a few years before I learnt about other 'solid-state electronics' and saw them being introduced to the railways.