Great Western Coffee Shop

From The Telegraph (http://www.telegraph.co.uk/news/2017/08/30/saltwater-proof-trains-run-brunels-storm-battered-great-western/)



Not sure if we've had a Dawlishable specific thread on the 80x series?

Article goes on to get a bit confused between HSTs which the 80x series is replacing and Voyagers which , as I understand it, are the trains that have particular salt water problems and are not yet being replaced.

Not one 80x has been actually tested in anger at an angry Dawlish yet though...

I did wonder ...

They can, and obviously should, test with gazillions of gallons of seawater, but they don't have gazillions of years of time to leave it, rinse and repeat.

But I've learnt one thing about the HSTs and I presume diesel-electric trains in general:
I did not know that regenerative braking had been around so long and in non-purely electric vehicles.

It appears that the article has now been amended/corrected and states that the 40 year old High Speed Trains are not affected and it is the newer Voyagers that are

....didn't realise that Dawlish was in Somerset.... ::)

I've trotted this out a few times so my apologies, but Hitachi need the 80x's to be seen as a success in order for their UK and European business to grow. Having trains that don't work properly when it gets a bit stormy would be a major embarrassment, so you can bet your last Yen that a lot of time and energy will have gone into making them as Dawlish-proof as possible.

Given that Japan has some fairly dramatic coastal railways (many electrified), and rather extreme weather from time-to-time, I would have thought that Hitachi would have many decades of experience in producing trains that can withstand exactly the sort of conditions that they would encounter at Dawlish (not to mention the rather damper and colder Scottish climate).

It's in the IEP specification that the trains have to work while being exposed to salt spray...

...and in other news, cricket pitches are specified to be 22 yards long. (Now that statement is certainly a hostage to fortune!)

I don't think this will condemn me to the Pedantry thread, but it is not regenerative braking. That term is used when the power generated by braking is returned to the electricity supply. This is rheostatic braking, where the electric motors of the train are in effect used to heat up a few industrial sized electric heaters on the roof, the heat being dissipated into the air. Both are examples of dynamic braking. True regenerative braking is only possible when the train is attached to an electricity supply.

Resistors also rarely have moving parts...

... unless they are variable resistors or potentiometers...  ;D

I'd actually learnt this from other sources in between my post and yours, but thanks. And it's too well explained to be mere pedantry!

Makes a change - thanks!

Dynamic braking that is using traction motors as generators and dumping the energy in to resistors is not new, London Underground C60 stock used it, the BR class 76 and 77 on the Woodhead route used it, difference with the class 76  77 was the resistors were located in the substations. 

What is newer is regenerative braking, this is where the energy is dumped into the traction power system or where necessary on board resistors, class 387 have regen braking although I am not sure if this has been enabled for use on the GW yet.

As for Dawlish given its a known problem with the XC units I would have though Hitachi would have come up with a workable answer.  The sea spray from Dawlish may not cause an immediate issue at Dawlish for the braking resistors, its when the train travels a few hundred miles on and its raining what had become dry salt becomes very conductive water.  Also salt water is highly corrosive especially where dissimilar metals are used, one of the worst combinations being stainless steel and aluminium. 

The term 'regenerative braking' was not actually new with its recent descriptive usage in the (British) rail industry though?  Google "regenerative braking" and you'll find reference to it in descriptions of trolley buses and milk floats, cranes and other machinery; and indeed in descriptions of modern road vehicle hybrid technology.  

Although people seem to get into heated :) discussions about what (railway vehicle) regenerative braking is, I would put the case that Voyagers still have regenerative braking. Present day (railway) usage seems to expressly use the term 'regeneration' for when the energy is passed back into the supply system, but IMHO there is no technical problem with describing the Voyager set up as regeneration.  The difference in where the produced electrical energy ends up is just a point of detail.

The historic problem in the DC supply area (hinted at in the earlier mention of Woodhead locos) is that the supply rectifiers were (and I think generally still are) usually one way devices.  They could not pass energy back to their supply side. Effectively DC trains regenerate into the third rail only, but because it is a wide area operating with supplies in parallel the energy can be dissipated into other trains that happen to be motoring.   AIUI DC testing has usually taken place in outlying areas, because the problem comes when there are no 'motoring' trains to absorb the power.  If the third rail voltage rises too high the energy must then be diverted into onboard resistors.

The AC system is always supplied by transformers, and these are inherently two way devices, and regeneration is straightforward as long as the protection devices can be altered to allow for the two way power flow.

By the way, the Telegraph's brief explanation from that linked article earlier:

"...fault in which their brake resistors, which dissipate energy during braking and turn it back into electricity, etc"

is fundamentally back to front anyway,  It should be something more like:

"...fault in which their brake resistors, which dissipate electrical energy generated during braking by turning it into heat, etc"

Paul

There are few other issues with regen on the third rail system, the rail voltage must not exceed 1000V Within the London area the rectifier voltage was set to 650V and regen braking not permitted this was due to the interfaces with LUL now that all of their older stock has gone (C and D stock) NR are increasing the rectifiers voltage to 750V.

Another problem is balancing the regen braking against the rectifiers, NR rectifiers are at a set output, that is there is no voltage regulation so if the rectifier offers a lower source impedance than a trains regen the train will switch its regen to on board resistors. 

The best solution to DC rail system use of regen braking would be on board storage (eg batteries)


The "Distance" protection relays need to have the phase angle set correct to around 70 deg.  Generally the AC regen breaking works better than DC because there is a bigger receptive load ie the National Grid.

So is there anything left in that article that is actually (correct) news