Benefits of 3rd rail?

[CosherB]

Were they the eight 3 car sets built to the same specification as the 92 3 car sets built in 1949 to polulate the newly electrified Liverpool Street-Shenfield service in London?

They were 3-car sets; a motor/brake/driving, a trailer, and a driving trailer, with a pan on the motor/brake/driving. Peak time trains were 2 sets coupled together to make 6 car trains; MBD-T-DT-DT-T-MBD.

Picture here:

http://www.lner.info/locos/Electric/msja.shtml

 

[me123]

There is the aesthetic benefit as well on more scenic lines such as the West Highland Line. People often say that OHLE doesn't really affect the view from the train, and I'd say it was right. There are now OHLE masts between Haymarket and Newbridge Junction which I completely missed at first! But look at this stunning view of Glenfinnan Viaduct.

http://www.faegour.co.uk/images/GlenfinnanViaduct.jpg

Stunning, isn't it? Stick the OHLE up, and you've ruined that view. Not merely for passengers, but also for tourists, walkers and the photographers you've mentioned. I'm all for electrification, but regardless of the green benefits of OHLE, you cannot ruin the West Highlands. The same argument must apply elsewhere.

 

[jopsuk]

Does OHLE "ruin" the view of the scenic mountain railways in Switzerland?

 

[gordonthemoron]

Does OHLE "ruin" the view of the scenic mountain railways in Switzerland?

ofcourse not

 

[CosherB]

Does it spoil the view down the Lune Gorge on the WCML? Of course not. But the M6 wrecks it! And fills it with continuous noise!

 

[Oswyntail]

IIRC, there was a special design of mast to minimise the effect on the view of Durham viaduct

 

[gordonthemoron]

IIRC, there was a special design of mast to minimise the effect on the view of Durham viaduct

there is indeed

 

[Broken Viking]

Hail all!
I must admit that I generally prefer OHLE, but then that might be because I live in a TRE'd area and am probabally overused to it. I wouldn't be surprised if some of the Northerners amongst us have the same view on OHLE.

One thing that I cannot really understand though is why - When OHLE uses much thinner and thus flimsier (And more wind-prone) conductors than TRE - Why OHLE has the higher operational speed? OHLE has been tried and tested at speeds of up to 350mph and it appears to work fine even at those speeds. However pure logic would suggest that TRE should be able to handle at least 10x the maximum speed of OHLE as - Unlike a wire - The traction current rail isn't constantly flopping about in the wind and always maintains it's position in relation to the running rails. Aside from that, the heavier material in both the rail and the pickup shoe should be able to handle a lot more high-speed battering than the flimsy structure of most pantos...Shouldn't it? :?

I remember someone saying above that TRE requires a lot more substations per 100 miles to keep the current consistant, but I'd personally put that issue down to the fact that TRE typically runs at much lower DC voltages and higher amperage than OHLE - As lower voltages are more affected by line attenuation than the 25Kv that OHLE uses.
Aside from the possible risk of arcing between the running rails and third rail - Which could probabally be overcome by insulating the third rail with thick plastic insulation at the sides - Can I ask what there is to stop 25Kv AC being supplied via a third rail insted of a wire?
(I only have a fundamental undestanding of HV electrics, but logic suggests that 25Kv~ should be able to run through a third rail with no issues at all, AND the number of substations required would be 1/2th to an 1/8th of those required for the OHLE equivalent! )

Farewell...
>> Death <<

 

[gordonthemoron]

all those fried tresspassers

 

[Broken Viking]

all those fried tresspassers

I know...It's that and my impression that TRE should be able to handle much higher top speeds than OHLE that means that - Though I prefer OHLE for it's unusual "look 'n' feel" - I consider TRE to be technologically superior and having much more top-end potential than OHLE. That, and the fact that TRE has far less visual impact than OHLE, too... 8)

 

[90019]

You'd have to have much better insulation to stop it arcing.
Also, I think OHLE can cope with higher speeds better because it has some flexibility in it, whereas TRE is completely fixed.

 

[gordonthemoron]

and just think of all the high speed railways around the world which use third rail...........

 

[jopsuk]

With OHLE the pan is in (or should be!) constant contact, with firm postive pressure pushing it against the wire- high speed lines run much higher line tensions to help with this and reduce wire movement. On third rail especially at junctions and stations, the power rail switches sides, has gaps etc. I'd have thought one of the limits to speed would involve the impact as the sprung shoe hits the "ramp" part of the conductor.

Also, the area of the shoe in contact with the rail is much, much higher than between a pantograph and wire. This leads to increased contact friction, so I'd assume wear would be much higher on the shoe/rail. Pantographs of course use "disposable" carbon contacts which can be relatively easily and regularly replaced.

 

[Skie]

3rd does have some benefits, off the top of my head:

No Neutral sections
You can install it in older tunnels without major clearance work
Cheaper to install and maintain

It also has plenty of other downsides, as it is unable to supply enough power for much more than commuter services and the number of trains able to take power from the same section is also limited.

 

[90019]

Cheaper to install

Is it actually?

 

[me123]

I also heard, however, that you need 15 times more substations on 3rd rail, so whilst the basic infrastrucutre is cheaper, the substations would add a lot on to the cost. This is based on an earlier post in this thread.

 

[Skie]

Probably depends on the circumstances and area. If your doing 100miles of TRE through the middle of nowhere it would cost a fortune compared to OHLE due to the need for substation feeds, but 100 miles of it in a dense, built up area would mean less hassle with Substation supply and no need to shift bridges around.

Though its not like there is much TRE expansion going on, certainly not up North

 

[Broken Viking]

With OHLE the pan is in (or should be!) constant contact, with firm postive pressure pushing it against the wire- high speed lines run much higher line tensions to help with this and reduce wire movement.

Ye obviously havn't travelled in the panto car on a Pendo recently then! The second move that I did on my ALR earlier this year saw me sat in seat C18 which is almost right underneath the leading pantograph when heading Northbounde, and the amount of clanging, bumping and "twanging" that I could hear throughout the journey - Even with my MP3 player on and fairly loud - Suggested to me that the catenery on the WCML must be in pretty bad shape! hock:

Also, the area of the shoe in contact with the rail is much, much higher than between a pantograph and wire. This leads to increased contact friction, so I'd assume wear would be much higher on the shoe/rail.

I have wondered on several occasions why shoes are used insted of rollers or wheels - The latter would probabally still give good enough electrical pickup, and there'd be much less friction than with either conventional TRE or OHLE...

It also has plenty of other downsides, as it is unable to supply enough power for much more than commuter services and the number of trains able to take power from the same section is also limited.

I also heard, however, that you need 15 times more substations on 3rd rail, so whilst the basic infrastrucutre is cheaper, the substations would add a lot on to the cost. This is based on an earlier post in this thread.

Hence why I suggested running 25KvAC through the third rail insted of the paltry 630vDC that SWT are currently running on. After all, if a 15mm dia. catenery wire can carry enough current to (Just) power both ends of a 373 efficiently, then a single third rail - With it's much greater diameter and steel density - Could easily carry enough 25KvAC current to power every train on the WCML simultaneously...The third rail itself is basically a whacking great busbar, and has a lot more high current potential than an OHLE wire, IMO...

 

[O L Leigh]

No Neutral sections

No, but there are lots of gaps that effectively do the same job as a neutral section. While it is not impossible to "gap" an AC unit in a neutral section you would have to be either incredibly daft or very unlucky.

You can install it in older tunnels without major clearance work

Not many tunnels have required clearance work to permit wiring. In fact, some are positively roomy inside. After all, when they were constructed there would have been some height allowance made in order to prevent smoke from the engine entering the carriages of the train. Therefore quite a few tunnels have more clearance than is necessary to install OLE.

Cheaper to install and maintain

I think that's a moot point. OLE could easily be made more robust to make it more reliable and less likely to fail, but the basic cost of electrification using OLE compared to CRE (Death: it's Conductor Rail Equipment not TRE) is broadly comparable.

As for Death's ideas of having 25kV AC on the floor, I really can't see that one working. The insulation and shielding required just to stop the juice arcing out would be massive, plus you'd still have the problems of icing and flooding.

O L Leigh

 

[jopsuk]

There is, of course, also non-contact linear induction (including inductive loop supply for control, communication, climate and lighting power). Used at much higher speeds than OHL (maglev), though I belive Moscow has a metro line on tradtional tracks that uses it, amongest others.

Proabably a bit pricy to convert the entire network and rolling stock to it...

 

[90019]

Hence why I suggested running 25KvAC through the third rail insted of the paltry 630vDC that SWT are currently running on. After all, if a 15mm dia. catenery wire can carry enough current to (Just) power both ends of a 373 efficiently, then a single third rail - With it's much greater diameter and steel density - Could easily carry enough 25KvAC current to power every train on the WCML simultaneously...The third rail itself is basically a whacking great busbar, and has a lot more high current potential than an OHLE wire, IMO...

yes, but the OHLE wire is very well insulated, surrounded by metres of air and insulators, whereas TRE is only a few inches from the ground, so you would have to have huge amounts of insualtion around the rails because of the high voltage. You'd also probably have to either move the TRE further away from the rails or insulate the rails and the trains so that it doesn't arc from the 3rd rail to the one next to it.

 

[GB]

having CRE energised to OHLE levels would also prevent staff from doing their basic maintenance due to its close proximity.

 

[O L Leigh]

Oh yeah. Would you want to get down and put "clips" on the line with that amount of juice close by...?

O L Leigh

 

[jas_sl]

It was not meant as a joke or whatever you may have thought it was.

Apologies - I completely misread the original sentence. I must have early in the morning.

 

[coral reef]

With it's much greater diameter and steel density - Could easily carry enough 25KvAC current to power every train on the WCML simultaneously...The third rail itself is basically a whacking great busbar, and has a lot more high current potential than an OHLE wire, IMO...

To me this is quite an interesting proposal, my gut tells me its a terrible idea but I have no idea why! I think the OHLE system employed the world over is the way it is for a reason, i.e. it is close to optimum for the requirement.

CRE would be able to take the power all along the WCML probably, but it would need to be supplied by one hell of transformer the likes of which may not ever have been built, and the national grid would not be able to do that all at one point without affecting the balance in the rest of the grid, and causing local issues in supply.

I don't think you could supply the same power bus from different points up the WCML with multiple transformers, as I believe this would induce problems resulting from slight differences in the phase of the power from the grid at different points, hence the requirement for neutral sections in the standard system. Perhaps this is to avoid galvanic corrosion too.

It could be powered all from one power station, but thats too operationally risky and inefficient, effectively negating the point of the national grid.

But, I'm now more interested than ever to know why they do it the way they do.

 

[CosherB]

I think there is some basic lack of electrical knowledge being displayed on here.

Put 25KV into the 3rd rail, and it'll immedately arc over to anything nearby - the other rails, the ground, passing trains... anything. That's why 25KV is put into overhead lines - well away from everything except passing pans.

Powering a train at low voltage (600V, as is 3rd rail) requires much heavier currents than powering the same train with a high voltage (25KV, as with OLE). That's why OLE lines can be so much thinner than 3rd rails, and why 1500V OLE wires and masts are much heavier than 25KV OLE.

So high voltage reduces the line current required, which also reduces the voltage drop due to resistance over distance. That's why high voltage OLE requires far fewer feeder power stations than does low voltage 3rd rail.

Another advantage of 25KV AC is that it can be easily taken from the national grid - all you have to do is transform it down from grid voltage to OLE voltage. For 600V DC you need to rectify it to DC as well as reduce the voltage right down.

It's all explained by V=IR.

 

[krus_aragon]

Put 25KV into the 3rd rail, and it'll immedately arc over to anything nearby - the other rails, the ground, passing trains... anything. That's why 25KV is put into overhead lines - well away from everything except passing pans.

Reading that made me think of wartime scrap metal drives. "That frying pan of yours could be recycled into a Lancaster bomber..."

 

[tripleseis]

Is there a policy now of not installing any new 3rd rail? Putting down a juice wire to Exeter via Salisbury, on the Oxted line and over the non electrified bits of the North Downs line would certainly put paid to a lot of diesel running, and would I guess be cheaper than putting up OHLE.

The costs can certainly be justified for putting down third rail on these routes as it would be filling in gaps. Opens up the possibility of running dual-voltage electric trains between say Brighton and Birmingham if they OHLE the Reading to Coventry line as well. There's also a case for running a third rail between Reading and Basingstoke but it would probably be more wise to just use OH wires as it would be a continuation on the GWML OHE. Again you have the possibility of running dual-voltage trains between London Paddington and Weymouth, Birmingham and Weymouth and possibily further afield.

 

[DaveNewcastle]

I have wondered on several occasions why shoes are used insted of rollers or wheels - The latter would probabally still give good enough electrical pickup, and there'd be much less friction than with either conventional TRE or OHLE...

No! No! No! That idea only moves the problem of an electrical contact between two moving surfaces elsewhere - how would you then get the current flowing from the wheel to the motors? Through the bearings perhaps, or through another shoe that's in contact with the wheel?
So you get all the arcing and consequential pitting on the bearings and wheel which quickly changes their nice circular shapes into rough, pitted, oxidised surfaces which will only compound the problems. And concentrate thm into a tiny space, which quickly worsens - very quickly. At least with a shoe then one of the surfaces is the rail - spread out over massive distances and not concetrated in a tiny ball bearing!

Hence why I suggested running 25KvAC through the third rail

And again, No! NO! NOO!
Others have pointed out the continuous flashover you would experience at those voltages. (Have you any basic electrical knowledge at all? You want to pass 1000Amps through moving parts?). Rail contractors are expected to keep absolutely everything at about 3 meters distant from live 25k conductors, or request an isolation - limbs get burnt off bodies that get closer. For ever. So what are we proposing? Putting exposed 25k a few mms above the ground? Hmm -
Stations? Train Depot Crew? Level crossings? P/way crew? Snow? Rain?
on exposed 25kV conductors on the ground?
There would be a public outcry just about the loss of wildlife before we started looking at regular the human fatalities!
Really, is there any sense in putting live exposed conductors on the ground other than mass murder and power losses well over 50% ?

 

[Merseyrail]

How expensive are the third rails, in monetry terms? I remember doing Psyshics in school and our teacher telling us they were rather valuable. So much so that apparently Merseyrail keep their third rails turned on on Christmas Day, despite their being no sceduled timetable, just to prevent the local scallys from stealing it! Is that true?

Also when the workmen are working on electryfied third rail lines. How close do they actually get to the rails? Do they have to step over live rails, or do they have specified gaps with no rails where they can walk accross the track? Or do they just turn the rail off on the sections where they are working?