Our two electrification systems

[MK Tom]

Bit of a vague topic this, but I mainly want to discuss 750V DC third rail electrification and what people think its future holds. Does it have a place on a modern railway network? Over the last 10 years we've seen the North London Line replaced with 25kv AC overhead, we've seen wires appear at Ashford and in the next decade the wires will meet the third rail network again at Reading. As electrification expands overhead and third rail will keep coming into contact with each other - so is there any chance of any sizeable third rail lines being converted to overhead? The other point of course is the 100mph maximum speed third rail imposes - it's limited the potential of lines like the Brighton Main Line and the SEML. If the West of England Main Line were to be electrified, which system would be used? I know NR have a policy that says extensions only for 3rd rail, but what is the exact wording of that?

Sorry to ask a million questions at once, hopefully the conversation that ensues will throw lots of light on it and be of help!

 

[MidnightFlyer]

The SWML is electrified third rail and has been for decades...

 

[Smudger105e]

.The other point of course is the 100mph maximum speed third rail imposes .!

I was told some years ago that 3rd rail is able to take higher speed running then overhead. A pantograph bouces on the wires at high speed, and pressure cannot be simply applied as this would lift the wire. You can appaly a lot of pressure to the third rail before causing problems...

 

[Old Timer]

Under the Electricity at Work Regulations new third rail systems have been banned from further use. Extensions to existing routes may be made with the agreement of the ORR.

In comparison with OHL, third rail is not particularly efficient electrically, and it requires a lot of heavy duty electrical switch gear and power supplies which make it vastly more expensive to construct and operate.

 

[yorksrob]

I must admit, bearing in mind the number of trains and the distance of stations on routes such as the BML, I'm not sure how much scope there is for 100mph+ running on the Southern even with overhead.

 

[MK Tom]

The SWML is electrified third rail and has been for decades...

Sorry I meant the West of England Main Line (the one to Salisbury etc)

 

[ushawk]

I think its already been reported that it would be incredibly expensive converting 3rd rail to OHL and then you need to convert all the stock for AC running (granted its not that hard for 377s but it still takes work). But why should this happen when there are plenty of other routes in the UK which need electrifying but arent.

With 3rd rail, it should only be used for "filling in" the diesel islands in the south or adding extensions to the current 3rd rail network, if there was to be any, all other lines should be OHL - but done decently.

Edit - the only places on the BML where 100mph running could properly be used is the Brighton Expresses and the Gatwick Express.

 

[Holly]

Three systems
750V DC overhead (Manchester Metrolink etc.)

 

[OxtedL]

Three systems
750V DC overhead (Manchester Metrolink etc.)

If we're going down that route, don't forget 1500V DC overhead on the Tyne and Wear.

I don't think this is relevant to the thread however, which appears to be about the two systems widely used on the rail network.

 

[swt_passenger]

Edit - the only places on the BML where 100mph running could properly be used is the Brighton Expresses and the Gatwick Express.

The BML goes to Bournemouth though...

...and didn't we have an extensive thread on conversion of the third rail to OHLE some weeks ago when the RSSB announced it was a good idea to start at Weymouth and work towards London?

I'd provide a link if the search engine could find it...

 

[ushawk]

Sorry, meant the Brighton Mainline, maybe should have a better abbreviation

 

[yorksrob]

Edit - the only places on the BML where 100mph running could properly be used is the Brighton Expresses and the Gatwick Express.

And even then you've still got a lot of trains calling at Clapham Jnc and East Croydon sharing the fast lines.

 

[Yew]

If we used 25kvac on third rail conductors, could it allow higher speed running (and less wires falling down) than current ohle?

 

[mumrar]

I was told some years ago that 3rd rail is able to take higher speed running then overhead. A pantograph bouces on the wires at high speed, and pressure cannot be simply applied as this would lift the wire. You can appaly a lot of pressure to the third rail before causing problems...

Well, overheads have been used to power a train doing well over 300mph, don't think third rail's come close to that.

 

[507 001]

Isn't the reason for 100mph only something to do with the shoe beams and mounts not being able to withstand the pressures put on them at 100mph+?

 

[Zoe]

Sorry, meant the Brighton Mainline, maybe should have a better abbreviation

VTB is a good one.

 

[jopsuk]

as I understand it, the speed-limiting issue with 3rd rail is the "ramps" at the end of each conductor section. As far as I know, there's a "high speed" and a "low speed" varient of the ramp- because at low speed full contact ASAP is required, whilst at high a gentler "hit" is better- but even so, that's where the problem is.

Think there would be insulation issues with having 25kV AC at ground level. Certainly safety issues for track workers/depots.

As far as I'm aware, Network Rail has a sort-of aspiration that one day it might be nice to take the Southern region to 25kV OHL. This is, though, a very, very long way down the priority list.

Linear induction allows delivery of power and traction without contact and without relying on railhead adhesion- it's what's used for maglev, but can be used for "conventional" rail as well

 

[yorksrob]

I always count BML as the Brighton mainline. As in BML1, BML2 (proposed).

 

[WatcherZero]

NR is considering beginning to replace 3rd rail in the south with overhead when the 3rd rail comes up for renewal in about a decades time. Its really not suited to outer suburban services with the power loss due to lower voltage, need for about 5x the density of transformer stations and problems with under voltage supply to nearby smaller trains when a long 100mph train is passing through the area as its drawing too much power. Its also not really feasible for 3rd rail to supply trains going over 100mph, being unable to supply enough juice.

Back to the two types, Merseysides 3rd rail network uses a different shoe alignment, I believe theres still a good chance of 3rd rail being expanded there as it doesnt suffer the same problems (train length and high speed).

 

[Zoe]

I always count BML as the Brighton mainline. As in BML1, BML2 (proposed).

I certainly wouldn't use those as BML1 is Waterloo to Northam with BML2 Northam to Dorchester.

 

[Eagle]

The fastest speed any third-rail train has done was 108 mph a 444 on the Hampshire part of the SWML. I think they are capable of being made dual-voltage and could probably be upgraded to proper 110 mph like their 350 cousins.

Interesting question: if it weren't for the third-rail 100 mph limits, which bits of the south would be suitable for 110 or even 125 running? (In fact 125mph units already work the SWML, of course, but the limits are 100.)

 

[507 001]

The fastest speed any third-rail train has done was 108 mph a 444 on the Hampshire part of the SWML. I think they are capable of being made dual-voltage and could probably be upgraded to proper 110 mph like their 350 cousins.

Interesting question: if it weren't for the third-rail 100 mph limits, which bits of the south would be suitable for 110 or even 125 running? (In fact 125mph units already work the SWML, of course, but the limits are 100.)

Didn't a 442 go faster than that at one point? 110 iirc?

 

[Eagle]

Nope, 108 is the world record. And I mean world.

 

[ole man]

What speeds did or do the Class 395 do over DC?
And On the old channel tunnel route from Waterloo?

 

[Eagle]

What speeds did or do the Class 395 do over DC?
And On the old channel tunnel route from Waterloo?

They were running off the third rail, so it can't be more than about 100.

Of course, a Voyager might have broken 110 in the southern region (it's not running off the third rail), that's feasible.

 

[Peter Mugridge]

Nope, 108 is the world record. And I mean world.

I think I need to dig into my photo albums - I know I have a picture somewhere of a REP speedo with the needle fully against the stop pin...

 

[GarethW]

The fastest speed any third-rail train has done was 108 mph a 444 on the Hampshire part of the SWML. I think they are capable of being made dual-voltage and could probably be upgraded to proper 110 mph like their 350 cousins.

Interesting question: if it weren't for the third-rail 100 mph limits, which bits of the south would be suitable for 110 or even 125 running? (In fact 125mph units already work the SWML, of course, but the limits are 100.)

I thought the 108 mph was the 442??

Certainly Wikipedia seems to think so and I remember the record being broken soon after the Wessex Electrics started running on the SWML back in the late Eighties.

Unless it was subsequently broken again when the 444s were introduced but I think that unlikely what with the modern concern for 'ealth and safety.

 

[MK Tom]

I'm pretty sure the 108mph record was set by the class 442. My driver's eye view of the Weymouth line seems to think so.

What form do people think a potential electrification of the West of England Main Line should take? I'm not suggesting one's likely, it's just a great example of a line that could be the focus of a debate between the two systems. It's a long line but does have a small amount of 750V DC out to Basingstoke. Personally I'd want to see it wired to match with the GWML and not give the south west two systems. Would it be practical to wire though east of Basingstoke alongside the existing third rail? If not what then?

 

[Eagle]

I'm pretty sure the 108mph record was set by the class 442. My driver's eye view of the Weymouth line seems to think so.

Yeah you're right. Got the two confused.

 

[Frosty]

Track access for maintenance / faulting is becoming a premium and I'd imagine over head lines give a greater flexibility than 3rd rail