Why TASS?

[stanley T]

Every other country, to my knowledge, manages tilting trains with differential speed limits and does not go into all this complicated extra lineside stuff.

The justification I have heard is that there are places where clearance is insufficient to allow the full tilt which line curvature would allow. But would not initial runs with testing equipment be sufficient to establish what are the safe speeds - and then Trust the Driver?

The net effect has been to stymie further tilting train use beyond the WCML, see those class 221s with their tilt mechanism out of action. Other places crying out for tilt:
- the MML
- the West country lines. With super voyager type trains London to Plymouth would be 2h30mins, Penzance 4 hours

 

[HSTEd]

.... Trusting the driver like we trust the drive to obey red signals?

TASS Balises are not the expensive part of the system, they are entirely passive standard ETCS balises that are available from multiple manufacturers.

The cost is the testing that you allude to, it requires high resolution gauging of the track and defining where the edge of each line's envelope can be moved to.

 

[ainsworth74]

The cost is the testing that you allude to, it requires high resolution gauging of the track and defining where the edge of each line's envelope can be moved to.

And then tweaking the infrastructure if there's no other way of avoiding it. I imagine TASS itself is probably quite cheap in the grand scheme of things.

 

[The Ham]

- the West country lines. With super voyager type trains London to Plymouth would be 2h30mins, Penzance 4 hours

Timings would be subject to Dawlish not causing problems.

Just by having automatic train doors it would speed up the timetables for those services (about 7 minutes when you compare GW with XC between Plymouth & Penzance). This then leaves the speed improvements of tilting trains needing to make up about 20 minutes between Plymouth and Penzance and 30 minutes (on the current fastest train) between London & Plymouth, which could well be pushing it.

 

[HSTEd]

A better choice for obtaining significant journey time reductions in the South West would likely be electrification (and I discovered that there is a 400kV sub station connected to atleast three "circuits" at Indian Queens, so basing a substation that far west should not be too troubling, it is half a mile from the atlantic coast line) and then using all-axles-motored units to get very good acceleration.

And the low axle weight of such units might allow differentials.

 

[Zoe]

A better choice for obtaining significant journey time reductions in the South West would likely be electrification (and I discovered that there is a 400kV sub station connected to atleast three "circuits" at Indian Queens, so basing a substation that far west should not be too troubling) and then using all-axles-motored units to get very good acceleration.

When this was talked about last time, the concern was that although there is a 400 kV network west of Exeter, it may not be able to cope with the demand that would be placed on it by rail electrification.

 

[notadriver]

.... Trusting the driver like we trust the drive to obey red signals?

TASS Balises are not the expensive part of the system, they are entirely passive standard ETCS balises that are available from multiple manufacturers.

The cost is the testing that you allude to, it requires high resolution gauging of the track and defining where the edge of each line's envelope can be moved to.

Drivers can't be trusted to observe speed limits ?

 

[HSTEd]

Drivers can't be trusted to observe speed limits ?

If they can be in all circumstances why do we have TPWS and such systems?
Surely they would be unneccesary if we were prepared to trust drivers above all else.

 

[Yew]

Dont forget that Pendolinos do go out of guage when tilting, whereas a domestic design would not.

 

[HSTEd]

When this was talked about last time, the concern was that although there is a 400 kV network west of Exeter, it may not be able to cope with the demand that would be placed on it by rail electrification.

The two 400kV circuits connecting Indian Queens to Landulph station alone rate for nearly 2800MVA - According to the National Grid 7-year statement. The two circuits connecting Indian Queens to "Averdlscott" are similarly rated.

I think they would barely notice the phase imbalance caused by the Cornish main line being electrified.

 

[Zoe]

I think they would barely notice the phase imbalance caused by the Cornish main line being electrified.

But it would be pointless to just electrify that part of the GWML, the rest would need to be done or you end up with bi-mode, loco changes are cutting back intercity services. Would you be able to feed GWML and all branches from Exeter to Penzance from just Exeter and Indian Queens?

 

[HSTEd]

But it would be pointless to just electrify that part of the GWML, would you be able to feed the entire line west of Exeter (including branches) from just Exeter and Indian Queens?

There are other 400kV stations west of Exeter, the two obvious Grid Supply Points are Indian Queens and Landulph which is near Plymouth.

That means it is basically two 60-70km stretches, one bridged Indian Queens and Landulph and the other just Indian Queens to Penzance. Power demands of the Looe and St Ives lines which are at distant points from the GSPs are trivial due to relatively lightweight short multiple units being in use.

Given the relatively low traffic densities on the line, especially west of Indian Queens (no freight at all right?) I think it is fairly reasonable to assume that it is doable.

Especially using auto-transformer feeding that is now in-vogue with Network Rail.

Looking East of Plymouth, there is another station at Exeter and another at Abham in the vicinity of Totnes railway station (well 5km away).

EDIT:
If a deal could be struck with the South Devon Railway to allow cables to be routed along the line in a concrete trench or similar, the distance between the right of way and the grid supply point at Abham over fields is only 940m.

 

[ainsworth74]

Just by having automatic train doors it would speed up the timetables for those services (about 7 minutes when you compare GW with XC between Plymouth & Penzance).

Surely that has more to do with the acceleration than the dwell time caused by slam doors? A Voyager will be able to get up to line speed much faster than an HST I'd have thought.

 

[Yew]

There is no 400kV substation at Exeter, the two obvious Grid Supply Points are Indian Queens and Landulph which is near Plymouth.

That means it is basically two 60km stretches, one bridged Indian Queens and Landulph and the other just Indian Queens to Penzance.

Given the relatively low traffic densities on the line, especially west of Indian Queens (no freight at all right?) I think it is fairly reasonable to assume that it is doable.

Especially using auto-transformer feeding that is now in-vogue with Network Rail.

Given the relatively low traffic, would it be financially viable? compared to bi-mode/loco swaps/British rails next fad

 

[Zoe]

There are other 400kV stations west of Exeter, the two obvious Grid Supply Points are Indian Queens and Landulph which is near Plymouth.

Does the supply have to be at 400 kV? There's a 132 kV substation at Newton Abbot, could this be used to feed the Torbay branch?

 

[The Ham]

Given the relatively low traffic densities on the line, especially west of Indian Queens (no freight at all right?) I think it is fairly reasonable to assume that it is doable.

There is little traffic at all on the line west of Indian Queens, given it is on the branch line to Newquay.
--- old post above --- --- new post below ---

Surely that has more to do with the acceleration than the dwell time caused by slam doors? A Voyager will be able to get up to line speed much faster than an HST I'd have thought.

It may well do, but if a slam door is not shut properly someone has to go and shut it (which is not a short walk if it's the wrong end of the train to the staff), which GW must allow for (at least a little) otherwise they'd often be running late.

 

[Zoe]

Given the relatively low traffic, would it be financially viable? compared to bi-mode/loco swaps/British rails next fad

But if you end the wires at Exeter then you have the sitatuon where Plymouth trains would be running under the wires for all but the last 50 miles and it could then be argued that you may as well cut back a significant number of intercity services to Exeter rather than having bi-mode/loco changes for just 50 miles of a mostly electrified route.

 

[The Ham]

There is a fairly good electrical supply at Hayle, as that is where the Wave hub project is based:

http://www.bbc.co.uk/news/uk-england-cornwall-15385686

Managers of a wave energy project in Cornwall have welcomed government plans to more than double the subsidy to wave and tidal energy projects.

Wave Hub, off the coast of Hayle, is a grid-connected test site for wave energy technology.

 

[Zoe]

There is a fairly good electrical supply at Hayle, as that is where the Wave hub project is based

That's only 132 kV though, could that be used for rail electrification or would this (and using the 132 kV substation at Newton Abbot to feed the Torbay branch) not be an option?

 

[ainsworth74]

It may well do, but if a slam door is not shut properly someone has to go and shut it (which is not a short walk if it's the wrong end of the train to the staff), which GW must allow for (at least a little) otherwise they'd often be running late.

Oh I agree that there will be an allowance in the timetable for it but I'm not sure you'd get seven minutes from just that.

 

[HSTEd]

Given the relatively low traffic, would it be financially viable? compared to bi-mode/loco swaps/British rails next fad

Well there is certainly a case for the line to Plymouth, it is included in the Cross Country proposals that get >5:1 BCRs in some analyses.
West of Plymouth is more troublesome, you would likely b e able to claim network effect from the East of Plymouth project, and there is also the fact that the project might be able to tap EU funding as Cornwall qualifies for development aid under the "Convergence criteria".

Does the supply have to be at 400 kV? There's a 132 kV substation at Newton Abbot, could this be used to feed the Torbay branch?

No, most railway electrification feeding stations are indeed fed from 132kV circuits and this under normal circumstances presents no problems.
However, since the grid in the South West is relatively weak, especially at this extremity, there is a question over whether using 132kV circuits would require expensive grid strengthening that can be avoided by using 400kV circuits.

I would imagine that the Torbay Branch could be single-end fed from the Exeter and Abham GSPs using the autotransformer system as its power demands are going to be relatively low, especially due to the branch having relatively low speeds.

There is little traffic at all on the line west of Indian Queens, given it is on the branch line to Newquay.

Alright, the line west of par then.

 

[Zoe]

I would imagine that the Torbay Branch could be single-end fed from the Exeter and Abham GSPs using the autotransformer system as its power demands are going to be relatively low, especially due to the branch having relatively low speeds.

Would the GWML need a feed from Abham to help the network cope with the Devon banks or could you just feed from Exeter and Landulph?

 

[HSTEd]

Would the GWML need a feed from Abham to help the network cope with the Devon banks or could you just feed from Exeter and Landulph?

Via the railway route, Plymouth to Exeter is more than eighty kilometres, under normal main line conditions it seems to be standard procedure to place substations every 50 or so, so I would believe that it would be best to have Abham, although you could probably do without it.
(It would likely reduce energy efficiency due to increased voltage drops, especially when trains go to notch 8 on the banks).