Great Western Coffee Shop

Yesterday as a blue sky and I had the day off I walked the old line from Yelverton into Plymouth and then on to Laira bridge. When passing under the new[ish] Marsh Mills concrete A38 flyover I could not help but notice the headroom of the track on the main line. A Voyager went under and it did not look as though there is enough clearance for an overhead catenary. The problem looked worse on the up line under the up slip road. Surely a modern structure such as this must have been constructed allowing for the required headroom?

This led me on to thinking what other structures would need altering before OHLE could be installed? If mainly a lot of small road overbridges then they could be done fairly quickly in advance.

As the Government is looking for quick public works with a lot of labour content then this could be ideal as it would give work to the construction industry that is suffering a downturn. Come the day of OHLE installation the works trains could work more efficiently as the preparatory work would have been completed.

Perhaps I am being too simplistic but I would be interested to know what quantity of structures would be involved. I am sure one of the members must have an idea?

(1555 train back to Cornwall was a 150 and horrendously crowded, not good as this train hits the jackpot of all stations from Plymouth to Penzance. It also sounded as if the driver was having trouble as it spent a lot of its time crawling along coasting with the occasional burst of power.)

Web site still very good.

The extra clearance needed is not as large as some people think, and in some situations the required height can be achieved by lowering the track slightly. Our resident expert, 'ElectricTrain', might be able to elaborate further?

agree lowering track is an option,i believe this is going to be happening in the tunnel coming out of southampton to accomodate the continental freight wagons in the not too distant future.

I don't think electrification is likely to reach Plymouth though due to the Dawlish sea wall and the loading gauge in the Dawlish tunnels.

what are the downsides to '3rd rail'

I suspect as it is a lower voltage it requires more lineside equipment to keep the voltage up (greater losses over a shorter distance) so it is better suited to areas where there are a lot of stations already there. Also I would guess that it simply doesn't deliver as much "grunt" as overhead.

Mayor problem with 3rd rail is Elf & safety, whilst Fill in schemes are allowed, NEW 3rd rail schemes are Not premitted on Elf & Safety grounds.

Max speed of 100 mph (the world record held by a Wessex Electric is only about 115 I think!).

I could give a rant about my views on Health and Safety, but I'll spare everyone.

Just two words- common sense.

thankyou guys i suspected it was safty reasons i always did think it was silly and tbh dangerous

Well, thank you, FarWestJohn!  :-[

A dynamic (ie after contact wire is lifted by the passage of the pan) clearance of around 600mm between any live components and anything at earth potential, in some very special cases the clearance is less by using insulating covering on the under side of bridges.

It has been policy since the early 1980's that any new structures needed to take into account any future 25kV electrification some exceptions are the SR and a few other areas, my guess is the route to Plymouth would need to take 25kV into account.  The use of dual voltage was abandoned in the 1970's the lines such as Liverpool St to Shenfield, Fenchurch to Southend and around Glasgow used 6.25kV where there were low bridges, this added complications such as out of sequence controls in substations to allow for emergency moving failed trains and extra line side equipment to step the voltage down dual voltage stock etc

Top-notch bit of elaboration there!  :D

Another problem initialy with the 6.25/25kv mix was the strain it put on the board equipment on the units such that it caused the transformers to blow up. This was especialy so in Glasgow where it was first used. I believe unfortunately there might have been fatalities on a train when its transformer blew. It was so bad that all EMUs were withdrawn and some steam locos and stock were hastily put back into service. Although the units did come back into use with strengthened transformers and proved very successful, such that Glasgow now has an almost all electric suburban service with new lines and stations.

There were also several instances out of Liverpool Street particularly on the services via Hackney Downs.
   

Regards the forthcoming blockade of one of the twin bore Marley tunnel between Totnes and Plymouth(Engineering work between Newton Abbot and Plymouth from Monday 26 until Friday 30 January 2009) does anyone know if lowering of the track for possible future electrification is being undertaken as part of the work.

No, NR are not that far sighted enough. 

This work is likely to only be funded ultimately by ORR / F/TOC for track renewals, lowering track beds often involves altering drainage which in tunnels my have to include pumps if the bed has to be lowered a significant amount. This is a lot of money to be spent on a route that if electrification were to happen it may well over a decade before it does

Third rail around Dawlish doesn't sound good with lots of salt water around on a windy day, but then neither does 25kv overhead.

Back to the Plymouth via Okehampton debate - but don't know where that leaves Newton Abbot/Torbay or Totnes.

Plymouth via Oak is no good, as it requires a reversal.

Reopen the Heathfield line - this also retains InterCity to Torbay and NA.

Not if you come from Waterloo ;)

Right, just so that I understand this correctly; a third rail is dangerous, rails one and two carrying a train weighing hundreds of tons at 100+ MPH isn't ? 

Can I go away and think about that one ?    ???

i think safty wise for workmen on the line while services are running this can be done in a safe way with speed restrictions however dodging trains and a big piece of metal that wants to fry you is not a good combo

If you come from Waterloo, it is slower than reversing!

And there aren't enough paths into Waterloo to have sufficient fast and slow trains.

Plus there would be ANOTHER reversal to get into Cornwall.

No good, the GWR is the best.

Although I personally regard speculation re electrification west of Exeter as 'pie in the sky', there is a coastal section of the Hutt suburban line in Wellington NZ, which bears close comparison with the Dawlish sea wall stretch.

(http://i260.photobucket.com/albums/ii4/mr_metaxa/182246469_bb88191918_m.jpg)

The NZ line is electrified at 1500v DC on the overhead system and has been in use since the 1930s.   Although this section is subject to storm damage, the salty atmosphere appears not to affect day to day operation and new trains are on order.

I'm no expert on OHLE, but there must be a rust/corrosion resistant material out there that is capable of conducting sufficient electricity?

Plenty of them, but as all of them are metal they are liable to corrosion, Dawlish could be electrified it will require some very special engineering and it would be expensive.

Third rail has been rule out by HRMI based on the 1989 Electricity at Work Act requirements for all new major route electrification, but this would not prevent infill's such Reading Basingstoke but would rule out Basingstoke Winchester Exeter.  The major disadvantage of 3rd rail is the amount of line understructure.

Just a comment that will baffle many but does any one know if the 25kv overhead electrification is 25Kv RMS or Peak? (RMS Root Mean Square)

To put it in layman terms the 230volt supply at home is RMS, the peak voltage is about 330volts.
The RMS is the Average voltage over 1/2 a sine wave.

quadratic mean (rms), but im often wrong... (along time since i did physics at school)

It is 25kV RMS as all ac voltage values are stated. the actual system range is min 21kV max 28kV although the system can function as low as 15kV only emergency movements can happen.  Typical grid intake from a 132kV grid site is 26MW and from a 400kV grid site it is 58MW, 26MW is the max that can be taken from a 132 before the single phase loading causes problems to the grid, at 400kV there less of a problem and power greater than 58MW is feasible, however the 400kV grid sites are only currently used on the WCML as part of the up grade and the power distribution along the railway is different the classic system previously used on the WCML and elsewhere in the UK the new system is similar to that used in France for the TGV and also that used on CTRL basically the distribution system on the WCML (in parts) uses a 50kV system but the trains still operate at 25kV.............. no one said electric traction systems where as easy a hornby train set

wait i got it correct?

So if the max voltage is 28000 volts (rms) then the overhead lines have to be able to withstand a peak of almost 40,000 volts, yes it's only at a peak for microseconds but Electrical voltage is better understand as being Electrical Pressure.
If the insulation isn't up to 40,000 it will break down.

Now to clear a Myth, is Water a conductor?

Rain Water cann't be otherwise in every rain storm overhead lines would blow up.

As a matter of physics it depends on the voltage and the purity of the water.  lots of ions (ie, sea salt) dissolved+ more conductivity,  Higher voltage = more conductivity (because the H2O moleule becomes more ionized itself to H+ and OH-).

As a matter of engineering.  Rain drops are small and don't conduct from the overhead line to the ground because there is no continutous stream of water.  The insulators are of interesting shapes.  i have always assumed that one reason for this was to prevent a continuous surface water film forming on them.