Great Western Main Line electrification - ongoing discussion

[whole diary]

[TonyK]

I’ve tried to understand what ET and others have explained re OHLE!.

Me too - very technical, but I think thanks to our experts here, I am getting the hang of it.

[Electric train]

I notice that the OHLE on the UM and DM between Pangbourne and Tilehurst is earthed (ie cables across the insulators), so it looks like following the publicity run with the 80x on electric it’s been switched off for now so installation work can be continued. 

The system is only enegised for the test runs at the moment, the full immunisation test have not been done, also there is no full time ECR yet, so the blue leads (portable earths, technically the ones they are using are construction earths) this so safety documentation can be issued for the OLE^▸ (Overhead Line Equipment, more often "OHLE") construction teams to continue working
 

Notice also that the autotransformer cables (ie the ones above the gantries) on the UM and DM between Pangbourne and Tilehurst are not yet all installed: presumably the test run with just the one train drawing power didn’t need the voltage stabilisation that the auto-transformer system provides

The system will be configured as classic 25kV for the test runs, the AT system is only needed for the service timetable

 (I’ve tried to understand what ET and others have explained re OHLE!).

Its simple really ....... feisty wiggly Amps into the OLE and tiered and worn out wiggly Amps come back in the running rails   

[SandTEngineer]

Its simple really ....... feisty wiggly Amps into the OLE^▸ (Overhead Line Equipment, more often "OHLE") and tiered and worn out wiggly Amps come back in the running rails 

Yes ET but those tired and worn out wiggly amps don't half play havoc with our signalling system if you don't send them off to their beds straight away and they want to go out and play first

[TonyK]

It's the other lots of wiggly amps with there 25,000 friends the extra Volts in the AT system that I remain unsure of.

[Electric train]

Its simple really ....... feisty wiggly Amps into the OLE^▸ (Overhead Line Equipment, more often "OHLE") and tiered and worn out wiggly Amps come back in the running rails 

Yes ET but those tired and worn out wiggly amps don't half play havoc with our signalling system if you don't send them off to their beds straight away and they want to go out and play first

I did say tired and worn out, they still have some life left in them and like their feisty friends they are still mischief makers 

It's the other lots of wiggly amps with there 25,000 friends the extra Volts in the AT system that I remain unsure of.

Ah the 25kV from the AT gives the feisty wiggly Amps in the OLE a bit of an extra zing by making the 50kV (its bit like Redbull for electricity it gives it wings    ) It also help to keep the tired and worn out wiggly Amp under control.

If you are still confuzlzzzed get some mirrors and smoke .............. its all done with magic 

[TonyK]

If you are still confuzlzzzed get some mirrors and smoke .............. its all done with magic 

For this concise and scientific answer, I am obliged to you, ET!

[Worcester_Passenger]

"Any sufficiently advanced technology is indistinguishable from magic." - Arthur C. Clarke

[broadgage]

"the electricity is sent out from the electric light works via a copper wire that is covered with gutta-percha in order to prevent escape of the electricity.  After passing through the electric lighting burners, the used electricity is returned to the works via a second wire in order that it may be re-used.
If this was not done, the electric light works would have to find a continual supply of new electricity.
This necessity for two wires (that must be kept separated at all times) is a decided drawback if compared to gas lighting, which as we all know requires but a single pipe"

From a very early account of the new electric light.

This was of course "continuous current" that flows nice and steadily, no silly wiggling around. Much simpler, only needs two wires.

[IndustryInsider]

I took a late night trip out from Paddington last night and I've never seen so much activity.  Pretty much constant (wo)men and machinery from West Drayton to Didcot all busy fitting and testing the various stages of works that have been reached in those areas.

[Noggin]

I took a late night trip out from Paddington last night and I've never seen so much activity.  Pretty much constant (wo)men and machinery from West Drayton to Didcot all busy fitting and testing the various stages of works that have been reached in those areas.

Amazing what some people will do to avoid their kids in the summer holidays eh?

[Electric train]

I took a late night trip out from Paddington last night and I've never seen so much activity.  Pretty much constant (wo)men and machinery from West Drayton to Didcot all busy fitting and testing the various stages of works that have been reached in those areas.

The plan is apparently to have all wiring complete between Airport Jcn and Maidenhead by the end of November (2016) so the planned EMU^▸ (Electric Multiple Unit) services from Maidenhead can commence as of the May 2017 timetable.

The difficult part is getting the foundations done and the structures erected on top, the 4 track portals requiring and all lines block, not to many of the on the GWML^▸ (Great Western Main Line).


Now back to this electric power stuff, what makes the Amps is the dancing pixies they dance to the tune of 50Hz

Now seriously the reason for the AT system, the concept is not new its been around for about 100 years, the Auto Transformer system of 25kv - 0 - 25kV allows the transmission of power at 50kV yet retain the  use of standard OLE^▸ (Overhead Line Equipment, more often "OHLE") 25kV components such as insulators and cables. 

Why 50kV? it is all to do with I²R which is power loss in effect doubling the Voltage halves the current which has dramatic effect in reducing the power loss for the same size conductors.  This allows for doubling the space between Grid supply points.  If the GWML had been electrified in the 1980/90's as original planned by BR^▸ (British Rail(ways)) between Paddington and Reading there would have been 3 Grid supply points, Old Oak Common, Iver, and Reading, all these would have come off of the 132kV network.  The largest 132/25kV transformers are 26MVA
Even in the 1980/90's the Electricity Supply Network were getting concerned over the impact of the railway large single phase loading, the ECML^▸ (East Coast Main Line) had to have a number of addition Feeder Stations added on the railway even though the 25kV supply came from the same Grid point, Grantham and Newark are examples of this, it was done to even the load on the 132kV network.

The GWML now has 3 Grid supply points between Paddington and Bristol!!  The BR classic 25kV scheme would have needed 8 or 9 and that does not include on the Berks n Hants.  The supply being taken from the 400kV Grid which allows for larger transformers of 50MVA, although this increases the fault level from 6kA to 12kA.  Kensal Green feed to the Mid Point at Maidenhead to Abbey Wood / Bow and Didcot Mid Point at Maidenhead to Wooton Basset (I believe), also to Oxford and Bedwyn (although if there is a service increase a new Grid supply from Bramley to Southcote Jcn is in the outline plan.  Each 400kV Grid supplies approx. 50 miles in each direction.

Didcot can feed right into Paddington if need to, with the Crossrail tunnels being fed from the Bow end.  I believe Didcot can even do emergency feeding into the Crossrail Tunnels although this would not be for service running.

See told you its all smoke n mirrors and dancing pixies   

[TonyK]

Why 50kV? it is all to do with I²R

Or P=IV, as V=IR. So P=I*(IR) which equals I²R. Lower current  because of higher voltage equals lower loss, hence why we don't run 240V from power stations. Eureka! I now know why the effective 50KV supply is so useful.

Now for the how. AAUI, there is only one winding in an autotransformer, and both 25KV feeds are taken from it with a common terminal. The catenary wire is energised to 25KV, the second feed is 25KV, but antiphase. But it doesn't seem to be involved in the circuit as the little sprites all run to the running rail. The antiphase feed merely connects to the next transformer, which leaves me puzzled still.

Edit: I see my mistake. The train does not at any time draw 50KV - that is the voltage between the two conductors, giving the economy. The 25KV to the train is returned via the running rail.

No, it is magic.

[Oxonhutch]

Now for the how. AAUI, there is only one winding in an autotransformer,

A single winding centre tapped at 0 (rail) voltage ?

[Electric train]

Why 50kV? it is all to do with I²R

Or P=IV, as V=IR. So P=I*(IR) which equals I²R. Lower current  because of higher voltage equals lower loss, hence why we don't run 240V from power stations. Eureka! I now know why the effective 50KV supply is so useful.

Now for the how. AAUI, there is only one winding in an autotransformer, and both 25KV feeds are taken from it with a common terminal. The catenary wire is energised to 25KV, the second feed is 25KV, but antiphase. But it doesn't seem to be involved in the circuit as the little sprites all run to the running rail. The antiphase feed merely connects to the next transformer, which leaves me puzzled still.

Edit: I see my mistake. The train does not at any time draw 50KV - that is the voltage between the two conductors, giving the economy. The 25KV to the train is returned via the running rail.

No, it is magic.

The magnetic circuit in the auto transformer forces the winding to balance (simplistically) Its difficult to explain without diagrams.  There are strange current flows in the system as the train (load) moves.  

Large grid transformers 400/132kV are auto transformers, they are used as it reduces the amount of copper and iron over a conventionally wound transformer.  auto transformers are not used in the UK^▸ (United Kingdom) for domestic supplies as we require isolation between the high voltage winding and the low voltage winding, they are quit common (or were) in the USA.   Veriacs are auto transformers

[Electric train]

Now for the how. AAUI, there is only one winding in an autotransformer,

A single winding centre tapped at 0 (rail) voltage ?

Yes

If you all want some bedtime reading - http://www.networkrail.co.uk/browse%20documents/track%20access/2%20completed%20consultations/2010/2010.06.11%20west%20coast%20trains%209th%20sa%20-%20consultation%20closed%2007%20july%202010/ec4t%20loss%20report%20v1.0.pdf