Once at line speed trains require very little energy to keep them going due to the very low rolling resistance
The ORR have not ruled out top contact third rail on new electrification. 

There are a number of constraints, improved fencing, NR to look at the risks in station areas for which a scheme has been developed for station platform areas for the power in the conductor rail to be off when not required by trains.  The main point the ORR want to see is management of the electrical risk to the general public and staff

 
The key points taken from the printed version of the article in Rail are

Modified Class 450 or 701 trains, batteries put into space that transformers would occupy if they were 25kv fitted.

15 third rail islands concentrated in areas of rapid acceleration such as stations.
 
Total 50 miles third rail.

Suitable electric connections identified avoiding needing very high voltage grid points.

Based on the above, islands would be approx. 3.3 miles long averaging 8 miles apart. Station spacing between Basingstoke and Honiton varies between 4 to 13 miles so would fit with the above. After Honiton they are more closely spaced so would not all need third rail.

 
As the article is behind a pay wall,

would anyone like to hazard the cost of the 125 miles if the construction started today?

 
Short sections of conductor rail for charging a static train in a platform should be acceptable to the healthansafety as they could be fitted with an interlock so as to be dead except when a train is parked over them.

I remain very doubtful about all but trivial extensions to conventional conductor rail systems for reasons already given.

25KV is the future especially if heavy freight or full length, fast passenger trains are expected.
Lightweight tramway style overhead at 750 volt DC is worth considering for local passenger services.

 
I feel that this scheme should be looked at as part of a long term future full electrification strategy, not just in isolation.
There must be a fairly good case for electrifying from Southampton to Reading via Salisbury and Basingstoke for the freight route to and from Southampton. If so then this, in all likelihood will be at 25Kv OHLE. Likewise from Yeovil to Exeter might have to be considered as part of the GWML diversionary route as well as the Devon Metro.
Thus the scheme chosen for the Basingstoke to Exeter line should be able to sit within this not just in isolation.
However, I wonder if the current thinking is along the lines of charging as on the Greenford branch, which appears to be progressing well. If so then sections of charging rails will be in stations, perhaps Salisbury, Yeovil, Axminster and New Yard, Exeter. This might be backed up with short sections of third rail where current drain is heavy, such as Sherborne, Honiton and Crewkerne banks.

 

I doubt that it will be allowed.
Someone, somewhere, will have to "sign off" the design as being as safe as is reasonably practicable, whilst knowingly rejecting safer alternatives such as OHLE, or batteries throughout. That person could be at risk of criminal prosecution, maybe decades later, when a trespasser is electrocuted.

 
Third rail

 
Are they proposing 25 KV AC or 750 volts DC ?
AC might be out nimbyed, DC is de-facto prohibited by the healthansafety.
My preferred system would be 750 volt DC overhead, lighter structures and smaller insulators so less liable to nimbys.
Use of this system reduces the need for costly grid upgrades, because the load is balanced three phase and therefore less disturbing to other consumers.

 

That has me thinking of this sort of thing - perhaps it should be a side-thread in "The Lighter side"

https://en.wikipedia.org/wiki/Panama_Canal_locks#/media/File:Mule_in_the_Miraflores_Locks.JPG



In all seriousness, third rail section between also between (say) Mottisfont and Dean, and between Wilton and Warminster, could also transform and electrify the Cardiff - Portsmouth service too.   Further of topic, my first ever departure on Saturday on board a train that was electric powered from Pilning. Clean, fast, good acceleration reducing the headway needed on that line to restart trains.

 

Too many variables to calculate I suspect. And it would depend upon WHICH miles were electrified, rather than how many miles were electrified.
Passing loops and stations would be a high priority, and inclines.

For new or heavily modified trains, energy use on battery power could be minimised, for example heat the passenger saloon to say 22 degrees on electrified sections but only to 20 degrees on battery power. In Summer, cool to 23 degrees on electrified sections, but to 25 degrees on battery power. Fill compressed air tanks to the maximum safe pressure on electrified sections, but to a lower pressure on battery power.
In cold weather, use waste heat from the electronic variable speed drive, to warm the saloon. Modern electronics are very efficient and the gain is moderate, but even a few KW per coach reduces battery drain for heating.

 
It's got to be The Electric Mule

 
Service to be marketed as the 'Sarum Sizzlers'.

Mark

 


I suspect there are too many variables to make for an easy answer.   Let's start with "will trains be charging while sat in the Tisbury loop" ... and "will there be pickup charging on each carriage or will it be the train as a whole that charges?".  "Does in need to be 75% all the time even when it arrives in Basingstoke"

 
So, at line speed, how many miles of third rail would be required how often to keep the b attery at least 75% charged? Or is that answer impossible?

 
At last, some common sense finally prevailing by extending third rail towards Exeter even if it’s discontinuous.

 
From Rail magazine online:

'Islands’ of third-rail electric power are being assessed for the West of England line between Basingstoke and Exeter.

Network Rail and South Western Railway have been working for two years on plans to remove diesel trains on the long-distance route.

They have involved train manufacturers and rolling stock leasing companies in studies to fit battery power to either Class 450 Desiros or new Class 701 Arterio trains, able to recharge on sections of discontinuous third-rail track.o


You need to log on to their site to read the rest.

https://www.railmagazine.com/news/2024/09/26/discontinuous-third-rail-idea-for-west-of-england-line

Edit to add link.