Longest electrified stretch fed from one end?

[snowball]

Where is the longest stretch of electrified track in GB that is normally fed from one end only?

This could be

(1) a stretch from a feeder station to the end of a line

or (2) a stretch from a feeder station to a point where electrification ends and the line continues unelectrified

or (3) a stretch from a feeder station to a track sectioning cabin where the other side is normally fed from a different feeder station.

A "stretch" for the purposes of this question could include parts of more than one line. For example if you want to know where the juice comes from to feed Blackpool North, you have to include, for a start, the whole Preston-Blackpool line, which has no feeder station of its own; but you must then also include also some distance north or south along the WCML to a feeder station. (I imagine Blackpool would normally be fed from Catterall, about 8 miles north of Preston.)

 

[Snow1964]

I am sure the third rail one is the substation at Lymington Junction, which feeds the branch all the way to the end at Lymington Pier.

 

[Nicholas Lewis]

I am sure the third rail one is the substation at Lymington Junction, which feeds the branch all the way to the end at Lymington Pier.

Newhaven down to Seaford is another contender

 

[Class 170101]

Hythe to Clacton / Walton

 

[snowball]

Of the two third rail examples mentioned so far, Lymington is longer.

Hythe to Clacton and Walton are each less than my example of Caterall to Blackpool. (If you include both Essex branches it might come out about the same, but that wasn't the question.)

Where is King's Lynn fed from?

I suppose autotransformer-fed +-25kV lines should be a separate category from plain 25kV.

 

[MadMac]

Greenhill-Alloa at 18 miles must be a contender.

 

[ABB125]

Is there a map which shows feeder station sites etc available publicly?

 

[InTheEastMids]

Isn't the MML as far as Corby currently fed from the new grid supply point near Sundon? That's quite a distance.

 

[Snow1964]

I think the GWR main line to Filton is fed from either Melksham or Didcot, although there is a substation at Wooton Bassett. So about 30 miles. From memory, Beyond Filton it is fed from Wales.

 

[AM9]

Hythe to Clacton and Walton are each less than my example of Caterall to Blackpool. (If you include both Essex branches it might come out about the same, but that wasn't the question.

In terms of an individual train at the extremities of those branches, the linear distance from the feed point dominates the impact. In the case of a mini network that is remotely fed, the worst case combination of trains at the ends has a significant effect, e.g. in the peak there could three 2x5car class 720s and single 5car set on the Thorpe-Walton shuttle, that could cause the line voltage to approach the minimum normal level.

 

[DarloRich]

Kings Lynn?

 

[Taunton]

I am sure the third rail one is the substation at Lymington Junction, which feeds the branch all the way to the end at Lymington Pier.

I seem to remember that when there was an issue at Lymington with the staff member there who had dared to access the track, it was said by management that it was so dangerous because of 750v in the conductor rail. Whereupon more informed staff said you were lucky to get 450v at Lymington.

 

[Class 170101]

Where is King's Lynn fed from?

Kings Lynn?

I think there is a small feeder at Kings Lynn itself

 

[Whistler40145]

Where's the Blackpool North to Preston line fed from?

 

[Bald Rick]

Kings Lynn?

There’s a feeder at Kings Lynn. However as there are long stretches of single line up there, there is a second 25kV line to keep the other end live in the event of a fault on the OLE over the single track concurrent with an outage at Milton (Cambridge).

 

[GRALISTAIR]

Where's the Blackpool North to Preston line fed from?

Catterall

 

[Elecman]

Where's the Blackpool North to Preston line fed from?

Catterall under normal circumstances but could be fed from Willow Park/Parkside

 

[59CosG95]

Isn't the MML as far as Corby currently fed from the new grid supply point near Sundon? That's quite a distance.

All due to change once Braybrooke goes online of course.

 

[McRhu]

Without wishing to deviate too much... Hypothetically, how far would a 25Kv feed travel through the OLE before it dropped to an unusable voltage? (Or to put it another way, if the WCML was fed from Euston what would the voltage be at Glasgow Central?)

 

[zwk500]

Without wishing to deviate too much... Hypothetically, how far would a 25Kv feed travel through the OLE before it dropped to an unusable voltage? (Or to put it another way, if the WCML was fed from Euston what would the voltage be at Glasgow Central?)

That answer rather depends on how much power is being consumed from the system!

At a rough guide, this document suggests feeder substations are required every 50-60km: https://www.bathnes.gov.uk/sites/de...ng/nr_a_guide_to_overhead_electrification.pdf
Various design and system factors would affect this. If you have just a few trains with a light power draw you would get further than if you had lots of trains or trains with high power demand.

 

[DarloRich]

I think there is a small feeder at Kings Lynn itself

There’s a feeder at Kings Lynn. However as there are long stretches of single line up there, there is a second 25kV line to keep the other end live in the event of a fault on the OLE over the single track concurrent with an outage at Milton (Cambridge).

of course - thank you x 2

 

[AM9]

That answer rather depends on how much power is being consumed from the system!

At a rough guide, this document suggests feeder substations are required every 50-60km: https://www.bathnes.gov.uk/sites/de...ng/nr_a_guide_to_overhead_electrification.pdf
Various design and system factors would affect this. If you have just a few trains with a light power draw you would get further than if you had lots of trains or trains with high power demand.

Presumably, auto transformers would be able to extend a long thinly-trafficed line further before the voltage dropped below the working minimum.

 

[zwk500]

Presumably, auto transformers would be able to extend a long thinly-trafficed line further before the voltage dropped below the working minimum.

I'm really no expert, but I suppose that hypothetically if traffic were light enough and sufficient power supplied at the feed point then autotransformers or boosters could keep the voltage within the parameters for a nearly indefinite distance. The laws of physics indicate there must be a limit, but its probably a 'half as much again' situation.

 

[bramling]

Presumably, auto transformers would be able to extend a long thinly-trafficed line further before the voltage dropped below the working minimum.

Yes ATs allow more trains within the same length of section, greater distance between feeders for the same number of trains, or a trade-off between the two.

 

[Richard Scott]

I seem to remember that when there was an issue at Lymington with the staff member there who had dared to access the track, it was said by management that it was so dangerous because of 750v in the conductor rail. Whereupon more informed staff said you were lucky to get 450v at Lymington.

Under load may drop to 450V but without a load may well be 750V.

 

[Bald Rick]

I seem to remember that when there was an issue at Lymington with the staff member there who had dared to access the track, it was said by management that it was so dangerous because of 750v in the conductor rail. Whereupon more informed staff said you were lucky to get 450v at Lymington.

450v or 750v DC, either way it will kill you.

 

[Taunton]

450v or 750v DC, either way it will kill you.

Not necessarily. Ian Allan, in his autobiography, wrote of more than one Southern employee in WW2 who in the blackout stumbled over the live rail, but was saved by the voltage being generally reduced due to fuel shortage. Not a sure thing, but it can help.

 

[AM9]

Not necessarily. Ian Allan, in his autobiography, wrote of more than one Southern employee in WW2 who in the blackout stumbled over the live rail, but was saved by the voltage being generally reduced due to fuel shortage. Not a sure thing, but it can help.

I doubt the RSS would accept any more 3rd rail on the basis that the voltage sometimes sags below 450V.

 

[Nicholas Lewis]

I doubt the RSS would accept any more 3rd rail on the basis that the voltage sometimes sags below 450V.

It shouldn't drop below that as CB's should automatically disconnect if voltage drops below 450V. Similarly on old EP stock the no volt relay was set to drop below 450V and that would stop the driver taking power. I guess same parameter is programmed into modern units.

 

[AM9]

It shouldn't drop below that as CB's should automatically disconnect if voltage drops below 450V. Similarly on old EP stock the no volt relay was set to drop below 450V and that would stop the driver taking power. I guess same parameter is programmed into modern units.

My comment was about the vain hope that the low voltage is 'safer'. 450V was mentioned by @Taunton as if the staff at Lymington were under the impression that it was safer. Any prolonged contact with a DC voltage over 200V is liable to be lethal.