Rising electrification costs caused by increased overhead electrification clearances

[najaB]

Anyone know what the required height on tunnels in for electrification using OHLE? So what is the height from top of rail to top of tunnel?

I imagine that would depend on a number of factors - including type of OHLE (solid bar vs traditional catenary).

 

[Charlie Smythe]

I imagine that would depend on a number of factors - including type of OHLE (solid bar vs traditional catenary).

Traditional gantry

 

[coppercapped]

Huh? Gantries? In a tunnel?

This book is an excellent introduction.

 

[Charlie Smythe]

Huh? Gantries? In a tunnel?

This book is an excellent introduction.

Obviously not gantrys in a tunnel. I should of been clearer. What is the clearance for tunnels for OHLE in under a bridge or out in the open and then what is the clearance for solid bar in tunnels?

 

[AM9]

Obviously not gantrys in a tunnel. I should of been clearer. What is the clearance for tunnels for OHLE in under a bridge or out in the open and then what is the clearance for solid bar in tunnels?

The ruling clearance for any component at 25kV is 370mm* istr. Special derogations are probably still possible to reduce it to 270mm*. How the conductor is formed and suspended would in part be determined by just how much clearance was available.
* these actual dimension could be wrong but the general principle of the mounting arrangements fitting the actual situation would apply, hence the variety of components in the Master Series OLE range.

 

[AndrewE]

Huh? Gantries? In a tunnel?

This book is an excellent introduction.

That is an excellent link, thanks very much.
A

 

[Charlie Smythe]

The ruling clearance for any component at 25kV is 370mm* istr. Special derogations are probably still possible to reduce it to 270mm*. How the conductor is formed and suspended would in part be determined by just how much clearance was available.
* these actual dimension could be wrong but the general principle of the mounting arrangements fitting the actual situation would apply, hence the variety of components in the Master Series OLE range.

I appreciate the information however when i mean clearance i mean how far from top of track head to the highest point of the electrical cable mounting system.

 

[superkev]

Huh? Gantries? In a tunnel?

This book is an excellent introduction.

Most interesting book link Thankyou. Nice to see someone has some expertise.
K

 

[coppercapped]

I appreciate the information however when i mean clearance i mean how far from top of track head to the highest point of the electrical cable mounting system.

The correct answer is: How long is a piece of string?

I don't understand the question that you are asking - and probably more importantly, why. The answer to 'why' may help in giving an appropriate answer.

There are upper and lower limits to the distance between the railhead and the contact wire. The upper limit is given by the reach of the pantograph when fully extended and on mixed traffic railways the contact wire height tends to be at at the upper limit at level crossings so as to give maximum clearance for road vehicles. The minimum height is at places where the contact wire has to pass under a low piece of infrastructure such as an existing bridge. For new-built high speed lines the aim is to keep the contact wire at a constant height above the railhead to give the best possible contact conditions at high speeds, this is clearly more difficult when electrifying an existing railway.

So not only does the contact wire height above the railhead vary but the separation between the contact and catenary wires at the registration points depends on the site constraints and the requirements at the adjacent structures. In other words the distance you are looking for also varies. The other point which is not obvious from your question is whether you are referring to the parts of the overhead which are live or whether you are referring to earthed components such as the masts or gantries.

I really suggest reading Mr Keenor's book that I linked to a couple of posts ago.

 

[coppercapped]

Most interesting book link Thankyou. Nice to see someone has some expertise.
K

I say this with great trepidation but I notice that with some noticeable and highly regarded exceptions engineering expertise is sadly lacking in many of the posts made on this forum.

This is not intended to reflect on those who seek information but there are some bald statements made which are simply wrong.

 

[najaB]

I don't understand the question that you are asking - and probably more importantly, why. The answer to 'why' may help in giving an appropriate answer.

I think it could be boiled down to: "What is the minimum tunnel diameter (assuming a spherical bore) that it is practical to electrify, using conventional OHLE?" Or, alternatively: "By how much would I need to increase the diameter of a spherical bored tunnel if I wish to add OHLE equipment?"

 

[AndrewE]

I think it could be boiled down to: "What is the minimum tunnel diameter (assuming a spherical bore) that it is practical to electrify, using conventional OHLE?" Or, alternatively: "By how much would I need to increase the diameter of a spherical bored tunnel if I wish to add OHLE equipment?"

It would be difficult to get into and out of a spherical bore! I think you might mean cylindrical...

 

[Charlie Smythe]

I think it could be boiled down to: "What is the minimum tunnel diameter (assuming a spherical bore) that it is practical to electrify, using conventional OHLE?" Or, alternatively: "By how much would I need to increase the diameter of a spherical bored tunnel if I wish to add OHLE equipment?"

Yes! That's is my question, except of course cylindrical bore. I wish i could of worded it like that instead of my long winded mess. Yeah so what does the diameter of a tunnel need to be for OHLE? Sorry if i have annoyed/confused anyone with my horrendous lack of knowledge on this subject.

 

[najaB]

It would be difficult to get into and out of a spherical bore! I think you might mean cylindrical...

Oh, you pesky 3-dimensional beings. Thanks for the correction.

 

[Charlie Smythe]

The correct answer is: How long is a piece of string?

I don't understand the question that you are asking - and probably more importantly, why. The answer to 'why' may help in giving an appropriate answer.

There are upper and lower limits to the distance between the railhead and the contact wire. The upper limit is given by the reach of the pantograph when fully extended and on mixed traffic railways the contact wire height tends to be at at the upper limit at level crossings so as to give maximum clearance for road vehicles. The minimum height is at places where the contact wire has to pass under a low piece of infrastructure such as an existing bridge. For new-built high speed lines the aim is to keep the contact wire at a constant height above the railhead to give the best possible contact conditions at high speeds, this is clearly more difficult when electrifying an existing railway.

So not only does the contact wire height above the railhead vary but the separation between the contact and catenary wires at the registration points depends on the site constraints and the requirements at the adjacent structures. In other words the distance you are looking for also varies. The other point which is not obvious from your question is whether you are referring to the parts of the overhead which are live or whether you are referring to earthed components such as the masts or gantries.

I really suggest reading Mr Keenor's book that I linked to a couple of posts ago.

I probably should of stated this earlier but anyway. This is why i want to know the height.

The tunnel between Exeter St Davids and Exeter Central on Exeter Bank doesn't look all that big and i am fairly sure you couldn't get OHLE into that tunnel as it stands. Therefor it would most likely need boring out but i don't think that there is enough room to bore the tunnel out to increase the height as the roadway above is not that far above the top of the tunnel. So if you increased the height of the tunnel by even a little bit you wouldn't be far of the road way above. It's just a strange observation i made the other day. Its quite hard to explain.

 

[Charlie Smythe]

I am probably making my self look stupid but i am just curious.

 

[kilonewton]

The tunnel between Exeter St Davids and Exeter Central on Exeter Bank doesn't look all that big and i am fairly sure you couldn't get OHLE into that tunnel as it stands. Therefor it would most likely need boring out but i don't think that there is enough room to bore the tunnel out to increase the height as the roadway above is not that far above the top of the tunnel. So if you increased the height of the tunnel by even a little bit you wouldn't be far of the road way above. It's just a strange observation i made the other day. Its quite hard to explain.

Never been near said tunnel, so can’t comment on the specific, but in general the first option would be to lower the floor to get greater clearance rather than raise the roof. Of course that means lowering the track over a greater distance to get down and back up to existing levels

 

[Charlie Smythe]

Never been near said tunnel, so can’t comment on the specific, but in general the first option would be to lower the floor to get greater clearance rather than raise the roof. Of course that means lowering the track over a greater distance to get down and back up to existing levels

I had thought that they might lower the track however i don't think this is viable as that you further increase the gradient on the line which is an already savage 1 in 37. So lowering the track would result in a lesser gradient before and then a far steeper gradient after the tunnel.

 

[Ianno87]

Today I spotted the novel way of addressing electrical clearances issue at Lostock (see photo)...

 

[najaB]

So lowering the track would result in a lesser gradient before and then a far steeper gradient after the tunnel.

It's a good thing that electric traction is better at climbing then. All things considered, I doubt the amount of lowering required would increase the gradient by that much.

 

[Charlie Smythe]

After reading the "Network Rail Guide to Overhead Electrification" document i found on the web, i now believe that 4780mm is required for fitted OHLE.

Source:
http://www.bathnes.gov.uk/sites/def...ng/nr_a_guide_to_overhead_electrification.pdf

 

[furnessvale]

It's a good thing that electric traction is better at climbing then. All things considered, I doubt the amount of lowering required would increase the gradient by that much.

A train of any decent length, hence weight, would be simultaneously on the original 1 in 37, the new short section of lesser gradient AND the new short section of steeper gradient cancelling out the effect.

 

[Charlie Smythe]

A train of any decent length, hence weight, would be simultaneously on the original 1 in 37, the new short section of lesser gradient AND the new short section of steeper gradient cancelling out the effect.

It is a good point. The only trains that use that section of track regularly are Class 150/2 units and SWR Class 159 units both of which are working hard up the bank but do manage it.