Cost of electrification

[JonD]

Everyone feel free to laugh heartily at such niavety, but if there is a problem of the wires blowing off the side of the pan, given that the pan curves down at both ends, why not have it curve up instead? Would this foul other parts of the OLE?

 

[Old Timer]

Old timer, what is the load case here? I see wire weight, structure weight and bending with shear up to the force required to fail the wire in tension as the starting point for the load case. I've just looked at one as this Pendo coasts painfully slowly through Rugby and it looks like an extruded I section so it's not exactly going to break the bank to make it stupidly thick anyway.

The forces acting on the single Structure are as follows :

Along track - Overturning, wind loading and Return Conductor. Overturning through mounted switchgear and transformers.

Across track - Overturning, wind loading and headpsan / cantilever arrangement, rotational (as catenary system moves back and forth under expansion/contraction), overturning as catenary system moves up and down through system uplift.

Portal and Gantry Structures have additional rotational forces based on the boom.

For the purposes of design, the OHL Equipment and fittings are considered to represent a "solid wall" against which a gale force 10 wind is blowing. As explained by the designers, you assume the system height (height between Catenary and Contact wires at the registration point) as being a solid sheet of plastic extending to the midpoint. Added to that is the total width across the Structure assumed vertically from top to bottom. The area is then taken as representing the surface area against which the wind loading is applied and the subsequent result is then increased by a factor of (I believe 1.5).

The foundation has to withstand this load, with the calculated dimensions increased to again provide a factor of safety (probably 1.5 again).

That is as explained to me a couple of years back

I am surprised that indemnity insurance plays such a part in decisions in the railways industry -I have a quote framed "There's no indemnity insurance that will do your jail time for you. If it's wrong, don't sign it." Do you have one that's actually worth having?

Indeminty Insurers require that a Designed works within accepted design parameters. Design liability stays for the life of the Structure and is both personal and corporate.

A Designer who steps outside of the accepted limits has to demonstrate that he/she has included for factors of safety and my understanding is that this links to the 1 in 100,000 year event.

If the Designer designs a Structure which then falls over, say, the Insurer will be liable for all associated costs, they are therefore very insistent that their Insurance cover requires that the Designer implements factors of safety so as to limit the risk to the Insurer. A failure to do so would result in an Insurer seeking to avoid liability.

Everyone feel free to laugh heartily at such niavety, but if there is a problem of the wires blowing off the side of the pan, given that the pan curves down at both ends, why not have it curve up instead? Would this foul other parts of the OLE?

Not a silly question.

The pantograph follows the natural curve of the loading / structure gauge.

Do not take comments about "blow-off" too seriously, whilst it happens, the occurrences are very rare and require that the Contact wire is already separated form the droppers to enable it to move laterally.

In high wind areas, the amount of blow-off is very carefully calculated to ensure that this cannot happen.

For a blow-off dewirement to happen therefore you need, the Contact wire to be free to move laterally under wind loading, a peak wind loading far greater than normal, and sufficient "vehicle sway" opposite to the wind direction sufficient to cause the pantograph to move in the opposuite direction to the Contact wire under wind loading.

As you will appreciate, the same wind loading on the OHL system will be acting against the side of the train and forcing the vehicle to sway with rather than against the Contact wire, thus retaining the pantograph with the wire.

 

[HITMAN]

Pendys could probably save some considerable time on the Berks and Hants, probably running at 125 for much of the route. The line needs resignalling anyway (headways are a bit of a problem) and might get wires as far as Newbury unless that gets cut. If you include the whole route to Penzance, there's a chance of cutting an hour off the time.

Curiously, if Brunel had had electric traction available instead of the atmospheric railway, the South Devon may have been given a third rail when new.

We would probably stand a good chance of getting 140mph with in cab signalling on that route which could save even more time. Also after Plymouth even the intercity trains stop quite frequently, and electric trains with better accelaration would deliver further time savings.

 

[Chris125]

Everyone feel free to laugh heartily at such niavety, but if there is a problem of the wires blowing off the side of the pan, given that the pan curves down at both ends, why not have it curve up instead? Would this foul other parts of the OLE?

While such a pan would be fine on plain track, it would make a bit of a mess at junctions where the wires join and divide in common with the track beneath.

Chris

 

[cyclebytrain]

The forces acting on the single Structure are as follows :

Along track - Overturning, wind loading and Return Conductor. Overturning through mounted switchgear and transformers.

Across track - Overturning, wind loading and headpsan / cantilever arrangement, rotational (as catenary system moves back and forth under expansion/contraction), overturning as catenary system moves up and down through system uplift.

Portal and Gantry Structures have additional rotational forces based on the boom.

For the purposes of design, the OHL Equipment and fittings are considered to represent a "solid wall" against which a gale force 10 wind is blowing. As explained by the designers, you assume the system height (height between Catenary and Contact wires at the registration point) as being a solid sheet of plastic extending to the midpoint. Added to that is the total width across the Structure assumed vertically from top to bottom. The area is then taken as representing the surface area against which the wind loading is applied and the subsequent result is then increased by a factor of (I believe 1.5).

The foundation has to withstand this load, with the calculated dimensions increased to again provide a factor of safety (probably 1.5 again).

That is as explained to me a couple of years back

Thanks for the numbers Old Timer,

by my back of the envelope that's about 1000 lbs of force at the concrete, modelled as a fully fixed joint. I don't know concrete at all, but that doesn't sound like it should be too deep a hole. Perhaps I missed something.

About the indemnity, I was thinking of a scenario that has no relevance whatsoever. Of course it's useful here. That's what I get for doing two things at once...

 

[Old Timer]

Thanks for the numbers Old Timer,

by my back of the envelope that's about 1000 lbs of force at the concrete, modelled as a fully fixed joint. I don't know concrete at all, but that doesn't sound like it should be too deep a hole. Perhaps I missed something.

About the indemnity, I was thinking of a scenario that has no relevance whatsoever. Of course it's useful here. That's what I get for doing two things at once...

No worries, happy to help.

As for the numbers, I leave all that to the clever guys with the pointed heads

 

[cyclebytrain]

I claim my head is only slightly pointed -there's no Dr. in front of my name yet

 

[Teaboy1]

Wind load is easy to understand but what consideration is given to the 'wash' coming off the front of a train at high speed? As we know only too well the we have to stand well back (behind yellow lines) because the wash will knock you clean over sometimes. I imagine that would wallop a single pole type mast fairly hard, which presumable is why the gantry type is much better.
Most of our locos /trains only seem to be streamlined in the vertical direction, horizontally they are still a bit of a brick !! It should be all about air-flow management just like seen on TGV / JR and the shock loading on a single pole that designers need to consider in addition to what the wind is doing.

 

[Old Timer]

Wind load is easy to understand but what consideration is given to the 'wash' coming off the front of a train at high speed?

All calculated by the pointy heads chaps with their computer based programmes.

Us mere mortals simply follow the AFC design and build it !

 

[cyclebytrain]

Wind load is easy to understand but what consideration is given to the 'wash' coming off the front of a train at high speed?

Back of the envelope again, assuming a speed of about 135mph and using a very pessimistic model for the no slip condition would give about 4000lbs force.

This wouldn't be an unreasonable model (but it's still pessimistic) for the top of a viaduct; but it is completely invalid in a cutting, probably about a third of that figure would be more appropriate.

With better modelling, both the numbers will be lower.