Curved catenary

[Fat Controller]

Brian,

 

A great deal of older railway catenary (OLE), up to and including the 1950s BR 1500V electrifications, was of the "fixed tension" type, Ie solidly anchored at each end and pulled tight on erection. The down side with this arrangement is that the tension changes with temperature as the wire expands and contracts. In winter, the risk is that the wire can get pulled so tight that it breaks, and in summer, with expansion, the wire sags. At the speeds prevalent in the 1950s, this was tolerable, but the ability of the pantograph and the wire to cope with higher speeds is limited, hence the development of "auto-tensioned" OLE, where the wire is tensioned by weights.

 

In the UK, it has been a problem on the Great Eastern main line, the inner end of which had been built as fixed tension with the original Southend electrification. The result was the imposition of speed restrictions in summer and, over the last few years, a major programme to completely replace the OLE with new auto-tensioned equipment.

 

Jim

The 'fixed tension' catenary on the former GE lines caused problems a few years ago; during a heatwave, it sagged enough to short to earth via a Class 47, which didn't do the loco any good. On some of the ex PO and Midi routes in France, draconian speed limits have to be imposed during hot weather.

[Suzie]

Going back to the OP, I hope Suzie now realises that 'curved catenery' is strictly restricted to model railways play-value train-sets and there's no such thing on the real thing and therefore any self-respecting model railway

 

 

In the U.K. yes, disappointingly, but lots of nice overseas prototypes.

 

I am beginning to wonder now if Milwaukee Road might have had some...

[Edwin_m]

Hi Edwin

 

As Sharpey and Jim have stated the OLE without tensioning weights is called "Fixed Tension". Plus all the BR documents and drawings I have laid my hands on call it so. We do not need another model railway term to muddy the waters so lets keep to what it is called on the real railway.

It wasn't me that invented it.  Both Wikipedia and this 1988 BR document refer to "fixed termination". 

[Brian Harrap]

Oh dear, but thanks anyway. I think I'll call my three phase OHL work non temperature compensated and hope to get away with it. B

[jim.snowdon]

Just don't get your wires crossed.

 

Jim

[Brian Harrap]

Thanks Jim, that's another area for discussion. When I travelled up the La Rhune (three phase mountain railway) I observed that the leading collector arm was lowered (manually, using a piece of rope tied to the arm) as it passed under the 'frog' in the overhead, then raised again and the rear one then lowered - quite comical to watch but not suitable for main line use I suspect. B

[keefer]

Brian,

 

A great deal of older railway catenary (OLE), up to and including the 1950s BR 1500V electrifications, was of the "fixed tension" type, Ie solidly anchored at each end and pulled tight on erection. The down side with this arrangement is that the tension changes with temperature as the wire expands and contracts. In winter, the risk is that the wire can get pulled so tight that it breaks, and in summer, with expansion, the wire sags. At the speeds prevalent in the 1950s, this was tolerable, but the ability of the pantograph and the wire to cope with higher speeds is limited, hence the development of "auto-tensioned" OLE, where the wire is tensioned by weights.

 

In the UK, it has been a problem on the Great Eastern main line, the inner end of which had been built as fixed tension with the original Southend electrification. The result was the imposition of speed restrictions in summer and, over the last few years, a major programme to completely replace the OLE with new auto-tensioned equipment.

 

Jim

 

I take it these were the sections which kept the original 1500v DC portals etc. when the voltage was changed to 6.25kV then 25kV AC?

[Fat Controller]

I take it these were the sections which kept the original 1500v DC portals etc. when the voltage was changed to 6.25kV then 25kV AC?

Correct.

[Dagworth]

I take it these were the sections which kept the original 1500v DC portals etc. when the voltage was changed to 6.25kV then 25kV AC?

6.25kv was never a system-wide voltage, it was only used for certain sections where it was originally thought that there was not enough clearance for the full 25kv.

 

Andi

[Clive Mortimore]

6.25kv was never a system-wide voltage, it was only used for certain sections where it was originally thought that there was not enough clearance for the full 25kv.

 

Andi

Hi Andi

 

On the GER lines the 6.25Kv used the same insulators as the 1500v dc. So I think there was a bit of cost saving going on.

 

Look at photos of AM9s at Stratford in the 1970s and then at them in the 1980s after conversion to 25kv.

[jim.snowdon]

For the benefit of Brian (and every one else), here is a rather wonderful example of 3-phase "knitting" installed on Italian State Railways c.1915,

 

 

and an example of curved single-phase OLE on the original Norfolk & Western electrification of 1915

 

 

Both pictures extracted from Dover's "Electric Traction", 1924 edition.

 

The structures, particularly those of the N&W, make interesting comparison with the behemoths being put up by Network Rail for the Great Western electrification, and being on a curve, the N&W ones weren't lightly loaded either.

 

Jim

[EL-3A]

Nah - it's only trigonometry ..............

But the term "Fixed Tension" is how it is described, certainly in all my dealings with OLE Engineers over 30 odd years.[/quote

 

Just saw this post. The Virginian Railway in the US used curved catenary. Google Virginian catenary and you should find some useful information. I built a Vgn layout some years ago but found, like the prototype in real life, as radii got sharper it was very difficult to maintain a curve.

[brigo]

Not sure if it is still classed as catenary but the prototype does occasionally resort to a heavier version with genuine curves.

 

http://www.fotocommunity.de/photo/murgtalbahn-1-roman-verlohner/11862247

 

This is on the Murgtalbahn which runs between Rastatt and Freudenstadt in the Black Forest. A former DB line, it now forms part of the Karlsruhe tram system. Because of clearance problems, when it was electrified at 15KV, they resorted to a solid conductor bar in the tunnels and sometimes between.

 

I believe a similar system is used in Salzburg's (Austria) main station on the platform roads.

 

Brian