British Railways OLE, part three, Anchor Points

[Clive Mortimore]

Sorry it has been a bit of time since I last posted anything regarding overhead line equipment. The main reason is that I have so many drawings that need dimensions changing from when I drew them and labelled them for 4mm scale modellers to the prototype measurements. Well I still haven't got round to doing this so please be patient with me and put up with the 4mm scale labelled drawings. Thank you.

 

 

Mid Point Anchor.

With Automatic Tensioned equipment the contact wire is held level by the weights either end. The contact wire could move towards one end or the other. This would cause a twist at the registration points. The drag on the contact wire by the locomotive or multiple unit pantograph tries to push the wire towards one end. To prevent this the catenary wire is anchored in the centre of the wire run. If you have more than 14 masts on your layout and do not want to have an overlap then a mid  point anchoris ideal.

 

 

 

On Mk1 one equipment it is a portal mast for both twin track and multiple tracks. In some locations it is a lattice mast normally lightweight construction but sometimes a medium weight and in other places a girder frame is used. Oddly for some reason many of the stations on the LTSR have an anchor point half way down their platforms.

 

 

 

 

Mk111 equipment has two differing types of anchor. Twin track uses three special masts. The two outer ones have a tie wire and a fasting point for the anchor wires. These anchor wires hold the modified cantilever arm in position longitudinally to the track. The special cantilever arm has with an apparatus that holds the catenary wire in place as well as fixing points for the anchor wires. Multi track equipment including headspan will be included in a later topic.

 

 

 

 

 

[Dagworth]

I'm glad to see Clive has posted this, mid point anchors have been very much on my mind with Ravensclyffe as there are an awful lot more than fourteen masts/portals. Because even the yard is more than the critical fourteen I needed either an overlap or a mid point anchor in the centre of the yard, where it will apply to six roads on the same portal. Rather than try to build overlaps across six roads a single anchor portal is the answer, there is automatic tensioning gear at each end of the yard already. A long while back I'd built a super heavy portal with the idea of it being the anchor and finally today I've been able to identify this type of portal in use as solely an anchor, normally super-heavy is used where wires start for crossovers and the likes, and as tension frames for multiple tracks. Anyway, Tring has such a mid point super-heavy portal half way along the platform so I can justify using the portal I built as an anchor knowing there is a prototype example :-)

(If I'd used it without being able to show an example in real life I could not have looked at the board without being doubtful if it was correct)

This is the beasty in question

On The Up In Tring - 87 017 by Sir Hectimere, on Flickr

 

Question is, does anyone have any more photos of this portal BEFORE it got converted to UK1 and ceased to be an anchor?

 

Andi

[Clive Mortimore]

Hi Andi

 

I have had a look at a 1976 1/2500 map http://www.old-maps.co.uk/maps.html and it shows a cross over from the slow to fast lines, could this mast also be a termination point for the wires for the cross over? 

 

A similar heavy mast acting as both a terminating point and a mid point anchor can be found at Kelvedon.

 

 

 

Sorry the drawing has not had its side view finished.

[Titan]

 Because even the yard is more than the critical fourteen I needed either an overlap or a mid point anchor in the centre of the yard, where it will apply to six roads on the same portal. Rather than try to build overlaps across six roads a single anchor portal is the answer, there is automatic tensioning gear at each end of the yard already.

Andi

 

Most yards would be Fixed Termination rather than Automatically Tensioned - i.e. no balance weights or mid point anchors, and the wires just sag a bit when it gets hot. There would normally be an overlap on the exit of the yard as the interface between Fixed Equipment and Automatically Tensioned, which may well be of the insulated type for sectioning purposes.

[Dagworth]

Slight change of plan, with being unable to justify using the super-heavy portal as an anchor I'm going to build a second one and make them both into tension portals and put an overlap on the main line alongside the yard...

 

Andi

[trisonic]

Clive what was the main difference between the old DC OHLE and the later AC?

 

I'm thinking of Shenfield (where there was a DC transformer supply just before the station (beside the bridge on the up side) am I right in thinking that  the power lines were a lot higher? Or is it just a tiny youthful trisonic not remembering correctly?

Great threads on this subject btw very valuable...

 

Best, Pete.

[Dagworth]

Further to what DM has said there, all that extra wire weighs a lot more and so needs substantially more support. The overhead through Stratford is a good example of DC infrastructure, multiple wires and massive portals. The DC stuff out of the Street was converted to AC in early November 1960. The main visible change was larger insulators, the rest of the overhead equipment remaining unchanged (Main change of course being the power supply arrangements!) This equipment was untensioned and remained so in AC use.

Shenfield to Clacton (and branches) was then electrified with BR Mk1 equipment. This uses lighter portals and cantilevers. Colchester to Harwich and Norwich was added in the mid eighties using Mk3 with headspans and cantilevers and with a significantly reduced encumberance.

 

A cab ride from the Street to Norwich was quite an education of the different types of equipment.

 

Andi

[George Leacon]

Very interesting stuff - thanks everyone for posting!