Great Western Main Line electrification - ongoing discussion

[whole diary]

[IndustryInsider]

The support structures may well be tailored to the location, (I don't think we've seen the details yet) and will be positioned to suit the piers of the bridge, rather than the normal distances apart. 
Something different to the usual has already been fitted at Moulsford, a more lightweight centrally mounted cantilever system.  So I suggest that Maidenhead bridge may be similar.

Some concrete bases with fixings have appeared in each of the recesses in the cess each side of the bridge, so I'd expect that to mean structures fitted there rather than in the middle.  Moulsford is essentially two separate bridges bolted together so much easier to fit structures down the middle - not sure there's the room over Maidenhead Bridge.

[paul7575]

The screen conductor is always with the other (non-OLE^▸ (Overhead Line Equipment, more often "OHLE")) cables.

I thought as installed between Tileshurst and Didcot the screen conductor was the lower one linking all the masts, not mounted on an insulator - is that just another earthing conductor?

Paul

[stuving]

I thought as installed between Tileshurst and Didcot the screen conductor was the lower one linking all the masts, not mounted on an insulator - is that just another earthing conductor?

Paul

I've not seen anything about a wire like that - but this is a description off the screen conductor, written about the change to ATF on the WCML^▸ (West Coast Main Line):

Further changes see the introduction of a return screen
conductor installed in parallel with the traction return
rail and is positioned within 200mm of telecoms cable
routes or normally within the same trough. This cable is
a 19/4.22mm (170mm2) and is connected to the
traction return rail every 400 metres this is normally via
structure to rail bonds or by dedicated spider plates

[Electric train]

The screen conductor is always with the other (non-OLE^▸ (Overhead Line Equipment, more often "OHLE")) cables.

I thought as installed between Tileshurst and Didcot the screen conductor was the lower one linking all the masts, not mounted on an insulator - is that just another earthing conductor?

Paul

The lower one on the masts is the earth wire which bonds all the structures together.  The screening conductor is laid in the trough routes and its called a "Mutual Screening Conductor" (MSC), this is connected to the running rails approx. every 400 metres, either directly to both where axel counters are used for train detection or via impedance bonds where conventional track circuits are used.   The principle of the MSC is it carries a small amount of return current which is anti-phase the contact wire, the MSC being placed right next to signal and telecom cables means it negates any induced voltage these cables may pick up, things like Signalling Loc cases are also bonded to the MSC.  The MSC is effectively earth but does not pick up every OLE structure this done by the earth wire.

[paul7575]

Thanks to Electric train for the additional details confirming that the cable on the masts is there for conventional earthing, and the screen is separate and located with the non-OHLE cabling.

I've found a photo I had taken at Pangbourne so I've added it just for interest to show the mast mounted cable I was referring to.

Paul

[Electric train]

Definatly the earth wire.

I did get my screen conductors muddled up    There are 2 types MSC and RSC - Mutual Screening Conductor and Return Screening Conductor.  The tpye use on the GW^▸ (Great Western) is actually an RSC as it use part of the return current, the MSC is still a conductor in the cable trough routes but it is not connected the traction retun, it has earth rods placed approx every 400 meters this type of screening is used on the "clasic booster transformer return" 25kV system.

The MSC is not as effective as the RSC, the MSC requiring more maintenace as the earth rods need testing every ew years

[BBM]

New structures have appeared in the last 2 days in Sonning Cutting between Duffield Road and Butts Hill Road bridges on the Woodley/Sonning border.

[BBM]

...and as I type, this is happening at the bottom of my garden (apologies for the state of my compost heap! )

[John R]

Have you set up a Facebook page yet "Save BBM's View", demanding different, less visually intrusive, overheads behind your garden?

[BBM]

Have you set up a Facebook page yet "Save BBM's View", demanding different, less visually intrusive, overheads behind your garden?

As long as I get a better train service from Twyford they can do whatever they like! 

(as you might guess from the photo my view of the structures is somewhat hidden by vegetation etc anyway)

[Bmblbzzz]

Perhaps regular travellers will set up a Facebook page demanding a more visually appealing BBM compost heap! 

[Thatcham Crossing]

Noticed lots of chaps in yellow with surveying instruments around the station area at Newbury the other day - perhaps work is due to start soon ;-)

[eightf48544]

Although fully wired pass my house in Taplow I can't see the O/H or the trains for the trees!

[TaplowGreen]

Although fully wired pass my house in Taplow I can't see the O/H or the trains for the trees!

Ditto - and let's hope it stays that way!!! 

[Gordon the Blue Engine]

I notice that the OHLE on the UM and DM between Pangbourne and Tilehurst is earthed (ie cables across the insulators), so it looks like following the publicity run with the 80x on electric it’s been switched off for now so installation work can be continued. 

Notice also that the autotransformer cables (ie the ones above the gantries) on the UM and DM between Pangbourne and Tilehurst are not yet all installed: presumably the test run with just the one train drawing power didn’t need the voltage stabilisation that the auto-transformer system provides (I’ve tried to understand what ET and others have explained re OHLE!).