Regarding the overhead wires on the GEML, I seem to remember reading somewhere that the electrification system dates back to 1949 on the section between London Liverpool Street and Shenfield.
As OHLE equipment is designed to have an operational lifespan of 60 years, does this mean that this section is being replaced and upgraded?
Furthermore, I believe it is the same if not similar design (the masts and portals at least, as the portals have the inverted "A" bracket for the registration arms to fit onto - forgive me if I've got the name of the part wrong) that is used on the section of the Manchester, Sheffield, & Lincolnshire Railway between Manchester and Hadfield/Glossop. Could somebody confirm if that is the case or not?
Yes, electric trains were introduced between Liverpool St and Shenfield on 31/12/1949, the first one was driven by the Minister for Tranpsort himself (accidentally, as it turns out).
The electrification was done in the couple of years before that, to a pre-war design. It was 1500v DC, and converted to 25kV AC (6.25kV AC from Chadwell Heath inwards) in the 50s over a long weekend. Although that sounds dramatic, actually it was fairly simple work; a lot of preparation and a simple switch over. The difficult part was getting the right trains (AC or DC) in the right places at the right time. The equipment is similar in design to that used on the 1500v DC system via Woodhead that was electrified around the same time.
Many of the structures are still in good enough condition that they have been reused for the re-electrification that has been ongoing since 2007. Some are being removed. The main differences are:
1) the new contact wire can be smaller in cross section, as it carries lower current than the original DC specified kit was designed to do (the contact wire was not changed when the conversion was done in the 50s)
2) the old kit was 'fixed tension' ie stretched* into place on each length and bolted* there. It is subject to thermal expansion like any metal, so in hot temperatures, like today, it sags and is more prone to failure. Hence speed restrictions on hot days. The new kit is 'auto tensioned' which as the name implies automatically adjusts the tension as the wire expands / contracts through temperature variation. When the whole route is done, there will be no need for summer speed restrictions for the OLE.
3) the old design was of a 'compound' form, partly because of the fixed tension. Between the contact wire and the catenary wire (the highest supporting wire, that sags over the longitudinal length between masts) there is an auxiliary wire. This helps keep the fixed tension contact wire in the right place.
Taken together, the old system has 3 thick wires in the air, plus lots of droppers between them. This is all heavy, and needed some big structures (masts, portals etc) and small part steelwork to hold it all up.
The new kit is much more lightweight, no auxiliary wire, and therefore needs less to hold it up. This is partly offset by the big structures needed to anchor each length and support the tensioning weights. Nevertheless, 3 times as much metal comes out compared to what goes back in; and the new stuff will be so much more reliable.
* technical terms.
Mr Phlopp may be along later to correct / add to the above.
