Cambridge to Kings Lynn has never been any other voltage. As mentioned by various others, the main reason for double track portals is to reduce the forces where their bases are attached, either because of ground conditions or where they are fixed to viaducts.
Great thanks for the help. In any case, it's a good start to have some official information on MVA Ratings. Have seen the YouTube video and I agree it's a good start for thinking about modelling for future Load demands.
Yes, I had thought that the main reason for the double track portals was the 1.5KV DC electrification on the Shenfield-Southend line.
I am a little curious to know what your project is though! Are you sketching what a potential power supply upgrade could look like for waml/fen line? Because if so I think it's worth considering the potential for the other lines to be electrified - mainly the felixstowe to Nuneaton corridor, and even the Breckland Line. Norfolk County Council's rail stratergy-ish of 2024 did actually mention electrifying that route. So capacity upgrades to the Fen line could be joined up with new lines-to-be-wired
Absolutely - a big +1 from me.
Are you sure that it's a 400kV line ? As the document you quoted in post #27 states that it's only 132kV.
There are likely two 132 circuits and two 400 circuits. The 400kV circuits are likely to be direct (and part of National Grid’s transmission network), whereas the 132s will connect other bulk supply points en route.
After finding another document (national grid, which is a lot clearer), the line is indeed 400kV (hence why I have now deleted my post). Burwell substation is 132kV after it's been transformered down from the national grid line.
In all my years of travelling on electric trains across the branch I'd always assumed that the feed was at Litlington near Royston.
I concur.
Tracking the feeding arrangements by what neutral sections are where is often the only evidence out there, but I think on ECML there can be a lot of red herrings around. Consider the original GN electrification of 1976 which is small enough and old enough to feature in John Glover's book in quite a lot of detail. Here both sides of Bowes Park NS are normally fed from the same single supply of Wood Green, and how Potters Bar MPTSC was bypassed in normal feeding.
Probably some more interesting things to see on that cabride - thanks for posting.
In the John Glover book there is vague mention of a Coreys Mill "substation" put in later on to help with Eurostar trains. But I think a good possible explanation is from this post:
Oh indeed. I'm fairly certain that the Royston branch was only supplied by Welwyn from the original electrification in the late 1970s. As you can see on this diagram I've seen in a couple of books that is apparently some level of officialness:
One thing I quickly learned in years of historical research is that something in books isn't necessarily right.
In 1990 a neutral section was apparently added to the WAML at Shepreth branch which suggests that wiring was extended from Cambridge station to the feeder station at Milton. The wires went all the way to Kings Lynn in 1992. Milton to Hitchin is a somewhat more sensible 27m 70c. Also, it's been said that Milton was originally a single grid supply until about 15is years ago when it was upped to two transformers as part of Thameslink works. Is this true, the only evidence is highly anecdotal and doesn't really make sense if you look at all the available arial imagery of the site from 1999 onwards. It looks like it always had two transformers, maybe they were uprated in the 2010s. If there's a cabride video of a train to or from Kings Lynn from the 1990s or 2000s that might be quite informative.
The 1978 electrification had 8 car trains to Royston, and lots of them.
Don't know about the original arrangement but when I worked on the SCADA Project (Hornsey & Doncaster ECR's to York) back in 2001, Milton FS fed the Cambridge lines down to the Mid Point at Litlington and Hitchin FS (via Corey's Mill Switching Station as was) fed from the ECML up to Litlington.