Rail Charging Converter system by Siemens

[Elecman]

I would have thought they'd use a cable from the substation, but not 25kv. It's about a mile. If 400kv is available then a pair of transformers at the railway would make for a relatively simple ATF feeder station.

All 25kV feeders that are in anyway remote of the 400kV grid connection point are cabled at 25kV to a remote NGET switch/control room at the railway end. Even short ones like Heyrod( literally across the road) to the more remote ones like Harker and Frodsham.

 

[plugwash]

I am not an electrical engineer, but as I understand it, instead of connecting to the 132kV supply and stepping down to 25kV, it connects to the local Distribution Network Supply (11kV?) and somehow stepping up to 25kV.

Conventionally the issue with railway traction supplies was not so much the voltage, its the fact that trains are very large single phase loads. Single phase loads drawing multiiple megawatts are not normal and electricity distribution networks are not normally intended to deal with them. Outside the railway industry most electrical loads are either small, or designed to accept 3 phase power.

The result of this was the railway had to tie into the grid at a higher level to avoid causing too much imbalance. "SFC"s avoid this by presenting a balanced 3 phase load to the grid, and converting that to single phase power for the trains.

 

[ABB125]

If I'm following correctly, is this the change?

Out of interest, where is this diagram from?

 

[GraphitProjekt]

I've been hunting down electrical grid schematics and maps etc, and I found out that most of the best info on the transmission system if you google the term "NESO" (National Energy System Operator) which I think if the official institution in charge of the transmission grid that just happens to be owned by the company National Grid. There are a few different files quite readily available online I found by Googling something like "NESO Network Diagram".

 

[Nicholas Lewis]

I'm pretty sure all single phase 25kV feeder stations are connected to 132kV or above networks, precisely because the disbalance would be too great for 33kV single phase. The only edge-cases I know of are for really short test track areas in depots like Selhurst and Ashford which run off the 33kV Network Rail system - but it's not like they can power more than one train, very slowly, probably only at night when the draw on the 33kV lines are low. I don't disagree that SFCs can allow way easier DNO connections for AC OLE - but there is basically no such thing as a single phase 33/25kV connection.

The LTS and parts of the GE were originally run at 6.25kV off the 33kV distribution system using Scott connected transformers. These transformers allowed a three phase supply to be converted to two phase (2 x 6.25kv) but that rarely presented a fully balanced load as unlikely both supplies had the same load on it.

 

[GraphitProjekt]

The LTS and parts of the GE were originally run at 6.25kV off the 33kV distribution system using Scott connected transformers. These transformers allowed a three phase supply to be converted to two phase (2 x 6.25kv) but that rarely presented a fully balanced load as unlikely both supplies had the same load on it.

this also allowed them to use the same distribution architecture as the previous 1.5kV system. Liverpool Street to Shenfield used to have 1.5kV substations at Bethnal Green, Stratford, Chadwell Heath, Gidea Park, Shenfield and Crosswall (Fenchurch Street) - connected via the railway's 33kV cables powered by the grid at Crosswall and Chadwell Heath (Crowlands 132/33 i guess), Bethnal Green became a grid supply point instead of Crosswall in 1960 when it was expected to power the WAML at 6.25kV as well. When it all to 25kV in 1980, I believe the 33kV cables were handed over to the local grid and were still in use by 2014. In the Ilford area, some of the brackets that carried them now carry the ATF line in trunking which is a nice moment of history kinda repeating itself.

 

[ABB125]

I've been hunting down electrical grid schematics and maps etc, and I found out that most of the best info on the transmission system if you google the term "NESO" (National Energy System Operator) which I think if the official institution in charge of the transmission grid that just happens to be owned by the company National Grid. There are a few different files quite readily available online I found by Googling something like "NESO Network Diagram".

Thanks, that's fascinating.
Do you know what the dotted lines mean? I'm guessing"out of service" or similar?

 

[GraphitProjekt]

Thanks, that's fascinating.
Do you know what the dotted lines mean? I'm guessing"out of service" or similar?

No idea unfortunately! Seems unlikely to me they'd have that much stuff let dormant. One of the problems of finding random files online is that you have no idea what their context is.

 

[Richard123]

Weren't all the GSPs agreed in the pre-Grayling era when they would all be 400/50kV single phase for at AT system (275 in the case of Chesterfield)? I share this forum's optimism for SFCs in general but I don't think it'd be worth it to change the design of something that's already in delivery.

Yes, with 7+ year lead time for supergrid supplies, NR committed the traction power supplies years for MML years ahead of scheme development.

 

[Nicholas Lewis]

Yes, with 7+ year lead time for supergrid supplies, NR committed the traction power supplies years for MML years ahead of scheme development.

As did Scotland with its grid supply points on the Borders line and in Fife neither of which looks like seeing anything to connect them to for a while yet.