Electric trains ( from Converting 3 phase to single phase )

[bernardgreen]

The 25 kV overhead supply for electric train traction is single phase.....

Does this mean the supply to Network Rail's power feeders is a single phase supply from the local electrical supply network which would create a significant un-balance in the local network.

Even if it is a "single" phase derived from two network phases there will be un-balance between the phases.

Or does the system take energy balanced across three pahses and then convert that energcy to a single phase supply to the overhead 25 kV ?

 

[aptsys]

As far as I know, the network is split into sections with the transformers across different phases. SVCs are used to stabilise the network.

 

[aptsys]

See image attached. Insulating sections are inserted where the supply is going to be fed from a different set of phases. Most of the transformers can be remotely switched between any of the two phases as needed.

 

[bernardgreen]

Impliies a single phase transformer.

I have e-mailed the question to Siemens who aare installing the local feeder station.

Partly for my own interest but also because a lady living close to the railway asked me " Will the light flicker when a train goes past ? "

I don't think they will flicker as the DNO will almost certainly require that the supply to Network Rail traction is a dedicated supply and not taken from any part of the local network

 

[aptsys]

View attachment 167657

Impliies a single phase transformer.

Yes, single phase transformer, but each is fed from different phases, and the output of which is separated by insulating sections on the overhead centenary wires

 

[Jackrae]

overhead centenary wires

Excuse me being pedantic but your 100 year-old wires are actually "catenary wires"

 

[IJWS15]

There was once a three phase locomotive built. The supply phases were connected in catenary and the two running rails.

IIRC It was the Swiss, probably a man called “Brown” of Brown Boveri later ABB following merger with ASEA.

Now on the original post think about how the train travels from one phase to the next, on load switching of the 25kv without drawing an arc at (in the UK) speeds of up to 150 mph. Look up Vacuum Circuit Breaker.

 

[Jackrae]

About 25 to 30 years ago, whilst driving north on the M74 in the very early hours of a dry and freezing winter's morning (pre dawn) I was overtaken by an electric passenger train. The whole train glowed with St Elmo's fire. A unique experience that I'll never see again.

 

[bernardgreen]

I was overtaken by an electric passenger train.

A passenger train on the M74, ? Reminds me of the station anouncement. The train standing on platform 4 will be the nine thirty service to London. if the driver can get it off the platform and back onto the track"

 

[mfarrow]

Sometimes the TNO will install load sharing equipment on site (though I’m not entirely sure what this consists of) to balance out a 2-phase supply across 3 phases.

400kV is generally the norm now unless not available. 132kV was the maximum possible when the original networks were installed from the 60s to 90s.