Awhile ago we had a brief discussion about the DC interconnector
between the UK and France. Daughter Elanor's partner Stuart is a
protection and control engineer with EDF, and I asked him about it.
He's done me proud as you can see:
Begin forwarded message:
> With reference to [power transmission], losses are less with AC
> transmission
> because high voltages are used, typically 275kV and 400kV at National
> Grid
> level. High volts = same power, less current. Transformers used to
> reduce
> this to acceptable domestic levels will only work with AC.
>
> Three phase AC is used because winding the machines only needs
> marginally
> more effort than a single phase one and also, if you keep the system
> balanced, you only need three conductors, whereas you will always need
> two
> for single phase (in effect a live and neutral).
>
> The chain is thus: generation at typically 12kV, transmission at 275kV
> and
> 400kV, down to the Distribution Network Operators (i.e me) at 132kV,
> then
> 33kV, 11kV and 415/240V. There are odd bits of network around that
> operate
> at 66kV, 22kV, 6.6kV, 3kV and 2kV. All tend to be legacies of the old
> municipal electricity authorities that operated as distinct
> organisations
> prior to the formation of the area boards and the British Electricity
> Authority (latterly the CEGB) in 1947.
>
> The 2000MW DC link to France enters the UK at Folkestone and there is a
> converter station at Sellindge. That is a 400kV site operated by
> National
> Grid, but we also have a substation there. I had a tour once. I think
> it was
> completed in about 1986 - the dying days of the CEGB prior to
> privatisation.
> The supergrid transformers are of an unusual design and unlikely to be
> available again, so they had an extra made specially and it is
> 'parked' in
> its own bay ready to be used if the need should arise. It always used
> to
> import to the UK, but I remember that changing in around 2001 when
> flows
> regularly passed in either direction. That flexibility is brilliant
> for the
> market, but often causes unpredictability and problems for engineers!
>
> DC transmission is ideal for interconnection between two systems with
> different synchronism operating at different frequencies. Over large
> distances, conventional HV AC overhead transmission also becomes
> uneconomic.
> The number of substations, insulators and the lengths of conductor are
> more
> expensive than building converter stations and having two DC
> conductors (+ve
> and -ve). I think China is forging ahead with a number of HVDC links.
> As
> with many things, they are leading the world in developing their
> infrastructure rather than letting it rot.
>
>
––
All the best
Bruce
"Houses are but badly built boats so firmly aground you cannot think of
moving them" Arthur Ransome, 'Racundra's First Cruise'
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