On 28/07/14 12:30, The Other Mike wrote:

How do you phase lock the French grid to the Belgian Grid to the Dutch Grid to
the German one to the Swiss one etc etc. It doesn't in the main involve DC and
at AC it is no real problem.

Are they phased locked? I don't know.

If they are, then they have relatively long borders which means lots of
interconnections.

You aren't going to hold 2 disparate grids in sync with one or two cross
channel links - National Grid has enough trouble holding the UK grid in
phase between Scotland and the South (they have (or had at Bankside at
least) a phase indicator colloquially known as the "scottish wobblemeter".

If it started oscillating, a certain amount of panic ensued...

There is potentially 'as big a problem' with the UK grid system if it splits
during a major disturbance into a two or more islands of load and generation. In
this case (since the late 80's or so) the synchronising systems have an
additional mode where they just sit there primed until the phase angle and
voltage discrepancy falls with certain limits (which are deliberately set wider
than for normal operation) and the breaker then closes, a successful closure
could potentially take a few hours.

Yes. There's an interesting document that you can google for which
outlines the Nat Grid Blackstart procedure. Rather involved...

As the grid system operator is separate from the generation operator in the UK
there is no generation intervention required as such, just switchgear that can
take occasionally take a bit of abuse and generator governors that can hold a
set point frequency.

P.S. There is a long established 400kV AC link between Spain and Morocco with a
similar distance underwater to the UK - French link.