On Tue, 6 Mar 2018 14:57:56 +0000, Chris Green wrote:

Andy Bennet wrote:
On 06/03/2018 13:52, newshound wrote:
On 06/03/2018 13:46, Andy Burns wrote:
They've lost 5 minutes worth of cycles since mid-January

https://www.entsoe.eu/news-events/announcements/announcements-archive/Pages/News/Frequency-deviations-in-Continental-Europe-including-impact-on-electric-clocks-steered-by-frequency.aspx


Seems surprising.

I'm not sure if the continental grid is kept synchronised across all
countries. In the UK, any daily lag is usually fixed overnight.

Good job the interconnctors are DC!

It's exactly *why* they're DC as I understand it, the difficulty of
synchronising our grid with the French grid.

Isolating the grids into separate frequency regions is useful with a relatively
weak connection but it's not just for system stability and frequency purposes,
the losses are lower and above all you have the ability to alter power transfer.
If the UK agrees with France for a 500MW export from our end that is nothing
more than a few key presses away. They can set a specific export level almost
regardless of the prevailing conditions on the AC network with small balancing
adjustments in the order of 10's of MW's easy to make. The effect of that
transfer will be to make the UK frequency and voltage to drop and the
continental frequency and voltage to rise. That will be corrected by the
generator governors responding throttling back the continent and raising in the
UK.

Reverting to a fully floating state and reversing flow without physically
breaking the connection is also extremely rapid.

That transfer adjustment can be done on an AC network with quadrature boosters,
but then the losses end to end would be significantly higher and there would be
no separation of frequency region.

For longer cables DC makes sense for other reasons but for the 25 odd
miles across the channel I'm pretty sure it was the synchronisation
issue that was the reason for using DC.

Weren't they originally huge mercury arc rectifiers or is that just my
wierd imagination? :-)

The original link built back in the 60's did, the 2GW link from the 80's uses
thyristors. Fully updated and refitted a few years ago with a new control
scheme and uprated power electronics.


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