UK National Electric Grid has changed to DC

well, there is a DC link between France and the UK :-D

Ummmmm..... Obviously someone has got the connections mixed up!

DIY monitoring to the rescue

Thank heavens for that!

A very interesting page at the "Why 50Hz" link. I had no idea that generators were hydrogen cooled, and have been for 85 years! Also, I know there are some in the NG interested in legal matters. The should follow the link on the "Something interesting" paragraph at the bottom of that page. Who knew?!

Looks like the BMreports site has f***ed up.

Grid extranet is fine tho.

Oh Dear, the programmer obviously went to lunch and forgot where he was up to. Brian

As an aside, what is the reasoning about transmitting current via DC over long distances?Surely its got to be more complex to make it AC at the other end?

I'd have thought the reasons why its AC are down to the mechanics of generators and the number of phases and rotation speed etc. I mean if the generators ran much much faster, transformers would be much smaller and more efficient, but DC was abandoned due to fluctuations due to porr connections and the inability to change voltage levels for long distance uses. Brian

Lower losses when using undersea cables. Also, AC between countries would tend to mean you've got to keep a much larger area in phase, which is not feasible over a large area.

Yup it is more complex (and costly - due to the conversion required at each end), but for long distances you get lower losses (no capacitive coupling to the surroundings, so lower dielectric losses - this is particularly important for under water cables). You can use less copper for a given amount of power because you get no skin effect, and no losses from corona effect/discharge.

AC generally still wins out for most transmission due to the ease of generation and the ease of voltage conversion. Once you get over 300 miles or so (less in water), then DC starts to win on cost and efficiency.

I presume there are several DC links between different groups of mainland European countries which share electricity, so there are several different grids each with their own frequency (*). Or does every single country have its own grid - is *every* link between countries a DC one?

(*) Even if they all strive to maintain a 50 Hz average over any 24-hour period.

It's not black and white. There is a *very* big synchronous grid but not all the supplies within all the countries are connected to it.

That seems to have fallen of the bottom of the scale though.

During my thin sandwich degree course with what became GEC (and subsequently Alst[h]om), I did have spells at both Eggborough and Fiddlers Ferry, which included crawling about within the alternators.

The 500 MW alternators are indeed partially cooled by hydrogen circulating within the alternator enclosure. There is also direct water cooling of the stator windings.

Within the stator casing there are a number of water-filled heat exchangers (look like radiators) which then cool the hydrogen.

At Eggborough you climb into the spaces normally occupied by the vertical cooling water coils, and that isn't too bad. You then worm your way between bulkheads to get where you need to be. The hand lamp I had been given was just a mains fitting with reflector, so there I was, making my way around the stator end-windings and cooling water tubes, when there was a fizz and the light went out. There I was, in intimate contact with lots of earthed metal, not sure if I was about to be fried. Luckily, the problem was intermittent, and I lived to tell the tale (literally, obviously).

At Fiddlers Ferry, the technique was to stand on the alternator main bearing, facing an access panel. This was just about wide enough for me, so a no-go area for any more portly staff. The internal excursions were rather more tricky, with not a lot of room to get around. You had to exit feet first, feeling for the bearing housing before you could climb down again.

Chris

There are I think two mainland European grids. They are phase locked.

GB is another one. Ireland another one

To follow myself up, a couple of anecdotes:

The stator enclosures, when complete, are explosion proof.

Before and after maintenance they are purged using CO2.

A power station which had been extended only had a regulating valve in the hydrogen line where a shut-off valve should have been. After some maintenance work, having been partially boxed up again, the electrical kit was high-voltage tested. Enough hydrogen had seeped past the inappropriate valve for there to be a significant explosion, with IIRC the internal end-plates being damaged.

On another occasion, I was not surprised to see a "no smoking sign" near one of the alternators, when it was running.

What made it rather pointless was that someone working nearby was being kept warm by one of those rocket-like paraffin burners. I never heard a bang.

Chris

I've had that one for a while. I'm not sure how to interpret it's readings. Sometimes the needle swings wildly up and down, then suddenly seems to get stuck. At other times it goes off-scale, and stays there. It rarely agrees with the Gridwatch meter.

All these electrons come to my house down one cable and all of them get to go back.

I'm not keeping any of them, or destroying them

why is there a bill I'm paying?