Strange structure in the Thames Estuary

[pandroid]

I've sailed past a couple of these offshore farms in Denmark, and they dont seem to cause any issues (admittedly about 10 poles rather than 30), in fact I thought they were rather pretty, and at least you can see 'em. In terms of disturbance, the marina clubhouse at Borkum has one right outside the building, and it didnt keep me awake.

Having sailed past this site last year, I dont think they are as near the Spitway as they might appear on the map. Certainly the existing Met mast is a long way from the Spitway. (Yes - I know the Spitway moves occasionally, but I'm assuming they have done those sums). These things really are on the sandbank,

At the local RYA seminar last year, the RYA seemed to be against them, but they got shouted down by all the locals who thought, on balance, they were a good thing.

Anyone who has kept their boat near to Grain or Kingsnorth power station will know what I mean. The boat gets covered with an oily sludge.

 

[Twister_Ken]

Hydrography question

Could it be that by siteing a lot of pylons in a relatively small area, that the local tidal flow will be slowed, leading to greater deposition of silt, leading to shallower depths, leading to slower tidal flow, leading to greater deposition of silt, etc. And of course this would increase the tidal flow through the channels, leading to greater scouring, leading to greater depths, leading to faster flows, leading to...

Maybe you're going to end up with lots of new islands in the Thames estuary.

 

[Mirelle]

60 cycles AC?

presumably they will be supplying alternating current at 60 cycles, so the speed of rotation must be constant, and the 60 cycles ensured either by gearing or by the means of winding the rotors and stators? Could use an expert here!

 

[Mirelle]

Its fearsomely complex!

I have not meade measurements, of course, but the WW2 anti-aircraft fort complexes, such as the Red Sand and Shivering Sands forts, and the old Gunfleet pile lighthouse, don't seem to have made any difference to the sands that they sit on.

The tidal flow in the estuary is very odd, at certain states of the tide it sets across the banks rather than along them. Colne Bar, for instance "should'nt" be where it is at all!

 

[IanPoole2]

Re: Colne Bar

Where's it supposed to be then?

 

[Jacket]

Re: 60 cycles AC?

Did all this stuff years ago, and forgotten most of it including all the fancy names that power engineers have for everything, but here goes.

Yes, the speed of ratation has to be kept constant to produce a constant frequency output- any numper of rotations per minute will do, as long as it can be multiplied up to a frequency of 60 Hz. I think the "multiplication" is done through the number of stators installed rather than gearing, which would provide unwanted friction, though that may have changed.

The interesting bit is that the rotors can't be made to rotate faster or slower than its set speed. If it does, it starts trying to produce power at a different frequency. But because the generator is connected to the national grid, which effectively is fixed at 60Hz, any change in speed by the generator leads to the generator acting as a motor, and either slowing down or speeding up the wind turbine to its proper speed. This obviously draws power away from the national grid, and is to be avoided. Therefore you want to be careful that you don't build the turbines in an area where the wind is gusty- yes, you can change the angle of the turbine blades to control rotation speed, but its not instantaneous.

Not sure how much of the above is correct, but its a good guess.

 

[Mirelle]

Well, how about across the mouth of the river?

like most river bars are?

But it isn't - it lies more or less across the Wallet, and pretty much in line with the river itself - at 90 degrees to where it "ought" to be!

The other odd thing about it is that the tide sweeps over it, so it "ought" to have been swept away....which shows that the banks dont just lie where the tide is slack.

Very odd stuff.

 

[IanPoole2]

Re: Well, how about across the mouth of the river?

Is it not that the water from the Colne is pushed around by the ebb from the Blackwater causing it form where it is, and should be called the Colne & Blackwater bar?
Then again the Colne's silting up fairly rapidly now so I would be amazed if much suspension made it out of the river at all!!

 

[Twister_Ken]

Doesn\'t all this winter rain...

...give the rivers a good flush, or do they not drain enough hinterland to carry much fresh water?

 

[Mirelle]

I hink the problem is

that Colchester Hythe is no longer a port, so the channel is no longer dredged, and water abstraction has greatly reduced the flow of the Colne. In earlier times (well, down to the 1930s) the Colne was important for its water mills, so the flow was always reasonably constant. Reclamation for building and water abstraction have greatly reduced this, and the ending of commercial shipping means that the channel is no longer dredged. So it is silting up like nobody's business, but so are our other local rivers, so maybe changes in farming have something to do with this as well.

 

[Anchorite]

Re: Sorry wrong answer, wrong person! NM

§

 

[Anchorite]

Re: Wind in the wallows

The hard facts from the Dunkerque "farm" (how can it be a farm??): there are 9
units. Rotor is 28 meters diameter. Turns at 43 rpm (so tip speed is 140 mph).
Geared inside up to 1500 rpm to produce 300 kW with windspeed 30 mph (a good Force 6). Turbine is orientated by hydraulic motor in the hub housing which also contains a variable speed mechanism. They expect an output efficiency of about 30% over a year.

 

[Gunfleet]

Re: I hink the problem is

If you'd seen the water at the bottom of the park in Colchester a couple of weeks ago you'd have thought there would be plenty of flow in the Colne.

 

[peterb]

Re: 60 cycles AC?

I thought the standard European power frequency was 50 Hz? It's certainly 50 Hz in the UK!

 

[Anchorite]

Re: CPS or Hz (frequency)

Correct: zones of British influence are 50 Hz, those "aided" in the past (or
present) by the Americans are 60 (like Saudi, Korea etc). American influence
also leads to 127 volt singlephase voltage. Anyway no-one has the right plugs.

 

[oldgit]

Just a quick comment.

FWIW.As a local (sort of) I would much prefer a wind farm on the horizon as opposed to the 3 coal/oil/gas stations that I have on my doorstep. Find it very difficult to understand the objections raised by the good burgers of Whitstable to the proposed site near to the existing forts.Bit Of nimbyism perhaps or would they like to have the next coal fired station down by the harbour instead.?
Same thing with waste incineration.People have no problem stuffing dustbins full of rubbish,but god help anyone who suggests putting an incinerator in their locale.IMHO

Oooh look its still not dark and its nearly 5pm

 

[DanTribe]

re- nimbyism

Is that when people use their mobile phones to organise protests against local mobile phone masts?

 

[Mirelle]

My fault

years in zones of American influence led me astray.

 

[Guest]

Re: 60 cycles AC?

Well, yes and no. You don't have to do all that keeping the blades going at exactly the right speed stuff these days if you don't want to - at least my dad's designs didn't. Gou can gear it appropriately into a generator and then feed the whole thing into a lump of power electronics called a static frequency changer (for example) which by cunning control keeps the output frequency constant irrespective of what's going into it. Don't know if these guys do that but it's one option. Control of the blade speed should only be necessary within a certain range, and particularly to stop them overrunning in high winds and breaking up.

Sorry, bit of nerd there. Oh yes, it's 50Hz too. Can't wait till they start building them and I can take my sons out from West Mersea to see them. there should be some going up off great Yarmouth and Lowestoft too. Some enterprising offshore oil rig engineering companies are using their experience to diversify and good luck to them I say.

 

[Twister_Ken]

23 rpm

At the windfrarm I was staying near:

<A target="_blank" HREF=http://www.natwindpower.co.uk/towlaw/index.htm>http://www.natwindpower.co.uk/towlaw/index.htm</A>