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Topic Title: Distribution of power from windfarm
Topic Summary: Cable ratings for windfarm connection to grid
Created On: 23 April 2013 09:29 PM
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 23 April 2013 09:29 PM
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seeker

Posts: 319
Joined: 10 March 2007

A new windfarm is being built in my area (East Yorkshire) which will ultimately have 12 turbines and which I believe will be rated at 3Mw each So far four are erected and the blades turning which leads me to think they are possibly generating a reduced amount.
The site presently only has one three conductor 11kv overhead line leading to it. Can someone tell me what is the normal maximum current carrying capacity of the conductors of such an overhead line assembly is?
A deep duct was installed under the road in front of the site but as yet no other excavation has taken place either from the windfarm or towards a distribution substation about 3 miles away. I am guessing there will be a new connection possibly at 33kv or more but seek informed comment.
 23 April 2013 10:20 PM
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Zuiko

Posts: 521
Joined: 14 September 2010

Hi Seeker,
The conductor size, and so current carrying capacity, of a 11 kV overhead line can vary quite a bit from as low as 90A (sometimes less) up to 250A (per phase)

Taking a middle of the range 150A conductor, this is about 3 MVA; which is about the capacity of each of your turbines.

36 MW (12 turbines of 3 MW each) is generally the realm of 33 kV distribution, which depends on how far away the nearest grid 132 / 33 kV substation is (3 miles is not far for a 33 kV line) And of course on what the power company expects as a actual maximum demand on the wind farm. 36 MW may well be the maximum possible demand, but the actual load is going to be usually always much much less than this.

Edited: 23 April 2013 at 10:46 PM by Zuiko
 23 April 2013 11:57 PM
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JonathanHill

Posts: 225
Joined: 09 September 2002

The main limiting factor for connecting distributed generation at 11kV is voltage rise. This effect is progressively more noticeable the further along the 11kV circuit is from the Primary Substation. A general rule of thumb limit @ 11kV is between 3 - 4MW.km (ie 3 - 4MW @ 1km; 0.375 - 0.5MW @ 8km).

In general, generation capacities at >5MW; <60MW will connect at voltages >11kV - most likely 33kV.

It's possible that the connecting cable for this wind farm may be installed by horizontal directional drilling, which avoids the need for a trench.

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Jonno
 28 April 2013 01:46 PM
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ArthurHall

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Wind turbines can be damaged if they stand for a long period without turning, vibration causes the bearings to become indented. If there has been a delay in the grid connection they may have connected an LV supply to the control circuits to allow the turbine to turn but not generate
 04 June 2013 09:52 PM
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seeker

Posts: 319
Joined: 10 March 2007

Thanks for the responses. I strongly suspect the 33kV link has yet to be provided. There are now ten turbines erected and sails fitted but only the first four have been observed to rotate. I am deeply suspicious that the site may become entitled to receive constraint payments for the completed units until such time as a link is provided. Maybe I'm just cynical but the wind companies seem to have developed milking the system to a fine art.
The contracts being described in various parts of the media seem to have been written by complete amateurs on the one side and Gordon Gecko on the other.
 04 June 2013 11:02 PM
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JonathanHill

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Yes, I'm inclined to agree, you do seem to be overly cynical! My experience is that DNOs get a very easy ride in that I've never known them accept any meaningful penalty for being late with their delivery of the (final) connection, unlike all the other contractors that will be locked into Liquidated Damages with significant penalties.

Also, my understanding of the constraint payments is that each meaningfully-sized generator bids in a price for constraining off if NGET has an embarrassment of generation in a section of network. It seems that wind generators are pitching in with lower payments than the other generators, thus making them the first to receive NGET's request to constrain. Therefore, a less cynical person might consider the wind generators to be public spirited.

I'd welcome those experienced in the trading aspects to confirm my understandings, because the mis-informations being traded are not helpful to a meaningful debate.

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Jonno
 07 June 2013 12:54 PM
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Ipayyoursalary

Posts: 265
Joined: 21 November 2009

fossil-fuelled power stations submit negative bids to the system operator indicating they will pay National Grid a certain sum per MWh if asked to reduce output.... What has become clear over the last year is that the amount charged by wind farms is very significantly in excess of the value of the subsidies foregone. For example, the average price paid to Scottish wind farms to reduce output in 2011 was £220 per MWh, whereas the lost subsidy is approximately £55 per MWh. The amount paid by conventional plant such as coal and gas was approximately £34 per MWh to reduce output in 2011. Ultimately the cost of balancing electricity is paid by the electricity consumer so this large difference in cost is not in the consumer interest.
From here

So poor people and pensioners on fixed incomes are forced to pay a ransom to rich landowners and foreign energy companies to reduce the erratic output from their wind subsidy farms. Whereas conventional generators actually pay money back when asked to reduce their output. And yet the LibLabCon are building thousands more of these hideous subsidy farms?
 07 June 2013 01:13 PM
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Zuiko

Posts: 521
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better still; people that live in the countryside are being bribed with money taken from energy users that live cities to accept the construction of wind farms etc.

This tends not to happen with other types of power station that can be be built in less affluent areas.

Could it be that the people of affluent shires have voices that are better heard in the corridors of power?
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