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Topic Title: Copper used and utilisation in collecting power from wind farms
Topic Summary: How much is required and how well is it used?
Created On: 23 July 2012 12:06 AM
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 23 July 2012 12:06 AM
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Does anyone have any idea how much copper will be used in a typical wind farm installation? Not just inside the towers but to collect the risable amount of energy that inermittently flows.
 23 July 2012 12:16 PM
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Lots! And its very expensive, especially for offshore schemes where the cables need to be buried or laid. Also, turbines are often connected in long "strings" and so the "string" cable is rated for the peak power from the whole string whereas towards the end of the "string" only a fraction of this power flows. You can taper the cable diameter down the string to compensate for this to minimise CAPEX, but that means keeping stocks of different cables, careful protection settings, etc. and this may cause more confusion/difficulty than simply installing a single diameter.

The cost is a serious issue for offshore schemes, being a significant part of the overall scheme cost since the cumulative cable length is long, and the main aim for developers is to keep the overall cost of the scheme down to competetive levels.

So, all of the above sounds very expensive and "bad" use of copper.

However, the voltage of collection is in the 11-33kV range and so cable diameters per MW are suitably reduced. Also, compared to the load factor of (for example) your house, where the copper in the cables is only used towards its peak ratings for very small amounts of time, the use of copper in windfarms is actually quite effective. Consider for example the chunky copper cable in your home connected to the electric shower. Its ~40A capacity to supply about 9.2kW @ 230V. That would be capable of supplying 221kWh if used at its full rating for 24 hours. However, every day it's probably only used for 10-20 minutes (2-4 people?), so only 1.5-3kWh are actually supplied via this cable. Thats a load factor of 0.7-1.4%, which is far less effective use of copper than your average wind farm cable.

The figures are just as bad if you start to look at your domestic 32A rings which supply TVs, table lamps etc. On a typical house with 3x 32A rings and a single 40A shower supply, thats a peak capacity of about 31kW (which you probably never come close to achieving) but the average daily use is only about 12kWh .Thats a load factor of 1.6%, and I didn't include other stuff like lighting circuits and garage wiring which are all included in that average domestic 12kWh consumption statistic.

So, if "inefficient" use of copper is your worry, perhaps start in the home first!

Dr. Andrew Roscoe
 23 July 2012 02:00 PM
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Transmission voltages across the world are not standardised. To enable worldwide sales cable and switchgear makers make products to suit a band of voltages.
An offshore windfarm I worked on recently used the non UK standard voltage of 150kV rather than 132kV for the onshore connection. The spec of the switchgear and cables was not changed but they could transmit an extra 10% power for the same amount of copper. The transformers at each were of course wound for 150kV but they were being built especialy for the job anyway.
 25 July 2012 09:52 PM
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The fact that domestic installations are rated for their peak power is missing the point. Wind Farms produce power intermittently but have to have interconnections to collect that power based on their name plate rating which they never achieve continuously. Whereas a base load system gas or coal will be utilising that transmission connection nearly continuosly.

The intermediate collection system may well be at 11 or 33KV but there is a considerable connection length at a voltage much less than that. In some cases the insulation rating of the generators is only 690V. So my question still remains, How are these small (in relative terms) generators connected efficiently to collect the energy and transmit it to the grid. Does each tower have a transformer or do they go to a central hub and from there to a switch yard and transformer etc.
 25 July 2012 11:49 PM
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There are generators out there that choose to only run for a very limited time because that happens to suit their financial model - how might their utilisation be derived?

As we frequently find in engineering, the electrical topology for a wind farm is a balance between engineering elegance, capital & operating costs/ cost benefit. Typically, each WTG generates at between 660V and 1,000V and has it's own transformer usually converting to 11kV, 20kV or 33kV - determined by the connection voltage to the DNO network. Some WTGs have transformers located at/ adjacent to the bottom of the tower, others have the transformers located in the nacelle, with LV cable runs as much as 10m. I do recall a small wind farm in the olden days that had 4 x 225kW WTGs and ran all the outputs @ LV to a single LV/11kV transformer, located at the centre of the group. (I believe the copper was recovered for recycling at the end of project life - the WTGs went on to have another life on a new site).

From an efficiency perspective, WTGs, and other renewable technologies achieve very high scores - the fuel is free and will return for as long as we're around to benefit from it. Will coal, nuclear fission, gas .....?


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