electrickery.....

[selectortone]

45% wind power is very impressive. The NIMBYs here in Bournemouth put up a massive campaign that stopped a wind farm being built in the bay. It would have been a long way out but they wouldn't have it spoiling thd view from their retirement condos on the overcliff. Personally, I think they look great. Like something out of the sci-fi stories I read as a boy in the 60s.

That would have added a few more gigawatts to the grid. Now, as they grumble about rocketing gas prices I wonder if the implications of that decision even enter their heads. People are stupid.

 

[Sandyn]

And we could cover the sahara with solar panels and have free power for life?

I'm sure I remember Tomorrow's World doing an article about Nuclear Power, saying something like, we could look forward to free power in the future, or was I dreaming?

 

[Phil Pascoe]

I'm sure I remember Tomorrow's World doing an article about Nuclear Power, saying something like, we could look forward to free power in the future, or was I dreaming?

Like Harold Wilson's promise that we'd all be working about twenty hours a week in the future?

 

[stuart little]

Not aware of this story, or its specific veracity but:
Drop in the cable can be minimised by transmission at high voltage /low current. Thus reducing the effect of resistive loss. Its easier to raise voltage at the input end and reduce it at the output end if dealing with ac as it only needs simple transformers. But there's nothing inherent in ac that reduces the loss.

'Green' electricity? Does that mean we can see coming!

 

[Spectric]

I'm sure I remember Tomorrow's World doing an article about Nuclear Power, saying something like, we could look forward to free power in the future,

Just another something that began life as a "miracle of invention" until the point we fully understand and it ends up as a disaster, others being Asbestos and Thalidomide.

 

[Krome10]

I remember a couple of years ago chatting to an electrician who said he used to have a job which was something to do with wind farms. He was grumbling that there isn't enough infrastructure in the UK to make use of and distribute all of the electricity generated by them. And as such some of it isn't used and is wasted. I think he went on to say that that's why you often see a number of turbines within a farm that are motionless while others are spinning; they have been turned off.

I don't really know anything about all this kind of stuff, but certainly listened to him with interest and what he said stuck with me. But now reading the above - which is all totally new news to me - I question what he said seeing as there is all this cross country and even cross continental infrastructure...

So does anyone know if there's some truth in what he said? I should add that is was 2 and a bit years ago when we spoke...

 

[Sandyn]

Just another something that began life as a "miracle of invention" until the point we fully understand and it ends up as a disaster, others being Asbestos and Thalidomide.

This is interesting

 

[ivan]

The AC skin effect is frequency related - the effect is quite negligible at 50Hz. The steel core is to give the grid cables the strength to stretch between pylons.
Saharan DC could be used to separate hydrogen from sea water, which could be pumped north. Hydrogen has extremely low viscosity so can be pumped long distances with very low powered pumps. Could even run your heating.

 

[Woody2Shoes]

I remember a couple of years ago chatting to an electrician who said he used to have a job which was something to do with wind farms. He was grumbling that there isn't enough infrastructure in the UK to make use of and distribute all of the electricity generated by them. And as such some of it isn't used and is wasted. I think he went on to say that that's why you often see a number of turbines within a farm that are motionless while others are spinning; they have been turned off.

I don't really know anything about all this kind of stuff, but certainly listened to him with interest and what he said stuck with me. But now reading the above - which is all totally new news to me - I question what he said seeing as there is all this cross country and even cross continental infrastructure...

So does anyone know if there's some truth in what he said? I should add that is was 2 and a bit years ago when we spoke...

Nobody would build a wind farm without a proper connection to the grid so that power generated could be sold. I think what your friend was probably referring to was the 'intermittency' of things like wind and solar - we have no control over how much or when the wind blows or the sun shines (although these two often tend to complement each other quite nicely) what is a problem is that we have no easy way (at grid scale) to store excess energy and use it later. There is progress on the storage front, but not as far or as fast as we'd all like. Things like tidal are at least predictable.

 

[clogs]

u know, I'm really glad I asked the question....
very interesting reading.....
such clever people on the forum.....
ta...

 

[nickds1]

The AC skin effect is frequency related - the effect is quite negligible at 50Hz.

Not so. At 50Hz, the Skin Effect puts something like 60% of the current in the outer 9mm of the cable for copper and about 12mm for aluminium - as I mentioned before, with cables under 18mm in diameter, this effect is not important. But the OP was asking about power distribution networks where cables have to be large for tensile strength & current carrying ability. This is why, even in generating plants, you will not see busbars thicker than 20mm or thereabouts - they'll be wide for sure, but making them thicker than 20mm or so is just a waste of copper.

ACSR cables (the type generally used for grid distribution) are designed specifically to take advantage of the Skin Effect - the cables need to be strong, hence the steel core, but the large majority of the current flows in the outer layers, in this case high-purity, highly conductive aluminium.

The layering of the Al strand winding direction is important - even number of layers wound in alternating directions to minimise hysteresis losses in the steel core, plus a larger cable diameter (in the case of HVAC) to minimise corona discharge losses.

The importance of the skin effect can also be seen in how different countries electrically rate these cables for AC & DC - the ATSM include the steel core; the IEC don't for AC.

See: Skin Depth/Skin Effect and Calculator - Ness Engineering Inc. (or many other calculators on the www)

 

[Spectric]

"turbines within a farm that are motionless while others are spinning; they have been turned off "

If the grid has enough energy to meet demand then they instruct windfarms to turn off their generation as it is not needed, but they still used to pay as if it was but that was going to change.

In the days I designed SMPS's the skin effect became a problem above 20 Khz, to get over the problem we would use copper tape for the winding or use multiple smaller insulated copper wires all in parallel, you can buy it under the name of litz wire and use ferrite cores to prevent saturation of the core.

 

[Stuart Moffat]

I am not an expert and someone may gain say me, but I think that solar farms and wind generally are supplying their power at relatively low voltage, and the infrastructure allows it to be used relatively locally but not transformed up to the voltage necessary to be distributed more widely. something along this line has been used locally to decline installing more solar fields.

 

[nickds1]

Generally, wind turbines generate DC and solar panels/photovoltaic converterss always do.

They may be intermediate storage, e.g. batteries, but the DC is converted to AC at the appropriate voltage and frequency by inverters.

Doing it this way is obvious when you think about it - the wind doesn't blow at a nice consistent speed and the sun doesn't always shine, especially at night!

Using DC then an inverter means that you always get the frequency and voltage you want, though the available current will vary.

Once you have AC at a known frequency, you can use passive gear, e.g. transformers, to step the voltage up/down. If you are providing capacity to the grid, the inverter will be phase-locked to the grid.

Offshore wind farms often have a platform with an HVDC converter so that the wind farm to shore link runs at HVDC for efficiency and cost reasons.

 

[Spectric]

Thats interesting because alternators replaced the old dynamo on vehicles because dynamo's used commutation to convert the generated Ac in the rotating armature into Dc which required brushes that carried the full output current whereas the alternator being an Ac machine used a stationary stator and semiconductor rectification with either permeanent magnet armature or a field winding that only carried a low current via the brushes.

But a syncronous Ac generator would make more sense because it can produce a three phase Ac output and in conjunction with a constant velocity gearbox you have a solution.

 

[MuddyFunster]

Just my two penn'rth

The Turbines have 2 basic configurations, where the low voltage (>1000v) is transformed up to the HV. in some turbines it's TX'd in a separate external building co-located with each turbine (with bigger turbines, this can also be in the (large) base of the turbine). In other types, the transformer is up in the nacelle with the drive train.
Once the HV is generated it goes to the windfarm substation and for connection to the grid. with larger offshore windfarms, that are a longer distance out, they have offshore substations too, for example at "Robin Rigg" in the solway firth.