camelot-forum.co.uk

more than just a think, are we not doing that already and if not why not.

In short, yes, we are already doing this, e.g.

https://www.nationalgrid.com/national-g ... -175-clean

"The £90 million investment includes replacing conductors – the wires strung between the 229 transmission towers (known as pylons) on the route – with new cables which can operate at a higher temperature and therefore allow more power to pass through the transmission circuit.

The upgrade of approximately 3000MVA (Megavolt-Amperes) will allow increased flow of electricity out of South West England on the high voltage network, removing a constraint for the 175 projects looking to connect in the region which currently have connection dates of 2028 and beyond.

The project has been brought forward a year and will now begin in January 2024, finishing in October 2025, with National Grid – in partnership with the ESO – discussing accelerated connection dates with customers as part of each individual project’s development.

dan_b wrote: ↑Mon Mar 25, 2024 2:16 pm In short, yes, we are already doing this, e.g.

https://www.nationalgrid.com/national-g ... -175-clean

"The £90 million investment includes replacing conductors – the wires strung between the 229 transmission towers (known as pylons) on the route – with new cables which can operate at a higher temperature and therefore allow more power to pass through the transmission circuit.

I am surprised there isn't a smarter option than this. Higher temperature presumably means that there are planned not to fail from resistive heating - i.e. power wastage!
I would have thought that something like a thicker lighter cable (hollow aluminium conductorrs?) but with a stronger steel core to resist wind forces would have been worthwhile. Am I correct in remembering from school that current flows on the outside of conductors? (Although if that was true, how come the choice of metal involved is so important?)

Aluminium conductors are already in use, and carbon fibre cores are also being installed.

AE-NMidlands wrote: ↑Mon Mar 25, 2024 2:38 pm Am I correct in remembering from school that current flows on the outside of conductors? (Although if that was true, how come the choice of metal involved is so important?)

Only at high frequencies, you won't get much skin effect at 50Hz.

Stig wrote: ↑Mon Mar 25, 2024 4:45 pm

AE-NMidlands wrote: ↑Mon Mar 25, 2024 2:38 pm Am I correct in remembering from school that current flows on the outside of conductors? (Although if that was true, how come the choice of metal involved is so important?)

Only at high frequencies, you won't get much skin effect at 50Hz.

Thanks, I have read that... so maybe

the current density is largest near the surface of the conductor and decreases exponentially with greater depths in the conductor. It is caused by opposing eddy currents induced by the changing magnetic field resulting from the alternating current. The electric current flows mainly at the skin of the conductor, between the outer surface and a level called the skin depth.

explains the growing use of HVDC connectors? I guess advances in insulation materials might have changed the game? Shall we see HVDC on pylons?

I must admit it seem counter intuitive to go higher temperature - and it does beg the question of what the temperature limit of the existing conductors actually is? Household cables ate typically limited to 70°c due to the thermosetting PVC insulation going soft. But HV pylon cables are bare metal on ceramic insulators - although aluminium probably can't go very high temp. That does remind me of an overnight coach trip in India a couple of decades ago:- we went past a big electrical hub on the outskirts of a city and in the dark i could see several of the connections on the high voltage pylons were glowing red - and i thought "probably not aluminium conductors then"

I suppose it's logical to sacrifice efficiency if running at higher temp allows you to use more of the available wind before curtailment. And i guess if the existing pylons cannot take more weight or wind loading then replacing with cables that can run hotter is better than upgrading to bigger cables on stronger pylons.

Skin effect is not the limitation on HVAC transmission, it's capacitance and power factor i think: over long distances the power factor drops and you need expensive and inefficient power factor correction stations to bring it back to unity. The limit for HVAC is about 1000km IIRC, or 60km underwater/underground, so thats when HVDC is worth the cost and a.c./d c. conversion efficiency hit. There are overhead pylon HVDC interconnectors in other (bigger) countries, but due to the unpopularity of new pylons and nimbyism here it's easier to put the HVDC cables offshore.

There is technical data below for one manufacturer of ACCC cable. There are a lot of sizes available.
https://apar.com/wp-content/uploads/202 ... e-ACCC.pdf

They do run hot... up to 180 deg C! That must be quite some power loss.
Do they steam when it rains?