Materials for very high voltage conductors...

[Externet]

Greetings.
Very high tension transmission lines do not need to be made of copper as the cost would be prohibitive and also, at very high voltages, the current can be reduced to convey a given power. For the reduced current and increased voltage, conductors can be a more resistive aluminium, and much thinner.
That is the picture I always had since learned day one.

A conductor made of iron as the mechanical-strength reinforcing core used in high tension overhead aluminium transmission lines also conducts reasonably well if its length is not abused... I think.

Can anyone confirm if this is reasonable or flawed ?

For a million Volts; 10,000 Amperes, is an iron conductor too bad for a 10 metres length to a point it is not to consider instead of copper ?

 

[KlausST]

Hi,

1 million Volts, 10,000 Amperes makes 10gigaWatts ... that´s the power of about 10 nuklear plants combined.
Nothing to play with. Neither for long term powere, not even for microseconds.

Can anyone confirm if this is reasonable or flawed ?

You can easily look up electrical conductivity of the materials. Math is not difficult either.

Klaus

 

[Easy peasy]

many power lines over 110kV are steel cored with AL outer to give strength and current carrying capability

 

[Externet]

Thanks. That considerable power is typically ~100 microseconds to less than a millisecond in a lightning strike.
Why conductors from lightning rods-to-ground are not plain iron reinforcing bars as used within concrete, but copper ? Is it the extra profit of selling it in copper by installers ? Would even galvanized metal water pipe suffice for the task ?. Am I wrong ?

 

[barry]

Thanks. That considerable power is typically ~100 microseconds to less than a millisecond in a lightning strike.
Why conductors from lightning rods-to-ground are not plain iron reinforcing bars as used within concrete, but copper ? Is it the extra profit of selling it in copper by installers ? Would even galvanized metal water pipe suffice for the task ?. Am I wrong ?

iron rusts, copper does not. Copper conducts about 5 times better than iron, about twice as well as aluminum. I’m pretty sure there’s not a plot to coerce people into buying copper.

 

[Externet]

Understood. Galvanized water pipes in my house are 64 years old. There is calcium build-up inside, irrelevant for electrical conduction.
Copper conducting 5 times better than iron, yes. Is that relevant for very high voltages for less than a millisecond ? Aluminium being also a better conductor, yes. Is that relevant for very high voltages during less than a millisecond ?
Have not seen lightning rod grounding using aluminium wire. But inserted in the soil, iron bar does the grounding.

 

[KlausST]

Hi,

in post#1 you talk about transmission lines only.
In post#4 you talk about a lightnin strike.

For transmission lines:
* voltage matters, since you need to take care about isolation.
* you need to take care for long term power/current

For lightning strikes:
* the excitation voltage does not matter at all
* the current matters
* and the voltage drop across the conductive part
* and the timing matters

From your posts it seems you did not do the math on you own.

Water pipes:
* are not meant to be bended
* are not made for electrical connectivity (impurity of Fe my decrease conductivity, screwed connections, ....)
* need much more time to get installed.
* are more expensive than copper rods with the same conductivity

It´s not unusual that lighning strike protection is made of galvanized steel ... but not of water pipes.

Klaus

 

[Easy peasy]

steel or iron is a poor choice for a lightning conductor as the self inductance is very high - meaning the lightning will seek other paths thru the building

lightning conductors are wide flat copper conductors for this very reason.

 

[D.A.(Tony)Stewart]

Your assumptions are not based on calculations and lack specifications.

For such high power, the HVDC source needs the best feasible conductor to be made by the best supplier, such as Sumitomo with defect-free insulation rated for 140 kV/mm, multi-stranded copper with 90'C rating then a solid copper foil shield with a steel-armor reinforced electrical and mechanical shield in a moisture-proof jacket.

The heat produced by lighting can also be substantial, reaching temperatures five times hotter than the sun's surface.
With 20kA flowing from a cloud, a lossy conductor might not survive with skin effects reducing the conduction area yet might be adequate for DC if thick enough.

The HVDC cable has been designed with multiple layers of different materials to withstand the stress of ingress and nano-particles of contamination at such high E-fields.
It must also conduct with lower impedance and skin effects than your suggestion to withstand 90 'C operational specs.

Ref

Ref
Underground XLPE