Aerial and subterranean electric lines

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    Electric Lines
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Discussion Overview

The discussion centers on the differences between aerial and subterranean electric lines, focusing on their physical characteristics, such as diameter and weight, as well as their implications for electromagnetic fields and thermal properties. Participants explore the mechanical and thermal considerations, costs, and potential environmental impacts of both types of lines.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants note that aerial lines have a smaller diameter and lower weight compared to subterranean lines, questioning the reasons behind these differences.
  • There is a discussion about whether subterranean lines require more insulation than aerial lines, with some suggesting that this could be a factor in their design.
  • One participant raises the question of whether subterranean lines produce less electromagnetic intensity at the surface compared to aerial lines, prompting further inquiry into the underlying reasons.
  • Another participant discusses the ampacity of cables, suggesting that the heat tolerance of aerial cables may differ from that of subterranean cables, depending on their respective thermal management in air versus soil.
  • Mechanical considerations are mentioned, with a participant noting that aerial cables must be self-supporting, which influences the design and strength of transmission towers.
  • There is a mention of the cost implications of burying electric lines, with some participants acknowledging that while subterranean lines are more expensive, they are also perceived to reduce electromagnetic radiation exposure.
  • One participant questions the necessity of larger diameters for subterranean lines, seeking clarification on the material requirements for their construction.
  • The relative permittivity and conductivity of dry terrains are introduced in relation to electromagnetic radiation, with a participant seeking to understand the impact of burying lines on radiation levels.

Areas of Agreement / Disagreement

Participants express various viewpoints on the differences between aerial and subterranean lines, with no consensus reached on the implications of these differences for electromagnetic radiation or the necessity of larger diameters for subterranean lines. The discussion remains unresolved regarding the overall advantages and disadvantages of each type of line.

Contextual Notes

Participants acknowledge the complexity of factors influencing the design and performance of aerial versus subterranean lines, including thermal management, mechanical support, and environmental considerations. There are unresolved assumptions regarding the impact of electromagnetic fields and the specific material requirements for subterranean lines.

Clausius2
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I've read in a newspaper aerial electrical lines (conductors) have less diameter than subterranean lines. Also, the typical weight of subterranean lines is 30Kg/m, while aerial ones is 2Kg/m. Why do they have such differences of diameter and weight? Must the subterranean lines be more isolated than aerial ones?

Another question: do you think subterranean lines causes less electromagnetic intensity field in the surface road than aerial ones?. Why?

Thanks in advance.
 
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The ampacity of cable is mainly due to two things, how much heat it can take and still remain strong enough not to stretch (areial). Or how hot it will get before the thermoplastic insulation will flow, or otherwise stop becoming an insulator (buried). Which case do you think will require more heat?, neglecting thermal heat transfer into air or soil.
 
Even thinking of it as a purely mechanical problem, aerial cables have to be self-supporting to some extent, and the transmission towers (pylons) have to be able to bear this weight too. If the cables were 15 times heavier, the towers would have to be so much stronger (and more expensive).

The other thing I thought of, - perhaps subterranean lines are more frequently used over longer distances and carrying more current, but with a bit more thought I guessed that this (at least the distance bit) is probably not the case, as it is much more expensive to tunnel a cable than to string it up... Just a thought!
 
Thanks to brewnog and wwtog.

I see what you mean, brewnog. But nowadays the local governments make the effort of burying electric lines to avoid electromagnetic radiations, as they say. Subterranean lines are more expensive, due to the proper process of burying, but I got surprised when I realized that external diameter of those lines are larger too. Why is it needed more material?.

Talking about electromagnetic radiation, the relative permitivity of usual dry terrains is [tex]\epsilon_r=4[/tex], the electric conductivity is about [tex]10^{-5} S/m[/tex] and I haven't found any figure for the permeability.

Is it true that burying the electric lines enhances less electromagnetic radiation in the surrounding?
 

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