6 ms·

Possibly a stupid question, but is it possible to add a new wire in addition to the old one, on the same holder? Are wires that heavy that the structure that h

by ars 3y ago

Possibly a stupid question, but is it possible to add a new wire in addition to the old one, on the same holder? Are wires that heavy that the structure that holds them is always maxed out?

GauntletWizard 3y ago
It's a combination of heavy and tense, but yes - Trasmission towers are typically overengineered for their load, but not so much that you can go adding additional conductor strands to them. Further, there's significant distance requirements between strands - otherwise you get arcing.
- eru 3y ago
  They are overengineered also to have a margin of safety, and you don't want to eat into that margin of safety without good reason.
  - Ekaros 3y ago
    Specially when that overengineering is for things like wind load which of extremes we can expect to become more common.
- ars 3y ago
  The distance doesn't matter, the additional cable would be at the same voltage as the one adjacent to it.
  - GerryB 3y ago
    The different lines are at the same AC voltage, but have different phases (almost always three phases), so there's an instantaneous potential difference between them. The lines need to keep the conductors seperated to prevent potential arcing chances to essentially zero even in wet weather. The higher the voltage, the more seperation is needed.
    - ben_w 3y ago
      My mental image for this whole thread is a UK steel pylons with 7 sets of cable — 3 groups of 4 wires on the left, same on the right, and a lone cable on the top. I assume that's 3 because 3 phase. But the point is, each is a group of 4: https://en.wikipedia.org/wiki/Overhead_power_line#/media/File:Pylon_ds.jpg https://en.wikipedia.org/wiki/Overhead_power_line#/media/Fil... I think the question is: can towers holding single wires for each (phase?), support e.g. four like this?
necheffa 3y ago
Assuming above ground lines: On the same "holder", no, just due to how the wire is fastened to the poll. On the same poll, maybe, depends on how much poll real estate is available. Usually though there is not extra space available. High voltage conductors use the air gap as part of its insulation so to prevent arcing the conductors need to be spaced out so far apart.
- persolb 3y ago
  Is the air gap actually an issue in this case? If I'm understanding correctly, the suggestion is to put up additional cable instead of thicker cable. The two ends of the cable are both still connected to the same electrical phase, so there should be no arcing between them.
  - doctorwho42 3y ago
    Let's assume just high voltage cables (110kV [110,000 volts]}, if you put two cables connected to the same source and terminus, over 100 miles of cable you will easily see resistance variation between the two... Not including any environmental changes. High voltage starts to become a bit of magic when it comes to shielding it. You could have an inch of rubber insulation around that cable, and still have a static charge build up on the outside. If another cable or ground path is within a certain distance, you are going to cause arcs depending on the RH% in the air. One arc will cause degradation to the point it arcs to, and if it's the other cable - that will improve it's ability to arc again. Long story short, when you start to enter the kV range, your traditional rules of thumb go out the window. I have first hand experience with trying to keep a particle accelerator from arcing, and that was a nightmare ... I can't imagine mixing in high current as well.
    - 7952 3y ago
      HV powerlines often use bundles soacedd at around 40cm that are regularly linked with conducting fittings.
Teever 3y ago
I'm not an engineer but I would imagine that they're maxed out in the sense that they either rated to hold exactly what they're holding, or they designed them for some sort of planned upgrading later, but they're not going to overbuild them because doing so would be a waste of resources. Why build a tower that can hold like 2 tonnes of wire when it will only ever carry 1 ton for it's entire life?
- sudodudeo 3y ago
  Well theoretically so that when you decide to, y'know, improve the grid in 50 years time, you can just add more wires instead of replacing everything?
  - danans 3y ago
    Why would investors today put additional money into something that might be useful in 50 years? They would never see a return on the additional investment. Would you make that investment? The only entities that can make such long term investments are governments, via taxes, and not all governments at that. And such investment is usually reserved for either basic research or incentivizing production by mobilizing human capital (i.e the IRA in the US), not building excess capacity of questionable utility.
    - eru 3y ago
      To be a bit more sophisticated: Whether it's worth it depends on interest rates, not on how long your investors live. It's just that 50 years is a long time, so the savings from leaving the additional space would need to be quite big to be worth it today when discounted back. In addition, you have lots of uncertainty: overbuilding the infrastructure in this way only takes care of exactly this one contingency, but there's plenty of other reasons why you might want to replace your pylons. Eg perhaps in 50 years we will have figured out how to send power without wires, or we will move to buried lines everywhere, or we will get our power as laser beams from orbital solar satellites, or we need new pylons in new places because settlement patterns have changed, etc.

by ars 3y ago

Possibly a stupid question, but is it possible to add a new wire in addition to the old one, on the same holder? Are wires that heavy that the structure that holds them is always maxed out?

GauntletWizard 3y ago

It's a combination of heavy and tense, but yes - Trasmission towers are typically overengineered for their load, but not so much that you can go adding additional conductor strands to them. Further, there's significant distance requirements between strands - otherwise you get arcing.

eru 3y ago
They are overengineered also to have a margin of safety, and you don't want to eat into that margin of safety without good reason.
- Ekaros 3y ago
  Specially when that overengineering is for things like wind load which of extremes we can expect to become more common.
ars 3y ago
The distance doesn't matter, the additional cable would be at the same voltage as the one adjacent to it.
- GerryB 3y ago
  The different lines are at the same AC voltage, but have different phases (almost always three phases), so there's an instantaneous potential difference between them. The lines need to keep the conductors seperated to prevent potential arcing chances to essentially zero even in wet weather. The higher the voltage, the more seperation is needed.
  - ben_w 3y ago
    My mental image for this whole thread is a UK steel pylons with 7 sets of cable — 3 groups of 4 wires on the left, same on the right, and a lone cable on the top. I assume that's 3 because 3 phase. But the point is, each is a group of 4: https://en.wikipedia.org/wiki/Overhead_power_line#/media/File:Pylon_ds.jpg https://en.wikipedia.org/wiki/Overhead_power_line#/media/Fil... I think the question is: can towers holding single wires for each (phase?), support e.g. four like this?

necheffa 3y ago

Assuming above ground lines: On the same "holder", no, just due to how the wire is fastened to the poll. On the same poll, maybe, depends on how much poll real estate is available. Usually though there is not extra space available. High voltage conductors use the air gap as part of its insulation so to prevent arcing the conductors need to be spaced out so far apart.

persolb 3y ago
Is the air gap actually an issue in this case? If I'm understanding correctly, the suggestion is to put up additional cable instead of thicker cable. The two ends of the cable are both still connected to the same electrical phase, so there should be no arcing between them.
- doctorwho42 3y ago
  Let's assume just high voltage cables (110kV [110,000 volts]}, if you put two cables connected to the same source and terminus, over 100 miles of cable you will easily see resistance variation between the two... Not including any environmental changes. High voltage starts to become a bit of magic when it comes to shielding it. You could have an inch of rubber insulation around that cable, and still have a static charge build up on the outside. If another cable or ground path is within a certain distance, you are going to cause arcs depending on the RH% in the air. One arc will cause degradation to the point it arcs to, and if it's the other cable - that will improve it's ability to arc again. Long story short, when you start to enter the kV range, your traditional rules of thumb go out the window. I have first hand experience with trying to keep a particle accelerator from arcing, and that was a nightmare ... I can't imagine mixing in high current as well.
  - 7952 3y ago
    HV powerlines often use bundles soacedd at around 40cm that are regularly linked with conducting fittings.

Teever 3y ago

I'm not an engineer but I would imagine that they're maxed out in the sense that they either rated to hold exactly what they're holding, or they designed them for some sort of planned upgrading later, but they're not going to overbuild them because doing so would be a waste of resources. Why build a tower that can hold like 2 tonnes of wire when it will only ever carry 1 ton for it's entire life?

sudodudeo 3y ago
Well theoretically so that when you decide to, y'know, improve the grid in 50 years time, you can just add more wires instead of replacing everything?
- danans 3y ago
  Why would investors today put additional money into something that might be useful in 50 years? They would never see a return on the additional investment. Would you make that investment? The only entities that can make such long term investments are governments, via taxes, and not all governments at that. And such investment is usually reserved for either basic research or incentivizing production by mobilizing human capital (i.e the IRA in the US), not building excess capacity of questionable utility.
  - eru 3y ago
    To be a bit more sophisticated: Whether it's worth it depends on interest rates, not on how long your investors live. It's just that 50 years is a long time, so the savings from leaving the additional space would need to be quite big to be worth it today when discounted back. In addition, you have lots of uncertainty: overbuilding the infrastructure in this way only takes care of exactly this one contingency, but there's plenty of other reasons why you might want to replace your pylons. Eg perhaps in 50 years we will have figured out how to send power without wires, or we will move to buried lines everywhere, or we will get our power as laser beams from orbital solar satellites, or we need new pylons in new places because settlement patterns have changed, etc.