7 ms·

I think there's a difference between them being "attracted" to the short range field, and being disoriented as they climb over the cable. Maybe it's the heat or

I think there's a difference between them being "attracted" to the short range field, and being disoriented as they climb over the cable. Maybe it's the heat or inductive heating effect they like. EM shielding the cables would make them too heavy. Switching to DC transmission might fix it, but the cable loss would be higher and the cost of rectifying and remodulating to AC would be high. Two thoughts come to mind. More cables in parallel carrying less current, which gives the added advantage of redundancy. Short breaks in the flow, like a railway crossing for crabs, for 5 minutes or however it takes them to get unstuck and go along their crabby business.

croisillon 5y ago
crabby business <3
jakear 5y ago
Combine the two? Several smaller cables with a cycling subset powered at any given moment.
7952 5y ago
More cables could disrupt the sea bed more during construction and cause more harm to plants and animals.
xxs 5y ago
>Switching to DC transmission might fix it, but the cable loss would be higher AC loses due to reactive impedance and skin effect should always be higher than DC transmission. DC might make sense if the generation is solar based, as it naturally generates DC, although converting it to higher voltages must have an AC step.
- roomey 5y ago
  The highest capacity sub sea transmission cables are DC now I think. There is an interconnect between Ireland and France that is DC if memory serves. I think it's only efficient for the largest capacity lines tho
  - 7952 5y ago
    AC cables are just more expensive per km, I think due to skin effects.
    - Johnythree 5y ago
      That and the enormous capacitance between a long cable and the sea.
  - XorNot 5y ago
    DC is also used because you avoid grid synchronization issues, and this is generally the trend for long distance connects now in general. It means the grids can have frequency divergence without affecting the transmission line itself.
    - Lascaille 5y ago
      The issue with DC transmission in subsea cables is that the XLPE insulation can become polarized and - from what I remember - have water drawn into it due to the consistency of the field.
      - spookthesunset 5y ago
        You could probably flip the current at periodic intervals to deal with this.
        Lascaille 5y ago
        You're talking about flipping the polarity, going occasionally from conductor-positive to conductor-negative (the shield must remain at ground potential.) If I remember correctly that actually makes things much worse if you've operated at one potential for a considerable amount of time. You could operate the cable at AC ~ 0.1Hz but your ability to actually transmit MWH would suck.
    - pfdietz 5y ago
      And DC avoids problems caused by induced currents due to geomagnetic storms (you get a voltage shift, but that's no big deal, compared to what happens to transformers.)
- lathiat 5y ago
  Informative but entertaining video on high power DC transmission from Electroboom. To my recollection it’s generally always better transmission wise except the DC-AC and AC-DC converters are both expensive and physically large. https://youtu.be/DFQG9kuXSxg https://youtu.be/DFQG9kuXSxg
  - londons_explore 5y ago
    Both size and cost are dropping pretty quick with the development of better MOSFETs - the same ones that are soon to get very cheap because they're used in electric car motor inverters. I predict that in 100 years the majority of big power links will be DC (although we'll probably still have an AC grid too)
lm28469 5y ago
> More cables in parallel carrying less current, which gives the added advantage of redundancy. Every time we have a problem with tech the answer always is "just add more", idk how to feel about that
- politelemon 5y ago
  Or more abstractions. Where the original problems that we were trying to get away from, resurface in new ways, and previously solved problems have to be reimplemented.
- riskable 5y ago
  Adding more of something is often the simplest and cheapest way to fix problems. Example: Adding a few more VMs or containers costs almost nothing. Paying developers to eke out 10% more performance is expensive. Another example: Microcontrollers that have loads of pins (e.g. 100) and support many different peripherals (i.e. protocols like I2C) are expensive (say, $10-20). Little ones with a medium amount of pins (e.g. 56) and support for limitless protocols are cheap ($1). So if your PCB needs just a few more GPIO pins to accomplish something it makes more economic sense to just "add another" little MCU rather than "go big". Even if it makes programming the thing slightly more complicated.
HPsquared 5y ago
Maybe a barrier to prevent underwater critters from getting too close to the cable. Some kind of tubular fence?
rand0mx1 5y ago
You are claiming that DC losses are high, can you cite any source.
- bluGill 5y ago
  Probably only historical ones. In the past it wasn't easy to get high voltages with DC, so losses where higher. These days we are better at changing voltages, and so DC losses the same as AC with similar voltages (skin effects still can be a small difference). I understand we can actually run DC at higher voltages than AC, though I'm not enough of an EE to explain why. IF this is true, then DC losses would be less than AC.
- riskable 5y ago
  DC-to-AC losses used to be high (historically) because of inefficient inverter technology. These days we have 90-95% efficiency inverters (that are built to match their HVDC voltages). It's interesting because the reasons why we built everything using AC in the past don't really apply anymore (well, most of the time). DC is more efficient for most domestic and industrial electricity utilization. Things like lighting, air conditioning/heating, refrigerators, etc are all more efficient if fed from DC. Think about it: How many "wall warts" have we got in our homes these days? All our LED light bulbs have built-in inverters and that decreases their efficiency. Our PCs use DC for literally everything internally. The list goes on and on. I had also read a while back that grid-scale DC power transmission could be more resilient because the power transformers aren't as expensive. It's like $8 million for one of those giant high voltage AC transformers they have at power stations whereas with high voltage DC the equipment is cheaper but you have more of it (or something like that; I wish I could remember the details but this was an explanation given to me from a DC fanboy lineman over 10 years ago). The idea being: If bad weather breaks your giant $8 million AC transformer that's a real expensive pain in the ass but if it breaks a handful of small DC transformer components that's a quick (and cheap) fix.
  - pitaj 5y ago
    > LED light bulbs have built-in inverters Think you meant rectifiers here.

croisillon 5y ago

crabby business <3

jakear 5y ago

Combine the two? Several smaller cables with a cycling subset powered at any given moment.

7952 5y ago

More cables could disrupt the sea bed more during construction and cause more harm to plants and animals.

xxs 5y ago

>Switching to DC transmission might fix it, but the cable loss would be higher AC loses due to reactive impedance and skin effect should always be higher than DC transmission. DC might make sense if the generation is solar based, as it naturally generates DC, although converting it to higher voltages must have an AC step.

roomey 5y ago
The highest capacity sub sea transmission cables are DC now I think. There is an interconnect between Ireland and France that is DC if memory serves. I think it's only efficient for the largest capacity lines tho
- 7952 5y ago
  AC cables are just more expensive per km, I think due to skin effects.
  - Johnythree 5y ago
    That and the enormous capacitance between a long cable and the sea.
- XorNot 5y ago
  DC is also used because you avoid grid synchronization issues, and this is generally the trend for long distance connects now in general. It means the grids can have frequency divergence without affecting the transmission line itself.
  - Lascaille 5y ago
    The issue with DC transmission in subsea cables is that the XLPE insulation can become polarized and - from what I remember - have water drawn into it due to the consistency of the field.
    - spookthesunset 5y ago
      You could probably flip the current at periodic intervals to deal with this.
      - Lascaille 5y ago
        You're talking about flipping the polarity, going occasionally from conductor-positive to conductor-negative (the shield must remain at ground potential.) If I remember correctly that actually makes things much worse if you've operated at one potential for a considerable amount of time. You could operate the cable at AC ~ 0.1Hz but your ability to actually transmit MWH would suck.
  - pfdietz 5y ago
    And DC avoids problems caused by induced currents due to geomagnetic storms (you get a voltage shift, but that's no big deal, compared to what happens to transformers.)
lathiat 5y ago
Informative but entertaining video on high power DC transmission from Electroboom. To my recollection it’s generally always better transmission wise except the DC-AC and AC-DC converters are both expensive and physically large. https://youtu.be/DFQG9kuXSxg https://youtu.be/DFQG9kuXSxg
- londons_explore 5y ago
  Both size and cost are dropping pretty quick with the development of better MOSFETs - the same ones that are soon to get very cheap because they're used in electric car motor inverters. I predict that in 100 years the majority of big power links will be DC (although we'll probably still have an AC grid too)

lm28469 5y ago

> More cables in parallel carrying less current, which gives the added advantage of redundancy. Every time we have a problem with tech the answer always is "just add more", idk how to feel about that

politelemon 5y ago
Or more abstractions. Where the original problems that we were trying to get away from, resurface in new ways, and previously solved problems have to be reimplemented.
riskable 5y ago
Adding more of something is often the simplest and cheapest way to fix problems. Example: Adding a few more VMs or containers costs almost nothing. Paying developers to eke out 10% more performance is expensive. Another example: Microcontrollers that have loads of pins (e.g. 100) and support many different peripherals (i.e. protocols like I2C) are expensive (say, $10-20). Little ones with a medium amount of pins (e.g. 56) and support for limitless protocols are cheap ($1). So if your PCB needs just a few more GPIO pins to accomplish something it makes more economic sense to just "add another" little MCU rather than "go big". Even if it makes programming the thing slightly more complicated.

HPsquared 5y ago

Maybe a barrier to prevent underwater critters from getting too close to the cable. Some kind of tubular fence?

rand0mx1 5y ago

You are claiming that DC losses are high, can you cite any source.

bluGill 5y ago
Probably only historical ones. In the past it wasn't easy to get high voltages with DC, so losses where higher. These days we are better at changing voltages, and so DC losses the same as AC with similar voltages (skin effects still can be a small difference). I understand we can actually run DC at higher voltages than AC, though I'm not enough of an EE to explain why. IF this is true, then DC losses would be less than AC.
riskable 5y ago
DC-to-AC losses used to be high (historically) because of inefficient inverter technology. These days we have 90-95% efficiency inverters (that are built to match their HVDC voltages). It's interesting because the reasons why we built everything using AC in the past don't really apply anymore (well, most of the time). DC is more efficient for most domestic and industrial electricity utilization. Things like lighting, air conditioning/heating, refrigerators, etc are all more efficient if fed from DC. Think about it: How many "wall warts" have we got in our homes these days? All our LED light bulbs have built-in inverters and that decreases their efficiency. Our PCs use DC for literally everything internally. The list goes on and on. I had also read a while back that grid-scale DC power transmission could be more resilient because the power transformers aren't as expensive. It's like $8 million for one of those giant high voltage AC transformers they have at power stations whereas with high voltage DC the equipment is cheaper but you have more of it (or something like that; I wish I could remember the details but this was an explanation given to me from a DC fanboy lineman over 10 years ago). The idea being: If bad weather breaks your giant $8 million AC transformer that's a real expensive pain in the ass but if it breaks a handful of small DC transformer components that's a quick (and cheap) fix.
- pitaj 5y ago
  > LED light bulbs have built-in inverters Think you meant rectifiers here.