Naked Science Forum
Non Life Sciences => Technology => Topic started by: scientizscht on 15/04/2019 16:32:02
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Hello!
How do they connect two cables underwater?
How they manage to be totally dry under subsea conditions?
Thanks!
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Either make the connection in air, wrap it in plastic and then submerge it (if you can't pull the cable up from the sea floor, use a diving bell) or use AC magnetic coupling (like a contactless phone charger).
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Either make the connection in air, wrap it in plastic and then submerge it (if you can't pull the cable up from the sea floor, use a diving bell) or use AC magnetic coupling (like a contactless phone charger).
I am talking about the situations that you need to connect something subsea.
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Either make the connection in air, wrap it in plastic and then submerge it (if you can't pull the cable up from the sea floor, use a diving bell) or use AC magnetic coupling (like a contactless phone charger).
I am talking about the situations that you need to connect something subsea.
Not uniquely.
if you can't pull the cable up from the sea floor, use a diving bell
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Cable-laying ships make joins in the cable (eg for telecommunications repeaters) before dropping the cable in the sea.
For making repairs, cable-repairing ships (usually the same ship) first cuts the cable, attaches buoys to the ends, then drags each end up to the surface, splices in a new segment, and drops the lot back down to the seafloor.
There are rumors that various countries have submarines equipped to attach a monitoring tap to undersea telecommunications cables, but to do the operation entirely underwater, so they are not spotted. They could do it in air (inside the submarine) or perhaps in oil.
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So there is no available technology to plug something underwater?
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So there is no available technology to plug something underwater?
The video shows a robot capable of manipulating a pipe, a plug or a cable underwater - in very clear, probably fresh water.
If you had pipes carrying gas or liquid, with connectors that sealed when inserted, that could be very practical.
It does not show the effect of a cable carrying 50,000 Volts DC through this plug when exposed to salty sea water (which conducts electricity fairly well). To prevent an explosion when the power is turned on, you want the parts carrying the electrical voltage to be totally insulated from the sea water.
It also does not show the effect of plugging together optical fibers underwater, which need alignment to within 1 micrometer, and to obtain a signal loss of 0.1dB. To achieve this requires isolation from water (water absorbs infra-red light, causing signal attenuation) and is usually achieved with a "fusion splice", which heats the glass up near its melting point (not something you could easily do when submerged in water).
So yes, this robot may be able to plug in power cables or optical fibers underwater - but you probably wouldn't want it to. Best to have pre-sealed joints.
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There are rumors that various countries have submarines equipped to attach a monitoring tap to undersea telecommunications cables, but to do the operation entirely underwater, so they are not spotted. They could do it in air (inside the submarine) or perhaps in oil.
Presumably that practice will phase out with increasingly more comms going via fibre?
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Presumably that practice will phase out with increasingly more comms going via fibre?
The greatest volume of underseas communications has been via optical fiber since about the 1980s. The capacity of optical fibers (with digital encoding) was far greater than the previous generation of undersea copper cables (with analog coding).
There are ways of (delicately!) shaving away the outer sheath of an optical fiber, leaving the core intact. That allows some light to "leak" out of the core. Attach an optical fiber and an optical amplifier, and you are monitoring everything going through that fiber - and the countries being monitored will detect only a very slight reduction in signal power.
Or so say the rumors...
See: https://en.wikipedia.org/wiki/Submarine_communications_cable#Optical_telephone_cables
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more comms going via fibre
Edward Snowden started these rumors...
See: https://www.smh.com.au/technology/edward-snowden-reveals-tapping-of-major-australianew-zealand-undersea-telecommunications-cable-20140915-10h96v.html
https://en.wikipedia.org/wiki/Tempora
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Where can I buy technology that connects electric cables underwater but not in extreme depths?
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technology that connects electric cables underwater but not in extreme depths?
Bear in mind that sharks use their sense of electrical field strength to find prey.
The electrical field around undersea electrical cables (and even around optical fiber cables) means that sharks are attracted to them.
The first undersea optical fiber cables broke down surprisingly quickly, and when the damaged cable was recovered, they found lots of small cuts in the cable, and embedded sharks teeth where it had been savaged by sharks.
Ever since, cables in shallow waters (on the continental shelf) have been protected by a steel framework to prevent sharkbite.
Around the year 2000 (long before Google started investing in undersea cables) I had the opportunity to visit an undersea cable plant, and they had an enormous machine that wove steel bar around the cable.
You may need to do something similar with your undersea electrical plugs (which will make them harder to connect and disconnect!).
See: https://www.theguardian.com/technology/2014/aug/14/google-undersea-fibre-optic-cables-shark-attacks