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Topic: Alu Cables for Aeroplanes  (Read 2763 times)

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Offline Enthalpy

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Alu Cables for Aeroplanes
« on: March 12, 2023, 05:56:36 PM »
Hello nice people!

High voltage lines use aluminium wires: lighter and cheaper than copper at identical resistance. Homes don't because bad contacts created accidents. Even aeroplanes don't, seemingly for that same reason.

But as aeroplanes care about mass and their future is hybrid or electric, with Zn-air batteries or liquid hydrogen and fuel cells, they strongly need aluminium wires, and have the means to develop good contacts.

Bad contacts shall possibly result from more conductive but creeping alloys like AA1350. The cable's end squeezes over time, the contact pressure vanishes, the contact gets bad.

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Plane designers could first check if the solutions for high voltage lines fit planes.

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I suggested already to solder Ag-coated Al cables in Cu-alloy clips.
  scienceforums
Sn-Pb solder is reliable, Sn-Pb-Ag is more caring with the Ag layer. But this builds corrosion couples usually forbidden in plane design. So here are proposals using Al-alloy cable ends, of corrosion-safe alloys like AA5083, AA5457, AA6062, AA3004 and few more.

Electric planes will transmit >2×30MW. Friction stir welding, FSW can join the massive AA1350 bars on AA5083 ends
  wikipedia
I trust the resulting alloy gradient. Would the method even keep cold-work hardening, welcome at the contact?

Welding is to slow for smaller cables. If soldering, corrosion lets me prefer an Al-base filler. The usual eutectic AlSi13 filler melts at 580°C, excluding parts of much-alloyed Al, especially AA5083 that melts at 580-640°C. Melting at 450°C, the less usual AlMg38 eutectic might solder AA1350 cables in AA5083 ends. And could a heat sink protect the cold-work hardening at the tip that makes the mechanical contact?

Marc Schaefer, aka Enthalpy

Offline Hunter2

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Re: Alu Cables for Aeroplanes
« Reply #1 on: March 13, 2023, 06:38:45 AM »
Quote
High voltage lines use aluminium wires: lighter and cheaper than copper at identical resistance.
No copper has lower resistance as aluminium.

https://instrumentationtools.com/wp-content/uploads/2020/03/Specific-resistance-table.png

The Alloys of aluminium have more higher resistance, so they will be not used. For signal Iines glasfibre should be considered, for higher voltage still copper or coated aluminium with copper should be used.

Offline Enthalpy

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Re: Alu Cables for Aeroplanes
« Reply #2 on: March 13, 2023, 03:11:22 PM »
Harder but corrosion-safe alloys (AA6101, AA6063, AA6060, AA5083, AA5754 and more) are easily welded with high-conductivity aluminium, so many processes can join harder tips with massive bars.

Friction welding is fast and simple on round conductors, feasible on other sections too.
  wikipedia - wikipedia
Or just TIG and MIG, which accept many sections and can be automated.

Offline Enthalpy

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Re: Alu Cables for Aeroplanes
« Reply #3 on: March 13, 2023, 03:15:45 PM »
[...] copper has lower resistance than aluminium[...]

Hi Hunter2, nice to read you!

At identical dimensions, copper has a lower resistivity.

But we can increase the section of an aluminium bar to have the same resistance, and thanks to its much lower density, the aluminium bar is much lighter than the equivalent copper.

This is useful at high voltage lines, and even more at aeroplanes.

Offline billnotgatez

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Re: Alu Cables for Aeroplanes
« Reply #4 on: March 13, 2023, 06:06:15 PM »
@Enthalpy
In my youth I worked on helicopter electrical systems.
I have no memory of aluminum wires being used.
Have things changed that much?
So you have examples of published specs?
I do remember Chromel and alumel are used for turbine EGT thermocouples

Offline billnotgatez

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Re: Alu Cables for Aeroplanes
« Reply #5 on: March 13, 2023, 06:44:36 PM »
I have not gone farther than to read this in WIKI and it does surprise me.

Quote
Aluminum building wiring is a type of electrical wiring for residential construction or houses that uses aluminum electrical conductors. Aluminum provides a better conductivity to weight ratio than copper, and therefore is also used for wiring power grids, including overhead power transmission lines and local power distribution lines, as well as for power wiring of some airplanes.

I do note that it says
Quote
of some airplanes
and
Quote
power wiring
which implies very limited usage.




Offline Borek

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Re: Alu Cables for Aeroplanes
« Reply #6 on: March 14, 2023, 04:08:19 AM »
I have no memory of aluminum wires being used.

In my limited experience with aluminum wires they are more rigid than the copper ones, which makes installation more difficult, and contacts have tendency to oxidize.

My bet is that they are problematic and require much more maintenance, so the mass gain is not worth the hassle.
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Offline Enthalpy

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Re: Alu Cables for Aeroplanes
« Reply #7 on: March 14, 2023, 01:04:06 PM »
Hi, thanks for your interest!

I thought aeroplanes never use alu wires after accidents happened at homes. Good to read that the situation evolves.

Alu gets more interesting as the electric power increases. For 100kW it's nothing vital, then safe design goes first, especially for the short wires of a helicopter.

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Present step: 1300kW at ±270Vdc from the Dreamliner's APU. This needs 2400A. Accept to waste 2×200W/m (danger!), it needs 2×34μΩ/m.

Cu then needs 2×500mm2. Over 20m from the APU in the tail to the wing, that's 180kg. Al needs 2×800mm2 and weighs 80kg. That's 1 paying passenger more, >2M$ over just one plane's life. Sell 250 planes, the difference is 0.5G$, so airliners will develop Al wiring. My figures are taken from thin air but you grasp the conclusion.

So "power wiring of some airplanes" may very well mean "the Dreamliner" up to now. Other airplanes use more hydraulics and less electricity.

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Next step: electric engines, like 30MW each. The fuel cells will be near them, in the engines or in the wing, but for redundancy, designers would transmit electricity between the engines, like 15MW over 20m.

This will probably happen at 3kVdc since components exist for locomotives. It still leaves 5000A.

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Fibre optics make already the data networks, but smaller electric cables still power many apparatus. Doors, stairs, radar, light, etc etc. For these many cables, welding is too slow, soldering can be much faster and done in batch.

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