Effects on a cable at sea level compared to 35,000 feet

In summary, the cable at 35,000 feet has a decrease in temperature which leads to a reduction in resistance.
  • #1
joe465
94
0
Hi Guys,

Struggling to find any information on the changes to a cable at altitude compared to at sea level. The initial task was to calculate the resistance of generator wires and then change them from copper to aluminium cables to save weight. I have done this leading me onto describing the effects of the cable at 35,000 feet compared to at sea level.

All i can think of is a decrease in temperature causing a reduction in resistance but would ideally like to provide an example but struggling to find a formula to fit. I know copper has a temperature coefficient of resistance of 3.9 * 10^-3 and aluminium is the same.

Are there any other major effects to the cable at altitude?

Cheers,

Joe
 
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  • #2
The temperature depends on the environment. 35000 feet above sea level is a typical altitude for an airplane, so temperature will depend on the position of the cable in the airplane.
You also get a bit more radiation, but that should be negligible for cables, and I don't see any effect of a changed air pressure.
 
  • #3
Thanks, it is for an aircraft, it is generator cables for a 747. No environment stated so i could possibly just go with the 2 degree decrease every 1000 feet?. What would you recommend?
 
  • #4
If temperature is important, I would recommend to check the design, and the expected temperature range for the cable.
 
  • #5
I don't have any answers, but do have some questions.
At 35,000 feet the breakdown voltage of air is much less than at sea level.

Would there be a problem with cable terminations breaking down at 35,000 feet?
Would cable have corona at 35,000 feet? (Very short life)
Cooling of cables will be less at 35,000 feet. What is temperature rise?
Will cables outgas at 35,000 feet? Is this a problem?
 
  • #6
It is impossible to answer those questions in general.
 
  • #10
joe465 said:
No environment stated so i could possibly just go with the 2 degree decrease every 1000 feet?. What would you recommend?

If this is a "homework" exercise, I think using the International Standard Atmosphere would be defensible set of design conditions. Or use ISA + or - 20C, whichever is the worst design conditions.

If it is "for real", you need to find the relevant section of the Joint Airworthiness Regulations (JARs) - sorry, I'm not an "electrical" guy so I can't tell you which section you want, but don't expect it to be easy bedtime reading!

Remember your generator probably has to work after sitting on the ground all day in the Middle East in air temperatures of +50C, as well as at -80C on a cold day at 35,000 ft!
 

1. What is the difference in temperature between sea level and 35,000 feet?

At sea level, the average temperature is around 15°C, while at 35,000 feet, the average temperature is around -60°C. This means that there is a significant decrease in temperature as you go higher in altitude.

2. How does the temperature difference affect the cable at sea level and 35,000 feet?

The difference in temperature can affect the cable in several ways. At sea level, the warmer temperature can cause the cable to expand, while at 35,000 feet, the colder temperature can cause the cable to contract. This can put stress on the cable and potentially affect its performance.

3. Is the air pressure a factor in the performance of the cable at sea level and 35,000 feet?

Yes, air pressure can have a significant impact on the performance of the cable. At sea level, the air pressure is higher, which can increase the resistance and hinder the flow of electricity through the cable. At 35,000 feet, the air pressure is lower, which can decrease the resistance and potentially improve the flow of electricity.

4. How does the altitude affect the conductivity of the cable?

The altitude can affect the conductivity of the cable in two ways. First, the colder temperature at 35,000 feet can decrease the conductivity of the cable, making it less efficient. Second, the lower air pressure at 35,000 feet can also affect the conductivity, potentially increasing it due to the reduced resistance.

5. Are there any other environmental factors that can affect the cable at sea level and 35,000 feet?

Besides temperature and air pressure, there are other environmental factors that can affect the cable at different altitudes. These include humidity, wind, and exposure to UV radiation. These factors can impact the durability and performance of the cable, especially over long periods of time.

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