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Temperature on a cable
Posted 16 févr. 2017, 08:18 UTC−5 Electromagnetic Heating, Low-Frequency Electromagnetics, Heat Transfer & Phase Change, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 5.2 5 Replies
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I am trying to verify the temperature on three cables representing a transmission line due to the heating caused by the current passing through them, but the temperature shown in the Results is uniform on the cables, even though the current in one of them is significantly greater. The geometry consists only of three parallel aluminium cilinders.
I have specified the Ground node to one end of each cable and assigned an External Current Density to them, (I have also tried assigning Normal Current Density to the opposite end of the cable) and also assigned a convective heat flux on the cable domains with the aluminium heat tranfer coefficient.
I was following the electric heating on a busbar tutorial as I am new to COMSOL.
The idea is then compare the temperature of the same cables but with a layer of a non-conductive material around one of them.
Is it not possible to verify the Joule Heating using a current density? Do I need a box of air around the cables?
Thank you in advance for any help
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I am not quite sure what you mean by verification, but Joule heat is resistivity*(current density)^2. It comes as a heat source in the heat transfer problem (W/m^3). Surely higher current should give higher temperature.
BR
Lasse
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I know what you mean, and thats how I know there is something wrong with my model, but I wasn't able to find the problem. I was able to find the temperature of the cables if I assigned a voltage on them that would produce the current that I am supposed to have on them. I was wondering if there is a way instead of using the Electric Potencial on the cable I could specify a current on it, or a current density.
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I made a small model with Heat Transfer in Solids and Electric Currents physics. I used current boundary condition at one end and ground at the other, and I realized that hardly no temperature raise was achieved because the resistivity of aluminum is so low. On the cable boundaries I used heat flux BC with the heat transfer coefficient 100 W/m^2/K.
If there is an insulating layer around the cable temperature raise would be higher.
BR
Lasse
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The original question in this thread did mention three cables, which might point to three-phase power transmission lines.
If that is the case, then you might find this article helpful:
www.comsol.com/blogs/how-to-model-the-electromagnetic-heating-of-underground-cables/
Best Regards,
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I was able to simulate the temperature of a cable, now I wanted to see the effects of a certain insulating material around the cable in the temperature of said cable.
My doubt is: I have set the domain of the cable as a Heat Source and it has a Heat Transfer in Solids node as well. But for the boundaries that represent the contact between the cable and the insulating material do I need both Thermal Contact and a Boundary Heat Source node? I have checked and the results are slightly different if I use both or just one of them. I get a small orange circle next to them in the model builder saying that they are contribuiting to each other, I just can't tell if it's necessary.