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Surge impedance of transmission tower

Posted Apr 22, 2013, 4:06 a.m. EDT 8 Replies

Eric Yeap
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Hi everyone.

I am trying to model an overhead line system, in which the transmission tower should be defined as a surge impedance. I expect the wave will go down the transmission tower and get reflected back up, hence the need of surge impedance. In RF module, which boundary condition is required so I can let COMSOL to know the existence of such impedance.

Please find the attached snapshot of the tower model. One end of the conductor is assigned with lumped port(coaxial, excitation on) and another end with lumped port (coaxial, excitation off), while the rest is perfect electric conductor. However, it seems from my simulation that the wave travelling across the conductor does not cross over the tower arm, which it is not supposed to be. My guess is that something goes wrong on the boundary between conductor and tower arm.

Appreciate if anyone can shed some light! Thank you!

Attachments:

8 Replies Last Post Oct 16, 2016, 8:45 p.m. EDT
Eric Yeap
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Posted: 1 decade ago Apr 22, 2013, 9:50 p.m. EDT
Anyone kindly enlighten me?
Anyone kindly enlighten me?
Edgar J. Kaiser Certified Consultant
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Posted: 1 decade ago Apr 23, 2013, 2:33 a.m. EDT

You probably don't get a response because your description is not clear. You might add a sketch of your setup or your current model.

Cheers
Edgar

--
Edgar J. Kaiser
www.emphys.com
You probably don't get a response because your description is not clear. You might add a sketch of your setup or your current model. Cheers Edgar -- Edgar J. Kaiser http://www.emphys.com
Eric Yeap
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Posted: 1 decade ago Apr 23, 2013, 3:39 a.m. EDT
Hi Edgar,

I am still new to this forum. Thanks for your advice. I have edited my post and hope it is now clearer to read.

Eric
Hi Edgar, I am still new to this forum. Thanks for your advice. I have edited my post and hope it is now clearer to read. Eric
Edgar J. Kaiser Certified Consultant
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Posted: 1 decade ago Apr 23, 2013, 4:13 a.m. EDT

Hi Eric,

I am wondering which way you set up the coaxial ports. Is the conductor a coaxial cable? Then there is no field outside the shield and thus the tower wouldn't see a wave. Shouldn't the conductor be isolated from the tower?
Which wavelength are you considering and how big is the tower in comparison to the wavelength?

The picture is still not clear.

Cheers
Edgar

--
Edgar J. Kaiser
www.emphys.com
Hi Eric, I am wondering which way you set up the coaxial ports. Is the conductor a coaxial cable? Then there is no field outside the shield and thus the tower wouldn't see a wave. Shouldn't the conductor be isolated from the tower? Which wavelength are you considering and how big is the tower in comparison to the wavelength? The picture is still not clear. Cheers Edgar -- Edgar J. Kaiser http://www.emphys.com
Eric Yeap
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Posted: 1 decade ago Apr 24, 2013, 5:03 a.m. EDT
Hi Edgar,

You are right. Now it finally makes sense to me why the wave won't go down the transmission tower.

Sorry for the confusion, I actually mean conductor as ground wire. I am trying to see what will happen when the ground wire is excited with surge voltage and the response of tower. In that case what boundary condition should I assign to the ground wire? I used the uniform lumped port, but the error saying "error in lumped port setup" came up.

I study the transient electromagnetic wave so the frequency is not the concern. Or is it?

Attached is the model.
Hi Edgar, You are right. Now it finally makes sense to me why the wave won't go down the transmission tower. Sorry for the confusion, I actually mean conductor as ground wire. I am trying to see what will happen when the ground wire is excited with surge voltage and the response of tower. In that case what boundary condition should I assign to the ground wire? I used the uniform lumped port, but the error saying "error in lumped port setup" came up. I study the transient electromagnetic wave so the frequency is not the concern. Or is it? Attached is the model.

Attachments:

Edgar J. Kaiser Certified Consultant
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Posted: 1 decade ago Apr 24, 2013, 7:06 a.m. EDT

Eric,

your model has a couple of severe problems.

First you have to enclose everthing with an 'air-domain'. Otherwise you don't see any field between the wire and the tower.
The port has to connect two conductors, either PEC or Impedance BC.

I would recommend you study a couple of the electromagnetic examples in the model library to make yourself more familiar with the basics. It is all in there.

Cheers
Edgar

--
Edgar J. Kaiser
www.emphys.com
Eric, your model has a couple of severe problems. First you have to enclose everthing with an 'air-domain'. Otherwise you don't see any field between the wire and the tower. The port has to connect two conductors, either PEC or Impedance BC. I would recommend you study a couple of the electromagnetic examples in the model library to make yourself more familiar with the basics. It is all in there. Cheers Edgar -- Edgar J. Kaiser http://www.emphys.com
Eric Yeap
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Posted: 1 decade ago Apr 25, 2013, 2:33 a.m. EDT
Hi Edgar,

Thanks for pointing out the problems. Now I know why it doesn't work.

I am using the Electromagnetic Waves, Transient as the physics, the impedance boundary condition is nowhere to be found though. In that case what is the boundary condition of the transmission tower if I want it to act like the surge impedance? Besides that, is it correct that I assign the uniform lumped port on the both end of ground wire?

Appreciate your advice very much.
Hi Edgar, Thanks for pointing out the problems. Now I know why it doesn't work. I am using the Electromagnetic Waves, Transient as the physics, the impedance boundary condition is nowhere to be found though. In that case what is the boundary condition of the transmission tower if I want it to act like the surge impedance? Besides that, is it correct that I assign the uniform lumped port on the both end of ground wire? Appreciate your advice very much.
Anderson de Araujo
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Posted: 8 years ago Oct 16, 2016, 8:45 p.m. EDT
Hi Eric, how are you?My name is Anderson Justo, a doctorate student from Brazil, and I will work on the project whose subject is related to what you studied here. I have some questions about Comsol and how can I model a transmission tower. How can we talk about it? my email: anderjusto@yahoo.com.br
Thank you so much
Best Regards.
Hi Eric, how are you?My name is Anderson Justo, a doctorate student from Brazil, and I will work on the project whose subject is related to what you studied here. I have some questions about Comsol and how can I model a transmission tower. How can we talk about it? my email: anderjusto@yahoo.com.br Thank you so much Best Regards.

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