Skin Effect Heat Tracing

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dman504

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I have a 600 meter piping system which has recently been modified. It has had 6 meters added to it. This system has FSE heat tracing. The mechanical people have simply de-energized the FSE system and modified the piping. I am familiar with the installation requirements for the heat tube, pull boxes, power conductor, etc, but I have a couple questions regarding the calculations.

Can I derive a resistance value from know operating parameters. (voltage & current)?

Can I then take this value and derive an ohms/meter value from the original design length?

Can I then apply this ohms/meter value to the new length?

Thanks in advance.
 
dman504 said:
I have a 600 meter piping system which has recently been modified. It has had 6 meters added to it. This system has FSE heat tracing. The mechanical people have simply de-energized the FSE system and modified the piping. I am familiar with the installation requirements for the heat tube, pull boxes, power conductor, etc, but I have a couple questions regarding the calculations.

1.Can I derive a resistance value from know operating parameters. (voltage & current)?

2.Can I then take this value and derive an ohms/meter value from the original design length?

3.Can I then apply this ohms/meter value to the new length?

Thanks in advance.
Click to expand...
Ohms law applies to the 3 questions. I don't understand the reason for the caculations. The existing cable should have info that may answer your question. This info may assist you in your effort to choose the correct cable.

http://heattracecables.com/pdf/Heat Trace Select Guide.pdf
 
dman504 said:
Can I derive a resistance value from know operating parameters. (voltage & current)?

Can I then take this value and derive an ohms/meter value from the original design length?

Can I then apply this ohms/meter value to the new length?
Click to expand...

I'd say, yes, of course, but this shouldn't require a calculator at all. Can't you just say that you added 1% of length, and thus resistance, and reduced the current by the same 1% (or more precisely, the reciprocal) ?
 
Actually, I think the current will increase. (If this is heat trace cable with parallel impedence, like the type I've seen. I'm not sure what FSE is.) But I think 1% should be pretty close to being correct.

Heat trace calculations are usually done in Watts. You wouldn't worry about ohms. Self regulating heat trace has a resistance that varies with temperature. So you won't get the maximum current if you don't take measurements on the coldest day of the year.

I agree that there should be a marking on the cable that you can probably look up on the internet, and find all the info you need.

Steve
 
Ferromagnetic Skin Effect heat tracing is a bit different from other forms in that the piping itself is part of the current path. It uses relatively high currents and relatively low voltages. It is (VERY moderately) described in Art 427, Part IV.

The basic circuit parameters may be computed pretty much as the OP suggested. Ultimately the current will stay about the same, the voltage will see a slight increase to maintain the same W/ft as the previous design.

Edit add: This is slightly more descriptive:

http://www.tycothermal.com/usa/english/heat_tracing/applications/industrial/longline_heating/technologies/skin_effect_tracing_system.aspx
 
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Thanks for the input folks;

I am fairly confident that I can use the same cable (conductor) type that I have in the heat tube now, I was a little unsure if I could increase the resistance proportionaly to the length of the heat tube.

FSE always seems like a "dead short" to me and I had to re-affirm my faith in the skin effect principles. Thanks for the wisdom.

Dman
 
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