Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

Skin Effect in Wires.
Skin Effect in Wires.
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 16th May 2019, 02:32 AM   #301
jneutron is offline jneutron  United States
diyAudio Member
 
jneutron's Avatar
 
Join Date: Jan 2004
Location: Long Island NY
Quote:
Originally Posted by Mark Tillotson View Post
The skin depth of copper is 8mm or so at 60Hz, why the 2" thick walls?
It drops off slowly. The exponential equations (what almost everybody touts as "skin effect") actually does not describe what happens within a cylindrical conductor. It describes penetration depth for E/M waves that are normal to a flat surface. As the conductor morphs from flat to cylindrical, the fields within fail to fall off as the planar model describes.
If you wish to know the exact skin depth, you need to use
Bessels. And they do not describe skin depth as shallow as the exponential.


Quote:
Originally Posted by PRR View Post
Skin effect is hardly important. As discussed, when wires get hot, you need *surface area* more than *area*.

Continue my 1" wire up to 4". By area, it would carry 16X the current; by surface area, only 4X current. So it can only carry 4X the current, if current is limited by heat. Then you want 4X the copper in 16X the area: you want 3/4 hollow. 3.46" ID 4" OD pipe, 0.27" walls.

That's just an example from an assumption that a 1" conductor gets hot at high current. JN asserts that 2" walls work for him--- he does bigger stuff than I want to work with. The implication is that conductor 2" thick and cooled on one side is about as thick as is worth doing; any thicker is a waste of copper. At some point we could write an equation comparing lateral thermal resistance to lengthwise electrical resistance, then factor in acceptable temperature and cost of metal (of various shapes).
Well, write the equations... Show the exact solution, but use Bessels, as the exponential is wrong.

I will say, all your discussion of heating, surface area are are spot on. But you are not positioned to even worry about the regime I speak of. So glibly discounting the science... That is not an accurate position. However, the regime discussed is beyond the experience of most so is not a worry..

As a point of interest, my warm to cold feedthroughs traverse the room temp to 4.5 Kelvin domain, and as the copper gets colder the conductivity rises. As that happens the skin depth decreases. At 60 hz the conductivity at 20 to 50 Kelvin increases so much that the skin depth decreases to the .050 inch range, and the current density related dissipation begins to compromise the connections between the copper and superconductor, not a good thing. While we start with a 2 inch diameter copper conductor, by the time it gets to liquid helium temps it's just a 2 inch diameter shell of .050 thickness, resistive wise.
The navy with their superconducting motor drive r and d...the superconducting windmill turbines..all have to worry about these details..me, I just worry about lunch...

Jn
__________________
I hate all these smart gadgets..I refuse to buy things that are smarter than me. I've made a list of those things... Cabbage just made the list.

Last edited by jneutron; 16th May 2019 at 02:45 AM.
  Reply With Quote
Old 16th May 2019, 10:54 AM   #302
jneutron is offline jneutron  United States
diyAudio Member
 
jneutron's Avatar
 
Join Date: Jan 2004
Location: Long Island NY
As an added interest....
One of the reasons for load PFC is skinning and proximity effect caused conductor dissipation because of the harmonics. A load panel and it's bus bars will have a specific ampacity at 60 Hz, but 120 and 180 Hz currents from non corrected loads can exceed the panel ratings heat wise even though the base load draw is within the ratings.

If your load draws large 2nd and 3rd (or 12th as in some of our large scr based 3 phase supplies), you have to consider additional derating of the load panel.

Most consider only the harmonic impact on transformers, and neglect the poor load panel..

Jn
__________________
I hate all these smart gadgets..I refuse to buy things that are smarter than me. I've made a list of those things... Cabbage just made the list.
  Reply With Quote
Old 16th May 2019, 12:32 PM   #303
audiofan is offline audiofan  Canada
diyAudio Member
 
Join Date: May 2003
Location: quebec
I found this on internet... quite easy to read ....

What Is the Skin Effect? | Reactance and Impedance -- Inductive | Electronics Textbook
  Reply With Quote
Old 16th May 2019, 05:09 PM   #304
jneutron is offline jneutron  United States
diyAudio Member
 
jneutron's Avatar
 
Join Date: Jan 2004
Location: Long Island NY
A quick google search for skin and proximity effect heating provided this article...pardon my not knowing how to properly cite it..it is excellent, a must read for anybody working multiconductor, tray, conduit in high current distribution systems.

Proximity Heating Effects in Power Cables
Jonathan Blackledge, Eugene Coyle and Kevin O’Connell
Engineering Letters, 21:3, EL_21_3_01
(Advance online publication: 19 August 2013)

I copy verbatim the discussion as it pretty much reinforces what I've been stating..they do some really neat analysis..


X. DISCUSSION
The phenomenon of both the skin and proximity effect,
although recognised as reducing the ampacity of cables, has
not yet evolved into a set of de-rating tables that can be easily
applied on a day to day basis in engineering design. The
problem in quantifying harmonic heating effects is that they
are a function of frequency. The greater the harmonic distortion present, the larger the number of harmonics present.
Each harmonic current generates its own individual heating
effect and thus, a harmonic rating factor has to be taken into
account for a large number of individual elements. Further, in
general, proximity effects tend to be understated because the
effect on extraneous metalwork including metal enclosures
such as cable trays and metal cladding on cables, has, to
date, not been fully considered either experimentally or in the
Standard International Electrotechnical Commission 60287-
1-1. It is for this reason that, the model considered in the
paper has been developed

jn

ps...the only caveat to this discussion as well as that paper, is that it is being assumed that that stranded copper wire is isotropic. IT IS NOT!! A solid conductor will have isotropic conductivity, but a stranded one has higher conductivity axially and less radially. As a result, several things additionally happen. First, as the strands twist along the cable, for the current to remain crowded at one edge of the conductor, the current has to jump from strand to strand. That introduces a resistive proximity effect loss component that a solid conductor will not have. Second, a stranded conductor will not have as much skin and proximity effect as a solid one. Third, a very aged stranded conductor will be even worse w/r to radial conduction, showing more anisotropy.

This is a very common concern in the superconductor rutherford cable used for magnets.
__________________
I hate all these smart gadgets..I refuse to buy things that are smarter than me. I've made a list of those things... Cabbage just made the list.

Last edited by jneutron; 16th May 2019 at 05:29 PM.
  Reply With Quote
Old 16th May 2019, 06:55 PM   #305
Guerilla is offline Guerilla  Denmark
diyAudio Member
 
Join Date: Feb 2018
Location: Aalborg Denmark
What a jurney this thread ��
  Reply With Quote

Reply


Skin Effect in Wires.Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
ESL wires bshaw147 Planars & Exotics 1 3rd October 2008 08:41 AM
SPKA wires 70s music Multi-Way 0 1st July 2007 01:21 PM
Conductors (I.C.'s, RCAs, internal wires, speaker wires) bigphil Parts 1 25th November 2005 06:47 PM
The Skin Game sully Everything Else 184 29th October 2003 09:34 PM
skin effect of a solid copper wire DUG Multi-Way 8 30th March 2003 09:38 PM


New To Site? Need Help?

All times are GMT. The time now is 07:30 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki