Of course, but it's a negligible contribution to the heating, in a typical
extension reel (large diameter air core, 50Hz..)
On Mon, Feb 24, 2014 at 6:58 AM, Michael Ross <michael.e.r...@gmail.com>wrote:
> Aside from the resistive heating, if you have a coil and pass an
> oscillating current though it a vibrating field is created which will
> interact with any conductor sufficiently close to it - including itself.
> Each "line for flux" creates an eddy in a conductive material it
> intersects, like little tiny motors inside the material each line as it
> rises and falls has a resulting tiny circular current around it - an eddy.
>
> All this depends on the AC nature. DC current does not cause this after
> its first rise, after switching. A regularly switched DC has the same
> inductive effects as continuous AC.
>
> If you pass AC in two directions along parallel wires, there is a
> possibility they will cancel - but also a possibility they do not. I doubt
> the cancellation is perfect. Is the magnitude great? I don't know. The
> third conductor is presumably a ground in DC? It will have eddies in it.
> In three phase AC where each phase is out from the others is ther any
> cancellation of inductive effects? I don't know. I am a lowly ME.
>
> It is worth noting that frequency of oscillation is very important and
> material specific.
>
>
> On Sun, Feb 23, 2014 at 10:22 AM, Evan Tuer <evan.t...@gmail.com> wrote:
>
> > Because there's current flowing through a resistance, producing heat.
> > Normally it's fine, the few Watts per metre lost as heat are easily
> > conducted away from the wire. If you bundle lots of cable (therefore
> lots
> > of Watts) into a small space, the temperature can build up until the wire
> > insulation melts.
> >
> > Makes no difference whether it's AC or DC.
> >
> >
> > On Sun, Feb 23, 2014 at 8:24 PM, Martin WINLOW <m...@winlow.co.uk> wrote:
> >
> > > "three conductor wire" - Do you mean 3-phase?
> > >
> > > Why do ordinary domestic AC mains cable reels heat up if used coiled,
> > > then? MW
> > >
> > >
> > > On 22 Feb 2014, at 17:26, Bill Dube wrote:
> > >
> > > > AC, not DC powered. Transformer changes ~13 kv distribution voltage
> > down
> > > to 480 vac.
> > > >
> > > > Cord reels ("coils") consist of three conductor wire with current
> > > flowing equally in both directions, so there is no inductance
> associated
> > > with the "coil". Thus no inductive heating from the AC.
> > > >
> > > > On 2/22/2014 3:55 AM, Martin WINLOW wrote:
> > > >> Hi Bill,
> > > >>
> > > >> I'm assuming the power must be DC... or otherwise wouldn't the coils
> > > get V hot? Or is this what the transformer you mentioned deals with?
> > > >>
> > > >> MW
> > > >>
> > > >>
> > > >> On 21 Feb 2014, at 17:53, Bill Dube wrote:
> > > >>
> > > >>> Electric coal mining equipment is cord-connected. Even enormous
> > > draglines ("steam" shovels on steroids) are typically cord connected
> with
> > > 13 kV cables. It is a mature science. Coal mining equipment has been
> > > electric powered since the early 1900's. Specialized cables, reels,
> > > transformers, and equipment for the mining industry. Easily
> transferable
> > > technology to agriculture.
> > > >>>
> > > >>> They typically put a reel on the back of the mining machine that
> pays
> > > out (or pulls in) the cable as needed. They have a "load center"
> > > transformer that is moved around as the mining process proceeds.
> > > >>>
> > > >>> Electric shuttle car for underground coal transport from working
> > face:
> > > >>> http://www.undergroundcoal.com.au/fundamentals/11_face.aspx
> > > >>>
> > > >>> Nifty tutorial on cables for mining EVs:
> > > >>> http://www.cdc.gov/niosh/mining/content/deratingfactors.html
> > > >>>
> > > >>> Dragline cable:
> > > >>>
> > >
> >
> http://www.miningphoto.com/details/2140/dragline_working_in_background_removing_overburden_with_drill_rigs_drilling_blas
> > > >>>
> > > >>> Bill Dube'
> > > >>> (Used to work as an Electrical Inspection intern for the Mine
> Safety
> > > and Health Administration, MSHA)
> > >
> > > _______________________________________________
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>
> --
> Put this question to yourself: should I use everyone else to attain
> happiness, or should I help others gain happiness?
> *Dalai Lama *
>
> Tell me what it is you plan to do
> With your one wild and precious life?
> Mary Oliver, "The summer day."
>
> To invent, you need a good imagination and a pile of junk.
> Thomas A. Edison<
> http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html>
>
> A public-opinion poll is no substitute for thought.
> *Warren Buffet*
>
> Michael E. Ross
> (919) 550-2430 Land
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