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VK2ZRG > TECHNI 28.05.06 16:13l 50 Lines 2051 Bytes #999 (0) @ WW
BID : 28641_VK2TGB
Read: DL1LCA GUEST
Subj: Re: Skin depth in copper
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Sent: 060528/1203Z @:VK2TGB.#SYD.NSW.AUS.OC #:28641 [Valley heights] FBB7.00i
From: VK2ZRG@VK2TGB.#SYD.NSW.AUS.OC
To : TECHNI@WW
VK2ZRG/TPK 1.83d Msg #:2352 Date:28-05-06 Time:12:55Z
From Patrick DF3VI
>> Bet you thought skin depth at 50 Hz was irrelevant, I did until I
>> did the sums.
>> Frequency Skin depth
>> 50 Hz 9.35 mm
>
>That IS irrelevant. Even for somewhat higher frequencies you rarely have a
>_massive_ conductor where skin depth matters. A massive copper conductor of
>almost 20 mm diameter (300 mm^2) cannot be handled, that is why stranded
>conductors are used. Now it is the diameter of each strand that counts.
>So yes, skin effect does not start to matter until you are in the MHz,
>or in the high power/current transmission.
>
>73, Patrick
Hello Patrick,
It doesn't matter whether the conductor is stranded or not unless all the
strands are insulated from each other. Such wire is called Litz wire which
is useful up to a 2 MHz or so for making high Q inductors. You will often
find such wire on the ferrite antenna rod in AM broadcast radios. Litz wire
is also used for I.F. transformers at a few hundred kilohertz to obtain a
higher Q. So, yes, skin effect matters at frequencies well below a megahertz.
If the strands aren't insulated then the AC current still flows on the
outside. Think of the inner conductor of a co-axial cable such as RG213.
It doesn't have lower loss than a co-ax cable with a solid core, quite the
opposite in fact. The losses are higher because of the rough surface of the
inner conductor.
A 20 mm cable is large for some purposes, but what size are the conductors
from a 200 mega watt alternator? A lot more than 20 mm for sure. I seem to
remember reading about a large hydro electric power station that had hollow
water cooled conductors of something like 150 mm diameter. There wasn't any
extra power loss in the conductors over what a solid conductor would have,
because of skin effect, even at 50 Hz.
73s from Ralph VK2ZRG@VK2WI.#SYD.NSW.AUS.OC
Taglines by Colin Coker G4FCN
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