# Re: Skin Effect

From: 	DR.RESONANCE[SMTP:DR.RESONANCE-at-next-wave-dot-net]
Sent: 	Saturday, August 02, 1997 9:52 AM
To: 	Tesla List
Subject: 	Re: Skin Effect

To: Robert Davis

Could you expound on the equation for dynamic resistance of copper wire?
Is it C (conductance) multiplied by r (radius) multiplied by X (reactance
??????) or is the X a multiplication symbol?  If X is a multiplication
symbol where is the freq (F) brought into the equation?  Without some F
this equation won't work because the dynamic resistance certainly does
change with frequency buy I was unable to determine where you entered this

DR.RESONANCE-at-next-wave-dot-net

----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: 'Tesla List' <tesla-at-poodle.pupman-dot-com>
> Subject: Re: Skin Effect
> Date: Thursday,July 31,1997 8:24 AM
>
>
> From: 	John H. Couture[SMTP:couturejh-at-worldnet.att-dot-net]
> Sent: 	Thursday, July 31, 1997 3:25 AM
> To: 	Tesla List
> Subject: 	Re: Skin Effect
>
> At 11:53 PM 7/29/97 +0000, you wrote:
> >
> >From: 	Robert Davis[SMTP:RE.Davis-at-btinternet-dot-com]
> >Sent: 	Tuesday, July 29, 1997 4:35 PM
> >To: 	'tesla-at-pupman-dot-com'
> >Subject: 	Skin Effect
> >
> >Hi,
> >
> >I have the formula for skin depth as:
> >
> >	Depth (mm Copper) = 66/sqrt(freq)
> >
> >Where the depth is the attenuation of current density from the surface
> >value/e.
> >
> >Question 1:  Is the surface value the same as the DC resistive value for

> >copper wire of a given size?
> >
> >Question 2:  From the above the dynamic resistance of a copper wire at a

> >given frequency appears to be:
> >
> >	Resistance = L/(Cr X ((PI X R^2) - (PI X (R-D)^2)))
> >
> >Where:
> >	L = Length of wire
> >	D = Skin depth
> >	C = Conductivity of copper
> >	R = Radius of conductor
> >
> >	Is this correct?
> >
> >Question 3:  The skin effect calculation assumes that there is only one
> >wire, skin effect being then caused by the magnetic field motion form
the
> >oscilating currents in that wire, BUT we are winding coils with wires in

> >close proximity, does anyone have a correction factor to take into
account
> >
> >If this is the case then the thickness of insulation of wire used
(assuming
> >the coil is close wound) will have some effect on the dynamic resistance
of
> >the coil and hence the Q of the coil, I think proximity of other turns
will
> >increase the dynamic resistance, is this correct?
> >
> >
> >
> >Rob Davis (UK)
> >
> >-------------------------------------------------
>
>   Rob -
>
>   You are talking about effective resistance which includes all of the
> effects you mentioned. The effective resistance Reff is found by
>
>         Reff = Xl/Q
>
>   The Xl is easily found and you can find the Q using a scope as I show
in
> the Tesla Coil Notebook. This is the only way to find the Q of a coil
> operating at high voltage. The Q is found by
>
>         Q = 1.364 x A   where A = 10% amplitude from the log dec.
>
>   John Couture
>
> >
> >
>
>