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Re: Skin Effect
From: DR.RESONANCE[SMTP:DR.RESONANCE-at-next-wave-dot-net]
Sent: Sunday, August 03, 1997 2:53 PM
To: Tesla List
Subject: Re: Skin Effect
To: Rodney Davis
Thank you for the explanation -- this makes it clear.
Good luck with the coil.
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: Sunday,August 03,1997 8:51 AM
>
>
> From: Robert Davis[SMTP:RE.Davis-at-btinternet-dot-com]
> Sent: Sunday, August 03, 1997 9:27 AM
> To: 'Tesla List'
> Subject: RE: Skin Effect
>
>
>
> Dear DR.RESONANCE,
>
> Sorry the calculation was not clear. I used the X as multiplication.
> In the second calculation for effective wire resistance the skin depth
> term varies with frequency. Also the lower case r was a typing
> mistake. The ^ symbol meaning, to the power of. The 66 in the first
> formula becomes 0.066 after converting skin depth in mm to meters.
> The full equation is given below (without multiplication symbols)
> after substituting the first formula for the skin depth term:
>
> Dynamic Resistance = L/C((PiR^2)-(Pi(R-(0.066/sqrt(F)))^2))
>
> Where:
> F = Frequency (Hz)
> L = Length of wire (m)
> R = Radius of Conductor (m)
> C = Conductivity of copper = 5.8 x 10^7
> Pi = 3.1415927
>
> In the above I use sqrt() as the square root function.
>
> Is this correct?
>
> Thank you for your reply, Rob Davis (UK)
>
>
>
> 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
> factor into your equation.
>
> 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
> > >fields from adjacent wires?
> > >
> > >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?
> > >
> > >Thank you in advance.
> > >
> > >
> > >Rob Davis (UK)
>