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Re: Skin Effect
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)