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Re: skin depth in round conductors Re: 8 kHz Tesla Coil



Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Robert,

Tesla list wrote:

Original poster: "Bob (R.A.) Jones" <a1accounting@xxxxxxxxxxxxx>

>
> It should be noted that the current is not uniform around the wire.
> The current density will occur adjacent to magnetic fields. In an
> iron core transformer, the current flow through a conductor is drawn
> to the high permeability core side of the winding. In an air core
> transformer, it's toward adjacent wires. In a helical single layer
> coil, toward the 2 adjacent wires.

My understanding is:
The core flux has the effect of pushing the current to the outside of the
winding.
The flux from adjacent wire has the effect of push the current away from the
adjacent areas.
The net effect is the current tends to flow more on the outside of the
solenoid.
I should clarify the core as I did use the term "transformer". With the secondary next to the core and primary wound around the secondary on a typical E-core, the greatest field strength is between the two windings and is where the current density, i.e, current flow, will occur.

In a single winding (typical E-core with small center air gap), the field outside the winding is completely shorted out and the field intensity is greater in the gap than in the winding area within the core because of the energy stored in the gap. Current flow is concentrated on the inside surface of the winding and no current flow on the outside of the winding.

The flux from adjacent windings can attract or repel and that depends on the current flow direction in each winding. Typically the current flow is in the same direction on a solenoid winding and current flow is attracted to the outside near each winding and on the inside where the field strengths are greatest in a solenoid (which is where the dielectric just happens to be on Tesla transformers).

That's my understanding anyway. The cause of greatest losses I believe has far more to do with proximity and dielectric losses than with skin depth in our coils. We are on the low frequency end of the spectrum. We aren't running lot's of power at MHz ranges, we are running moderate power at low KHz. I think there is too much emphasis on skin depth and not enough on proximity and power losses. I am guilty of this.

Take care,
Bart