Eddy Currents in Switchboards/Enclosures

Here's all you need, plus a bunch engineering knowledge to properly apply these equations from Wikipedia:

http://en.wikipedia.org/wiki/Eddy_current

'...Strength of eddy currents

Under certain assumptions (uniform material, uniform magnetic field, no skin effect, etc.) the power lost due to eddy currents per unit mass for a thin sheet or wire can be calculated from the following equation:^[7]

where

P is the power lost per unit mass (W/kg),B_p is the peak magnetic field (T),d is the thickness of the sheet or diameter of the wire (m),f is the frequency (Hz),k is a constant equal to 1 for a thin sheet and 2 for at thin wire,ρ is the resistivity of the material (Ω m), andD is the density of the material (kg/m³).

This equation is valid only under the so-called quasi-static conditions, where the frequency of magnetisation does not result in the skin effect; that is, the electromagnetic wave fully penetrates the material.

Skin effect

Main article: Skin effect

In very fast-changing fields, the magnetic field does not penetrate completely into the interior of the material. This skin effect renders the above equation invalid. However, in any case increased frequency of the same value of field will always increase eddy currents, even with non-uniform field penetration.^{[citation needed]}

The penetration depth can be calculated from the following equation:^[8]

where δ is the penetration depth (m), f is the frequency (Hz), μ is the magnetic permeability of the material (H/m), and σ is the electrical conductivity of the material (S/m)..."

Your first step is to calculate the power density and convert that to heating energy so you can figure out the temperature rise. You then calculate the penetration depth to see what percentage of the field (and hence the heating effect) remains in the enclosure instead of passing to the outside of the enclosure.

As you can see you need to know everything about the materials involved, plus the layout and dimensions of your busbars relative to the surface of your enclosure. Material selection will play an important role since a magnetic material such as certain steels will have very different results than using aluminum, thickness also makes a big difference.

There are probably general guidelines on the web, but for really high currents and tight dimensions this is as basic as it gets, to be sure you should test your design before you put it into production. As an added benefit this exercise will help you distinguish yourself from the engineering wannabes out there.