Different styles of HV electrodes

[MRMILSTAR]

On large Marx generators, CW multipliers, and other HV equipment I often see large shielding electrodes  composed of many smaller bowl-shaped elements. I assume that this construction technique is used because its simpler to build and is a close approximation to an ideal shape such as a toroid or sphere.

Other times I see the shielding electrode made from tubular sections which, in the Tesla coil world, we usually call a skeleton electrode which again is a close approximation to an ideal shape.

And then other times I see an actual spun aluminum electrode with the ideal shape.

Does anyone know why one technique is used instead of another? I assume that its just simplicity of construction and cost for the large electrodes. The attached image shows examples of these.

[johnf]

Steve
it all has to do with electric field control
for lightning protection a technique called rolling sphere is used to protect objects by shadowing them within the area inside the rolled sphere area
here is an article describing it so you do not need entire structures just a skeleton will do as long as there are no sharp edges
Joe Crispino - Surge Presentation.pdf

[Steve Ward]

I'd agree with your original thoughts that it mostly comes down to manufacturing cost or other practical considerations.

The more perfectly smooth the surface is, the more stress it can stand before breakdown, but only marginally.  In my FEMM simulation, the breakdown voltage was reduced by maybe 20% when going from ideal toroid to a "ring" or skeleton toroid as you call it, and this was acceptable.  It depends on the radius of the conductors and how they are grouped, as they will partially shield eachother, reducing the e-field.  That is to say, a single ring would have a far lower breakdown voltage than a group of rings approximating the shape of a toroid with larger cross section.  Similarly, grouping a cluster of spheres together would raise the breakdown potential compared to a single sphere of the same diameter.