I've seen these stacked-disc structures on high voltage power lines everywhere. I could not find any information regarding this particular shape, though.

Insulator on Railways (From Wikimedia Commons)

Another example of insulator

From what I've noticed, high voltage ceramic insulators only insulate conductors end-to-end (not inside to outside, like traditional plastic insulators). I can only assume the shape makes it difficult for an electric arc to travel along the ceramic material, as opposed to, say, along a solid cylindrical piece.

Why exactly are ceramic insulators shaped like that? Is it to reduce cost? Thermal concerns (from possible electric arcs)?


1 Answer 1


Electricity can more easily travel across a surface of an insulator. If the surface is made longer it makes the surface path longer and thus is able to withstand higher voltages before breaking down.

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    \$\begingroup\$ Plus the shape is intended to ensure at least part of the "cup" stays dry in most normal weather; water tends to reduce the surface impedance. \$\endgroup\$
    – user16324
    Dec 28, 2013 at 10:23
  • 2
    \$\begingroup\$ @BrianDrummond Indeed, imagine if it was a smooth, ceramic cylinder. In heavy rain, a rivulet of water could easily run along its length between the two terminals. \$\endgroup\$
    – Kaz
    Dec 28, 2013 at 15:52
  • \$\begingroup\$ @BrianDrummond could be added as another answer \$\endgroup\$
    – mateos
    Feb 6, 2018 at 7:44

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