Why is the surface of porcelain insulators made of corrugated shapes?

(1) Extending the arc climbing length can increase the arc climbing distance within the same effective height, and each can also play a role in blocking the arc.
(2) When encountering rainy days, it can play a role in blocking water flow, and sewage cannot directly flow from the upper part of the porcelain bottle to the lower part to avoid flying and causing confusion.
(3) When the dust falls on the corrugated porcelain insulator, the distribution is uneven, thus ensuring the strength of the porcelain bottle to a certain extent.