Fog and Anti-Fog Insulator

First question: they serve the same function. Different manufactures, some call them fog disc insulators others call them anti-fog insulators.

Second question: Location, voltage, ph of the water, pollution levels, temperatures ranges, Flash over voltage, seismic loads, mechanical loads, wind loads.

I'm sure there more than I've listed. Here a Google Book link Insulators for high voltages

Here another Google Doc link for a Bidding Contract.

Good luck with your studies.