Arcing Horns

...""Arcing horns" are projecting conductors used to protect insulators on high voltage electric power transmission systems from damage during flashover. Overvoltages on transmission lines, due to atmospheric electricity, lightning strikes, or electrical faults, can cause arcs across insulators that can damage them.Sep 10, 2015"...

https://en.wikipedia.org/wiki/Arcing_horns

Arcing horns are the last ditch defence to save a substations switchgear and transformers from transient over voltages. MOV’s at the substation intake should be able to shunt transient voltages, unfortunately it isn’t always the case.

What is MOV here?

Best Regards,

metal-oxide-varistor (MOV)

https://www.researchgate.net/publication/3172824_MOV_Surge_Arresters_Improved_Substation_Equipment_Protection

http://www.acronymfinder.com/MOV.html

In the case the OP cites, the arresters, MOV or much older and harsher technology air gap arresters have been isolated from the line. Normally directly attached to the protected item, typically a (high value) substation transformer.

I have never seen the arcing horn design applied to protect insulator strings, learn something new every day. The arc horns I've seen are simple stiff wires designed to stretch out the arc as the disconnect switch opens, like this:

https://www.youtube.com/watch?v=VrY_k_pdlCs

Once the switch is open, the gap between the two circuit elements (arc horn and isolated element) is so large, I doubt that it could account for any protection at all, as the idea is to isolate the load side of the switch.

It is more likely that the incoming switch insulator would flash over before the air gap between the arc horn and the switch load side, and that's how you would want it, don't couple an external surge to your high value arresters & transformer.