Arcing Horn Design Help 1

[adeel1001]

I need to design an arcing horn that will be used with a 95kV BIL insulator. I am not familiar with the electrical engineering side of things so I was wondering how do I calculate the proper air gap distance between the arcing horns? Also, how does material play a role? I am assuming using copper is ideal.

 

[potteryshard]

No one with actual knowledge has jumped in here, so I will... The first question would be why? The wording of the query seems to imply that the putative arcing horn would be line-to-ground across a 95kV BIL insulator. This is protection that is now usually handled by a MOV arrestor.

The only common use for arcing horns these days is for use as arc transfer horns above switch contacts. In such a case, the BIL doesn't have much to do with horn design; the spacing of the throat is near zero, and opens with the main contacts so that the resultant arc sucessfully transfers to the horns which self-extingush the arc. Taper I would expect is more determined by available space than anything else.

I would expect the ultimate width of the horns to be fairly critical, but wouldn't have an idea of what usual practice calls for. It should be noted that many current switch transfer arc horns are arranged so that one arm is spring-loaded to snap open very quickly to sretch the arc as quickly as possible.

If your application is indeed for switch transfer horns, I'd suggest looking at examples. Since most of the switch will be designed based on staying above critical flashover distance to prevent starting phase to phase or phase to ground arcs, but the horns are instead designed to extingush an already existing arc, it would seem that the widest part of the horn needs to be several to many times the critical flashover distance.

 

[ghostbuster7]

Many years ago I designed and tested an arcing horn system for insulators on high voltage lines in Kenya.Apparently in Kenya,they have over 150 lightning days per year.I believe we shipped several 1000 of these systems to Kenya.They consisted of a steel arm bolted to each end of the insulator string and an approx. 1" dia. steel ball on the end.All assemblies were hot dipped galvanized.

 

[adeel1001]

Thanks for the responses... The system where this insulator/arcing horn will be used is not a typical set-up, but I am looking to protect the system from possible lightning strikes. A MOV arrestor might be another solution to look into.

ghostbuster7, how did you determine the proper spacing between the two steel balls on the ends? Currently I have 1/4" stainless rods on each end of the insulator with 1.75" spacing. I plan on testing this, but it would be nice to know if there is a standard calculation to follow.

 

[jghrist]

The purpose of the arcing horns in this application is to ensure that any flashover occurs across the arcing horns instead of across the porcelain. This prevents damage to the porcelain insulator. There are graphs in the Westinghouse (now ABB) T&D Reference Manual that show flashover characteristics of arc gaps. Select a spacing that has lower flashover than that of the insulator.

Using arc gaps will lower the BIL of the system (by making the flashover lower than that of an insulator alone) and result in more flashovers and momentary outages (if there is reclosing). There may be fewer permanent outages because of fewer failed porcelain insulators.

 

[adeel1001]

The Westinghouse T&D Reference Manual is exactly what I was looking for, thanks.