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Question edit
What if the horns are vertical (many are). In which direction does the arc then travel?--Light current 02:03, 21 March 2006 (UTC)
- At low and medium voltages, or in air break switches, the pair of wires forming the horn may be nearly vertical. In this configuration the arc climbs the horns, hopefully extinguishing the arc. Magnetic forces can also help to drive the arc towards the widening gap end of the gap between the horns (and away from the insulator to prevent damage). However, external interrupters are still often required to ensure that the arc is extinguished.
Examples of vertical arcing horns:
- http://www.impulsenc.com/pdf/ocs_catalog/sinsulator.pdf (see page 5, KT insulator with arcing horns)
- http://www.schneider-electric.com/cahier_technique/en/pdf/ect151.pdf (see diagram on page 14)
Yeah those look like proper horns to me!--Light current 03:49, 21 March 2006 (UTC)
- In other designs, the horns form a simple spark gap across an insulator or insulator string. In this case, the arc will generally not self-extinguish, and other protective equipment (such as a cutout, circuit breaker, or fuse) must remove power in order to kill the arc. These gaps are used primariy to protect insulator strings from "follow through" arcing following a string flashover from a direct, or nearby, lightning strike. Because of their superior clamping time and self clearing capability, MOV type lightning arrestors have largely replaced arcing horns in most modern power systems. Here's an example of simple arcing horns used to protect an insulator string:
The first desc. sounds like a Jacobs ladder system reling on the bouyancy of the hot gases! OK. The horns Im thinking of are simple spark gaps mounted vertically or at an angle of say 45 deg on 11kV or 33 kV to LV transformers etc as per pic on electrical engineering page. In these cases, I think you must be correct in saying that some other device must interrupt the arc. However, for transient overvoltages only, would the arc not self extinguish at the zero crossing of the wave form? (maybe). When you say follow thro- do you mean power freq follow thro?--Light current 03:37, 21 March 2006 (UTC)
- Unfortunately, once a power arc begins, the gases in the arc channel become so hot that the arc easily reignites after every zero crossing. "Follow through current" is indeed the power frequency current that follows (and continues to heat) the hot spark channel that was initially created by the over voltage transient. Unless you are able to stretch a power arc (such as via an air blast) or otherwise remove most of the heat in the channel (such as switching under oil), the arc will tend to reignite after every zero crossing and will fail to extinguish. Bert 05:43, 21 March 2006 (UTC)
Yes this of course makes sense! I had my brain in neutral when asking that question!--Light current 07:07, 21 March 2006 (UTC)
This last link is not a bad picture of horns. Can we include it in the article (ie is it free of copyright?)--Light current 03:37, 21 March 2006 (UTC)
I was just looking for an example picture to answer your question. Unfortunately, I don't own the copyright for this image... Bert 05:43, 21 March 2006 (UTC)
Picture edit
Anyone got a nice pic of arcing horns?--Light current 02:19, 21 March 2006 (UTC)