Arcing horns
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Arcing horns are a pair of conductors (usually steel) used to protect insulators or insulator strings from damage due to system overvoltage conditions.
[edit] Location
Arcing horns can be found on transformer bushing insulators, overhead line insulators etc. Sometimes, more than one set are placed across the insulator discs to protect the individual discs against damage.
[edit] Principle of operation
Arcing horns form a spark gap that enables any abnormal overvoltage to break down the air gap between the conductors, forming an electrical arc. The hot arc then travels upwards (as hot air rises). The arc becomes increasingly longer as the wires climbs the horn, and is eventually extinguished as it approaches the top of the horns.
[edit] Disadvantages
The presence of the arcing horns also necessarily disturbs the normal electric field distribution across the insulator string due to their small but significant capacitance.
