Arcing horns

Arcing horns (sometimes arc-horns) are projecting conductors used to protect insulators or switch hardware on high voltage electric power transmission systems from damage during flashover.

Arcing horns provide a path for flashover to occur that bypasses the surface of the protected device.

[1] Horns are normally paired on either side of an insulator, one connected to the high voltage part and the other to ground, or at the breaking point of a switch contact.

Overvoltage events may cause the electric field to exceed the dielectric strength of air and result in the formation of an arc between the conducting parts and over the surface of the insulator.

Under a worst case, this process may take as long as several seconds, during which time the insulator surface would be in close contact with the highly energetic plasma of the arc.

The geometry of some designs encourages the arc to migrate away from the insulator, driven by rising currents as it heats the surrounding air.

Other designs can utilise the magnetic field produced by the high current to drive the arc away from the insulator.

The presence of the arcing horns necessarily disturbs the normal electric field distribution across the insulator due to their small but significant capacitance.