Arcing Horn Description

For MV and HV overhead lines, some insulator sets are fitted with line and earth-end arc horns. Arc horns are made of galvanized steel. Where the tube is used, the wall thickness should be approved by the client and both inner and outer surfaces are galvanized. The parts of horns where arcs are expected to make contact are solid.

The design of arc horns is to obviate damage to clamps and conductors and to prevent cascading over the line end insulator units when flashover occurs. The arcing horn should be suitable for use with hot line tools. The amount of lift and general shape should at the same time give maximum values of power frequency and impulse flashover voltage consistent with the above provisions. In particular, the lift of line end horns is such that their points extend beyond the disc of the line end unit, as shown on drawings. Arcing horns cannot be attached to insulator pins or caps.

Details of the arcing horns are in accordance with the following:

(a) Normal and Heavy Suspension Insulators - Double point horns should be arranged

in the vertical plane containing the conductors. The lower arcing horns are strong enough to support a man weighing 90 kg standing on the horizontal portion with adequate security.

(b) Tension Insulator - Single-point arc horns are fitted so as to provide a horizontal arc path above the insulator string.

(c) Light Duty Tension Insulators - Light duty tension insulators for use at the upper end and lower end of the slack spans are fitted with arc horns at both line and earth end, providing arc gap adjustable from 800 - 1200 mm for 132 kV lines and from 1200 - 1860 mm. for 220kV lines. Line end horns are fixed and the earth end horns are adjustable.