Horn Gap Arrester: Operation, Advantages & Limitations

☛Fig. shows the construction details of horn gap arrester.

☛It mainly consists of two horn shaped metal rod A and B separated by a small air gap and a series resister R and inductor L.

☛The horn are so constructed that distance between them gradually increase towards the top.

☛The horns are mounted on porcelain insulators.

☛One end of horn is connected to the line through a resistance R and choke coil L while the other end is effectively grounded. ☛Since the reactance of a coil is mainly depends on the frequency, it offers small

reactance at normal power frequency current but a very reactance at transient frequency current.

☛Thus the transients are blocked / bypassed before it enters the apparatus, The resistance R helps in limiting the fault current to a small value.

Operation of Horn Gap Arrester

☛It stated above that all gap type of arresters have same working principle.

☛The gap between the horns is so adjusted that normal supply voltage is not sufficient

to cause brake down of gap between the horns.

☛Under normal condition supply voltage is insufficient to initiate the are between the gap and gap remains non-conducting.

☛When there is a voltage surge, spark takes place across the small gap.

☛Due to magnetic effect of the arc, a force is exerted on the arc and causes it (arc) to travel up in the gap.

☛Fig. shows the details of horn gap arrester. And position 1, 2 and 3 shows that are moves progressively upward (points A and B).

☛At some position of the arc, the distance may be too great for the voltage to maintain the are. This causes the extinction of the arc.

circuit diagram of horn gap lighting arrester

Advantages of Horn Gap Arrester

(i) Since the magnetic effect draws the arc away causing increase in the length of the are. Thus the arc is self-extinguished. Therefore this type of arrester does not cause short circulating of the system after the surge is over as into the case of rod gap arresters.

(ii) Series resistance and reactance limits the fault current to a small value.