switchgear-What is liquid type fuse?

                            

What is Liquid type fuse?

Liquid fuse

In the earliest liquid fuses, the arcs were quenched in a liquid and this principle has been used for many years to produce fuse links. Many liquid fuses are in use in the UK. Liquid fuse has a body consisting of a glass top with metal ferrules at each and within it is the element. This is normally of silver strip or wire, with a strain wire across it except for low current ratings, say10Amp and below, in which a wire is used as the element and this is made strong enough to make a separate strain wire unnecessary. In all liquid fuse designs, the element is positioned near the top of the tube so that it is shielded from Corona discharge by the upper ferrule. In liquid fuse the element is held in tention by a spring anchor to the lower ferrule and the tube is filled with an Arc extinguishing liquid usually a hydrocarbon. when the element melts during operation, the spring collapse and arc are extinguished in the liquid. In liquid fuse, to relieve the tube of excessive pressure, a diaphragm on the upper ferrule is ejected except under every moderate condition. Provision is usually made to allow the user to recharge by inserting a new fuse element assembly and new liquid. figure 5.4 shows a cross-sectional view of a typical liquid fuse-links. These fuses are only in use outdoors and provision is made for removing from and replacing the fuse links into their mountings by poll operation from the ground, a bayonet fixing arrangement being usual. Liquid fuses are intended for the protection of 11 and 33KV pole or pad mounted transformers on rural systems and also for Spurs, feeding a number of transformers.

The breaking capacity of these liquid fuses is limited to values below those of expulsion fuses and although, they have given and indeed still are giving good service. Liquid fuses are no longer recommended for new installations.