AU654206B2 - Drop out expulsion fuse - Google Patents

Description

420 S F Ref: 220125

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

o Name and Address of Applicant: Australian Electrical Maintenance Pty Limited Unit 3/3 Carnegie Place A c, Blacktown New South Wales 2148 S AUSTRALIA 1. Actual Inventor(s): Wolfgang Joseph Rebholz Address for Service: Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Invention Title: Drop Out Expulsion Fuse ASSOCIATED PROVISIONAL APPLICATION DETAILS [313 Application No(s) [33] Country [32] Application Date PK8287 AU 10 September 1991 The following statement is a full description of this invention, including the best method of performing it known to me/us:-

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-2- The present invention relates to high voltage fuse links used in drop-out expulsion fuses in high voltage, overhead, electricity distribution systems, and in particular, to a fuse link which is substantially spark free.

Fuse links which are used in expulsion drop-out fuses in high voltage electricity distribution systems usually comprise a metallic head at one end and a metallic tail fitting at the other. The fuse element is located between these two elements with a deionising tube surrounding the fuse element. When the fuse element is fused due to a fault, the metallic tail element pulls away from the metallic head fitting due to the fact that the expulsion fuse is under tension, thereby ensuring a break in the body of the expulsion fuse. At low currents the arc is confined within the deionising tube and therefore in most instances is extingui,hed.

The fuse which is located in a carrier which pivots on a hinge to assist the break and also to provide a visible indication that the fuse has blown.

One disadvantage with known fuse links and hence expulsion fuses is that the arc which is produced when the fuse fuses has been known to produce sparks which have also been known to cause fires in the location of the fuse.

Another disadvantage associated with expulsion fuses is that the break in the fuse is not always reliable and if the fuse does not work correctly, substantial damage can be caused to the electrical equipment the fuse is supposed to be protecting, as well S" 20 to the fuse carrier which could burn and fall onto the ground and cause a bushfire.

It is an object of the present invention to provide an improved fuse link which is reliable.

According to one aspect of the present invention there is disclosed a drop out I expulsion fuse link for a low current rating or a high current rating, said fuse link 25 -'comprising a fuse element surrounded by a sleeve of vulcanised fibre material which is covered by a flame retardant heat shrink material, wherein said vulcanised fibre material is a spiral wound electrical insulation grade fibre, and wherein said fuse element comprises a strain element which is made of a metal alloy wire, and said strain element is used as the only fuse element at low current iratings, whilst for high current ratings an extra fuse element is connected in parallel with the strain element.

One embodiment of the present invention will now be described with reference to the drawings in which: Fig. 1 is a side view of a fusible element of the preferred embodiment, and Fig. 2 is a side view of the fusible element of Fig. 1 shown without the deionising tube and heat shrink tube.

(N:\libcc]00192:HRW i -3- The fuse link 1 of the preferred embodiment as illustrated in the drawings shows the element/strain cord 4 located between a top ferrule 2 and a bottom ferrule 6. The element/strain cord 4 is crimped by both the top and bottom ferrules 2 and 6 respectively. A flexible cable or pig tail 3 is also crimped to the other end of the bottom ferrule 6 as illustrated in the drawings.

The element/strain cord 4 is used for current ratings between 3.15 amps 20 amps whereas an additional fusible element 5 made from a tin alloy is rated for currents between 25-100 amps. The strain cord 4 is preferably made from brass wire having a temper in the range from hard o odrawn to half hard drawn.

Also seen in Fig. 2, a heat shrink tube 7 is shown surrounding the pig tail 3 adjacent the bottom ferrule 6. This section of pig tail 3 has :o.00 been crimped in order that this section of the pig tail 3 is stiffened, and 15 for high current ratings, namely, 50-100 amps the heat shrink tube 7 is also required to provide extra stiffness.

The deionising tube 9 as illustrated in Fig. 1 is seen to surround "o the fusible element and is secured at the top ferrule 2 and at the other o0 end surrounds the heat shrink tube 7. The deionising tube 9 is made of vulcanised fibre composite and has a plastics fire retarded heat shrinkable 0o° 5 tube 10 located on the outside thereof. The vulcanised fibre material is a 0o"o spiral wound electrical insulation grade fibre. The vulcanised fibre deionising tube 9 has the properties that at a low current interruption, 2 the strength of the vulcanised fibre sleeve 9 is strong enough to contain 25 the pressure and as the vulcanised fibre burns or erodes during low current interruption, enough gas is generated to quench the arc thus providing a fast interruption.

Another property of the vulcanised fibre is that for high current interruption, the vulcanised fibre deionising tube 9 is weak enough to disintegrate and thereby minimise the pressure within the deionising tube 9 which then dissipates within the fuse carrier (not illustrated). One cause of problems with fuse links as described above is that the pressure buildup within the fuse link can provide an explosion if the deionising tube 9 does 4 not disintegrate at a relatively low pressure.

The use of the heat shrinkable tube 10 over the vulcanised fibre: increases the bursting strength of the vulcanised fibre tube; and does not allow water ingress which results in dimensional instability of the vulcanised fibre tube.

HRF/0455c

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The element/strain cord 4 is constructed of brass wire and as this is a substantially "chemically inactive material", when the fuse fuses or melts, the brass does not produce enough hot particles to ignite fires. The use of such a brass wire assists in the quenching of any sparks which can occur. One advantage of the element/strain cord 4 being made of brass wire is that the strain cord and the element are actually combined for low current ratings. This means that the construction costs of such a fusible element are substantially lower.

Another advantage of using a metallic strain cord is that this construction ensures positive fuse separation once the element fuses. Some "minimum spark emission" fuse links which have non-metallic strain cords, which under certain conditions do not burn and therefore cause "hang-up" (ie. fuse carrier does not dropout). However, with the metallic strain cord, once the fuse fuses, the current flows in the strain cord which, in turn, fuses. Consequently hang-up cannot occur.

The foregoing describes only one embodiment of the present invention, and 15 modifications obvious to those skilled in the art can be made thereto without departing from the scope of the present invention.

For example the 1-2 amp fuses can utilise a wire made of a nickel-chromium alloy as an element.

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Claims (6)

1. A drop out expulsion fuse link for a low current rating or a high current rating, said fuse link comprising a fuse element surrounded by a sleeve of vulcanised fibre material which is covered by a flame retardant heat shrink material, wherein said vulcanised fibre material is a spiral wound electrical insulation grade fibre, and wherein said fuse element comprises a strain element which is made of a metal alloy wire, and said strain element is used as the only fuse element ht low current ratings, whilst for high current ratings an extra fuse element is connected in parallel with the strain element.

2. A fuse link as claimed in claim 1 wherein said metal alloy wire is formed from a metal alloy comprising nickel-chromium alloy.

3. A fuse link as claimed in claim 1 wherein said metal alloy wire is formed from a metal alloy containing copper. 15 4. A fuse link as claimed in claim 3 wherein said metal alloy is brass. A fuse link as claimed in claim 4, wherein said metal alloy is a brass wire having a temper in the range from hard drawn to half hard drawn. rtn si the range between 3.15 to 20 amps.

7. A fuse link as claimed in any one of the preceding claims, wherein said extra fuise element is fabricated from a tin alloy.

8. A fuse link as claimed in claim 7 wherein said extra fuse element has a current rating of between 25-100 amps.

9. A fuse link substantially as described with reference to the 25 -accompanying drawings. DATED this Twenty-first Day of July 1994 Australian Electrical Maintenance Pty Limited Patent Attorneys for the Applicant SPRUSON FERGUSON [NA~bccjOO192:HRW ABSTRACT DROP OUT EXPULSION FUSE A fuse link comprising a fuse element crimped between a top ferrule and a bottom female A flexible cable or pig tail is crimped to the other end of ferrule A dionising tube surrounds the fuse element and is secured to the top ferrule and extends down to the pig tail The dionising tube is made from vulcanised fibre composite and has a plastics fire retarded heat shrinkable tube located on the outside thereof. Figure 2. 0 013 0 0 o 04 0 13 a1 HRF/0455c 3 0 0