AU650043B2

AU650043B2 - Improvements in fuse links

Info

Publication number: AU650043B2
Application number: AU83455/91A
Authority: AU
Inventors: Rainer Dornauer
Original assignee: NGK Stanger Pty Ltd
Current assignee: NGK Stanger Pty Ltd
Priority date: 1990-08-30
Filing date: 1991-08-30
Publication date: 1994-06-09
Anticipated expiration: 2011-08-30
Also published as: AU8345591A

Description

.4 6,50043 AUSTRAL IA Patents Act 1990

ORIGINAL

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COMPLETE SPECIFICATION STANDARD PATENT Invention Title: IMPROVEMENTS IN FUSE LINKS The following statement is a full description of this invention, including the best method of performing it known to me:- 0

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I -2- IMPROVEMENTS IN FUSE LINKS Field of the Invention This invention relates to electrical fuse links and particularly, but not exclusively, to fuse links of the expulsion type.

Description of the Prior Art In order to appreciate both the prior art and the present invention, it is useful firstly to consider the SO.. installation and operation of expulsion type fuse links.

1 0 Figure 1 shows a fuse 20 installed in a fuse carrier The fuse carrier is disposed in an operational position and 9.95 fixed to a mounting bracket 40. The mounting bracket 66009 9 typically would be attached to a power pole or some other suitable structure.

The fuse 20 is retained within the fuse holder by a head connector 24 which is slidably received into a pressure contact 32 to form a secure mechanical fixing, and also ensure a sound electrical connection between the head connector and the contact. A rigid fuse carrier 22 retains the electrical conductors and fusible elements which are the operational components of the fuse. The fuse carrier 22 typically is lined with heat retardant vulcanised rubber. The fuse 20 is secured at its bottom end by a sleeve 34 which is part of the trunnion 33.

25 Extending out from the end of the envelope 22 past the sleeve is a part of the tail conductor 26 of the fuse 20, which loops about to the secured by a bolt 39 to the trunnion. The trunnion itself is of electrically conductive material such as brass. A conductor from the electrical supply would be connected to the cable clamp 36 which is attached to the trunnion 33. The top cable clamp 38 provides further connection to the supply, itself being in electrical connection with the contact 32.

In operation of the fuse 20 upon an overcurrent fault being experienced, a fusible element within the fuse will disintegrate causing a subsequent explosive force 3 which will rupture the fuse carrier 22 near where the fusible element is sited, whereafter the resultant lower part of the fuse 20 is free to swing away by hinge 35 so as to provide a visual indication of the fuse having been activated. As a result of the explosion a number of incandescent particles will be freely distributed; these particles can constitute a serious fire hazard.

The ring 37 is provided to effect isolation of a fuse, whereby the mechanical fixing between the head connector 24 and the contact 32 can be broken. When activated, the whole arm will swing down under influence of the hinge 35 to be in an isolated position.

Having briefly described operation of expulsion itype fuse links, it is necessary to consider the prior art 15 in relation to such fuse links.

cooo o. Figure 2 shows detail of a fuse link 50 in the 0 o. prior art which would be contained within a tubular envelope such as envelope 22 shown in Figure 1. Two views, A and B, illustrate different features of the construction.

The fuse link 50 comprises a head connector 51 which is attached to a top conductor 52 and forms one end of the fuse link. A tail conductor 53 forms the other end of the fuse link. Intermediate of the top conductor 52 and tail conductor 53 is a fusible element 54 and strain element in composite form. The strain element 55 is designed to withstand the normal operational strain exerted longitudinally on the fuse link 50 in its installed ooo.

position, as has been illustrated in Figure 1. The fusible

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element 54 may also have a degree of strain resistance, however its primary function is to serve as the element which fails upon an overcurrent.

View B of Figure 2 shows more clearly the fixing of the fusible element 54 and strain element 55 to the top conductor 52 and to the tail conductor 53. At the point of fixing with the tail conductor 53 a part of the fusible element 54 and the strain element 55 are laid over the outer surface of the tail conductor so there is continuity of the electrical path, then mechanically crimped to tail conductor 53 by means of an externally arranged ferrule 56.

4 A similar arrangement is provided at the fixing of the fusible element 54 and the strain element with the top conductor 52 as is shown by ferrule 57.

Because of this particular fixing arrangement there is a serious disadvantage in the prior art. On a particularly high fault level, such as twenty times the rated current for the fusible element 54, the fuse will explode. The force of the explosion can be such as to fracture the ferrule 56 away from the tail conductor 53, whereby the ferrule itself will be discharged. The ferrule 56 is incandescent at the time of expulsion and therefore could easily cause a fire to start if it were to fall onto combustible materials such as dry leaves or grass.

The possibility of such fires is of great concern to Electricity Authorities, and to this end an Australian Standard (AS 1033.1 1990) has been developed which sets maximum sizes for discharged particles resulting from operation of such a fuse as function of the size and rating of the fuse. Particularly, expulsion type fuse links are S: 20 required to satisfy a minimum spark energy test which relates to the size of partic¢les discharged.

It is an object of the present invention to provide a fuse link which alleviates the disadvantage of se: the prior art in discharging oversized hot particles in S 25 operation, and is simple to manufacture whilst not adding to the costs of such fuse links.

It is a further object of the invention to provide for efficient extinguishing or cooling of hot particles which are expelled from a fuse link when 30 operated.

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*Summary of the Invention ~Therefore, the invention provides a fuse link Soso comprising: a terminal at one end of the fuse link; a flexible tail conductor at the other end of the fuse link; and a fusible element fixed to be intermediate of the 5 terminal and the tail conductor and being electrically conductive therewith, wherein an end of the fusible element extends internally of the tail conductor and fixed to the tail conductor by means wholly internal of the tail conductor.

The invention also provides a method for fixing a fusible element to a flexible tail conductor in a fuse link comprising the steps of inserting an end of the fusible element to extend internally of an end of the tail conductor and causing the fusible element to be fixed to the conductor by means wholly internal of the conductor so it is electrically conductive therewith.

Brief Description of the Drawings The invention will be more clearly ascertained when considered against the accompanying drawings, certain of which relate to examples of embodiments as will now be described. Particularly: Figure 3 shows a cut-away view of an assembled fuse link constructed in accordance with an example of an 20 embodiment of the invention; Figure 4 shows the elements of the fuse link of Figure 3 in a different view; Sees Figure 5 shows an outer auxiliary tube; and

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S" Figure 6 shows a fuse link having an outer 25 auxiliary tube in place.

Description of Preferred Embodiments A preferred embodiment of the invention will be described with reference to Figures 3 and 4. Figure 3 is a view of a section of a fuse link in accordance with the 30 embodiment, and Figure 4 is a view of the fuse link of Figure 3 with the tube 7 removed.

The fuse link shown in Figure 3 has component parts which are common with the prior art fuse link 50 of se 6 Figure 2.

A terminal is provided by the head connector 1 and an associated flange 8 which assists in fixing of the fuse link 10 into a fuse carrier, and is particularly suited to the contact 32 as shown in Figure 1. There is also provided a top conductor 2 and a tail conductor which are both typically tinned copper material arranged as a twisted flexible cable. A strain element 3 is shown in parallel arrangement with a fusible element 4. The strain element 3 would normally be made of nichrome-stainless steel or some other load bearing material which would C: necessarily have a greater current capacity than the Sfusible element 4. It is possible the fusible element 4 could also serve the function of load bearing, in which 15 case the strain element 3 would not be required. The fusible element 4 would typically be constructed of copper .or silver. Because of the reduced cross-sectional area of the fusible element 4 in relation to the conductors 2,5, it will fail by melting due to higher resistance per unit length (1 2 R) losses at a lower current value than the conductors The fuse link 10 has a plastic sheath 6 surrounding both the top conductor 2 and the tail conductor a;o 05, and is also provided with an auxiliary tube 7 formed about the plastic sheath 6 in a portion of the length of the fuse link 10. The tube 7 would typically be made of vulcanised paper. It is possible that fibreglass or bakelite fuse carrier, similar to the carrier 22 in Figure 4 1, could be included to envelop the fuse link. The portion of the tail conductor 5 outside of the tube 7 forms a looping tail 26 as illustrated in Figure 1. The plastic sheath 6 would simply be stripped away from the end of the tail conductor 5 to allow clamping by the bolt 39.

The fixing of both the fusible element 4 and the strain element 3 to the tail conductor 5 is such that they are, in part, inserted into a hole drilled along the central axis of the tail conductor 5 as shown at the point identified as 9, so as to be wholly enveloped or internal of the periphery of the conductor 5. In accordance with 7 this arrangement, there would be no significant bulging of the tail conductor 5 at the point of fixing. The fixing procedure is concluded typically by spot welding, whereby the material of both the strain element 3 and fusible element 4 fuses with the surrounding material of the tail conductor 5. Alternatively, a soldering technique could be provided, whereby the strain element 3 and fusible element 4 are pretreated by dipping in a tin solder. A hole is then drilled in the end of the tail conductor 5 whereafter the respective ends of the composite elements 3,4 are inserted in that hole and heat applied externally of the tail conductor 5, to cause melting of the solder thereby oo o fixing the composite elements 3,4 within the adjacent material of the tail conductor 5. It may also be necessary 6000 15 to envelop the whole area 9 during soldering to prevent the wire strands of the tail conductor 5 from expanding. This S .procedure then represents a type of moulding. Other forms of fixing, such as induction welding, are possible. This fixing avoids the need for any means to be fixed external of the tail conductor. A similar procedure could be adopted for fixing of the top conductor 2 to the elements 3,4.

0 In the manufacture of the fuse link 10, the 0.0 fixing between the elements 3,4 and both the top conductor 2 and tail conductor 5 would need to be accomplished before applying the plastic sheath 6 and the tube 7.

0*90 ~The arrangement of fixing between elements 3,4 oo o and the tail conductor 6 has alleviated the possibility of large incandescent particles being emitted when the fuse link 10 operates, such as was the case discussed for the prior art. Further, the method of construction of the fuse link is simple and easy to achieve using known techniques without requiring a specially machined ferrule or crimping sleeve and tool. Because there is a far lesser possibility of large incandescent particles being discharged during operation of the fuse link 10, the possibility of consequential fires is greatly reduced.

Since the head connector 1 is solidly fixed (in use) within the fuse carrier (as previously discussed), it 8 is possible the internal fixing adopted between the elements 3,4 and the tail conductor 5 as described above may not be required at the respective point of fixing with the top conductor 2. Figure 4 shows the situation were a ferrule 11 has been used at the point of fixing of the strain element 3 and fusible element 4 with the top conductor 2. It is known that ferrules associated with a head connector 1 or a top conductor 2 are less prone to fracturing and dispersing incandescent particles in operation of a fuse link 10. This phenomenon almost exclusively occurs in relation to ferrules or other crimped S. sleeves used and associated with fixing the elements 3,4 to o a tail conductor.

It is also possible to choose the material of the 0@O* plastic sheath 6 within the region of the strain element 3 Sg. and fusible element 4 to be of a high temperature withstand *0 plastic material, which may assist in resisting the dispersion of hot particles upon operation of the fuse link or even delay the release of such particles such that they have cooled to temperatures which are less likely to •sos. cause a fire.

The inventive concept disclosed and described is not limited only to fuse links of the expulsion type. The 0 invention could be applied to any fuse links where a fusible element is to be fixed to a conductor.

For the fuse link 10 shown in Figures 3 and 4, a further or separate feature is provided by virtue of a second auxiliary tube 60 shown in Figures 5 and 6. The auxiliary tube 60 is fitted over the tube 7, which is now of reduced length, to envelop that tube, and extends from between the head connector 1 to the tail conductor 5. As can be seen from Figure 6 the knurled section of the top conductor 2 fixes the second auxiliary tube into place by mechanical interaction. The auxiliary tube 60 also has a single longitudinal slit 62 formed in its periphery. The slit 62 is typically 3 cm in length for a fuse link of cm in length, and is arranged to be partly coincident with the location of the fusible element 4 and extending backwards over the tail conductor 9 The function of the slit 62 is such that when the fusible element 4 ruptures the quenching capability of the fuse link is improved since there is a dual effect of the tube 7 and auxiliary tube 60 absorbing the rupture energy as well as the slit 62 allowing some of that energy to reach the vulcanised fibre in the fuse carrier 22. The geometry of the slit 62 governs the cooperative effect between the tubes 7,60 and the fuse carrier 22. It is also possible that no fuse carrier is provided, as is the case for Figure 6, and in this way the beneficial function of the slit 62 is still obtained, since there can be partial air quenching of the rupture gases thereby reducing the temperature of any particles which are then discharged as the tubes 7,60 rupture.

15 The fuse links described and illustrated are a. S* typically suited to applications up to 36 kV and current ratings of less than 100 A.

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Claims

1. A fuse link comprising: a terminal at one end of the fuse link; a flexible tail conductor at the other end of the fuse link; and a fusible element fixed to be intermediate of the terminal and the tail conductor and being electrically conductive therewith, wherein an end of the fusible element extends internally of the tail conductor and fixed to the tail conductor by means wholly internal of the tail conductor.

2. A fuse link as claimed in claim i, wherein the fusible element is fixed by soldering.

3. A fuse link as claimed in claim 1, wherein the fusible element is fixed by welding.

4. A fuse link as claimed in any one of the preceding claims further comprising a conductor section fixed intermediate of the terminal and the fusible element and being electrically conductive therewith. s A fuse link as claimed in claim 4, wherein the opposite end of the fusible element extends internally of the said conductor section and fixed to the conductor •section by means wholly internal of the conductor section. see:

6. A fuse link as claimed in any one of the preceding claims, wherein there is a strain element in parallel arrangement with the fusible element to form a composite arrangement, that one or both ends of the strain element being fixed in the same manner as the fusible element. A fuse link as claimed in claim 6 wherein at least the composite arrangement is enveloped by a sheath.

8. A fuse link as claimed in claim 7 further comprising an auxiliary tube enveloping at least the said sheath.

9. A fuse link as claimed in claim 8 wherein the auxiliary tube has a longitudinal slit in its periphery, Sthe slit being coincident with a part of the fusible 11 element and extending backwards to coincide with a part of the tail conductor. A fuse link as claimed in claim 8, further comprising a second auxiliary tube enveloping at least the said auxiliary tube.

11. A method for fixing a fusible element to a flexible tail conductor in a fuse link comprising the steps of inserting an end of the fusible element to extend internally of an end of the tail conductor and causing the fusible element to be fixed to the conductor by means wholly internal of the conductor so it is electrically conductive therewith.

12. A method as claimed in claim 11 wherein the said fixing is achieved either by welding or soldering.

13. A method as claimed in claim 11, wherein the said fixing is achieved by the steps of tin soldering an end of the fusible element, drilling a hole longitudinal of the end of the conductor, inserting the tin soldered end of the fusible element in the hole, and applying heat external of the conductor to effect soldered connection between the said inserted soldered end and the conductor bounding the said hole. o14. A fuse link substantially as herein described and as illustrated with reference to any one of the examples in ,Figures 3-6 of the accompanying drawings.

15. A method for fixing a fusible element to a flexible tail conductor in a fuse link substantially as herein described and as illustrated with reference to any one of the examples in Figures 3-6 of the accompanying oo*o drawings. *.o DATED THIS 6TH DAY OF APRIL 1994 oo MORLYNN CERAMICS PTY LTD By Its Patent Attorneys: GRIFFITH HACK CO., Fellows Institute of Patent SAttorneys of Australia ABSTRACT This invention relates to electrical fuse links. The fuse link (10) has a head connector and tail conductor between which is sited a composite fusible element and strain element There is a top conductor associated with the top connector At least the tail end of the composite elements are arranged to be fixed to the tail conductor to be internal of the tail conductor Typically the end of the composite elements is tin soldered, a hole drilled in the end of the tail conductor the tinned end inserted in the hole and heat applied externally of the tail conductor to fix the parts together. Part of the fuse link (10) is enveloped by a tube There is also provided an auxiliary tube having a slit (62) formed therein to assist in arc quenching upon an overcurrent experienced by the fuse link S