US2216661A - High tension fuse - Google Patents

Description

Oct. 1, 1940. K DANNENBER`G 2,216,661

HIGH TENS ION FUSE Filed Sept. 7, 1937 2 Sheets-Sheet 2 .I [A7 6 GUNPowDE Patented oct. 1, 1946 UNITED STATES- PATENTy OFFICE Application September 7, 1937, Serial No. 162,789 y In Great Britain September 29, 1936 18 Claims.

This invention relates to electric high tension fuses of high rupturing capacity wherein the fusible element or elements are embedded in an insulating, arc-extinguishing powder filling in a sheath.

In high tension fuses it has been found that corona discharge caused deterioration of the elements along their length or at one or more points along their length with the result that the fuses broke down or otherwise interrupted their circuits at or below the loads at which the fuses were rated.

It may be mentioned that 6,000 volts is considered in the art to be the base at which protection from or .prevention of corona is necessary;

and it is known that many variables, for example temperature and humidity, causel or allow a corona discharge, sometimes an invisible discharge, to take place onA the fusible element at potentials as low as 3,000 volts.

My researches show that an insulating and arcextinguishing powder can be used to prevent deterioration of the fusible elements owing to corona discharge if the sheath be hermetically sealed and 'the density of the filling which the powder forms and the way in which filling is effected be such that the oxygen in the interior of the sheath is eliminated to an extent sufficient to prevent oxidation of the fusible element or elements and the grains of powder are sufciently close to the fusible element or elements to enable ions discharged from the element or elements to cancel the electric field between the element and the grains without impairing the arc-extinguishing property of the powder.

Grains of marble powder having a maximum diameter of 0.1 mlllimetre and lled or packed into the sheaths by mounting the sheaths in a shaking jig vibrating at least 150 times per minute have been found to prevent corona discharge, the

necessary duration of the shaking process being in direct proportion to the length of the sheath; Vand the marble powder, which is an endothermically reacting powder, has the further property of ensuring that the embedded element or elements on operation are instantaneously dissipated along their whole length.

In the accompanying drawings: Figure 1 and Figure 1a together constitute a sectional view of a single element cartridge fuse; Figure 2 and Figure 2a together` constitute a sectional view of a cartridge fuse with replaceable support and elements;

Fig. 3 is an end view of a replaceable ring carrying contact fingers;

Fig. 4 is an end elevation, on an enlarged scale, of the element support illustrated in Fig. 2;

Fig. 5 is an end view of an element support provided internally with longitudinal ribs adapted to retain a fusible element in zig-zag formation 5 within the support whilst another element or elements are wound around the ribs on the outer surface of the support;

Fig. 6 is a sectional elevation, on an enlarged scale, of one end of the element support provided 10 with an indicator;

Figure 7 and Figure '1a together constitute a development of a support bearing a fusible wire in zig-zag formation;

Fig. 8 is a plan view, partly in section and on an 15 enlarged scale, of an end of a rib illustrated in Fig. l and has been given to show, more particularly, the manner in which the peaks of the zig-zag stand out of contact with the ribs;

Fig. 9 is a sectionalelevation of a rib provided with nodules for use in conjunction with a strip element; and l Fig. 10 is a development of part of a ribbed support bearing a fusible wire in the form of .a zig-zag the axis of which is helical. 25

In Fig. 1 the fuse wire I lies within the bore 2' of a hollow cylindrical, refractory support 3 and is connected at its ends to metal caps 4 cemented by means of litharge, plaster of Paris or the like to the support 3. K This hermetically closes the 3o inside of the support or sheath to atmosphere but before the closing is effected the bore is filled with powder in the vibrating jig, the degree of neness of the powder being as previously stated.

In Fig. 2 a hollow, refractory cylinder 5 formu ing the sheath of the fuse or vcartridge has caps 6 cemented to it at its ends, asbestos rings 1 lying between the ends of the sheath and the inwardly turned flange 8 of the caps. A ring 9 (see also Fig. 3) with spring contact fingers I0 is secured to each flange 8, the fingers Il projecting into the hollow of the sheath, by means of screws II passing through clamping rings I2, gaskets I2* and discs I3 of foil.

The support for the fusible elements or wires I4 s and I5 consists of a hollow cylinder I6 of uniform, refractory material along the outer surface of Y which are ribs I1 (see also Fig. 4) giving pointsupport to the wires Il tightly wound around the support, whilst the hollow of the support accommodates the helically coiled wire Il. The wires Il and I5 are connected at their ends to caps I8 sealed to the ends of the support.

'I'he hollow of the support is filled with arcquenching powder II and the space between the support and the interior of the sheath, which sheath is of larger diameter than the said support, is-filled with arc-quenching powder 20.

An assembly comprising the support and wires I4 and I5 is inserted through one end of the sheath 5 until one of the caps I8 is properly gripped by a set of ngers IQ. The powder 2li is then packed into lthe space between the support and the sheath and the remaining set of ngers secured to their cap S. -The fuse is thus complete.

It will be seen from Fig. 6l that one of the end caps i8 has a re-entrant portion 2l lying within, the end of the cylinder I6. Within the portion 2l is a capsule 22 containing gunpowder 23. One end of the wire I5 is straight and passes through the inner end of the portion 22, through an insulating washer 2G which ensures that the said wire does not make electrical contact with the portion 2l, and through the centre of the capsule to a point where it is electrically connected to the capsule. The outer end of the said capsule has a bolt 25 xed to it whilst a buier 26 surrounds the inner end of the said bolt. A short wire 2l electrically connects the bolt to the cap l 8 so that an electrical circuit is complete from the wire I5 to the cap, said circuit consisting of parts 22, 2l, 25 and 2l. A disc 28 of aluminum or tin foil closes the re-entrant portion 2l and, therefore,

seals the interior of the cylinder or support i6, the other end of the support being sealed by the other cap.

When the fuse operates the wire I 5 in the capsule 22 ignites the gunpowder with the result that the bolt 25 is caused topierce thel disc 28 and the adjacent disc I3, thus indicating the said opera-v tion. The buer 26 contacts with the bent parts of the ngers I@ or with a, bridge piece 23 in a clamping ring I2 to ensure that the bolt is not vcompletely ejected from the fuse.

A' linesman wishing to recondition the fuse replaces the support I6 by a similar support with intact wires, the linesman Vwithdrawing the dead support and. inserting the new through that end of the fuse Where the foil is punctured after the llnesman has removed a ring I2, the punctured foil and a ring 9 from the sheath, it being understood that the powder I9 is emptied out of the sheath before the inner support is inserted and replaced or replenished by fresh powder. Both sets of contact fingers can be examined at the time of reconditioning the fuse and, if necessary, either or both can be replaced by undamaged ones carried by rings as 9.

The present invention also comprises a fuse having one or more fusible elements helically wound aroundthe outside of a ribbed or pointsupport and embedded in the arcsquenching powder and thermally balanced with respect to a helically coiled fusible element/embedded in the filling within a longitudinal bore in the support. The thermal balancing, i. e. causing substantially the same cooling effect to be produced on both fusible elements, is obtained by arranging that a I quantity of powder equal to that tightly lled into the recesses between the supporting points of th body and -lying underneath the element or ele ments wrapped around the support and chosen in amount to suit the number of elements and their dimension is lled into the hollow of the coil of the inner fusible element, said inner element being arranged to take part in the process of interruption or acts as a main element of good conductivity leaving the final interruption to an element of higher resistance on the outside pointsupport surface. This fuse has a rupturing capacity considerably greater than that of known fuses of substantially like dimensions.

The wires lf3 are thermally balanced with respectv to the wire I5. This controls the heatingup'of both the inner and the outer elements along their length and ensures an equal cooling eiect on both wires along their whole length Ywith the result that the rupturing capacity of the fuse is considerably increased with respect Ito that of a fuse of like dimension but without the thermal balancing.

The wire I5 is preferably the main element and consists of silver whilst the wires Ill are the auxiliary element and consist of tungsten.' The auxiliary element may, however, be arranged on the insidel of the support and the main element on the outside thereof. -When the wires (e.-g., the auxiliary element) consist of like tungsten, tant alum or molybdenum metals there is no need to take special steps to apply the corona protection to them.

Instead of employing a helically wound wire I5 the bore of the support I may contain longitudinal ribs 3@ in the ends of which are notches 3GB so that a wire 3l can be made to take the zigzag formation shown in Fig. 7. It will be seen that each length of wire between the bends of the Zigzag extends from one end of one rib to the opposite end of the next rib, the notches being located at the ends of the said ribs. manner the said lengths of ,wire lie in recesses provided by the ribs. The hollow of the 'bore is. of course, filled with arc-quenching powder.

If desired, the wire or wires on the-outside of BIB In this the support may be wound zig-zag fashion and in this case the development of the outside of the support will be as shown'in Fig. 7, an odd number of longitudinal ribs 'being provided.

The peaks 32 of the zig-zag preferably stand well away from the inner ends of the notches, as

v illustrated in Fig. 8. When the wire 3| melts the parts adjacent to the peaks thereof thus provide a numberv of horn gaps in series. It is found that.

when tungsten wire isused there is no difficulty in arranging the peaks in this way, the toughness of the tungsten permitting this. In Fig. 9 the rib I'l is provided along its leng with-a number of nodules 33 and the fusible element instead of being of wire consists of strip material 34 which is wound in helical form around a support along which the ribs with nodules are provided.

Fig. 10 illustrates another form of zig-zag Winding suitable, more particularly, for application to- It will be seen that in the forms of the invenl nos illustrated the. surfaces ofthe fusible elements are 1excep't for a very negligible proportion surrounded by the powder, the ribs forming recesses enabling the powder to get between the wires and the supports. This surrounding is es;

sential to ensure that corona discharge is pref` -wire alone.

vented and to ensure the dissipation of the elements along the whole of their length under short circuit conditions. A

It is believed that the following electrical action takes place in the present fuse when corona discharge is prevented. When the field strength at the surface of a fusible element, usually of silver wire, becomes sufiiciently great new ions are formed, negative ions are driven off the element and strike powder grains adjacent thereto. This causes the powder grains to be negatively charged whereby the field between the element and the A powder is cancelled and the corona discharge is suppressed. The necessary quantity of ions is very small. the element andthe grains the better is the effect, which is dependent upon the ne graining `of the powder and the density of the powder filling.

It is important to note that the powder employed has a maximum grain diameter limit of 0.1 mm., and that this is one of the controlling factors of the present invention. It is well known that with the fuse w-ire surrounded with powder. there would be animprovement with respect to the corona discharge overthe use of a bare fuse Experience has 'proven that even under these circumstances, and particularly where the powder was of usual course grain, the improvement obtained was comparatively slight and insuiilcient to cover the high working` voltages which are now used. It was developed by the applicant that in a powder having a grain size less than thatl usually employed, he provides complete corona suppression at higher voltages than heretofore possible. The grain-size of the powder employed in the present application is, therefore, critical and must be regarded as a distinctive fundamental fact of the present improvement. It has been previously known that powder filled cartridge fuses improved the rupturing capacity of the fuse. It was necessary, however, to conipromise in the design of such fuses insofar as one could not incorporate adequate corona protection whenever very high rupturing capacities were desired. This was because the Faraday metal cage then employed for corona lprotection interfered with the insulationof the fuse when clearing very heavy faults.

The high' tension fuse of the present invention succeeds for the first time in solving the problem of producing a high voltage fuse of extra high rupturing capacity and still providing the necessary corona protection, thereby preserving the life of the fuse under normal service conditions.

What I claim is:

1: A high tension 'fuse of high rupturing ca-j pacity comprising a refractory insulating sheath, a dry'insulating arc-extinguishing powder such as marble dust filling in said sheath the powder grains having a. maximum diameter of 0.1 mm., a fusible element embedded in said powder lllng, and hermetic closures at the ends of the sheath, the herein specified diameter of the powder grains insuring that the physicaland electrical relationship oi' the powder grains to the fusible element is such that the grains will completely suppress corona discharge from the element.

2. A high tension fuse as defined in claim 1, wherein the element is of uniform cross section and `the powderj is endothermically reacting, whereby the fusible element is instantaneously dissipated along' the whole oi' its length under short circuit conditions. y

3. A high tension fuse as dened in claim 1,

The smaller the air distance between of higher resistance being arranged on the outside including a ceramic support within the sheath of hollow form with longitudinal ribs on its outer surface, there being provided two fusible elements which are respectively wound one on. the outside of the support transverse the ribs and one 5 disposed within the hollow formation of said support, one of such elements being embedded in the powder having the characteristics recited in claim 1, the element on the outside of the support having contact with the ribs.

4. A high tension fuse as defined in claim l, including a ceramic support within the sheath of hollow formation and with longitudinal ribs on the outer surface, with the provision of two fusible elements of relatively different specific resistances, the element of higher specific resistance being arranged within the hollow of the support and embedded in the powder, the element of lower specific resistance being arranged on the outside of the support in contact with and transverse said ribs, the element of higher specific resistance taking part in the process of interruption.

5. A high tensionfuse as defined in claim 1,-including a ceramic support within said sheath of hollow form with longitudinal ribs on the outer -25 surface, there being provided two fusible elements of relatively different specific resistances, the element of lower resistance being arranged within the hollow of the support and the element of the support in contact with and transverse the ribs and embedded in the powder, the element of lower resistance acting as a main element of good conductivity leavingthe final interruption to the element of higher resistance.

, higher resistance taking part in the process of interruption.

7. A high tension fuse as denned in claim l, including av ceramic support within the sheath of hollow form with longitudinal ribs on the outer surface, there being provided two fusible elements of relatively different specific resistances both embedded in the powder, the element of lower specific resistance being within the hollow of the support and the element of higher specific resistance being on the outside off the support in contact with and transverse the ribs, the element of lower specific resistance acting as a main element of good conductivity with the final interruption provided in the element of higher specic resistance.

8. A high tension fuse as defined in claim 1, including a ceramic support within the sheath, said support being of 'hollow form with longitudinal ribs/on :the outer and inner surfaces, there being two fusible elements of 'different specific resistances, one element being wound around the outside of the support in contact with and transverse' the ribs and the other element being arranged in point-supported zig-zag manner in the 7o hollow of the support, the element of higher speciiicresistance lbeing embedded in the powder.

9. A high tension fuse as defined in claim 1, including electrical contact members at the end of the sheath, electrical -contact members at the 7g ends of the support and electrically connected to the fusible elements, the electrical contact members at the ends of the support being adapted releasably to cooperate with the contact members carried by the ends of the sheath, and a hermetic closure device at each end of the sheath, one of such closure devices being readily replaceable.

10. A high tension fuse as defined in claim 1, including a longitudinal ceramic support within the sheath, said support being of hollow form with longitudinal ribs on the out'er surface, the fusible factor including a fusible element wound around said support in contact with and transverse the ribs and thereby free of contact with the surface of the support, a fusible element of coil form within the hollow length of said support, the arc-quenching powder being disposed in the sheath and in the-hollow formation of the support to embed said fusible elements, the quantity of the powder accommodated in the total of the spaces bounded by the fusible element wound around the support, the ribs on the support and the surface of the support between the ribs being atleast equal to the quantity of powder filling the v hollow portion of the coil of the fusible element in the hollow length of the support, the amount of powder being selected in more or less. definite relation to the number of turns of the fusible element and the dimension thereof.

11. A high tension fuse of high rupturing capacity comprising a refractory insulating sheath, electrical contact members at the ends'thereof,

a support for fusible elements with said support of hollow uniform refractory insulating material having longitudinai ribs on its outer surface, a

. fusible element wound tightly around said support to make. contact therewith, a second fusible element arranged within the hollow of the support, said fusible elements being of relatively different speciiic resistances with the second fusible element taking part in the interruption process, arc-quenching powder such as marble dust within the sheath and within the hollow support and embedding said fusible elements, the arc-quenching powder'grains having a diameter of approximately 0.1 mm., said support rigidly fixing the fusible element wound thereon to prevent the sagging .o r movement of said element otherwise incident to the flneness of the element necessitated by the high rupturing capacity of the fuse, the ribs on the support spacing the outer fusible element from-the surface of the support to permit the element to continuously carry a higher current than normal incident to the comparatively large area of the wire of the fusible element in contact with the powderv between the supporting points of the ribs, 'contact members the support electrically connected cooperate with contact members carried by the ends of the sheath, and hermetic closure devices quenching powder at the ends of the sheath, one of said closure devices being easily replaceable.

12. A high tension fuse as dened in claim 11, including xing means adapted to hold both a contact member'to the sheath and to secure said easily replaceable closure device to the sheath.

13. A high tension fuse as defined in claim 11, wherein end caps are provided on the sheath and means removably securing the contacts carried by the sheath to the said end caps whereby to permit the contacts to be readily replaced without removing the caps.

.14. A high tension fuse `as defined in claim 11, including material having highly refractory properties supplied to said support in the form of a coating.

15. A high tension fuse as defined in claim 11, including nodules on the projections of the support with the fusible element cooperating with said projections in the form of a strip wound around the support to make point contact with said nodules.

16. A high tension fuse according to claim 11, including longitudinal ribs forming the projections on the support, said ribs being notched, the fusible element to be Wound on said projections being seated in the notches to take a zig-zag form.

l7.- A high tension fuse as defined in claim 11, wherein the projections are in the form of longitudinal ribs having notches and wherein the fusible element wound on the projections is seated in said notches to take a zig-zag form, the fusible element being arranged at the peaks of the zigzag formation to stand away from the bottom of the notches, whereby to provide a number of 'horn gaps in series when the fusible element melts. 1

18. A high tension fuse of high rupturing capacity comprising a longitudinal,-refractory, in-

alongthe' external surface of `said support, a Y fusible element wound around said support and making transverse contact with the said ribs so as to be spaced from the surface of said support, a fusible element of coil form located within the hollow of said support, and arc-quenching powder such, as marble dust in said sheath and in said support embedding said fusible elements, the arcgrains having a maximum diameter approximating 0.1 mm., the quantity of powder held by the hollow of said coiled ele' ment being at east equal to the quantity of powderv tightly lled into the spaces bounded by the turns of the outer fusible element, the ribs and the support, said powder-'being chosen in amount ment and their dimension.

KURT DANNENBERG.

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