US2249945A

US2249945A - High tension fuse

Info

Publication number: US2249945A
Application number: US258274A
Authority: US
Inventors: Dannenberg Kurt
Original assignee: Individual
Current assignee: Individual
Priority date: 1938-02-24
Filing date: 1939-02-24
Publication date: 1941-07-22
Anticipated expiration: 1958-07-22

Description

July 22, 1941. K. DANNENBERG 2,249,945

HIGH TENSION FUSE .Fil-9d Feb. 24, 1939 and n.

Attorney I Patented July 22, 1941 UNETED STATES PATENT GFFCE Application February 24, 1939, Serial No. 258,274 In Great Britain February 24, 1938 Claims.

This invention has reference to high tension fuses having one or more fusible elements mounted on a support.

The primary object of the invention is to ensure good thermal insulation between the turns of the fusible element whilst making the fuse no longer or even shorter than existing fuses of the same current rating.

A further object of the invention is to decrease the length of fuses of high current ratings in order to give the fuses the same length as fuses of small current ratings at the same voltage in cases where the fusible element extends from end to end of the fuse.

Another object of the invention is to make the construction of high voltage powder filled cartridge fuses possible with low current ratings for instance under two amperes when the fusible elements extend from end to end of the fuse and at least two of the elements are of different specific resistance, a difficulty in connection with the construction of high voltage, low current capacity fuses being caused by the neness of the elements.

According to the present invention the fusible element comprises a number of wires or metal strips wound around the outer peripheries of two or more nested supports having ribs or projections on their peripheries making line or point contact with the tightly applied wires or strips. Owing, therefore, to the invention the spacing between the convolutions may be as great as desired to give the necessary degree of thermal insulation, the greater the spacing the more numerous the nested supports in order to accommodate the requisite number of elements. Further, the length of the sum of the supports is such as to enable elements extending along the length of the fuse and of high current ratings to be accommodated in a fuse having the same length as one cf small current rating, the rated voltage being the same in each case. In addition to these advantages it is possible to provide a fuse of low current capacity with a very fine wire of higher specific resistance than another or other wires or strips in the fuse because, the ne wire, being tightly wound around the outer periphery of the innermost support, is supported at a large number of spaced points.

It will be understood that the fusible element may be embedded in powder according to my copending patent application Serial No. 162,789.

The invention will now be described with reference to the accompanying drawing wherein:

Fig. 1 is a side elevation, partly in section, of one form of a two-support fuse; and

Fig. 2 is a side elevation of one end of a support with a fusible element of strip-like form applied to it.

In Fig. 1 a hollow support I of refractory insulating material is nested within a hollow support 2' of like material, both supports being longitudinally ribbed as described in my co-pending patent application Serial No. 162,739. The length of the support I is less than that of the support 2 so that the ends of I lie within the ends of 2 and the overall diameter of the said support I is less than the diameter of the bore of the support 2 to provide a space 3 between the supports. Contact sleeves 4 and 5 are fitted to the ends of the supports I and 2 so as to project from the said ends and, thereby, to provide sockets. Hollow stepped bushes as 6 are pushed into the said sockets and secure the said supports together whilst centering I within 2. Asbestos Washers 1 are located between the tread portions of the stepped bushes and the ends of the supports. Fusible elements 8 in the form of strips, for example, silver strips, are wound round the supports and connected to the sleeves 4 and 5, the contact between the supports and the strips being line contact owing to the ribs, and a central fusible element 9 of higher specific resistance than the strips 8, for example, tungsten, and in the form of a longitudinal coil is arranged within the hollow of the support I, the ends of the coil being electrically connected to the stepped bush.

The unit comprising the parts I to 9 is located within a sheath I0 of refractory, insulating material, the bore of the sheath being greater than the overall diameter of the support 2 to provide a space II. Contact sleeves I2 are cemented to the sheath at the ends thereof and each has an inwardly turned flange I3 at its outer end. A number of screw-threaded studs as I4 project from each flange I3 parallel to the axis of the sheath. The studs receive the flange of a hollow, flanged bush I5 which is a push fit in the hollow of the stepped bush 6, and the said flange is clamped between I3 and two clamping rings I E held in position by nuts on the studs. An asbestos washer I1 is located between each fiange I3 and the corresponding end of the sheath I0. Thus, the bush I5 centres the unit previously referred to within the sheath Il).

Tread portions of each bush as 6 and the flange of each bush I5 have Ventilating holes I8. The fusible elements 8 and 9 are embedded in powder preferably according to my cci-pending patent application Serial No. 162,789 and metal foil, not shown, seals the ends of the fuse so as to prevent powder unintentionally escaping from the fuse. The metal foil is preferably clamped between the two rings IS. The metal foil provides an outlet for gases in the event of excessive pressure being produced within the fuse.

Owing' to the construction and arrangement of the bushes a unit comprising the parts l to 9 can be easily removed from the sheath and replaced, or replaced by a similar unit.

The temperature of the fusible elements of high tension fuses at, say, 300 amperes rating is usually about 250 to 309 C. with the result that the solder used for connecting the fusible elements to their contacts is melted or dangerously overheated. In order to overcome this diiculty I connect the fusible strips 8 to their contact sleeves in a manner which we will now describe with reference, more particularly, to Fig. 2 of the accompanying drawing.l The strips 8 are pinched at two points at each end between the longitudinal ribs 2G on the support (as I or 2, Fig. 1) and binding wires 2l, 22. An end of each strip is soldered at 23 to the wires 22, said wires being further than the wires 2l from the sleeve (4 or 5, Fig, l) and both sets of binding wires are electrically connected to the sleeve by conducting fingers 1t will thus be seen that the soldered points between the strips and the binding wires E?. are not directly in the electrical circuit of the strips so the heating to which the soldering is subjected is reduced to about the operating temperature of the refractory supports, namely, about 160 to 120 C.

It will be understood that when a fuse is provided with more than two nested supports the steps of the stepped hush as E Yare increased in number correspondingly and the hollow of the outermost step receives the flanged bush, the lengths of the said supports decreasing from the outer support to the innermost support in order to accommodate the steps. An occasion when more than two supports would be employed is when the degree of iineness of the element such as 9 is such that it cannot satisfactorily be stretched from end to end of the hollow of the support as I, the said wire in this event being wound around a. longitudinally ribbed support.

What I claim is:

1. A high tension fuse unit comprising a number of nested supports of refractory, insulating material, ribs or projections on the peripheries of said nested supports and fusible elements tightly wound round said supports to make line or point contact at said ribs or projections, the supports providing separate independent compartments closed one against the other whereby the dissipation processes occuring when the fuse functions cannot interfere with each other.

2. A high tension fuse unit according to claim 1, comprising contact sockets at the ends of the supports, a co-axially stepped bush at one end of the unit engaging with the sockets at this end and. a second co-axially stepped bush at the other end of the unit engaging with the sockets thereat, each of said bushes connecting the sockets with which it is in engagement in electrically parallel manner and the bushes holding said supports cc-axially with respect to each other.

3. A high tension fuse unit according to claim 1, comprising pairs of metal binders arranged one pair at one end of a support, another pair at the other end thereof, a third pair at the end of another support, and so on, each tail of each element being united with the inner binder of the corresponding pair and the binders being electrically connected to contact elements at the corresponding ends of their supports.

4. A high tension fuse unit as defined in claim 1 wherein one of the fusible elements is arranged co-axially of the innermost support and wherein the other of the fuse elements is arranged circumferentially of the other support, the respective fuse elements being electrically connected at their ends.

5. A construction as dened in claim 1 wherein one of the supports is formed with longitudinally extending ribs and wherein the fuse element is tightly wrapped around said support for contact with the ribs, and free of contact between the ribs, whereby a considerable space is provided between the various points of support of the fuse element to prevent metallization of the intermediate space between said points.

KURT DANNENBERG.