US2296627A

US2296627A - Time lag fuse

Info

Publication number: US2296627A
Application number: US171946A
Authority: US
Inventors: George R Brown
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1937-10-30
Filing date: 1937-10-30
Publication date: 1942-09-22
Anticipated expiration: 1959-09-22

Description

Sept 22,1942 G. R. BROWN 2,296,627

TIME LAG FUSE Filed 001'.. 30, 1937 Inventor: George R. Brown,

Hi e Attorney.

Patented sept. 22, i942 'rma LAG rosa f" vcomo n. Brown, Stratford, com, minor to General Electric Company, a corporation of New York Application ootobor so, i931, sorua No. 111,940

' (ci. zoo-123) 6 Claims.

This invention relates to time lag fuses for use in circuits which are subject to' a partial overload for a brief period of time.

It is an object of the invention to provide a time lag fuse which will withstand for a brief period a partial overload of the circuit with which' it is connected, but which will blow if the overload is continued beyond this brief period, and which, in addition, will blow immediately if subjected to a heavy overload such as that produced by a short circuit.

Referring to the drawing, Fig. 1 isa longitudi- .nal section through the fuse; Fig. 2 is an exploded view of some of th'e fuse parts, and Fig. 3 shows a modified formof construction of one end of the fuse.

The fuse comprises a tubular insulating casing ID which may be formed of liber, or the like, and carries at each end metal ferrules II which are clamped to the ends of the tube and serve to make contact with the circuit in which the fuse is inserted. A fuse link I2 is inserted within the casing and occupies the right-hand portion thereof as shown by Fig. 1. The fuse link is fastened at one end to the ferrule I I by solder I3 and at the other end to a tab I4 by means of solder I5 having a relatively high melting point, for example, 360 F. The tab I4 is lanced from a plug I6 which may be formed of copper, or the like, and

which has a relatively large mass formed with The fuse link has a o large radiating surfaces. blow point I'I formed immediately adjacent the copper plug, so that as it is heated by a partial overload the heat will be absorbed by the copper plug I6 to prevent melting of the fuse link at the blow point. The heat absorbed by the copper plug is dissipated by virtue of its large mass and radiating surfaces.

The plug I6 rests against an inner tube lof insulating material, the inner tube being nested within the tube I at its left-hand portion as shown by Fig. 1, and being retained therein by the other ferrule I I. A brass cup I9 is inserted within a recess forming part of the copper plug I6 and holds a disk 2l in the bottom of the recess 20 where it covers an opening 22 formed in the wall of the copper plug at the point where the tab I4 is lanced therefrom. The disk 2I is formed from asbestos paper, or the like, and is adapted to hold a iiller material 23 coniined about the fuse link I2 'and prevent its sifting past the plug I6. The

brass cup I9 is fastened to the copper plug I6 by solder 24 having a relatively low melting point, for example, 220 F. The solder is disposed about the entire periphery of the cup I9- and recess 20, 55

in the manner shown by Fig. 1 and holds the cup I9 securely within the recess 2Il'where it retains the disk 2I in the bottom of the recess.

The brass cup I9 has a tab 25 lanced from the end wall thereof which is provided with an opening 26 adapted to receive one end of a coil spring 21, the other end of the spring being secured to the ferrule II by means oi.' solder 28. The spring is placed under tension and acts to' hold the plug I6 tightly against the inner tube I8. A conducting cable 29 is soldered to the tab 25 at one end and to the ferrule II atthe other end. This cable is formed' of stranded copper wire which has a low resistance and, consequently, there is a low voltage drop or watt loss through the fuse circuit. The inner tube I8 forms an expansion chamber 30 which houses the spring 21 and cable 29 and which is closed at its outer end by th'e ferrule I I. The ferrule II is provided with openings 3l to permit the gases in the expansion chamber incident to blowing of the fuse to escape from the interior of the fuse body. 'I'he openings 3l are covered by a screen 32 which acts to retain the flame consequent to the blowing of the fuse while, at th'e same time, permitting the gases to escape.

In the modification shown by Fig. 3 the ferrule in the link end of the fuse ls likewise provided with openings 33 protected by a screen 34 which confines the filler material within the tubular casing yet permits the gases formed by blowing of the fuse to escape through the opening 33 from th'e interior of the casing.

When the fuse is subjected to a partial overload, for example, as in motor starting, the fuse link I2 will heat up at the blow point II, but the vlarge plug I6 will prevent the heating action from melting the fuse link at the blow point because it will absorb the heat from the fuse link and dissipate it over its radiating surface. However, if the overloading is continued for more than a brief periodi' the plug will be unable to dissipate the heat as fast as it absorbs it from the fuse link and consequently the plug will heat up, and the low melting point solder 24 which unites the brass cup to the copper plug will melt, permitting the spring 21 to separate the cup from the disk and thereby opening the circuit through the fuse. 'Ihe spring 2'I acts to separate the cup from th'e plug quickly and completely and retains the cup at a considerable distance from the plug so that arcing between the plug and cup is prevented. In the event of a short circuit both the fuse link l2 and the low melting point solder 24 will melt giving an instantaneous interruption of the circuit by sepafuse link I2 will be absorbed to some degree by the inner nller'material 23, but the excess gas pressures will rupture th'e frangible disk 2l permitting the gases'to' escape into the expansion chamber 30 and thence through the screen 32 and openings ll to the atmosphere. The disk is designed so that it will break immediately upon blowing oi the fuse thereby liberating the gas pressures and preventing possible rupture of the casing I0. In some instances, for example, with a very high current occurring over a short time interval the link I2, only, will blow, in which 'case the resultant gas pressures will rupture or move the disk 2 I so that the gases will escape to' the chamber 30' v through the openings in the plug I6 and the cup I9. The screen I2 will catch any nller which may I be b1own through the opening 2z and retain it m the expansion chamber 3l. In the modincation shown by Fig. 3, the gas pressure may escape from the nller end oi the tube, as well as from the expansion chamber, the openings 33 permitting passage of the gas while the screen 34 retains the filler withinthecasing I0.

It 'should be noted that diilerent ratings o'f the fuse may be obtained by varying theradiating surface and mass of the plug I0,'the melting point of the solder 24 and the area of the blow point I1 of the link. For example, a higher partial overload could be sustained by raising the melting point of the solder 24, or by increasing the radiating capacity of th'e copper plug I6. It will be apparent to one skilled in the art that the three variables mentioned may be varied at will to design a fuse oi any desired capacity wherein the plug acts to prevent partial overload from blowing the fuse link. l

What I claim as new and desire to secure by Letters- Patent oi the United States, is:

l. In a fuse structure, afcasing, a fuse link in said casing, a plug having an opening therein, said plug holding fsaidfuse in one end of said l casing, and a disk covering said opening, said disk fuse to release said pressure from said one vend of the casing.

3. In a time lag fuse, a casing, a perforated plug separating said casing into two compartments, a fusible link in one compartment fastened to said plug, a cup in the other compartment, fusible material uniting said cup and plug, a disk covering said perforation andv disposed'between said cup and said plug, and spring means acting I to separate said cup and plug upon volatilization of said link and melting of said material under overloadof said fuse whereby said cup and plug are separated and said disk is released to permit gas pressure `in said one compartment to be released into said other compartment.

4. A time lag fuse comprising a casing, ferrules closing the ends of 'said casing, there being openings in the ferrule at one end of said casing, a screen covering said openings, a tension spring. a cup, said spring being connected at one'end to said vented ferrule and at the otherfend to said cup, a perforated element soldered to said cupv permit said spring'to retract said cup from engagement with said plug.

5. In a fuse structure, a casing, ferrules closing the ends of said casing, there being vent openings a plug having an opening therein holding said in said ferrules, screens covering said openings, a fuse link connected at one end to one of said ferrules, a plug of relatively large mass connected to th'e other end of said link, a cup soldered to separating said cup and plug upon melting of said v solder and said vents liberating the gas pressures in said casing caused by blowing of said fuse link. 6. In a time lag fuse, a casing, a perforated element in said casing, a fusible link connected tol and element upon volatilization of said link and melting of said material upon overload of said fuse whereby said member and element are separated and said disk is shattered to release the gas j pressure incident to1 blowing of said fuse.

` GEORGE R. BROWN.