CA1129914A - Fuse with low current trip mechanism - Google Patents

Abstract

17 48,283 ABSTRACT OF THE DISCLOSURE
A low current, expulsion-type fuse is taught.
The low current, expulsion-type fuse has a movable spring-biased rod which is capable of moving through a ferrule of the fuse to cause an unlatching operation. The rod is maintained in a spring-loaded disposition by a tripping mechanism with a mechanical advantage of sufficient magni-tude to allow a relatively thin fuse strain element to maintain the rod in the spring-loaded disposition. An eye hook extends from one end of the aforementioned rod and is captured by a spring-loaded lever during the manufacture of the fuse. The spring loading on the lever is such that it will release the aforementioned eye to allow the rod biasing spring to move the rod unless the aforementioned lever is retained by a retaining member. The retaining member operates through the aforementioned lever against the spring thereof. It is maintained in the retaining disposition by the tensile force of the fuse strain ele-ment. When the fuse element blows, the retaining member and lever are moved by the main fuse rod spring to release the captured eye portion of the fuse rod.

Description

- `~

1 48,283 ~USE ~ITH LOW CURRENT TRIP MECHANISM
BACKGROUND OF THE INVENTION
The subject matter of this invention relates general~y to electrical fuses and trip mechanisms therefor and relates more specifically to expulsion type fuses with low current trip mechanisms contained therein, ` The boric acid expulsion type Euse is known in the art In the most basic of the expulsion type fuses, there is a spring loaded fuse rod which extends through a hollow cyllnder of solid boric acld material. The fuse o rod is restrained against the bias of the spring by a fuse element and;strain link.~ The~fuse e~lement is designed to provide certain current:~carrying and meltlng characteris-; tics.~ When a fault cu~rrent~;flows~;ln~the~system~protected by; th~e~ aforementioned~fuse, the~;f~se~element~ and~ the strain link melt, causlng ~the rod;~ to ;~e released by the biasing ef~ect of ~the~spring. ~This draws; the ~arc of interruption through~the~center~of~the boric~acid~cylinder Water vapor~ls~thus~created as the boric acid decomposes.
Due to~the~small voluma~of~the~bore o~f the~cy~nder pres-20~ sure develops.~ This~pressure~has a tendency to cool the arc and~blow the~arc~ouL. ~The~current rating of the fuse . i . , ~ . - , . - -, ~ ,. . . . . . .

2 48~83 is a function of the fuse element used. It is a general rule that a current of at least twice the fuse rating will cause melting of the fuse element. In more advanced expulsion type fuse designs the elements at the higher current ratings, approximately 15 amperes or greater are made from pure silver. This is due to certain inherent characteristics of silver which reduce the possibility of element damage from overload and surge currents. Silver, however, is a relatively soft material and does not have ln sufficient tensile strength to restrain the spring load of t~ the fuse rod. For this purpose, a strain link of high reslstance Nichrome is used in parallel with the silver fuse element. The resistance of this strain link is such that it melts almost instantaneously after rupturing of the main fuse element. In even more advanced expulsion type fuses, it has been found that on certain low current ratings the required size of the silver element becomes so small as to approach the resis~ance of the strain link.
; Furthermore, a fuse element of thi~s size becomes ~very ~20 difficult to assemble. As a result, for fuses with rat-ings in the area of approximately 3~amperes~to 10 amperes, ` only the Nichrome strain link is used as~ the fuse element;
howev~er, if~the rating of the fuse is ~below 3 amperes, ; whlch rating is necessary for certai~n~potential transfor-; mer applications for example~, even the Nichrome strain link becomes so small as not to be capable of restraining the spring force of the fuse ~rod,; ln order to provide a low current expulsion fuse of this type, it is necessary , ~ to provide some sort of mechanical advantage system or ,~s.,6~
:: ~
: :

.

~ ~ ~ , , ", "~ ~ 2 ~

3 4g,283trip mechanism. Such a mechanism is shown in U.S. Patent 3,508,184 entitled "Fuse Having Improved Means For Reduc-ing The Force Applied To Fusible Means" issued April 21, 1978 to F. L. Cameron et al and assigned to the assignee of the present invention. Fuses associated with the above-mentioned patent tend to be "refillable" for commer-cial purposes. This means that the boric acid section is separate from the spring section and is replaced following the interruption operation. During the original manufac-o turing and placement operation, the fuse rod is loadedthrough the boric acid core with the end that attaches to the spring going first and with the trip mechanism and the fuse element never actually passing through the core;
however, the aforementioned fuse has a disadvantage in regard to what is known as "single shot" fuse devices where all parts of the fuses are self-contained. In a fuse of this type, the spring is loaded with the fuse rod as it is assembled, and thus any elements or devices which are already attached to the other end of the fuse rod must pass through the entire length of the boric,acid cylinder.
Unfortunately, the size required for an effective trip mechanism prohibits this type of loading; thcrefore, it has been found in the past that something must be provided for attaching the trip mechanism to the rod after it has been loaded. Ln the past, this has b~en done by using a spring clip type linkage between the trip mechanism and the fuse rodS but this generally requires extra length in the fuse element area which leads to a shortening of the fuse rod or the interrupting chamber or both, which is , ~

~. .
.. , ; . . ~. : . . .
,. . . . .
.

`

4 4~,283 undesirable. Furthermore, the manufacturing process for reliably attaching the loose spring clip to the fuse rod during assembly provides a difficulty due to the fact that the spring clip is somewhat hidden by the trip mechanism which tends to occupy most of the void of the arcing chamber in which it is disposed. It would be advantageous, therefore, if apparatus for detachably securing the fuse rod to the trip mechanism could be found which requires no additional linkage such as a spring clip, requires r.o additional space and provides a reliable and easily made attachment between the fuse rod and the trip mechanism.
SUMMARY OF THE INVENTION
In accordance with the invention, a fuse is dis-closed which has a fuse barrel means upon which are dis-posed first and second ferrule means. Each of the ferrule means communicates with the internal portion of the fuse barrel means. There is also provided a movable spring loaded current carrying fuse rod means ~isposed within the barrel means in a disposition of conduction with the first ferrule means. The fuse rod means has an electrically conducting latch means thereon whlch is utilized to hold the rod in a spring loaded position when the fuse is in a nonblown fuse. A nonconducting support means is provided within the fuse barrel means~ upon which is movably dis-; posed an eléctrically conducting spring loaded capturing lever. The latter-mentioned capturing lever is disposed in a disposition to capture the catch means to thus main-tain the spring~loaded rod in a spring loaded disposition.
The latt~r-mentioned lever means i;s sprin~ biased to .

. . , - :

:~ ` :
.

4g,2~3 re~urn to the position of noncapture i~ not re~ained.
There is further provided an electrically conducting retaining lever means which is also movably disposed upon the support in a disposition to retain the capturing lever means in a disposition of capture provided the retaining lever means is itself in a first disposition. There is also provided an electrically conducting fuse strain element means which is disposed between the second ferrule means and the retaining lever means in a disposition to o maintain the retaining lever means in the aforementioned first position when the said fuse element means is in a nonblown disposition; however, the capturing means is rendered free to move to its noncapturing position when the retaining lever means is free to assume a nonretaining disposition upon the occurrence of the fuse element being blown. In the latter position, the biased fuse rod is forcefully moved through an opening in the upper portion of the first ferrule to trip a latch mechanism to there-fore allow the entire fuse barrel to rotate on one of its ferrules. The rotation is such as to move the other ferrule away from the terminal to which it is normally connected. This provides a relatively large nonconducting region between two ferrules which is very desirable in high voltage~electrical systems.
~IEE DESCRIPTION OF THE DRAWINGS
In accordance~wi~h the invention, reference may be had to the preferred embodiment thereof shown in the accompanying drawings in which:
Figure 1 shows a prior art expulsion type fuse , ., " , ~ .... . ~ .
~,: : . : : , -, . .
.
I
,. . .

:
6 48,283 and mounting terminals therefor;
E~igure 2 shows a elevation, partially broken away and partially in section of an expulsion type fuse utilizing the concepts of the present invention, the upper portion of the fuse in Figure 2 being shown in a schematic form for si~plicity of illustration;
Figure 3 shows a front elevation of the trip mechanism of the fuse of Figure 2; and Figure 4 shows a side elevation of the trip mechanism of Figure 3.
DESCRIPTION OF THE PREFERRED EMBODIMENT
.. ... _ _ Referring now to the drawings and Figure 1 in particular, a prior art expulsion type fuse 10 with mount-ing terminals is shown. There are provided two vertically spaced mounting terminals 12 and 14 having an upper latch terminal assembly 16 and a lower support assembly 18, respectively. Electrical conductors 20 and 22 such as the kind which may be connected to an external circuit for protection thereof are shown interconnected with ~he 2~ bushings 12 and 14 for electrical interconnection with the terminal assembly 16 and 18. A fuse 24a for protection of an external circuit is provided. A fuse 24a has on a bottom ferrule 25a thereof a set of abutments 26a which reside in a corresponding opening 28 in the bottom termi-nal assembly lg. The fuse 24a has an upper terminal assembly 29a which is latchably connectable to the upper terminal assembly 16 and which may be manually detached therefrom by actuation of the unlatching lever at 30a such as may be done by using a well known hook stick or the ", , , ~ , ~ , -~ . , ' ' ~

7 48,2~3 like. Upon unlatching, the fuse 24a rota~es through the pal:h 3] to the position ~hown at 32. After unlatching and rotation, a vertical space is maintained between the terminal assemblies 16 and 18 which is advantageous in high voltage situations. Also, the expulsion type fuse has disposed therein a fuse mechanism, which upon blowing, releases a spring loaded rod which protrudes through the top of the ferrule 29a and automatically unlatches the fuse to a~low it to rotate to the position 32.
0 Referring now to Figure 2, a fuse 24 is shown which comprises an embodiment of the present invention.
In particular, a fuse ferrule 25 is shown disposed upon a fuse body 34 such as by way of a magnetic crimping or attachment process, the result of which is shown by the indentation 35. The ferrule 25 is electrically conducting while the fuse body 34 is electrically insulating, and may comprise glass melamine material, for example. There is disposed on the upper portion of the fuse barrel 34 another ferrule 29 which is also attached to the barrel 34 as shown at portion 35. The upper fuse ferrule 29 in-cludes a schematically shown latching mechanism at 30 which may operate similarly to the latching mechanism shown at 30a of Figure 1. There is provided within the hollow fuse barrel a cylindrical solid boric acid portion 38 having a central cylindrical bore 40 therein. A fuse rod 42 which is comprised of electrically conducting material is disposed centrally of the axial bore 40. An arc chamber is formed by a hollow cylindrical member 44 upon which the boric acid member 40 is disposed. An ,,;, ~,- ~, . . ~ ', `
,. ~ . ., : : , . ; , ~ ~ .. . ..

8 48,2~3 electrically conducting hook eye or latching member 46 extends downwardly from the fuse rod 42 as shown in Figure 2 and engages a portion of a trip mechanism 48. An elec-trically conducting bolt member 50 which is securely bolted to an electrically conducting member 51 maintains the tripping mechanism 48 in a fixed position relative to the remaining elements to the fuse 24 and also provides a path of electrical conduction between the fuse rod 45 and the ferrule 25. A pivoting conducting member 52 is pro-lQ vided within which the ferrule 25 snuggly seats for thepurpose of providing electrical continuity from the bolt 50 to the member 52. Cylindrical circular axes or pivots 26 are disposed upon the member 52 so that the fuse may rotate thereabout for moving out of a disposition of contact from an upper terminal assembly, such as 16 shown in Figure 1. There is also provided a fuse element 53 which is disposed between otherwise electrically isolated portions of the mechanism 48 in a manner which will be described hereinafter. In particular, when the fuse element 53 blows or fuses, the various linkages move in such a way that the fuse rod 42 may move upward in the direction 54 as the eye hook 46 is released, thus allowing a tip portion of the fuse rod assembly (not shswn) to protrude through the upper ferrule 29 at the opening 56 to thus initiate an automatic tripping action such as was described previously with respect to the prior art of Figure 1.
Referring now to Figures 3 and 4, enlarged views of the tripping mechanism 48 o~ Figure 2 are shown. In ':

, : ~:

9 48,283 particular, it can be seen that the electricalLy conduct-ing threaded bolt 50 is securely disposed in a disposition of electrical contact with a bottom electrically conduct-ing member 60, upon which is disposed on either side and vertically arising therefrom electrically insulating glass melamine support members 62. Members 62 are held in a secured disposition relative to the member 60 by way of rivets or other securing means 64. Disposed upon the upper portions of the electrically insulating members 62 are first and second pivot axles 68 and 74, respectively.
Axle 68 has disposed thereon internal to the two insulat-ing members 62 a first spring loaded capturing lever 70.
Spring loaded lever 70 additionally includes a spring 78 coiled about the pivo~in~ axle 68 in a disposition of r~
abutment with an ~ ly moving member 76. The spring 78 is anchored in one of the insulating members 62. The compression of the spring 78 is such that the lever member 70 is biased to rotate in an arcuate direction 80 unless somehow retained in the disposition shown in Figures 3 and 2Q 4. There is provided for the retaining purpose a retain-ing member 72 which pivots about the a~orementioned axle 74. The retaining member 72 when disposed in a position of intimate contact with the latter-mentioned capturing member 70 at a region 85 has transferred thereto at the l~tter mentioned region 85 the biasing force of the spring . Consequently, rnember 72 will rotate in the direction 82 as the lever 70 rotates in the direction 80 due to the action of the spring 78. Consequently, any attempt to dispose the members 70 and 72 into the disposition shown .~, ,, ~ . . ~ . .
-- - . ~ . . .

. :. . -:: - ', -' 48,2~3 in Figures 3 and 4 will be ~lawed by the movement o~ the elements 70 and 72 in the directions o~ 80 and 82, respec-tively, unless otherwise maintained in that disposition.
To meet the latter-mentioned end, ~usible material 53 is wound around abutment 75 and abu-tment 77 to maintain the distance between abutment 77 and abutment 75 as shown in Figure 3 to pre~ent movement of the element 72 in the direction 82 and thus to prevent movement of the lever 70 in the direction 80 even though it is biased to so move in that direction by the force of the compressed spring 78.
The eye member 46 which is securely attached to the rod 42 may be moved ln the direction 84 to cause the capturing lever member 70 to rotate in the direotion 86. mis continues until the opening in the eye bypasses the member 70 while moving in the direction 847 thus allowing a more fully compressed spring 78 to snap the member 70 back into the disposition of oontact at interface 85. Member 72 is now maintained in the disposltion shown in Fi~ure 3 by the tensile stress of the ~use element 53. In the arrangement shown in Figures 3 and 4, the meohanical advantage between the force applied to move lever 70 in the direction 54 and the retaining force required by the tenslle strength o~
the ~use element 53 is ~our to one ln ~a~or of the ~use element. Thuæ, a relatively small ~use element may be ut~lized ~or maintaining the latching mechanism to hold the rod 42 in its spring loaded disposition. As was mentioned pre~iously, this is neceæsary because o~ the relatiYely small cross sectional area and thus tensile strength of the ~uslng member 53. m e path of eleotrical , ,. " ,' ' ' ~ ' .
: .... . . .

r~
11 4g,283 continuity between the rod 42 and the bolt 50 includes the latching member 46, the lever 70, the retaining member 72, the fuse element 52 and the electrically conducting sup-port portion 60. When the current in the fuse exceeds a predetermined amount as determined by the characteristics of the fuse element 52, the fuse element 52 blows or fuses, thus removing the retaining characteris~ics thereof so that the element 72 may rotate in the direction 82 under the force of the element 70 rotating in the direc-o tion 80 as caused by the pull of the rod 42 under the influence of the main fuel rod spring (not shown). This frees the eye portion of the catch member 46, thus allow-ing another spring (not shown) which is biased against a position of the rod 42 to move that rod in the direction 54 to cause a portion of the rod assembly 42 to protrude through a portion of an upper ferrule to cause an unlatch-ing operation as was described previously. It will be noted that in assembly, the engagement of the latching member 46 with the lever member 70 causes a snap as the member 70 abuts against the member 82 forcefully at the interface 85. This is usable to alert the assembler of the fuse that a completed latching operation has occurred.
It is to be understood with respect to the embodiments of the invention that the mechanism shown is not limited to two vertical portions 62, although that is preferable. It is also to be unders~ood that the relative orientation of the protrusion 77 and 75 is not limiting nor is the length of the fuse element 52. The attachment for the fuse at 50 is not limiting an~ it is also to be . . ~ ,, . ~ , ,. ~

., : . , ~ : . , .: .
, 4~,2 understood that element 62 is not limited to glass mela-mine. Furthermore, it is to be understood the axle 74 need not be rotatable as long as member 72 can rotate ahout it.
The apparatus taught with respect to the embodi-ment of this invention has many advantages. One advantage lies in the fact that a boric acid fuse of this kind has an inherently simple design, low cost and significant interrupter rat~ng. Furthermore, the utilization of the spring loaded member 70 and the retaining member 72 re-quires the u~e of only two lever members where the prior art has taught three working levers to accomplish the necessary action. Furthermore~ the relative size of the latching member is significantly smaller than if a clip assembly were utilized as has been done in ~ome of the prior art. Furthermore J another advantage lies in the audible indication that a latching action has taken place during the a~sembly.

......... . . . . . . .
;
~ , . . . .
~ , . . .
.
:; :

.

Claims (8)

13 48,283 What we claim is:

1. A fuse, comprising:
a) fuse barrel means;
b) first and second spaced fuse ferrule means disposed upon said fuse barrel means and electrically com-municating with the internal portion thereof;
c) movable spring loaded current carrying fuse rod means disposed within said barrel means in a disposi-tion of conduction with said first ferrule means, said fuse rod means having a conductive latch means thereon which is utilized to hold said rod in a spring loaded position;
d) nonconducting support means disposed within said barrel means;
e) electrically conducting spring loaded cap-turing lever means movably disposed on said support means in a disposition to capture said latch means to thus maintain said spring loaded rod in a spring loaded posi-tion, said lever means being spring biased to return to a position of noncapture of said latch means if not retained in said disposition of capture;
f) electrically conducting retaining lever 14 48,283 means movably disposed upon said support means in a dis-position to retain said capturing lever means in said disposition of capture provided said retaining lever means is in a first disposition; and g) electrically conducting fuse element means disposed between said second ferrule means and said retain-ing lever means in a disposition to maintain said retain-ing lever means in said first position when said fuse element means is in a nonblown disposition; however, said capturing lever means being free to move to its noncaptur-ing position when said retaining lever means is free to assume a nonretaining disposition upon the occurrence of said fuse element being blown, said fuse rod thus being free to assume a non-spring loaded disposition for thus causing a usable operation.

2. The combination as claimed in claim 1 where-in said capturing lever means is rotatably movable.

3. The combination as claimed in claim 1 where-in said retaining lever means is rotatably movable.

4. The combination as claimed in claim 2 where-in said retaining lever means is rotatably movable.

5. A fuse of the type which rotates away from a mounting terminal in an electrical circuit upon fusing, comprising:
a) fuse barrel means;
b) first and second spaced fuse ferrule means disposed upon said fuse barrel means and electrically com-municating with the internal portion thereof;
c) movable spring loaded current carrying fuse 48,283 rod means disposed within said barrel means in a disposi-tion of conduction with said first ferrule means, said fuse rod means having a conductive latch means thereon which is utilized to hold said rod in a spring loaded position;
d) nonconducting support means disposed within said barrel means;
e) electrically conducting spring loaded cap-turing lever means movably disposed on said support means in a disposition to capture said latch means to thus maintain said spring loaded rod in a spring loaded posi-tion, said lever means being spring biased to return to a position of noncapture of said latch means if not retained in said disposition of capture;
f) electrically conducting retaining lever means movably disposed upon said support means in a dis-position to retain said capturing lever means in said disposition of capture provided said retaining lever means is in a first disposition; and g) electrically conducting fuse element means disposed between said second ferrule means and said retain ing lever means in a disposition to maintain said retain-ing lever means in said first position when said fuse element means is in a nonblown disposition; however, said capturing lever means being free to move to its noncaptur-ing position when said retaining lever means is free to assume a non-retaining disposition upon the occurrence of said fuse element being blown, said fuse rod thus being free to move to a position where a portion thereof extends 16 48,283 through an opening in said first ferrule means for the purposes of freeing said fuse from said mounting terminal to initiate said rotation.

6. The combination as claimed in claim 4 where-in said capturing lever means is rotatably movable.

7. The combination as claimed in claim 4 where-in said retaining lever means is rotatably movable,

8. The combination as claimed in claim 6 where-in said retaining lever means is rotatably movable.