Note: Descriptions are shown in the official language in which they were submitted.
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~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
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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
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~ to provide some sort of mechanical advantage system or
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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.
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