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Патент USA US2408353

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Sept. 24, 19460
CIIGL sun's
2,408,351
CURRENT-LIMITING FUSE
Filed Nov. 11, 1942
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Patented Sept. 24,, 1946
2,408,351
UNITED STATES PATENT OFFICE
2,403,351
CURRENT-LIMITING FUSE
Chauncey G. Suits, Schenectady, N. Y., assignor
to General Electric Company,
a. corporation of
New York
Application November 11, 1942, Serial No. 465,205
1
1 Claim. (Cl. 200-120)
2
My invention relates to fuses and more partic-'
ularly to- fuses of the current-limiting type.
Current-limiting fuses are known which con
associated is capable of producing. The insert.
ed resistance causes rapid current decay and
subsequent interrupting of the current ?ow with
sist in the main of a fusible element in the form
of one or more conductors of suitable metal such
as silver or zinc embedded in an inert granular
negligible mechanical disturbance there being no
gassing or discharge of vapors or particles and
practically no noise.
It is an object of my invention to provide a new
or refractory arc-extinguishing material of high
dielectric strength such as sand or relatively ?ne
ly divided quartz, the conductor or conductors in
and improved current-limiting fuse of the type
escribed above.
Further objects and advantages of my inven
of high temperature resistant ceramic material.
tion will become apparent as the following de
To these parts are added an enclosing housing
scription proceeds and the features of novelty
and terminals for the conductors.
which characterize my invention will be pointed
Upon subjection of such fuse to currents of
out with particularity in the claim annexed to
large magnitude, such as upon short circuit, the
fusible element attains fusing temperature and 15 and forming a part of this speci?cation.
Referring now to the drawing, I have illus
dissipates or vaporizes throughout a fusible sec
trated in a single ?gure a cross-sectional view
tion of considerable length as distinguished from
some instances being wound on a supporting core
10
of a current—limiting fuse embodying my inven
dissipation only at a point of reduced cross-sec
tion.
tion, whereupon arcing occurs and the metal va
pors rapidly expand to many times the volume 20 As was mentioned above, the fused shell which
forms upon operation of a current-limiting fuse
originally occupied ‘by the fusible element itself.
of the type referred to above is a relatively good
The force of this expansion throws the metal
insulator and although it is shunted across the
vapors out of the arc path and into the spaces
terminals of the circuit to be interrupted, it does
between the granules of inert ?ller material.
25 not under ordinary conditions limit the inter
These vapors condense upon the surfaces of the
rupting ability seriously. However, near the
relatively cool granules and no longer are avail
maximum voltage condition, under which the fuse
able for current conduction so that arcing is con
will operate and when relatively minor impuri
ties are found in the otherwise pure inert gran
ular material such as quartz sand, the current
conduction in this fused column does lead to in
tact between the hot arc column and the rela
tively cool granules causes an exceedingly rapid
transfer of heat from the arc to the granules
resulting in a very high voltage gradient or a
high voltage drop per unit length of arc column.
The arc energy is dissipated in this heat transfer
with practically negligible net pressure within the
gurite formation is avoided, the fusion of the
fuse housing. During the arcing period the
powder forming globules or beads instead of a ,
terruption failures. I have found, however, that
when a very ?ne grain crystalline quartz powder
such as will pass through a 200-mesh sieve is
used instead of the coarser quartz sand, the ful
continuous tube, as described above. I have
granules in the vicinity of the arc melt and upon
cooling form a hollow shell or fulgurite consist 40 found also that the voltage gradient, or volts per
centimeter of length, is considerably increased
ing of fused quartz if the arc-extinguishing ma
with the ?ne quartz powder due to the increased
terial is granular quartz and a small percentage
cooling action on the arc column as compared
of metal from which the fusible conductor is
with relatively coarse grain quartz sand such, for
made. This fused shell has the properties of an
insulator and in the normal operation of the fuse 45 example, as 80-mesh sand.
The interrupting action and the current-lim
does not constitute a current~conducting element
in the current path.
iting action of the current-limiting type of fuse
are greatly improved when an intimate mixture
As a result of the actions referred to in the pre
ceding paragraph there is in effect suddenly in
serted into the path of the current at the instant
of melting of the fusible element, the high re
sistance formed by the arc column which ini
tially limits the current to a magnitude which
is only a small fraction of the current which the
of relatively coarse grain and relatively ?ne grain
inert arc-extinguishing material is used as the
arc-quenching medium, and I have found that
particularly satisfactory results are obtained with
a mixture of 80-mesh and ZOO-mesh granular
material such as fused quartz, silica or the like.
system with which the current~limiting fuse is 55 The ?ne grain material greatly increases the volt
age gradient to produce a much higher current
2,408,351
3
limiting action while the coarse grain material
tends to provide a more gradual insertion of re
sistance into the circuit so as to some extent min
imize the voltage surges that are produced. By
varying the proportions of the diiferent grain
size materials which are intimately mixed, var
ious operating conditions can be obtained al
though I have found an intimate mixture of 80
-~
mixture of inert granular material indicated at
I6 and I1 embeds the current-interrupting ele
ment l5. As will be obvious from the drawing,
the core M is of generally star-shaped construc
tion in that it has a, plurality of longitudinally
extending ?ns or ribs, one of which is designated
as l8. Although the illustrated core M has four
such ?ns, a core having more than four ?ns may
be‘ employed depending upon the rating and size
mesh and 200-mesh inert granular arc-extin 10 of the particular fuse. The advantage of the star
guishing material most satisfactory from the
shaped core is that the current-interrupting ele
standpoint of high current-limiting action with
out introducing too great a voltage surge.
Referring now to the drawing, I have disclosed
ment IE or fusible element, touches the core only
at spaced points so that the maximum length
of the fusible element is exposed to the inert
a tubular enclosing casing [0 which is constructed
granular ?ller material indicated at It and I1.
15
of glass, porcelain or other suitable insulating
spirally winding the interrupting element on a
material.
Metallic terminal ferrules H are se
cured respectively on the opposite ends of the
casing :by means of any suitable form of glass-to
metal seal indicated at l2. The ends of ferrules
II are closed by caps l3 sealed in place although,
if desired, the caps may be made integrally with
the ferrules. An elongated insulating support or
core l4 comprised of high heat-resisting ceramic
or other suitable material extends longitudinally
in casing ID. This .core serves to support a cur
rent-interrupting element or conductorl5 adapt
ed to fuse throughout a section of considerable
length, which is spirally wound on the core 14.
Although the current-interrupting element H‘: of
the illustrated device comprises only a single con
ductor, it is common in the construction of such
current-limiting devices to employ one or more
vcore permits the installation of an element of
relatively great length in a casing of practical
dimensions.
The opposite ends of the fusible element iii
are electrically connected with the terminals or
ferrules H as by conducting means is which also
serve to support the core M at the axis of tubu
lar casing In.
It should .be understood that means to further
limit the surge voltage such as are disclosed in
Lohausen Patent 2,157,907, granted May 9, 1939,
and assigned to the assignee of the present appli
cation, may be employed, although with my im
proved fuse construction such means for limiting
the surge voltage may not be necessary.
While I have disclosed a particular embodiment
of my invention, it will be apparent to those skilled
in the art that my invention is not limited to
ing. This is for the reason that it has been found
the particular construction shown but that
35
that most effective current-limiting action is pro
changes and modi?cations may be made without
duced when conductors of very thin cross-section
departing from the spirit and scope of my inven
are employed. Hence, where the current rating
tion and I aim in the appended claim to cover all
demands a relatively large cross-section, it is de
such changes and modi?cations.
sirable to divide this total cross-section into a
What I claim as new and desire to secure by
number of parallel-connected conductors having
Letters Patent of the United States, is:
a thin cross-section such as a plurality of ?ne
In a high tension fuse of the current-limiting
silver or zinc wires.
.
type, the combination of a totally enclosed cas
The interior of casing H], in accordance with
ing containing a body of arc-quenching medium.
my invention, is ?lled with an intimate mixture
comprising an intimate mixture of 200-mesh and.
of relatively coarse grain and relatively ?ne grain
80-mesh granular inert material, and a conductor
inert granular arc-quenching material. The rela
embedded in said material which conductor is
tively coarse grain material which might be 80
adapted to dissipate throughout a fusible section
mesh fused quartz or silica, is indicated at US
of considerable length as distinguished from dis
while the relatively fine grain material which is
sipation only at a, point of reduced cross-section
preferably 200-mesh fused quartz, or silica, is in
upon subjection of the fusible section to excessv
dicated at [1. The intimate mixture of this ma
current of large magnitude.
terial produces an improved current-limiting ac
CHAUNCEY G. SUITS.
main conductors depending upon the current rat
tion without subjecting the associated circuits to
abnormally high voltage surges. This intimate
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