Fuse supporting means having notches containing a gas evolving material

A high voltage fuse comprised of a fuse element wrapped about a core, enclosed in a housing member, and surrounded by a granular quartz material is disclosed. The core has a plurality of cutouts along its outer surfaces having preselected dimensions relative to the width of a fuse element of such values as to assure that at least one cutout is interposed between adjacent turns of the fuse element. The interposed cutouts increase the creepage between the adjacent turns of the fuse element. The preselected dimensions of the cutouts relative to fuse-element width provide a single core that is capable of accommodating numerous types and different numbers of fuse elements. The core is also provided with a gas evolving material attached to the cutouts and separated from the fuse element by a predetermined amount to provide controlled release of arc-quenching gas, when arcing inside the fuse occurs.

BACKGROUND OF THE INVENTION 
This invention relates to a high voltage fuse and, more particularly, to a 
fuse core having a fuse element wrapped about it and constructed to 
provide increased creepage between adjacent turns of the fuse element and 
also to provide improved performance of the high voltage fuse. 
High voltage fuses conventionally comprise a fusible element embedded in a 
granular inert material of high dielectric strength such as sand or finely 
divided quartz. The fusible element may be in the form of a ribbon type 
silver material which is wound on a supporting core. When subjected to 
currents of fault magnitude, the fusible element attains a fusing 
temperature and vaporizes, whereby arcing occurs and the metal vapors 
rapidly expand to many times the volume originally occupied by the fusible 
element. The metal vapors are thrown into spaces between the granules of 
the inert filler material where they condense and are no longer available 
for current conduction. The current limiting effect results from the 
introduction of arc resistance into the circuit. The physical contact 
between the hot arc and the relatively cool granules causes a rapid 
transfer of heat from the arc to the granules, thereby dissipating most of 
the arc energy with very little pressure built up within the fuse 
enclosure. 
The core may be provided with angularly-spaced raised fins extending 
longitudinally of the core along its outer surfaces. The fuse elements 
having the form of a plurality of silver wires or ribbon may be wrapped in 
a helical manner along the fins. Such various type cores are described in 
U.S. Pat. Nos. 3,243,552; 3,294,936 and 3,437,971, issued to H. W. 
Mikulecky, Mar. 29, 1966, Dec. 27, 1966 and Apr. 8, 1969, respectively. In 
these patents the fins are provided with cutouts which have the effect of 
improving insulation between the adjacent turns of the fuse elements. In 
the fuses shown in these patents, the cutouts are generally large in 
relation to the fuse element width, and this, as well as other dimensional 
relationships, makes it generally necessary to use different core designs 
for different element numbers and/or winding angles. 
The aforesaid U.S. Pat. Nos. 3,243,552; 3,294,936; and 3,437,971 also 
describe a supporting core of insulating material positioned in contact 
with the fusible element that is adapted to evolve a gas in the presence 
of an arc. The gas evolving material provides a de-ionizing action that 
reduces the occurrence of restriking, that is, the occurrence of fuse 
conduction after the interruption of the transient overload current. The 
core typically has a high thermal conductivity characteristic that 
conducts heat away from the fuse element during an overcurrent condition. 
The cooling effect of the core reduces the available heat to melt the fuse 
element and thereby reduces the consistency of performance of the high 
voltage fuse. 
Accordingly, an object of my invention is to provide a core which is 
capable of accommodating fuse elements with various winding angles and in 
various numbers and yet which always has between adjacent turns the 
increased creepage distance provided by at least one cutout. 
A further object of my invention is to reduce the cooling effect of the 
supporting core and correspondingly improve the consistency of performance 
of the high voltage fuse. 
These and other objects of the present invention will become apparent to 
those skilled in the art upon consideration of the following description 
of the invention. 
SUMMARY OF THE INVENTION 
In accordance with this invention a high voltage fuse of the current 
limiting type having a tubular insulating casing and an inert granular 
material of high dielectric strength within the casing is provided. The 
high voltage fuse further comprises a core within the tubular casing 
extending longitudinally thereof, and one or more ribbon-type fuse 
elements of predetermined width wrapped around the core and having turns 
spaced apart along the length of the core. The core has a plurality of 
angularly-spaced fin members disposed about its center and extending 
longitudinally of the core. The plurality of fin members have a plurality 
of cutouts located on their outer surface so as to increase the outer 
surface area of the core. The cutouts have a predetermined width with 
immediately-adjacent cutouts being spaced apart from each other by a 
predetermined amount. The predetermined width of the cutout being less 
than the predetermined width of the fuse element. The predetermined width 
of the cutout and the predetermined amount of spacing between 
immediately-adjacent cutouts have a combined longitudinal distance along 
the outer surface of the associated fin member which is less than the 
distance along the fin member between adjacent turns of the fuse element 
or elements so that at least one of the cutouts is interposed between 
adjacent turns of the wrapped fuse element or elements, whereby the 
interposition of the cutout between the adjacent turns of the fuse element 
or elements improves the creepage between adjacent turns of the fuse 
element or elements. 
The features of the invention believed to be novel are set forth with 
particularity in the appended claims. The invention, itself, however, both 
as to its operation and method of operation, together with further objects 
and advantages thereof, may be best understood by reference to the 
following description taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a core 10 of the present invention having wrapped around it a 
fuse element 20. It is to be understood that the core 10 and fuse element 
20 are typically located within a tubular insulating housing having 
electrical terminals at its opposite ends and that the fuse element 20 
provides an electric circuit between these terminals. Such housing and 
terminals are not shown in FIG. 1, but reference may be had to the 
aforesaid U.S. Patent 3,294,936 for such a showing. This latter patent is 
incorporated by reference in the present application. 
While I have shown a single fuse element 20 wrapped about the core, it is 
to be understood that the invention also comprehends a fuse construction 
in which a plurality of fuse elements electrically connected in parallel 
are wrapped about the core and interconnect the terminals of the fuse. 
The fuse element 20 is of a conventional type having a ribbon type form and 
of a high conductivity material such as silver having a melting 
temperature in the order of 1,760.degree. F. The fuse element 20 has a 
plurality of circular perforations 22, spaced apart longitudinally 
thereof. The perforations 22 provide minimum cross sectional areas of fuse 
element 20 which under high fault conditions vaporize, resulting in the 
formation of arclets in series. This action causes progressive insertion 
of arc resistance into the circuit during the initial arcing period and 
thus limits the inductive voltage surges which may occur. The fuse element 
or element 20 are wound about core 10 in a desired pattern. The end 
portions of the fuse element or elements 20 are then affixed (not shown) 
at their final or terminal position to the terminals of the fuse. 
The core 10 has a cross-like shape with substantially the same length in 
its upright and transverse directions. The arms of the cross, which are 
designated 23 and extend longitudinally of the core 20, are referred to 
herein as fin members. The cross-like shape is desirable in that it 
reduces the contact area between the fuse elements 20 and the core 10. 
Similarly, the core 10 may also have a star-like shape to reduce the 
contact area between the fuse element 20 and the core 10. As is well 
known, reducing the contact area between a core, such as core 10, and a 
fuse element, such as fuse element 20, improves the performance of the 
high voltage fuse. The core 10 is formed of a dielectric material such as 
ceramic or mica having a typical dielectric constant of 5. Each of the fin 
members 23 has an outer surface, as shown in FIG. 1, having a plurality of 
cutouts 12. For the sake of clarity, only one cutout per outer surface is 
designated in FIG. 1. Each of the cutouts 12 has a length that transverses 
the width 15 of the fin member 23 as shown in FIG. 1. 
The cutouts 12, shown most clearly in FIG. 2, have a depth 14 extending 
into the outer surfaces of fin members 23 and have a width extending along 
the outer surface of fin member 23 by a distance 16 (W). Immediately 
adjacent cutouts 12 are spaced apart by a distance 18 (C). FIG. 2 further 
shows the fuse element 20 as having a width 22 (Ew) and a distance 24 (Es) 
between adjacent elements or turns of a single fuse element 20. 
The dimensions of cutout 12 are selected relative to the dimension of the 
width 22 (Ew) of a fuse element 20. The desired dimensions are selected in 
accordance with the following two relationships: 
EQU Ew&gt;W (1) 
EQU Es.gtoreq.C+W (2) 
wherein; 
Ew=width of fuse element 20 
W=width of cutouts 12 
Es=distance between adjacent elements (20) or turns of a single fuse 
element 20 
C=spacing between adjacent cutouts 12 
As it is known, the dielectric breakdown along a solid surface of a core, 
such as core 10, formed of ceramic of mica like material, is typically 
less than that through a similar distance of fuse filler medium such as 
the granular quartz material. The dielectric breakdown between two points 
on the core may be improved by increasing the surface distance along core 
10. Cutouts 12 are placed in the outer surface areas of fin members 23 of 
core 10 to increase the effective surface length of core 10 and therefore 
improve its dielectric breakdown characteristic. The cutouts 12 increase 
the surface distance between the locations at which the fin members are 
contacted by adjacent turns of the fuse element 20 so as to increase the 
voltage necessary to cause a dielectric breakdown between adjacent turns 
of the fuse element 20. As will be explained with reference to FIG. 3, the 
cutouts 12 interposed between adjacent turns of fuse element 20 may be 
filled with a granular quartz material 42 such as sand. The placement of a 
high dielectric fuse filler medium within cutouts 12 further increases the 
amount of voltage necessary to cause arcing between adjacent turns of the 
fuse element 20. This increase in the necessary dielectric breakdown 
voltage is commonly referred to as an increase in the creepage between 
adjacent turns of the fuse element. 
From equations (1) and (2) and review of FIG. 2 it is determined if the 
width 22 (Ew) of fuse element 20 is made greater than the width 16 of 
cutouts 12 and the spacing 24 (Es) between the adjacent turns of the wound 
fuse element 20 is equal to or greater than the combined longitudinal 
distance of the width 16 (W) and spacing 18 (C) between adjacent cutouts 
12, then at least one cutout 12 is always interposed between adjacent 
turns of the fuse element 20. Conforming the dimensions of cutouts 12 to 
the dimensions of the fuse element 20 in accordance with this relationship 
provides one core 10 that accommodates a wide variety of types and numbers 
of fuse elements 20 and is capable of accommodating a substantially 
unlimited number of desired spacing between adjacent turns of fuse element 
20. For example, a core 10 having desired dimensions of 2.54 mm (0.1 in) 
and 2.54 mm (0.1 in) for width 16 and spacing 18, respectively, of cutouts 
12 can accommodate a typical high voltage fuse having three elements 20 
rated at 8.3 kV for carrying a current of 80 amperes and having a width of 
4.75 mm (0.187 in). This same core with cutouts 12 having the width of 
2.54 mm (0.1 in) and the spacing of 2.54 mm (0.1 in) also accommodates a 
typical 15.5 kV fuse element 20 rated for a current carrying capacity of 
40 amperes and having a width of 4.75 mm (0.187 in). For each of these 
examples the desired adjacent element spacing may cover the wide range 
from 7.62 mm (0.3 in) to 12.7 mm (0.5 in), with different numbers and 
lengths of elements. 
It should now be appreciated that conforming the cutouts 12 to the desired 
dimensions given in equations 1 and 2 provides a core 10 on which a wide 
variety of fuse elements 20 may be wound at a wide variety of desired 
adjacent element spacing with assurance that at least one cutout will be 
located between each pair of adjacent turns of fuse element 20 to thereby 
increase the creepage between adjacent turns. 
The operational performance of core 10 may be further improved by affixing 
a gas evolving material 30 into some of the cutouts 12 of core 10, as 
shown in FIG. 3. FIG. 3 shows a partial cross section of a high voltage 
fuse 50 having a tubular enclosed casing 40 constructed of a suitable 
insulating material such as glass, fiber, or glass fiber impregnated with 
epoxy resin. The casing 40 is filled with a body of suitable pulverant 
refractory arc quenching material such as quartz 42 having a preselected 
grain size. 
The core 10 extends axially along the casing 40 and is radially spaced 
therefrom and is thus substantially surrounded by the quartz material 42 
except for portions of cutouts 12 having the gas-evolving material 30. The 
gas-evolving material 30 is affixed, by a suitable means such as epoxy, 
into the cutouts 12 which have the fuse element 20 contacting their outer 
surfaces. From FIG. 3 it is seen that the fuse element 20 is separated 
from the gas-evolving material 30 by a gap 32 formed at the outer surface 
of cutouts 12. 
The gas-evolving material 30 is adapted to evolve a gas in the presence of 
an arc. The gas evolving material 30 may be of such a composition 
comprised of a water-insoluble binder and an antitracking substance 
selected from the class consisting of the hydrates and oxides of aluminum 
and magnesium. The composition may also include other fillers such as 
mica, glass, fiber, asbestos or silica. One material suitable for the 
invention comprises approximately 75% aluminum hydrate filler, 20% 
polyester resin binder, and approximately 5% glass fiber. The active gas 
generated and anti-tracking ingredient may be of a commercial grade 
aluminum hydrate Al (OH).sub.3, magnesium hydrate Mg (OH).sub.2, an oxide 
of aluminum such as alumina, Al.sub.2 O.sub.3 or magnesium oxide. 
In one embodiment of the present invention the gap 32 is free of the quartz 
material 42. This freedom of quartz material 42 is realized by selecting 
the grain size of quartz material 42 to be greater than the dimension of 
gap 32. Conversely, a second embodiment of the present invention may be 
realized by selecting the grain size of quartz material 42 to be less than 
the dimension of gap 32 so as to allow the quartz material 42 to enter gap 
32 and contact the gas-evolving material 30. Both of these embodiments are 
to be described hereinafter. 
During the operating of the high voltage fuse device 50 if the current 
applied to the fuse element 20 exceeds the current carrying capability of 
the fuse element 20, the excessive current generates heat that initiates 
melting of the fuse element 20. When fuse element 20 is subjected to this 
current of fault magnitude, the fuse element 20 quickly attains fusing 
temperatures and vaporizes, whereby arcing occurs and the metal vapor 
rapidly expands to many times the volume originally occupied by the fuse 
element 20. These vapors are thrown into spaces between the quartz 
material 42 where they condense and are no longer available for current 
conduction. A current limiting effect results from the introduction of arc 
resistance into the circuit. It is desirable that the physical contact 
between the hot arc initiated by the melting of the fuse element 20 and 
the relatively cool granules cause a rapid transfer heat from the fuse 
element to the granules, thereby dissipating most of the arc energy with 
very little pressure build-up within the fuse enclosure 40. 
It is also desirable that the quartz material 42 in the immediate vicinity 
of the arc-initiating fuse element 20 melts and absorbs arc energy. The 
fulgurite resulting from the fusion and sintering of the quartz sand 
particles is in the nature of semiconducting glass body, and as it cools 
it ceases to be semiconducting, becomes an insulator and thus accomplishes 
its desired function. 
Furthermore, during the operation of fuse device 50 it is desired that the 
gas generated by material 30 produces a de-ionizing action on the arc 
produced by vaporization of the fuse element 20 as well as producing a 
cooling effect on the fulgurite in a manner so as to inhibit the 
"restriking" of the arc. By restriking it is meant the recurrence of fuse 
conduction after the fuse has interrupted the current. The placement of a 
gas evolving material 30 within cutouts 12 and the allowance of the gap 32 
within cutouts 12 provides a cooling and de-ionizing gas blast when an arc 
is initiated adjacent to material 30. 
Typically the thermal conductivity of the core 10 or gas evolving material 
30 is substantially higher than that of the quartz material 42 by a ratio 
of about five to one. The higher thermal conductivity of core 10 or gas 
evolving material 30 with respect to that of the quartz material 42 
provides a cooling effect which has a tendency to interfere with the 
desired heating of the fuse element 20 prior to its melting on 
overcurrents. The use of an air space between the element 20 and the gas 
evolving material 30 reduces the heat flow to, and cooling effect of, the 
core 10 and gas evolving material 30 in the period prior to fuse melting. 
The overall result of the reduction of the cooling effect of core 10 and 
gas evolving material 30 is to provide more heat to the desired locations 
within the fuse device 50 and therefore improve the operational 
performance of the high voltage device 50. 
As previously discussed, a second embodiment of the present invention 
having the gas evolving material 30 in cutouts 12 may be provided by 
supplying a quartz material 42 having a grain size smaller than gap 32 
such as to allow quartz material to enter the cutout 12 and contact the 
fuse element 20 and gas evolving material 30. The allowance of the direct 
contact between the quartz material 42 and the element 20 allows more of 
the heat emitted from fuse element 20 to be conducted to the quartz 
material 42. The increase in the heat conducted to the quartz material 42 
improves the fulgurite effect of the quartz material while also reducing 
the cooling effect of core 10 and gas evolving material 30. 
It should now be appreciated that the present invention provides various 
embodiments that introduce gas evolving material into the arcing process 
while reducing the cooling effect of core 10 and the gas evolving material 
30 before fuse melting occurs, allowing for improved operating performance 
of a high voltage fuse device 50. It should also now be appreciated that 
the above-described dimensional relationship between the fuse element 20 
and the cutouts 12 in the core 10 assures the interposition of at least 
one cutout 12 between adjacent turns of the fuse element 20 and therefore 
improves the creepage between adjacent turns of the fuse element 20. 
Although most of the above description refers to a single fuse element 
wound on the core 10, it is to be understood that the invention is also 
applicable to fuses that comprise a plurality of parallel-connected fuse 
elements wound in spaced side-by-side relationship on the core. In such a 
construction, the spacing between adjacent turns is the spacing between 
the immediately-adjacent turns of separate fuse elements. Whether there is 
a single fuse element or a plurality of fuse elements, complying with 
equations 1 and 2 hereinabove assures that at least one cutout will be 
located between adjacent turns. 
While I have shown and described particular embodiments of my invention, it 
will be obvious to those skilled in the art that various changes and 
modifications may be made without departing from my invention in its 
broader aspects; and I, therefore, intend herein to cover all such changes 
and modifications as fall within the true spirit and scope of my 
invention.