CA1128100A - Electric fuses employing composite metal fuse elements - Google Patents
Electric fuses employing composite metal fuse elementsInfo
- Publication number
- CA1128100A CA1128100A CA348,240A CA348240A CA1128100A CA 1128100 A CA1128100 A CA 1128100A CA 348240 A CA348240 A CA 348240A CA 1128100 A CA1128100 A CA 1128100A
- Authority
- CA
- Canada
- Prior art keywords
- fuse
- metal
- strip
- melting point
- composite
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
- H01H85/00—Protective devices in which the current flows through a part of fusible material and this current is interrupted by displacement of the fusible material when this current becomes excessive
- H01H85/02—Details
- H01H85/04—Fuses, i.e. expendable parts of the protective device, e.g. cartridges
- H01H85/05—Component parts thereof
- H01H85/055—Fusible members
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
- H01H85/00—Protective devices in which the current flows through a part of fusible material and this current is interrupted by displacement of the fusible material when this current becomes excessive
- H01H85/02—Details
- H01H85/04—Fuses, i.e. expendable parts of the protective device, e.g. cartridges
- H01H85/05—Component parts thereof
- H01H85/055—Fusible members
- H01H85/06—Fusible members characterised by the fusible material
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- Fuses (AREA)
Abstract
Abstract of the Disclosure The invention involves new high voltage current limiting fuses employing composite metal fuse elements. The composite element consists of at least two portions of different metals with different electrothermal properties extending through the melt and arc zone, the two portions being bonded to one another along their adjoining faces for good thermal exchange. One metal of the composite is aluminium which is of high conductivity and high melting point while the other is cadmium which is of low melting point, so that melting of the low melting point metal occurs at any and all locations along, the element when its temperature reaches the said low melting point. The resulting composite exhibits properties that are not the mean of the metals employed and has a reversible resistance characteristic thus facilitating the design of the fuse for low current fault interruption. An element having low melting temperature along its entire length results and gives essential arcing substantially simultaneously of the total element to improve the low current clearing performance of the fuse.
Description
8~0(~
ELFCTRIC FUSES EMPLOYING COMPOSITE
METAL FUSE ELEMENTS
Field of the Invention The present invention is concerned with imporovements in or relating to electric fuses employing composite metal fuse elements, and especially to such fuses of high voltagP current limiting type.
Review of the Prior Art It is known practice to protect an electric circuit by means of two different fuses, one of which is a current limiting fuse that will interrupt fault currents from its maximum interrupting rating to its minimum interrupting rating, and the other of which is a so-called weak lin]c expulsion fuse that will interrupt fault currents a value from slightly above the minimum interrupting current rating of the current limiting fuse. Obviously it is desirable to eliminate the practice of using two fuses, but the design of fuses for interrupting low currents just above (e.g. two times or more) the maximum current rating of the fuse has been a constant problem to the fuse designers, and has added substantially to the complexity, size and cost of the fuses.
Fuse elements for such fuses commonly consist of one or more strips or ribbons of metal mounted in a suitable casing, and the design of such a fuse element requires the careful choice of different parameters among which are the metal from which the element is made, the dimensions of the strip or ribbon, whether or not the strip is notched or provided with eutectic spots (Metcalf effect) along its length; whether or not the ele~ent is wound on a ceramic or deionizing gas producing core; whether or not the element consists of --8~
tw~ differentn~tals oonnected in series, and ~e choice of the matPrial surrounding the el~t. In a specific ~xample, the ribbon may be of silver and provided alony its length wi~h up to about 100 notches,or holes, each of which i5 the potential site for melting and the initial formation of an arc; the element is completely buried in quartz sand which acts to abso.rb the energy generated by the arcs, and also to receive the melted element material.
The choice of the me~al to be used is always difficult, since each metal usable in commercial practice has its own advantages and disadvantages. For example, silver has a desir-able high conductivity and resistance to oxidation, but has a high melting point ~960C), and a high heat of evaporation and is costly. When spots of tin are soldered along the silver element to make use of the so-called Metcalf or M-effect a eutectic alloy is formed, the meltinq temperature being lower at the spot (approximately 230C) to make the fuse applicable for low current operation, but such spots~ exhibit with time a non-reversible change under the effect of non-melting current flows that can lead to damage of the fuse. Additionally, while the spot initiates a single melt and subsequent arc at its location, approximately 700C greater temperature is required to result in further melting of the silver sufficient to interrupt the high voltage circuit. The added time required for the small overcurrent to produce the much higher element temperature limits the effect-iveness of the d~sign.
Cadmium is a low melting point metal (321C) with a vexy low temperature of evaporation (750C). It has an excellent ~L~Z~
arc extinguishing characteristic and therefore it is widely used in electrical contacts. Moreover, it has very high burn-back rate and is very convenient for interruption of low currents. Cadmium has low conductivity and current carrying capacity while the resultant cadmium ox.ide is a very good insulator.
Zinc is a low melting point metal (419C) that is resistant to oxidation, has a high burnback rate and has a non-linear coefficient of resistivity, which is useful, but has a conductivity 3 - 4 times lower than that of silver. Other metals and alloys thereof show some disadvantages when all of the necessary characteristics are evaluated.
Alum.inum has a high current capacity and low melting point (.658C) and the oxide produced is non-conductive, which are all desirable, but the oxide film prevents disbursement of the melted metal into the surrounding sand and the melting charac~ex-istic for low currents applied for long t.imes becomes inconsistent.
It is therefore an object of the present invention to provide a new electric fuse employing a new composite mat~rial as the fuse element.
In accordance with the present invention there is provided an electric fuse for use in circuits of at least 1000 volts and of the current limiting type, comprising:
a tubular housing of insulating material;
two spaced terminals mounted on said housing for .
connection of the fuse in an electric circuit;
1~2~
at least one metal fuse element mounted within the housing with the two ends of each element connected respectively to the said two terminals to form a respective conducting path therebetween;
each fuse element being embedded in and surrounded by silica sand disposed within the housing;
characterized in that:
each fuse element comprises a cadmium portion and an aluminum portion, each of which provides a corresponding continuous current carrying path between the said terminals;
each metal being pxesent in the fuse element in an amount not less than 3% by ~olume of the total;
t.he said portions: being bonded to one another at adjoining contacting surface~ to constitute a composite metal element wherein t~e cadm~um portion due to its lower melting point will melt before the aluminum portion to increase the current density through the unmelted aluminum portion.
Description of the Drawin~s Particular preferred embodiments of the invention 2Q will now be described by way of example, with reference to the accompanying diagrammatic drawings, wherein:
Figures 1 to 4 are respective perspective views of preforms from which fuse elements of the invention can be formed~
Figure 5 is a perspective vie~ of one form of fu~e con~tructed accoxding to this invention~
Figure 6 i5 a longitudinal cross-sectional vie~
of the structure of Figure 5, parts the.reof being shown broken away as necessary for clarity of illustration, and Figure 7 is an enlarged view depicting the specific details of construction of the fuse elements shown in Figure 6.
' ~Z83LI~
Description of the Preferred Embodiments A fuse element for use in an electric fuse of the invention consists of a-t least two separate metals, each of which is present in the form of at least one so-called separate fuse element portion, and preferably the different fuse element portions are metallurgically bonded to one another at their adjoining surfaces where they contact one another to form in effect a composite metal body.
For example, referring especially to Figure l, the fuse element preform illustrated therein consists of two thin flat portion~ lO and 12, each of which has the form of a thin flat strip or ribbon having two parallel wider faces and two parallel narrower faces or edges. The two strips are placed face to face and metallurgically honded to one another by, for example, co-extrusion, cold rolling or by hot rolling at below the meltingtemperature of the lower melting material. In another method the portion of lower melting temperature metal is formed by casting against the body portion of the higher melting temperature metal, the resulting composite body then being extruded, cold or hot rolled, etc.
In another embodiment illustrated by Figure 2, more than two separate portions are employed (three in this example); the metal of the portions lO and 14 can be the same, in which case the portion 12 is sandwiched between two identical other portions r or they can be of different metals. In the embodiment illustrated by Figure 3 one portion consists of a plurality of uniformly-spaced metal wires or rods lO which are enclosed in the second ~3L2~
body portion 12 by cas-ting the latter metal around them. The r~sultant rod or wire can then be rolled or extruded as required.
In the embodiment illustrated in Figure 4 a single body portion 10 is enclosed by the other metal portion 12. The metallurgical bonding of the two body portions at their abutting surfaces is further increased by hot rolling the cast body.
Each of the preEorms illustrated is processed, for example, to give it the specific dimensions necessary for fuse elements; notching and mounting the element between a pair of fuse-terminals; and embedding the element in a sui~able surroundingmedium, such as quartz sand, in a suitable container.
Referring now to Figures 5 to 7, there is illustrated therein an electric fuse consisting of a tubular housing 16 of an insulating material, provided with end caps 18 and 20 of a suitable conducting material at each end thereof. Outer caps 22 and 24 are secured about the end caps 18 and 20 respectively by a press fit and are secured to the tubular housing 16 by cement layers 26 and 28 respectively. An end terminal sleeve 30 and an end terminal cap 32 are fastened respectively to the inner surfaces of end caps 18 and 20, and the housing is filled with a granular filler consisting of silica sand 34. Disposed within the housing of the fuse and embedded within and supported by the sand filler are a plurality (5 in this embodiment) of coaxial helical fusible elements 36 through 44, each of which has its two ends connected respectively to the terminal 3Q and 32.` As is apparent from Figure 3 the helical fusible elements are each provided along its length with a large number o~ spaced notches 46 9~2~
, . . .
It is found that in meeting the special requirements of a fuse element, the properties of this composite metal element are not simply the mean values for those of the two constituents, but are complex and differ in important respects thereErom. The temperature/time charact~ristics of the composites of the invention are characteri~ed by two different stages. The initial stage is a normal exponential increase of temperature with time as the fuse is subjected to its normal load current.
Wllen an overload is present the temperature of course increases, and upon xeaching the melting temperature of the low~r melting component, there will be a rapid increase of temperature with time, due to a reduction in the cross sectional area of the element caused by successive melting of the lower temperature component and consequent increase in the current density through the rernaining component. This marked increase in characteristic at a specific point permits a more accurate predetermination of the fuse melting characteristic, without this characteristic being unduly afEected by aging or pre-melting temperature changes of the fuse element, resulting for example, from current surges pa~sing through it. The temperature/time characteristic of the composite is therefore al~ays reversible up to the temperature at which melting of the lower melting component begins , whereas by comparison the characteristic of a silver element with a tin eutectic spot was found to be irreversible thus leading to eventual damage.
A
The metals employed in a composite fuse element of the invention are specified as being different as to their electro-thermal properties, by which are meant any one or more of their characteristics; resistivity, thermal conductivity, melting point, boiling point, heat of fusion, and heat of evaporation.
It will be understood that different metals may have such similar electrothermal properties as not to be suitable for application of the invention. The different portions of the element have as intimate an interface as possible, in order to obtain the best possihle electrical and thermal conductivity between the metals without having the undesirable interaction of two metals during the premelting time.
Each metal present in the composite should be present in an amount not less than 3% by volume of the entire element body, since otherwise there will not be sufficient present to significantly affect the properties of the composite. It will be apparent that each metal must be present in the form of a separate body or plurality of bodies that will extend through the intend~d melt and arc zone of the fuse element in the direction of flow of the current therethrough~
When two metals are employed in the composite one of them ~ill be of high conductivity and high melting point namely aluminum in the preferred combination, while the other is of low melting point namely cadmium, so that element mel~ing i5 initia~ed at any and all locations along the element which reach the melting temperature of the low melting point constituent starting, of course, at the notches 46.
g _ ~,,,`
~ 3 It is found that a fuse element of the form illustrated by Figure 2 is preferred, in which a high meltiny temperature strip is sandwiched between two low melting temperature strips.
It is also found that there is a preferred ratio of width to thickness of each strip, and this should be about 10:1, and may of course vary between say ~:1 and 12:1. An 80 amp fuse as described above will typically employ 12 helical elements connected in parallel each measuring about 2.5mm by 0.2mm.
The silica sand filler 34 preferably is in the form of approximately spherical ~rains of random size within a given range. These grains preferably are composed of at least 99~
silica and approximately 98~ of the grains are retained on sieve mesh size 100 while approximately 2~ of the grains are retained on sie~e mesh size 30, Approximately 30% of the grains are retained on sieve mesh size 40 while approximately 75~ are retained on sieve mesh size 50. The pellets are identiied as 109 G.S.S~
In the e~ent of the occurrence ofa high magnitude fault current such as many times rated load current, the fusible elements 36-44 melt practically simultaneously at all of their reduced sections 46 to form a chain of arcs. These arcs quickly lengthen and burn back from their roots. The energy of the arc in the form of heat is absorbed by the filler material in the granular form 34. The exchange of energy between the arcs and the filler material is influence~ by the surface area of filler grains which is exposed to the arcs. The ~reater the area of this exposure the more efficient is the exchange of energy.
This factor is facilitated by the use of the filler described and by the fact that the fusible elements are of ribbon -form and that they are arranged as multiple elements rather than as one single element, although the invention in its broader aspects is not limited to a fuse using a plurality of parallel connected fuse elements.
Since the invention is concerned with high voltage currents of 1,000 volts and abov~, it is herein categorized as a high voltage fuse.
A fuse constructed according to this invention is well suited for use in protecting circuits and their connected apparatus such as transformers, capacitors, switchgear and the like. By the invention a fuse is provided which is capable of effective fast acting current limiting action for currents of high magnitude and which also operates reliably for low currents which are but slightly in excess of the normal rated current of the fuse due in part to the fact that the fusible elements may be raised by relatively low fault currents to temperature levels approaching melting without establishing an excessively high overall fuse temperature~
~2~
It will also be noted that the preferred illustrated fuse is of coreless design which is to be preferred~ In addition to their expense, cores are objectionable because contact with the fusible element reduces the area over which energy exchange between the arcs and the filler material can take place. Since the interrupting process requires that most of the arc energy be transferred to latent heat of fusion of the filler material an~ reduction of the area of contact with the filler material is undesirable. Moreover, the areas of contact between the elements and core can produce high temperatures in the core.
The ceramic materials commonly used exhibit marked reduction in their insulating properties at such elevated temperatures.
This reduction in insulating property of the core results in a non-uniform voltage distribution across the fuse in the period following arcing.
Under certain transient current conditions, an appreciable temperature rise in the fuaible elements may occur and may cause a de~ormation of the fusible elements. Repeated heating and cooling cycles may impose increasing tensile load on the fusible elements since they may not straight~n out due to construction of the sand. If movement of the elements is possible, as in a coreless construction~ thls tension may be relieved. In elements wound on a core, the opportunity for relieving tension is severely restricted and mechanical failure due to this increased tension may occur, since the increases may be sufficient to break the fusible element, particularly at the reduced cross section notches.
ELFCTRIC FUSES EMPLOYING COMPOSITE
METAL FUSE ELEMENTS
Field of the Invention The present invention is concerned with imporovements in or relating to electric fuses employing composite metal fuse elements, and especially to such fuses of high voltagP current limiting type.
Review of the Prior Art It is known practice to protect an electric circuit by means of two different fuses, one of which is a current limiting fuse that will interrupt fault currents from its maximum interrupting rating to its minimum interrupting rating, and the other of which is a so-called weak lin]c expulsion fuse that will interrupt fault currents a value from slightly above the minimum interrupting current rating of the current limiting fuse. Obviously it is desirable to eliminate the practice of using two fuses, but the design of fuses for interrupting low currents just above (e.g. two times or more) the maximum current rating of the fuse has been a constant problem to the fuse designers, and has added substantially to the complexity, size and cost of the fuses.
Fuse elements for such fuses commonly consist of one or more strips or ribbons of metal mounted in a suitable casing, and the design of such a fuse element requires the careful choice of different parameters among which are the metal from which the element is made, the dimensions of the strip or ribbon, whether or not the strip is notched or provided with eutectic spots (Metcalf effect) along its length; whether or not the ele~ent is wound on a ceramic or deionizing gas producing core; whether or not the element consists of --8~
tw~ differentn~tals oonnected in series, and ~e choice of the matPrial surrounding the el~t. In a specific ~xample, the ribbon may be of silver and provided alony its length wi~h up to about 100 notches,or holes, each of which i5 the potential site for melting and the initial formation of an arc; the element is completely buried in quartz sand which acts to abso.rb the energy generated by the arcs, and also to receive the melted element material.
The choice of the me~al to be used is always difficult, since each metal usable in commercial practice has its own advantages and disadvantages. For example, silver has a desir-able high conductivity and resistance to oxidation, but has a high melting point ~960C), and a high heat of evaporation and is costly. When spots of tin are soldered along the silver element to make use of the so-called Metcalf or M-effect a eutectic alloy is formed, the meltinq temperature being lower at the spot (approximately 230C) to make the fuse applicable for low current operation, but such spots~ exhibit with time a non-reversible change under the effect of non-melting current flows that can lead to damage of the fuse. Additionally, while the spot initiates a single melt and subsequent arc at its location, approximately 700C greater temperature is required to result in further melting of the silver sufficient to interrupt the high voltage circuit. The added time required for the small overcurrent to produce the much higher element temperature limits the effect-iveness of the d~sign.
Cadmium is a low melting point metal (321C) with a vexy low temperature of evaporation (750C). It has an excellent ~L~Z~
arc extinguishing characteristic and therefore it is widely used in electrical contacts. Moreover, it has very high burn-back rate and is very convenient for interruption of low currents. Cadmium has low conductivity and current carrying capacity while the resultant cadmium ox.ide is a very good insulator.
Zinc is a low melting point metal (419C) that is resistant to oxidation, has a high burnback rate and has a non-linear coefficient of resistivity, which is useful, but has a conductivity 3 - 4 times lower than that of silver. Other metals and alloys thereof show some disadvantages when all of the necessary characteristics are evaluated.
Alum.inum has a high current capacity and low melting point (.658C) and the oxide produced is non-conductive, which are all desirable, but the oxide film prevents disbursement of the melted metal into the surrounding sand and the melting charac~ex-istic for low currents applied for long t.imes becomes inconsistent.
It is therefore an object of the present invention to provide a new electric fuse employing a new composite mat~rial as the fuse element.
In accordance with the present invention there is provided an electric fuse for use in circuits of at least 1000 volts and of the current limiting type, comprising:
a tubular housing of insulating material;
two spaced terminals mounted on said housing for .
connection of the fuse in an electric circuit;
1~2~
at least one metal fuse element mounted within the housing with the two ends of each element connected respectively to the said two terminals to form a respective conducting path therebetween;
each fuse element being embedded in and surrounded by silica sand disposed within the housing;
characterized in that:
each fuse element comprises a cadmium portion and an aluminum portion, each of which provides a corresponding continuous current carrying path between the said terminals;
each metal being pxesent in the fuse element in an amount not less than 3% by ~olume of the total;
t.he said portions: being bonded to one another at adjoining contacting surface~ to constitute a composite metal element wherein t~e cadm~um portion due to its lower melting point will melt before the aluminum portion to increase the current density through the unmelted aluminum portion.
Description of the Drawin~s Particular preferred embodiments of the invention 2Q will now be described by way of example, with reference to the accompanying diagrammatic drawings, wherein:
Figures 1 to 4 are respective perspective views of preforms from which fuse elements of the invention can be formed~
Figure 5 is a perspective vie~ of one form of fu~e con~tructed accoxding to this invention~
Figure 6 i5 a longitudinal cross-sectional vie~
of the structure of Figure 5, parts the.reof being shown broken away as necessary for clarity of illustration, and Figure 7 is an enlarged view depicting the specific details of construction of the fuse elements shown in Figure 6.
' ~Z83LI~
Description of the Preferred Embodiments A fuse element for use in an electric fuse of the invention consists of a-t least two separate metals, each of which is present in the form of at least one so-called separate fuse element portion, and preferably the different fuse element portions are metallurgically bonded to one another at their adjoining surfaces where they contact one another to form in effect a composite metal body.
For example, referring especially to Figure l, the fuse element preform illustrated therein consists of two thin flat portion~ lO and 12, each of which has the form of a thin flat strip or ribbon having two parallel wider faces and two parallel narrower faces or edges. The two strips are placed face to face and metallurgically honded to one another by, for example, co-extrusion, cold rolling or by hot rolling at below the meltingtemperature of the lower melting material. In another method the portion of lower melting temperature metal is formed by casting against the body portion of the higher melting temperature metal, the resulting composite body then being extruded, cold or hot rolled, etc.
In another embodiment illustrated by Figure 2, more than two separate portions are employed (three in this example); the metal of the portions lO and 14 can be the same, in which case the portion 12 is sandwiched between two identical other portions r or they can be of different metals. In the embodiment illustrated by Figure 3 one portion consists of a plurality of uniformly-spaced metal wires or rods lO which are enclosed in the second ~3L2~
body portion 12 by cas-ting the latter metal around them. The r~sultant rod or wire can then be rolled or extruded as required.
In the embodiment illustrated in Figure 4 a single body portion 10 is enclosed by the other metal portion 12. The metallurgical bonding of the two body portions at their abutting surfaces is further increased by hot rolling the cast body.
Each of the preEorms illustrated is processed, for example, to give it the specific dimensions necessary for fuse elements; notching and mounting the element between a pair of fuse-terminals; and embedding the element in a sui~able surroundingmedium, such as quartz sand, in a suitable container.
Referring now to Figures 5 to 7, there is illustrated therein an electric fuse consisting of a tubular housing 16 of an insulating material, provided with end caps 18 and 20 of a suitable conducting material at each end thereof. Outer caps 22 and 24 are secured about the end caps 18 and 20 respectively by a press fit and are secured to the tubular housing 16 by cement layers 26 and 28 respectively. An end terminal sleeve 30 and an end terminal cap 32 are fastened respectively to the inner surfaces of end caps 18 and 20, and the housing is filled with a granular filler consisting of silica sand 34. Disposed within the housing of the fuse and embedded within and supported by the sand filler are a plurality (5 in this embodiment) of coaxial helical fusible elements 36 through 44, each of which has its two ends connected respectively to the terminal 3Q and 32.` As is apparent from Figure 3 the helical fusible elements are each provided along its length with a large number o~ spaced notches 46 9~2~
, . . .
It is found that in meeting the special requirements of a fuse element, the properties of this composite metal element are not simply the mean values for those of the two constituents, but are complex and differ in important respects thereErom. The temperature/time charact~ristics of the composites of the invention are characteri~ed by two different stages. The initial stage is a normal exponential increase of temperature with time as the fuse is subjected to its normal load current.
Wllen an overload is present the temperature of course increases, and upon xeaching the melting temperature of the low~r melting component, there will be a rapid increase of temperature with time, due to a reduction in the cross sectional area of the element caused by successive melting of the lower temperature component and consequent increase in the current density through the rernaining component. This marked increase in characteristic at a specific point permits a more accurate predetermination of the fuse melting characteristic, without this characteristic being unduly afEected by aging or pre-melting temperature changes of the fuse element, resulting for example, from current surges pa~sing through it. The temperature/time characteristic of the composite is therefore al~ays reversible up to the temperature at which melting of the lower melting component begins , whereas by comparison the characteristic of a silver element with a tin eutectic spot was found to be irreversible thus leading to eventual damage.
A
The metals employed in a composite fuse element of the invention are specified as being different as to their electro-thermal properties, by which are meant any one or more of their characteristics; resistivity, thermal conductivity, melting point, boiling point, heat of fusion, and heat of evaporation.
It will be understood that different metals may have such similar electrothermal properties as not to be suitable for application of the invention. The different portions of the element have as intimate an interface as possible, in order to obtain the best possihle electrical and thermal conductivity between the metals without having the undesirable interaction of two metals during the premelting time.
Each metal present in the composite should be present in an amount not less than 3% by volume of the entire element body, since otherwise there will not be sufficient present to significantly affect the properties of the composite. It will be apparent that each metal must be present in the form of a separate body or plurality of bodies that will extend through the intend~d melt and arc zone of the fuse element in the direction of flow of the current therethrough~
When two metals are employed in the composite one of them ~ill be of high conductivity and high melting point namely aluminum in the preferred combination, while the other is of low melting point namely cadmium, so that element mel~ing i5 initia~ed at any and all locations along the element which reach the melting temperature of the low melting point constituent starting, of course, at the notches 46.
g _ ~,,,`
~ 3 It is found that a fuse element of the form illustrated by Figure 2 is preferred, in which a high meltiny temperature strip is sandwiched between two low melting temperature strips.
It is also found that there is a preferred ratio of width to thickness of each strip, and this should be about 10:1, and may of course vary between say ~:1 and 12:1. An 80 amp fuse as described above will typically employ 12 helical elements connected in parallel each measuring about 2.5mm by 0.2mm.
The silica sand filler 34 preferably is in the form of approximately spherical ~rains of random size within a given range. These grains preferably are composed of at least 99~
silica and approximately 98~ of the grains are retained on sieve mesh size 100 while approximately 2~ of the grains are retained on sie~e mesh size 30, Approximately 30% of the grains are retained on sieve mesh size 40 while approximately 75~ are retained on sieve mesh size 50. The pellets are identiied as 109 G.S.S~
In the e~ent of the occurrence ofa high magnitude fault current such as many times rated load current, the fusible elements 36-44 melt practically simultaneously at all of their reduced sections 46 to form a chain of arcs. These arcs quickly lengthen and burn back from their roots. The energy of the arc in the form of heat is absorbed by the filler material in the granular form 34. The exchange of energy between the arcs and the filler material is influence~ by the surface area of filler grains which is exposed to the arcs. The ~reater the area of this exposure the more efficient is the exchange of energy.
This factor is facilitated by the use of the filler described and by the fact that the fusible elements are of ribbon -form and that they are arranged as multiple elements rather than as one single element, although the invention in its broader aspects is not limited to a fuse using a plurality of parallel connected fuse elements.
Since the invention is concerned with high voltage currents of 1,000 volts and abov~, it is herein categorized as a high voltage fuse.
A fuse constructed according to this invention is well suited for use in protecting circuits and their connected apparatus such as transformers, capacitors, switchgear and the like. By the invention a fuse is provided which is capable of effective fast acting current limiting action for currents of high magnitude and which also operates reliably for low currents which are but slightly in excess of the normal rated current of the fuse due in part to the fact that the fusible elements may be raised by relatively low fault currents to temperature levels approaching melting without establishing an excessively high overall fuse temperature~
~2~
It will also be noted that the preferred illustrated fuse is of coreless design which is to be preferred~ In addition to their expense, cores are objectionable because contact with the fusible element reduces the area over which energy exchange between the arcs and the filler material can take place. Since the interrupting process requires that most of the arc energy be transferred to latent heat of fusion of the filler material an~ reduction of the area of contact with the filler material is undesirable. Moreover, the areas of contact between the elements and core can produce high temperatures in the core.
The ceramic materials commonly used exhibit marked reduction in their insulating properties at such elevated temperatures.
This reduction in insulating property of the core results in a non-uniform voltage distribution across the fuse in the period following arcing.
Under certain transient current conditions, an appreciable temperature rise in the fuaible elements may occur and may cause a de~ormation of the fusible elements. Repeated heating and cooling cycles may impose increasing tensile load on the fusible elements since they may not straight~n out due to construction of the sand. If movement of the elements is possible, as in a coreless construction~ thls tension may be relieved. In elements wound on a core, the opportunity for relieving tension is severely restricted and mechanical failure due to this increased tension may occur, since the increases may be sufficient to break the fusible element, particularly at the reduced cross section notches.
Claims (7)
1. An electric fuse for use in circuits of at least 1000 volts and of the current limiting type comprising:
a tubular housing of insulating material;
two spaced terminals mounted on said housing for connection of the fuse in an electric circuit;
at least one metal fuse element mounted within the housing with the two ends of each element connected respectively to the said two terminals to form a respective conducting path therebetween;
each fuse element being embedded in and surrounded by silica sand disposed within the housing;
characterized in that:
each fuse element comprises a cadmium portion and an aluminum portion, each of which provides a corresponding continuous current carrying path between the said terminals, each metal being present in the fuse element in an amount not less than 3% by volume of the total;
the said portions being bonded to one another at adjoining contacting surfaces to constitute a composite metal element wherein the cadmium portion due to its lower melting point will melt before the aluminum portion to increase the current density through the unmelted aluminum portion,
a tubular housing of insulating material;
two spaced terminals mounted on said housing for connection of the fuse in an electric circuit;
at least one metal fuse element mounted within the housing with the two ends of each element connected respectively to the said two terminals to form a respective conducting path therebetween;
each fuse element being embedded in and surrounded by silica sand disposed within the housing;
characterized in that:
each fuse element comprises a cadmium portion and an aluminum portion, each of which provides a corresponding continuous current carrying path between the said terminals, each metal being present in the fuse element in an amount not less than 3% by volume of the total;
the said portions being bonded to one another at adjoining contacting surfaces to constitute a composite metal element wherein the cadmium portion due to its lower melting point will melt before the aluminum portion to increase the current density through the unmelted aluminum portion,
2. An electric fuse as claimed in claim 1, characterized in that each fuse element portion is in the form of a single thin flat strip having two wider faces and two narrower faces, and each strip has at least one wider face adjoining and contacting a wider face of the immediately adjacent strip.
3. An electric fuse as claimed in claim 2 characterized in that each fuse element portion is in the form of a plurality of thin flat strips, each strip having two wider faces and two narrower faces, and each strip has at least one wider face adjoining and contacting a wider face of the immediately adjacent strip, which is of a different metal.
4. An electric fuse as claimed in claim 2 or 3, characterized in that the width to thickness ratio of each strip is in the range 8:1 to 12:1.
5. An electric fuse as claimed in claim 1, characterized in that the aluminum portion is in the form of at least one wire or rod, and the cadmium portion surrounds the said at least one wire or rod and encloses it or them.
6. An electric fuse as claimed in any one of claims 1 to 3, characterized in that each fuse element is provided along its length with a plurality of spaced notches to provide respective sites of increased current density and consequent increased temperature.
7. An electric fuse as claimed in any one of claims 1 to 3, characterized by a plurality of coaxial helical metal fuse elements each connected respectively to the said two terminals so as to be in parallel with one another.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US2238179A | 1979-03-21 | 1979-03-21 | |
| US22,381 | 1979-03-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1128100A true CA1128100A (en) | 1982-07-20 |
Family
ID=21809303
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA348,240A Expired CA1128100A (en) | 1979-03-21 | 1980-03-20 | Electric fuses employing composite metal fuse elements |
Country Status (7)
| Country | Link |
|---|---|
| EP (1) | EP0016467A1 (en) |
| JP (1) | JPS55159537A (en) |
| AU (1) | AU533549B2 (en) |
| BR (1) | BR8001683A (en) |
| CA (1) | CA1128100A (en) |
| MX (1) | MX147542A (en) |
| ZA (1) | ZA801645B (en) |
Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6267445U (en) * | 1985-10-17 | 1987-04-27 | ||
| DE3909302A1 (en) * | 1988-03-23 | 1989-10-12 | Yazaki Corp | FUSE PROTECTION AND METHOD FOR PRODUCING THE SAME |
| US5099218A (en) * | 1990-12-07 | 1992-03-24 | Avx Corporation | Binary fuse device |
| DE10022241A1 (en) * | 2000-05-08 | 2001-11-15 | Abb Research Ltd | Melt conductor used in electronic devices to prevent overload currents comprises strip made from electrically conducting fusible conductor material and having doping site at which conductor material is displaced |
| JP3990169B2 (en) * | 2002-03-06 | 2007-10-10 | 内橋エステック株式会社 | Alloy type temperature fuse |
| GB0519489D0 (en) * | 2005-09-23 | 2005-11-02 | Yazaki Europe Ltd | A fuse |
| DE102006009236A1 (en) * | 2006-02-28 | 2007-09-06 | Infineon Technologies Ag | Device and method for temperature-interrupting protection of an electrical component |
| CN102543612B (en) * | 2012-01-13 | 2014-10-29 | 东莞市贝特电子科技有限公司 | Fuse wire, device for manufacturing fuse wire and manufacturing method of fuse wire |
| JP6336240B2 (en) * | 2012-12-28 | 2018-06-06 | Ｌｉｔｔｅｌｆｕｓｅジャパン合同会社 | Protective element |
| CN104347312A (en) * | 2013-07-29 | 2015-02-11 | 泰科电子日本合同会社 | Protective element |
| US10978267B2 (en) * | 2016-06-20 | 2021-04-13 | Eaton Intelligent Power Limited | High voltage power fuse including fatigue resistant fuse element and methods of making the same |
| JP7002955B2 (en) * | 2017-02-28 | 2022-01-20 | デクセリアルズ株式会社 | Fuse element |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR445270A (en) * | 1911-06-26 | 1912-11-07 | Vernon Hope | Fuse circuit breaker to control electric currents |
| DE624633C (en) * | 1933-06-11 | 1936-01-27 | Siemens Schuckertwerke Akt Ges | Process for the production of closed, short-circuit-proof and overcurrent-carrying fuses |
| DE664793C (en) * | 1936-03-04 | 1938-09-12 | Schiele Industriewerke Inhaber | Fusible link for electrical fuses |
| DE717681C (en) * | 1938-04-06 | 1942-02-19 | Wickmann Werke Ag | Overcurrent carrier glass cartridge fuse |
| US3268691A (en) * | 1963-07-22 | 1966-08-23 | Mc Graw Edison Co | Protectors for electric circuits |
| DE1563785C3 (en) * | 1966-12-15 | 1978-10-05 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Fusible link for slow fuse links |
| US3810062A (en) * | 1972-05-04 | 1974-05-07 | Chase Shawmut Co | High-voltage fuse having full range clearing ability |
| JPS5430089B2 (en) * | 1972-12-26 | 1979-09-28 | ||
| DE2551627A1 (en) * | 1975-11-18 | 1977-06-02 | Borchart Hans F Dipl Ing | Fusible conductor for inertial fuses - uses specified layer for separating conductor from alloying metal components |
-
1980
- 1980-03-20 CA CA348,240A patent/CA1128100A/en not_active Expired
- 1980-03-20 MX MX181664A patent/MX147542A/en unknown
- 1980-03-21 JP JP3600580A patent/JPS55159537A/en active Pending
- 1980-03-21 AU AU56714/80A patent/AU533549B2/en not_active Ceased
- 1980-03-21 ZA ZA00801645A patent/ZA801645B/en unknown
- 1980-03-21 EP EP80101485A patent/EP0016467A1/en not_active Ceased
- 1980-03-21 BR BR8001683A patent/BR8001683A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| BR8001683A (en) | 1980-11-18 |
| AU5671480A (en) | 1980-09-25 |
| EP0016467A1 (en) | 1980-10-01 |
| ZA801645B (en) | 1981-09-30 |
| MX147542A (en) | 1982-12-13 |
| AU533549B2 (en) | 1983-12-01 |
| JPS55159537A (en) | 1980-12-11 |
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Legal Events
| Date | Code | Title | Description |
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| MKEX | Expiry |