Claims:WE CLAIM:

1. A fuse system comprising:
a fuse link element axially placed inside an insulating and thermally conductive fuse body, wherein said fuse body is filled with a mixture of dehumidified quartz sand and a pulverized homopolymer in a definite proportion to extinguish arc;
wherein, said fuse body includes axially placed constrictions of reduced cross sectional area such that number of constrictions pairs indicate voltage handling capacity of said fuse-link element.
2. The fuse system as claimed in claim 1, wherein said fuse link element is electrically connected to a rectangular shaped conductive fuse knife made of copper or brass or any combinations thereof.
3. The fuse system as claimed in claim 1, wherein said fuse link element is centrally placed to the width of the fuse body.

4. The fuse system as claimed in claim 1, wherein an insulating thin polymer sheet liner is placed housing the inner wall of the fuse body.

5. The fuse system as claimed in claim 1, wherein an alloy of low melting point 180-200° C is thermally guided over said fuse element at a distinct location by a tooled fixture.

6. A current limiting fuse link assembly axially placed inside an insulating and thermally conductive fuse body, wherein said fuse body is filled with a mixture of dehumidified quartz sand and a pulverized homopolymer in a definite proportion to extinguish arc;
wherein, said fuse body includes axially placed constrictions of reduced cross sectional area such that number of constrictions pairs indicate voltage handling capacity of said fuse-link element.

Dated this 31st day of March 2018

Abhishek Sen
Of S. Majumdar & Co.
(Applicant’s Agent)

, Description:
TECHNICAL FIELD
[001] The present subject matter described herein, in general, relates to improvements in protectors for electric circuits. More particularly, this invention relates to improvements in electric fuses with fast interrupting fuse element which are used to protect relatively-high voltage circuits during short circuit and overload faults.

BACKGROUND
[002] The integral part of the electrical fuse system is the element. The element may be designed to perform both during short circuit and overload faults. These fuse elements can comprise of wires or metal strips with notches. These are either installed single or in multiple numbers in the fuse-link depending on the current carrying capacity of the fuse-link. The performance depends on the physical parameters of the element such as raw material, notch profile, element geometry etc. Notches are of vital importance for fuse characteristics. The vicinity of these circular notches to the low melting solder makes it beneficial for fast interruption of fault current.

[003] Reference is made to US3460086A, which discloses Fuse-links with relatively-high voltage fuse are provided with short casing which in which the arc-extinguishing filler material is amorphous material calcium sulfate. The positioning of the imperforate barriers of insulation adjacent the inner faces of the terminals of the electric fuse will keep arc plasma from extending between those terminals when the fusible element fuses.

[004] Reference is further made to US3601737A, which discloses fuse-link consisting of silicon rubber arc constricting structure encapsulating certain portions of the link having reduced cross-sectional areas. By confining and constructing the arc within the structure, the chance of creation of deleterious shunt current paths is minimized. The method disclosed encompasses flowing a still vicious room temperature vulcanized silicon rubber over a reduced portion of the fuse link to encapsulate the portion.

[005] Reference is still made to US3529270A, which discloses that the casing of an electric fuse having a high interrupting capacity and a small current rating is filled with quartz sand and provided with a fusible element in the form of a cadmium wire having ends that are conductively connected by soft solder joints to the terminal caps closing the casing of the fuse. An additional heat sink is operatively related to each of said pair of caps.

[006] Reference is further made to US3810062A, which discloses melamine with inorganic filler is used to achieve full breaking capacity in high voltage of 15 kV. Mandrels may be made of an inorganic or ceramic material, or of an organic material. There is no mandrel material in existence that is not adversely affected by the prolonged heating periods of overload currents.

[007] Reference is also made to US3979709B1, which discloses a casing of synthetic-resin-glass-cloth laminate housing said fusible element and said arc-quenching means, and a pair of terminal elements arranged at the ends of said casing and conductively interconnected by said fusible element.

[008] However, none of the existing fuse system utilizes a filler comprises of homogenous mixture of two insulating material so as to achieve a reduced total arcing time.

[009] Thus, there exists a dire need for an improved design of the fuse link element that can meet increased voltage requirement with same length of the element strip (L). The current-limiting action of these fuses commences as the small series of arc is generated opposite to the source voltage, which forces the fault current to zero. These current limiting fuse links can interrupt current at a value significantly lower than the actual peak.

SUMMARY OF THE INVENTION

[0010] The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

[0011] An objective of the present invention is to provide an improved design of the fuse link element which limits the arc voltage within the acceptable range.

[0012] Another objective of the present invention is to provide a fuse element in alliance with the quartz sand (filler) such that the properties of increased rated voltage and reduced arcing time can be achieved.

[0013] Accordingly to one aspect, the present invention provide a fuse system comprising: a current limiting fuse link element axially placed inside an insulating and thermally conductive fuse body, wherein said fuse body is filled with a mixture of dehumidified quartz sand and a pulverized homopolymer in a definite proportion to extinguish arc; wherein, said fuse body includes axially placed constrictions of reduced cross sectional area such that number of constrictions pairs indicate voltage handling capacity of said fuse-link element.

[0014] In another aspect, there is provided a current limiting fuse link assembly axially placed inside an insulating and thermally conductive fuse body, wherein said fuse body is filled with a mixture of dehumidified quartz sand and a pulverized homopolymer in a definite proportion to extinguish arc; wherein, said fuse body includes axially placed constrictions of reduced cross sectional area such that number of constrictions pairs indicate voltage handling capacity of said fuse-link element.

[0015] Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:

[0016] Figure 1 illustrates the assembly of fuse element with the fuse knife surrounded by the arc quenching medium, according to one implementation of the present invention.

[0017] Figure 2 shows the perspective view of the fuse-link assembly, according to one implementation of the present invention.

[0018] Figure 3 shows the longitudinal sectional view of the fuse-link, according to one implementation of the present invention..

[0019] Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0020] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

[0021] Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

[0022] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

[0023] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0024] By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

[0025] Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

[0026] It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0027] It is also to be understood that the term “module” is used in the specification to indicate an apparatus, unit, component and the like. The term “means” when used in the specification is taken to specify the mode by which desired result is achieved.

[0028] The present invention provides the innovative design of the fuse element in alliance with the quartz sand (filler) such that the properties of increased rated voltage and reduced arcing time can be achieved. The ability of the fuse to clear the fault depends on various parameters such as thermal conductivity of fuse ceramic body, thermal properties of filler, electro-mechanical properties of the element etc. The proposed number of notches and the distance between them are calculated to achieve desired fuse performance. The raw material properties of the element are predefined such as high conductivity copper. The centralized zone which accommodates the M-effect solder in continuance with the notches is significant to ensure overload performance.

[0029] The invention comprises of the below mentioned components/assembly:
• Fuse-link Element
• Filler
• Insulating Liner

[0030] In one implementation, reference is made to figure 1 which shows the functional orientation of the fuse link element with the fuse knife surrounded by the arc quenching medium.

[0031] In one implementation, reference is made to figure 2 which shows the perspective view of the fuse-link element.

[0032] In one implementation, reference is made to figure 3 which shows the sectional view of the fuse-link element.

[0033] In the implementation, the illustration in figure 1 and 2 represents the fuse element assembly where the fuse link element (1) is electrically connected to the rectangular shaped conductive fuse knife (4) made of either copper or brass. This fuse link element (1) is axially placed inside the highly insulating and thermally conductive fuse body (5). This ceramic fuse body (5) en-capsules the assembly of the conductive parts. This fuse body is filled with a mixture of dehumidified quartz sand and a pulverized homopolymer (3) in a definite proportion to extinguish arc. The element (1) is placed centrally to the width of the fuse body (5). The insulating thin polymer sheet liner (6) is placed housing the inner wall of the fuse body (5).

[0034] In the implementation, the axially placed constrictions (7) of reduced cross sectional area are designed such that number of constrictions (7) pairs indicate voltage handling capacity of the fuse-link. Every junction of the pair of notches or constrictions (7) act as area of reduced cross section for the element (1). For the sake of simplicity only one element is illustrated in the invention. The fuse characteristics are determined by profile of the constrictions (7) and their placement with respect to each other. These constrictions are of vital importance to the fuse performance. An alloy (2) of low melting point approximately 180-200° C is thermally guided over the element at a distinct location by a tooled fixture.

[0035] In the implementation, the current limiting fuse-link (1) is adapted to reduce let through energy generated by arc extinction. The let through energy generated between the commencement and extinction of the fault current in the system is important for the protection of power system. The important parameters of fuse arc are; profile of the fuse element (1), grain size and packaging density of the filler (3) and dimensions of the fuse body (5). However, this invention is entitled to the first two. This is attained in the illustration by embodying the fuse element in filler comprising of a homogeneous mixture of quartz silica sand and a homopolymer (3). This influences the pre-arcing period of the fuse performance through radial conduction thereby reducing the let through energy of the fuse-link corresponding to the given current rating.

[0036] In one implementation, arc is initiated once the current exceeds the minimum fusing current. Thus under an overload fault, the low melting M-effect alloy (2) near the central constrictions is first heated and melts subsequently as the alloying process commences. This results into generation of one or more series of arcs. The temperature gradient rises generously and the exothermic reaction melts the homopolymer and the M-effect solder (2). This generates a greater volume of molten plasma around the necks. The central zone with considerably closer constrictions localizes the fusing action and the length of the arc (improved arc voltage) increases gradually until the necks/ constrictions break forming a solid glassy material called as fulgurite.

[0037] In one implementation, the pre-arcing behavior is demonstrated by the time current characteristics of the fuse-link. The quartz silica filling can hold small volume of unfilled air, which increases the total arcing time. To avoid this, pulverized homopolymer is mixed with quartz sand to enable safe interruption of fault and avoids prolong arcing period. This homopolymer has the melting point similar to the M-effect solder (2). These granular substances have been chosen for two reasons. One, electric field created by these granular arc quenching medium is greater than liquid, sheet or air gaps. Secondly, they provide ease of usage and storage. The conductivity of quartz sand (3) increases at high temperatures and it also aids in damping the recovery voltage post arcing. . This invention advances over the previous art as it ensures consistency in performance with the homogeneous mixture of filler and the specified neck profile. This fuse-link is economical to manufacture.

[0038] In one implementation, during short circuit fault, the arc extends through the length of the fuse element (1) and the instantaneous axial electric field column is built as the element erodes. The arc pressure is built inside the fuse body (5) and the arc energy is dissipated through thermally conductive surrounding components. During this process the arc energy supplies the latent heat required for fusion of the filler (3). The filler (3) melts as the energy is lost into the fuse body (5) radically from the rectangular arc column formed. Further, adding to the resistance of the arc column so generated. Hence, this invention offers an improved insulation to the system. This results in melting and vaporization of the surrounding fuse element (1) which condenses with the silica filler (3). While molten plasma column is small all the energy is transferred to the filler such that the fulgurite expands. The arc energy and the axial arc field decreases slowly and remains almost constant depending on the grain size of the filler which has been carefully evaluated and materialized. The air gaps are filled with homopolymer hence fluctuations in axial electric fields are minimized. The un-melted filler (3) conducts the heat to the fuse body (5). The fuse body has excellent insulation properties, is non-absorbent and noninflammable. The ceramic fuse body (5) confines the arc energy resulting into high arc current density. Also the mechanical and thermal benefits of the fuse body (5) helps in holding the arc pressure build during fault generation. The mechanical strength of the end plates also aids in decreasing the strain developed into the assembly.

[0039] In one implementation, during fulgurite formation the molten plasma (mixture of sand granules and molten metal) will exert pressure on the walls of the fuse body (5). The fulgurite column formed by confined compression of silica sand is also influenced by the grain size and the packing density of the un-melted filler (3). Once the arc is extinguished the post arc current following through the fuse-link depends greatly on the length, cross-section and conductivity of the fulgurite. Hence, in this invention the insulation resistance has increased as compared to that with the use of standard filler.

[0040] In one implementation, the cross-section of the fuse element (1) is maximized to obtain fast interrupting characteristics via theoretical prediction. However, experimental values received are even lower than the theoretical ones. During arc quenching the erosion of the element various width of the elements is evaluated obtaining an optimized dimension.

[0041] Some of the non-limiting advantages of the present invention, are mentioned below:
• The present invention uniquely brings a combination of homogeneous filler, element with particularly spaced constrictions and distinctive liner that meets the performance requirements.
• Reduced total arcing time as additional element of homopolymer in filler is introduced.
• Reduced let through energy.
• Usage of same tool for manufacturing fuse elements by making minor arrangement in the same tool.
• Up gradation in technology for arc extinction instead of usage of traditional filler.
• Low inventory costs, usage of fuse body from the existing range of fuse-links.
• The performance can be evaluated using a combination of liner made of non-combustible material. The purpose of this liner is to prevent the arc flashes from reaching the housing.

[0042] Although a fuse system and an element thereof have been described in language specific to structural features and/or methods, it is to be understood that the embodiments disclosed in the above section are not necessarily limited to the specific features or methods or devices described. Rather, the specific features are disclosed as examples of implementations of the fuse system and an element thereof.