Patent Application
20150083558
The present invention relates generally to electrical contacts, and more particularly to electrical contacts for electrical interconnection devices such as circuit breakers, contactors, or switches.
Electrical interconnection devices such as circuit breakers are used in certain electrical systems for protecting an electrical circuit coupled to an electrical power supply. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow.
Circuit breakers may be conventional mechanical-type circuit breakers or electronic circuit breakers. One type of electronic circuit breaker is a ground fault circuit interrupter (GFCI). GFCIs are utilized in electrical systems to prevent electrical shock hazards, and are typically included in electrical circuits adjacent to water, such as in residential bathrooms or kitchens. Another type of electrical circuit breaker is an arc fault circuit interrupter (AFCI). AFCIs interrupt power to an electrical circuit when an arcing situation is detected within the circuit. Conventional mechanical and electronic circuit breakers (e.g., GFCIs and AFCIs) include tripping mechanisms that may include electrical contacts.
The electrical contacts generally carry the load current without excessive heating, and also withstand the heat of any arc produced when interrupting (opening) the connected circuit or branch. Service life of the contacts can be limited by the erosion of contact material due to arcing while interrupting the current. Further, during a current overload condition, arcing may occur which may result in degradation of contact welding or other degradation.
Accordingly, there is a long-felt and unmet need for electrical contacts having improved performance.
According to first embodiment, an electrical contact apparatus is provided. The electrical contact apparatus includes a first element of a first material having one or more apertures, and a second element of a second material positioned within at least one aperture of the one or more aperture, wherein the second material is different from the first material.
In an assembly embodiment, a circuit interconnect device is provided. The circuit interconnect device including a first element of a first material, the first element having one or more aperture, and a second element of a second material, the second element positioned in at least one aperture of the one or more aperture, wherein the second material is different from the first material, and the first element and the second element are attached onto a metallic support or a conductor.
In a method embodiment, a method for preparation of an electrical contact is provided. The method includes providing a first element, of a first material having a composition of silver having a range of about 40% to about 60%, the first element having one or more aperture, providing a second element of a second material having a composition of silver having a range of about 70% or more; inserting the second element into at least one aperture of the one or more aperture of the first element; and attaching the first element and the second element to at least one conductor.
Still other aspects, features, and advantages of embodiments of the present invention may be readily apparent from the following detailed description by illustrating a number of example embodiments and implementations. The present disclosed subject matter may also be capable of other and different embodiments, and its several details may be modified in various respects, all without departing from the scope of the present disclosed subject matter. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. The drawings are not necessarily drawn to scale. Like numerals are used throughout to denote like elements. The disclosed subject matter is to cover all modifications, equivalents, and alternatives falling within the scope of the disclosed subject matter.
The present invention relates to the field of electrical contacts. It relates more specifically to devices, methods, and assemblies related to electrical contacts including contact materials and its manufacturing process.
In some embodiments, the electrical contact can be incorporated into a group consisting of at least one type of circuit interconnect device, at least one type of circuit breaker, at least one type of switch or at least one type of other non-circuit breaker devices. The electrical contacts may be referred to as contacts, contact assemblies, and the like.
For example, electrical contacts may be adapted for the production of low voltage electrical contacts, such as electrical contacts whose normal operating range lies approximately between about 10 volts and about 1000 volts and between about 1 ampere and about 5,000 amperes. Such electrical contacts are generally used in the domestic and industrial industries, for circuit interconnection devices such as switches, relays, contactors, circuit breakers and other interconnection devices used to make/break electrical circuits.
The electrical contact embodiments may be adapted for residential applications, industrial applications or other applications. For example, residential circuit breaker applications can have a current range from 10 A to 250 A with a rating voltage range from 120V to 240V. Industrial circuit breakers can have a current range from 15 A up to 6000 A with a voltage rating from 240V up to 1000V. It is possible the electrical contacts may be adapted for electrical interconnection devices such as a circuit breaker for: (1) low voltage circuit breakers with less than 600 volts; (2) medium voltage circuit breakers with greater than 2.4 kv to less than 69 kv; (3) extra high voltage circuit breakers that are greater than 34 kV.
When a pair of electrical contacts is under voltage open, current may continue to flow from one electrical contact to the other, ionizing the gas through which it passes. This column of ionized gas, usually called an “electric arc,” has a maximum length that depends on various parameters such as the nature and the pressure of the gas, the voltage across the terminals, the contact material, the geometry of the equipment, the impedance of the circuit, etc.
It is contemplated that the electrical contact may be used in an interconnection device like a circuit breaker that employs a pair of mating contacts which establish a current path there between during normal operation of the circuit into which the breaker is installed. Wherein one of the contacts is a movable contact (e.g. circuit breaker arm) connected to an end of an elongated rotatable blade, while the other contact can be a stationary contact attached to a fixed metallic support or conductor.
The amount of energy released by the electric arc is sufficient, in some instances, to melt the constituent material of the contacts, which not only results in degradation of the metallic parts but also may sometimes result in the electrical contacts being welded together, with the consequence of locking the equipment.
In AC applications, arc cut-off is facilitated by the applied current passing through zero. However, certain protection devices cut off very high currents, resulting in arcs of sufficient energy to damage the contacts.
Thus, it may be desirable that the material properties of electrical contacts meet several specifications for use in oxidizing atmospheres and/or where severe arcing is anticipated. Example specifications include low contact resistance in order to avoid excessive heating when the current is flowing, good resistance to welding in the presence of an electric arc, and/or low erosion under the effect of the arc. Other material property specifications for electrical contacts may include acceptable mechanical and/or electrical wear properties. Mechanical wear properties can include wear with no load current such as loss of material due to sliding friction, and/or mechanical wear with load current. Electrical wear properties can be wearing due to electrical arcing under repeated applied stress and effect of electrical current. Meeting these desired requirements has been elusive.
To provide suitable material properties, in one or more embodiments, an electrical contact device/apparatus is provided that includes a first element of a first material having one or more aperture, and a second element of a second material, the second element positioned within at least one aperture of the one or more aperture, wherein the second material is different from the first material. Specifically, the first element could be considered an outer region arranged to surround the second element (or inner region), such that the second element occupies a hole or aperture located in a center region of the first element. However, many different shapes and orientations of the first element of the first material in relation to the second element of the second material are contemplated. For example, the donut-like configuration described herein is only provided as one example.
Further, the shape of at least one aperture of the one or more apertures of the first element could be one of the same or a different shape from the first element. Specifically this means, it is possible the first element could have the same or a different shape than the second element. Further, the second element would have an approximate similar shape as the at least one aperture of the first element.
Further still, the shape of the first element and at least one aperture of the one or more apertures of the first element can be one of a geometric shape, a non-uniform shape or a uniform shape. Further, it is possible that the second element could have one of a geometric shape, a non-uniform shape, or a uniform shape, so that the second element shape corresponds to the at least one aperture of the one or more aperture of the first element.
According to embodiments, the first element of the first material may possess material properties having superior mechanical and electrical wear properties. For example, material properties such as a low coefficient of thermal expansion, a high melting point, and/or a high tensile strength may be provided. Other beneficial material properties may include a low vapor pressure property, and/or a high density property, as well as a suitable hardness under standard operating conditions. For example, the first material can have one or more physical properties from the group consisting of one of a thermal conductivity range of 109 to 419 W/m·° K, a temperature coefficient electrical resistance range of 0.0014 to 0.0041/° K or an electrical resistivity range of 1.7 to 5.5 μΩ·cm.
By non-limiting example, the first material may be a material having a composition of Tungsten (W) and silver (Ag). For example, in some embodiments the composition may include about 50% tungsten and about 50% silver. Tungsten possesses material properties including superior mechanical and electrical wear properties. For example, Tungsten's material properties include: a relatively low coefficient of thermal expansion; a relatively high melting point (3,422° C., 6,192° F.); and a relatively high tensile strength. Tungsten's other material properties include having a relatively low vapor pressure (at temperatures above 1,650° C., 3,000 F), a very high density (a density of 19.3 times that of water) as well as being a hard metal under standard operating conditions. However, other materials other than tungsten are contemplated such as nickel.
Silver has a relatively high electrical conductivity material property, along with other beneficial material properties. It is noted that during operation, the tungsten-silver composition maintains superior mechanical and electrical wear properties when hot. It is possible the first material may have a composition of any silver or copper alloy, e.g. silver refractory metals, copper refractory metals, silver metal oxides, etc.).
The second material may possess material properties including superior electrical conductivity properties. Other beneficial material properties may include having relatively high thermal conductivity properties and/or relatively low contact resistance properties. For example, the second material can have one or more physical properties from the group consisting of one of a thermal conductivity range of 140 to 370 W/m·° K, a temperature coefficient electrical resistance range of 0.0014 to 0.0036/° K or an electrical resistivity range of 2.0 to 5.0 μΩ·cm.
By non-limiting example, the second material may have a composition including Silver (Ag) with graphite (C) material. Possible compositions of the second material may include a range of one of 70% to 98% silver, 85% to 98% silver or 92% to 98% silver, wherein another material may be included in the composition such as graphite. For example, one suitable composition may include 95% or more silver with at least a portion of graphite (or some other material having similar graphite properties). It is noted such mixtures provide relatively low resistivity material properties during operation. Further, the composition, when hot, typically becomes soft, wherein the first material, i.e., Tungsten-Silver composition, may provide support for the second material during operation. All percentages (%) herein are weight percentages.
Other types of materials considered for the second element can include any type of silver refractory contact materials including 60% Ag-40% W, three phase refractory contact 70% Ag-27% WC-3% C; Silver metal oxide contact materials in example AgCd10 (80% Ag-10% Cd), AgSnO2 8 along other Silver metal oxide contacts. Further, it is possible other types of materials considered for the second material may include any silver or copper alloy, e g. silver refractory metals, copper refractory metals, silver metal oxides, etc.).
In determining material compositions for the first element and the second element, at least one relevant consideration may include capillary action during melting of two or more materials during arcing, which may provide a wetting activity that maintains lower resistivity on the contact surface. For example, as noted above the first element may have a tungsten-silver composition, which tends to get hot during operation, it still provides superior mechanical and electrical wear properties. At least one benefit provided by the tungsten-silver composition is that it ensures suitable structure for supporting the silver-graphite second material, since the silver-graphite composition tends to get soft when hot during operation.
In some embodiments, the blending of materials as disclosed above may provide blended material properties that may not be provided from a single material. Additionally, in some embodiments, matching (or possibly fusion of) different material types can create a device that addresses unique performance properties such as superior mechanical and/or electrical wear properties or conductivity properties during operation. Specifically, using different material compositions for the first element and the second element can together provide desired performance attributes when used in arcing electrical applications (opening/closing) of an electrical circuit. Further, it is intended that the composition of the first element with that of the composition of the second element will perform differently under such conditions. It is noted that the electrical contacts may wear to a degree, but not to the point of not being able to provide electrical contact operation.
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While the disclosed subject matter is susceptible to various modifications and alternative forms, specific embodiments and methods thereof have been shown by way of example in the drawings and are described in detail herein. It should be understood, however, that it is not intended to limit the disclosed subject matter to the particular apparatus, systems or methods disclosed, but, to the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the scope of the disclosed subject matter.
