Electrical circuit breaker with thermally enhanced conductor and method of producing the same

Abstract

An electrical circuit breaker (1) for a high-voltage system comprises an electrical conductor having a conductor body (2, 3) with a first surface portion. The first surface portion has a surface roughness obtainable by abrasive blasting, shot peening, knurling and / or anodization, and is painted or dyed darker, or painted in a color within a HSB colorspace having a hue of 0–360 degrees, a saturation of 0–20%, and a brightness of 0–40%. The circuit breaker (1) further comprises a housing (4) containing a gas comprising at least 80% by volume of CO₂. A method of producing such a circuit breaker comprises providing the conductor body (2, 3), enlarging the surface area of the first surface portion by increasing its surface roughness, painting or dyeing the first surface portion darker, and filling the housing (4) with a gas comprising at least 80% by volume of CO₂.

Description

[0001] PS56305PC00

[0002] 1

[0003] ELECTRICAL CIRCUIT BREAKER WITH THERMALLY ENHANCED CONDUCTOR AND METHOD OF PRODUCING THE SAME

[0004] TECHNICAL FIELD

[0005] The present invention relates to electrical conductors in an electrical circuit breaker for use in a high-voltage system. Specifically, the present invention relates to temperature management of the electrical conductors.

[0006] BACKGROUND OF THE INVENTION

[0007] Electrical circuit breakers, such as live tank circuit breakers and dead tank circuit breakers, comprise electrical conductors. In high-voltage systems, some circuit breakers remain closed for long periods of time, thus conducting electrical current. As electrical current flows through the closed circuit breaker, a temperature of electrical conductors of the circuit breaker may rise. Regulations may specify maximum temperatures for such circuit breakers, which in turn affects their dimensioning to enable them to handle a design current without overheating. Higher design current typically requires a larger circuit breaker. At the same time, it may be advantageous to keep the size of such circuit breakers small. Accordingly, it would be advantageous to provide a circuit breaker which can be made smaller without overheating, i.e. without getting hotter than the regulatory maximum temperature for a specific design load (electrical current).

[0008] SUMMARY OF THE INVENTION

[0009] According to a first aspect, these and other objects are achieved by a circuit breaker as defined in claim 1, with alternative embodiments defined in dependent claims.

[0010] The electrical circuit breaker is suitable for a high-voltage system. The electrical circuit breaker comprises an electrical conductor comprising a conductor body comprising a first surface portion. The first surface portion has a surface roughness obtainable by abrasive blasting, shot peening, knurling and / or anodization.

[0011] A surface roughness obtained by abrasive blasting, shot peening, knurling or anodization is increased as compared to if the surface area would have been smooth, such as polished, machined with cutting tools, extruded or molded. Larger surface area promotes greater radiation of heat and greater convection. The first surface portion thus enables increased radiation of heat without requiring an increase of size of the conductor body. Anodization increases the emissivity of the conductor metal.

[0012] The first surface portion is painted or dyed darker, or painted with a color within a HSB colorspace having a hue of 0-360 degrees, a saturation of 0-20%, and a brightness of 0-40%, as determined by a spectrophotometer using CIE Standard llluminant D65 and the CIE 1964 10° Standard Observer. This HSB range defines objectively dark colors — low saturation combined with low brightness corresponds to colors that are near-neutral and dark, approaching black. Such colorsPS56305PC00

[0013] 2

[0014] exhibit high emissivity, meaning the surface radiates thermal energy more efficiently, thereby reducing the operating temperature of the electrical conductor.

[0015] The electrical circuit breaker further comprises a circuit breaker housing containing a gas comprising at least 80% by volume of CO2. CO2provides electrical insulation within the housing. The painting or dyeing is used to darken the first surface portion and thus improves heat emissivity of the first surface portion.

[0016] A remainder of the volume except for the portion of CO2of the gas comprises at least 90% by volume of O2.

[0017] The circuit breaker may be a live tank circuit breaker. In a live tank circuit breaker thermal management of the electrical conductors is particularly important. The thermally enhanced conductor surface described herein is therefore especially beneficial in this configuration.

[0018] A color used for said painting may be black. Additionally, or alternatively, an emissivity of at least the first surface portion may be in the range of 0.5-1.

[0019] Black color is dark and thus enables improved heat radiation properties of the electrical conductor. Emissivity of at least the first surface portion in the range of 0.5-1 provides for good heat emission.

[0020] The material of the electrical conductor body may comprise aluminum, an aluminum alloy, copper or a copper alloy.

[0021] Aluminum and copper are very good electrical conductors, thus providing low electrical resistance and a low generation of heat such that overheating is mitigated.

[0022] A second aspect of the invention relates to a method of producing an electrical circuit breaker for a high-voltage system, said method comprising:

[0023] providing a conductor body for an electrical conductor of the electrical circuit breaker, and enlarging the surface area of at least a first surface portion of the conductor body by increasing a surface roughness of at least said first surface portion of the conductor body.

[0024] To increase surface roughness is an easy and inexpensive way of increasing the surface area of the conductor body without increasing the size of the conductor body. Larger surface area promotes greater radiation of heat and greater convection.

[0025] The surface roughness is increased by shot peening, abrasive blasting, knurling and / or anodization.

[0026] Shot peening, abrasive blasting and knurling are readily available technologies for roughening the surface of the conductor body at low cost.

[0027] The method further comprises painting darker, or dyeing darker, at least a first surface portion of the conductor body. The method further comprises filling a circuit breaker housing of the electrical circuit breaker with a gas comprising at least 80% by volume of CO2.

[0028] The painting or dyeing darkens the first surface portion and thus improves heat emissivity of the first surface portion. Where painting is used, the color may be defined within a HSB colorspace having a hue of 0-360 degrees, a saturation of 0-20%, and a brightness of 0-40%, as determinedPS56305PC00

[0029] 3

[0030] by a spectrophotometer using CIE Standard llluminant D65 and the CIE 196410° Standard Observer. This HSB range defines objectively dark colors — low saturation combined with low brightness corresponds to colors that are near-neutral and dark, approaching black. Such colors exhibit high emissivity, meaning the surface radiates thermal energy more efficiently, thereby reducing the operating temperature of the electrical conductor.

[0031] A remainder of the volume except for the portion of CO2of the gas may comprise at least 90% by volume of O2. The presence of O2in this proportion supports the thermal performance of the gas mixture, contributing to a well-defined and consistent gas composition within the housing.

[0032] Said provision of the conductor body may comprise molding or extruding material to form the conductor body.

[0033] Molding or extruding the material provides a repeatable surface quality, suitable for roughening to a predetermined roughness.

[0034] The material molded or extruded may be aluminum, an aluminum alloy, copper or a copper alloy. Aluminum and copper are very good electrical conductors, providing low electrical resistance and thus low heat generation, which mitigates the risk of overheating. These materials are also well-suited to surface roughening processes such as abrasive blasting and anodization.

[0035] BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Fig. 1 shows a cross-sectional view of an electrical circuit breaker according to a first embodiment.

[0037] DETAILED DESCRIPTION

[0038] The present invention will hereinafter be described with reference to the appended figure. As shown in Fig. 1, the electrical circuit breaker 1 comprises at least a first conductor body 2, a second conductor body 3, and a circuit breaker housing 4. At least one of the first conductor body 2 and the second conductor body 3 is movable such that they can be brought into physical contact with each other, i.e. to make electrical contact, and such that they can be moved apart to break electrical contact. The electrical circuit breaker 1 may be a live tank circuit breaker. In a live tank circuit breaker, the circuit breaker housing is at line potential, meaning that thermal management of the electrical conductors is particularly important, as heat dissipation paths to ground are more limited than in a dead tank configuration.

[0039] As current is led through the electrical circuit breaker 1, resistivity of the electrical conductor bodies 2, 3 add thermal energy to the electrical conductor bodies 2, 3, thus promoting an increased temperature of the conductor bodies 2, 3. Heat is dissipating from the surface of the conductor bodies 2, 3 into surrounding gas and further from the gas through any enclosure, such as through the circuit breaker housing 4, and out to the environment. If more thermal energy is added than what is dissipated and / or conducted away, the temperature of the conductor body 2, 3 will rise. There is thus a limit to how high current can be fed through the electrical conductor bodies 2, 3 without exceeding a maximum temperature threshold (maximum allowedPS56305PC00

[0040] 4

[0041] temperature), since the dissipation of heat is limited. The electrical circuit breaker 1 comprises a circuit breaker housing 4 containing a gas comprising at least 80% by volume of CO2. CO2provides electrical insulation within the housing and acts as a quenching gas to suppress electrical arcs during switching operations. A remainder of the volume of the gas, excluding the CO2portion, may comprise at least 90% by volume of O2. This proportion of O2supports the thermal performance of the gas mixture.

[0042] The present invention enables higher current throughput through an electrical circuit breaker 1 by enabling higher radiation of heat from at least a first surface portion of an electrical conductor 2, 3 of the electrical circuit breaker 1. Specifically, increased radiation of heat is achieved by enlarging the surface area of said first surface portion of the electrical conductor 2, 3.

[0043] Additionally, radiation of heat is increased by providing said first surface portion with a darker color, such as black, effectively making the surface of the conductor body darker than what the surface was before the provision of the darker color, thereby increasing the emissivity of the first surface portion and further enhancing heat radiation.

[0044] Whether or not a surface portion has been made darker or not may typically be assessed by studying surrounding surface portions of the electrical conductor body 2, 3 for color differences or by simply scraping off added paint and studying the color of the surface beneath the paint. Upon manufacturing, the electrical conducting bodies 2, 3 of the electrical circuit breaker 1 get a certain surface structure and color as determined by the manufacturing process, for example molding, extrusion, and / or pressing (sometimes referred to as stamping), and any subsequent machining or processing such as milling, turning or anodization. The present invention suggests that treatment(s) of the electric conductor body(ies) 2, 3 is made, such as roughening of the surface and / or anodization and / or darkening of the surface.

[0045] Any suitable method may be used for roughening the surface of the electrical conductor body 2, 3. In particular, abrasive blasting, shot peening, knurling and / or anodization are suitable for roughening the surface of the electrical conductor bodies 2, 3. These are well-known methods as such and thus will not be explained in detail herein.

[0046] Any suitable method may be used for darkening the surface of the electrical conductor body 2, 3. In particular, spray painting or dyeing the surface has proven effective. Where painting is used, the color may be defined within a HSB colorspace having a hue of 0-360 degrees, a saturation of 0-20%, and a brightness of 0-40%, as determined by a spectrophotometer using CIE Standard llluminant D65 and the CIE 196410° Standard Observer. This HSB range defines objectively dark colors — low saturation combined with low brightness corresponds to colors that are nearneutral and dark, approaching black. Such colors exhibit high emissivity, meaning the surface radiates thermal energy more efficiently, thereby reducing the operating temperature of the electrical conductor.

[0047] A color used for said painting may be black. Specifically, color and / or surface roughness of at least the first surface portion may be adapted such that emissivity of the first surface portion is in thePS56305PC00

[0048] 5

[0049] range of 0.5-1. The emissivity number (or simply emissivity) is a measure of how efficiently a surface emits thermal radiation compared to a perfect black body at the same temperature. It is a dimensionless number ranging from 0 to 1. A perfect black body (ideal emitter) has an emissivity of 1 and absorbs and emits all incident radiation.

[0050] The material of the electrical conductor body 2, 3 typically comprises aluminum, an aluminum alloy, copper or a copper alloy. However, any other suitable material may be used instead.

[0051] The invention also relates to a method of producing an electrical circuit breaker 1, such as the electrical circuit breaker shown in fig. 1. The electrical circuit breaker 1 is suitable for a high-voltage system. The method comprises providing a conductor body 2, 3 for an electrical conductor of the electrical circuit breaker 1. The method further comprises enlarging the surface area of at least a first surface portion of the electrical conductor body 2, 3 by increasing a surface roughness of at least said first surface portion of the conductor body. The surface roughness may according to this method be increased by shot peening, abrasive blasting, knurling and / or anodization. The method further comprises painting darker, or dyeing darker, at least a first surface portion of the electrical conductor body 2, 3, or painting the first surface portion to assume a color within an HSB colorspace having a hue of 0-360 degrees, a saturation of 0-20%, and a brightness of 0-40%, as determined by a spectrophotometer using CIE Standard llluminant D65 and the CIE 196410° Standard Observer. If the electrical conductor body 2, 3 is anodized, any dyeing is typically performed after anodization of the electrical conductor body 2, 3. The method further comprises filling a circuit breaker housing 4 of the electrical circuit breaker 1 with a gas comprising at least 80% by volume of CO2. CO2provides electrical insulation within the housing and acts as a quenching gas. A remainder of the volume of the gas, excluding the CO2portion, may comprise at least 90% by volume of O2, which supports the thermal performance of the gas mixture.

[0052] In the embodiment shown in fig. 1, the electrical conductor bodies 2, 3 have been molded. In other embodiments, the provision of the respective electrical conductor body 2, 3 may instead comprise extruding material to form the electrical conductor body 2, 3.

[0053] In the embodiment of fig. 1, the material of the electrical conductor bodies 2, 3 is pure aluminum. In other embodiments, the material may be any other suitable material, as mentioned above. In the embodiment of fig. 1, the surface roughness has been increased by abrasive blasting and subsequent anodization. The electrical conductor bodies 2, 3 have in the embodiment of fig. 1 been painted darker, thereby increasing the emissivity of the first surface portion. In other embodiments, dyeing darker may be used as an alternative to painting.

[0054] Some common types of abrasive blasting are dry blasting, wet blasting, bead blasting and shot blasting. The skilled person would understand how to choose a suitable abrasive medium and blasting technique based on what electrical conductor material is to be blasted and what surface structure is to be achieved.PS56305PC00

[0055] 6

[0056] A common way to increase the cooling capacity of a metal body to be cooled would be to add larger cooling flanges to the metal body. The invention enables enlargement of the surface area of the electrical conductor bodies 2, 3, without substantially enlarging the total volume of the electrical conductor bodies 2, 3. According to the invention, the surface area can be substantially enlarged without adding cooling flanges and without increasing the overall size of the electrical conductor bodies 2, 3.

[0057] It is typically advantageous not to make the overall size of the electrical circuit breaker 1 larger, at least since the electrical circuit breaker 1 may need to fit into an existing installation.

Claims

PS56305PC007CLAIMS1. An electrical circuit breaker (1) for a high-voltage system, said electrical circuit breaker (1) comprises an electrical conductor, andsaid electrical conductor comprising a conductor body (2, 3) comprising a first surface portion, said first surface portion having a surface roughness obtainable by abrasive blasting, shot peening, knurling and / or anodization, andsaid first surface portion further being painted darker or dyed darker or painted in a color within a HSB colorspace having a hue of 0-360 degrees, a saturation of 0-20%, and a brightness of 0-40%, as determined by a spectrophotometer using CIE Standard llluminant D65 and the CIE 196410° Standard Observer, wherein the electrical circuit breaker further comprises a circuit breaker housing containing a gas comprising at least 80% by volume of CO2.

2. The electrical circuit breaker according to claim 1, wherein a remainder of the volume except for the portion of CO2of the gas, comprises at least 90% by volume of O2.

3. The electrical circuit breaker according to any one of claims 1-2, wherein the circuit breaker is a live tank circuit breaker.

4. The electrical circuit breaker according to any one of claims 1-3, wherein a color used for said painting is black.

5. The electrical circuit breaker according to any one of claims 1-4, wherein emissivity of at least the first surface portion is in the range of 0.5-1.

6. The electrical circuit breaker according to any one of claims 1-5, wherein the material of the electrical conductor body comprises aluminum, an aluminum alloy, copper or a copper alloy.

7. A method of producing an electrical circuit breaker for a high-voltage system, said method comprising:providing a conductor body for an electrical conductor of the electrical circuit breaker, said conductor body having a first surface portion having a surface area, andenlarging the surface area of at least said first surface portion by increasing a surface roughness of said first surface portion by abrasive blasting, shot peening, knurling and / or anodization, and further comprising painting darker, or dyeing darker at least the first surface portion of the conductor body, or painting the first surface portion to assume a color within an HSB colorspacePS56305PC008having a hue of 0-360 degrees, a saturation of 0-20%, and a brightness of 0-40%, as determined by a spectrophotometer using CIE Standard llluminant D65 and the CIE 196410° Standard Observer,the method further comprising filling a circuit breaker housing of the circuit breaker with a gas comprising at least 80% by volume of CO2.

8. A method according to claim 7, wherein a remainder of the volume except for the portion of CO2of the gas, comprises at least 90% by volume of O2.

9. The method according to any one of claims 7-8, wherein said provision of the conductor body comprises molding or extruding material to form the conductor body.

10. The method according to claim 9, wherein the material molded or extruded is aluminum, an aluminum alloy, copper or a copper alloy.

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