Magnetic retention system for an electrical protection device

Abstract

Magnetic holding system for an electrical protection device. Electrical protection device (100) comprising: - a fixed part including two power terminals (101, 102); - a movable part (120) adapted to come into contact with the fixed part and to move between an open position and a closed position of the electrical protection device, the movable part comprising an upper surface (120a), a lower surface (120b) opposite the fixed part and two contact points (121, 122) with the fixed part located on the lower surface; - two springs (151, 152) configured to apply a pressure force on the two contact points of the movable part in the direction of the fixed part; - a plate (130) placed on the upper surface of the movable part;- two magnetic bars (191, 192), each magnetic bar being placed in a loop (1011, 1022) formed between a contact point of the moving part and a power terminal of the fixed part; - two magnetic cheeks surrounding the moving part, each magnetic cheek being in contact with the two magnetic bars; characterized in that the electrical protection element also comprises a permanent magnet (131) placed above said plate between the two contact points of the moving part and between the two springs. Figure for the abbreviation: Fig. 2;

Description

Title of the invention: Magnetic retention system for an electrical protection device. Technical field

[0001] The present invention relates to the general field of electrical protection devices, such as electromechanical contactors and electrical contactors, more particularly to the protection of these protection devices during a short circuit. Previous technique

[0002] Electrical protection devices or electrical current limiting devices generally include a movable bridge pressed against fixed contacts of a fixed part by means of a spring.

[0003] When the current flowing between the moving bridge and the fixed contacts exceeds a predefined threshold, for example in the event of a short circuit, electromagnetic repulsive forces will be applied to the moving bridge and will compensate for, or even exceed, the force applied by the spring on the moving bridge. This causes the contacts of the moving bridge to levitate, i.e., the protective element between the moving bridge and the fixed part to open at least one of the contact points between the two. During the separation between the two, i.e., during levitation, the current continues to flow momentarily or permanently via an electric arc.

[0004] This levitation phenomenon can be used to limit the short-circuit current. Indeed, the opening of the protective device generates a resistance that is added to the circuit and thus tends to reduce the current. Documents WO 2013 / 119232, EP 3 232 457 and FR 3 095 890, for example, use this property in an ejector circuit associated with a circuit breaker; while document FR 2 108 623 uses this property to trigger another type of protection thanks to the voltage appearing across the terminals of the fixed and moving parts.

[0005] However, when the short-circuit current value is close to the predefined threshold, i.e., the current causing levitation, the protective device will indeed open under the effect of repulsive forces, but as soon as a gap appears between the fixed part and the moving bridge, the forces related to the constriction of the current lines will drop sharply. Only the purely electromagnetic forces will persist, which are much lower than the pressure forces created by the spring on the moving bridge.

[0006] This decrease in levitation forces then causes the protective device to close around a hot spot made of molten material. The fixed part and the moving bridge will thus weld together, rendering the protective device unusable.

[0007] Moreover, there are no sufficiently fast means to avoid this re-closing, because it would be necessary to detect the opening of the protective device, stop the force exerted by the spring and finally open the protective device.

[0008] It is therefore desirable to have a new electrical protection device whose risks of damage are reduced in the event of a short circuit. Description of the invention

[0009] The invention relates to an electrical protection device comprising: - a fixed part comprising two power terminals; - a movable part capable of coming into contact with the fixed part and moving between an open position and a closed position of the electrical protection device, the moving part comprising an upper surface, a lower surface opposite the fixed part and two points of contact with the fixed part present on the lower surface; - two springs configured to apply a pressure force on the two contact points of the moving part in the direction of the fixed part; - a plate placed on the upper surface of the moving part; - two magnetic bars, each magnetic bar being placed in a loop formed between a contact point of the moving part and a power terminal of the fixed part; - two magnetic cheeks surrounding the moving part, each magnetic cheek being in contact with the two magnetic bars;

[0010] characterized in that the electrical protection device also includes a permanent magnet placed above said plate between the two contact points of the moving part and between the two springs.

[0011] Thanks to the invention, when an electric current flows through the electrical protection device between the fixed and moving parts, a magnetic field is generated and channeled by the magnetic bars and magnetic cheeks. This creates a Laplace force that repels the moving part. This then lowers the levitation current threshold of the electrical protection device. The electrical protection device therefore levitates more quickly and the short circuit is broken more rapidly.

[0012] The fact that the electrical protection device includes two points of contact between the fixed part and the moving part makes it possible to multiply by two the voltage breaking capacity of the electrical protection device and to avoid using a braid on the moving part.

[0013] According to a particular feature of the invention, the distance between the plate and the permanent magnet is between 0.5 mm and 3 mm.

[0014] This distance, also called the air gap, can affect the opening threshold of the electrical protection device. Indeed, the permanent magnet exerts an attractive force on the plate and therefore on the moving part; thus, the smaller the air gap, the stronger the attractive force on the moving part. Therefore, the pressure force applied to the moving part by the two springs must be greater than this attractive force to keep the electrical protection device closed, that is, to maintain contact between the fixed and moving parts.

[0015] According to a particular feature of the invention, the electrical protection device comprises a first housing made of insulating material in which the moving part, said at least one spring, the plate and a second housing made of insulating material comprising the permanent magnet, the two power terminals of the fixed part being placed outside the first housing.

[0016] The insulating material used for the first and second housings is, for example, a thermoplastic material.

[0017] According to a particular feature of the invention, the electrical protection device includes a system for guiding the opening of the electrical protection device configured so that the moving part moves parallel to the fixed part between the opening position and the closing position of the electrical protection device.

[0018] The guiding system allows the electrical protection device to open parallel to the moving part. This notably prevents the moving part from becoming entangled.

[0019] According to another particular feature of the invention, the guidance system comprises at least one axis integral with the moving part sliding in a barrel and placed inside one of the two springs. Brief description of the drawings

[0020] Other features and advantages of the present invention will become apparent from the description given below, with reference to the attached drawings which illustrate examples of embodiment without any limiting character.

[0021] [Fig.1] Fig.1 represents, schematically and partially, a three-dimensional view of an electrical protection device according to an embodiment of the invention.

[0022] [Fig.2] [Fig.2] represents, schematically and partially, a cross-section longitudinal of the electrical protection device of the [Fig.l].

[0023] [Fig.3] [Fig.3] represents, schematically and partially, a view transverse of the electrical protection device of the [Fig.l]. Description of the implementation methods

[0024] Figures 1 to 3 schematically represent an electrical protection device 100 according to an embodiment of the invention. In particular, [Fig. 1] represents a three-dimensional external view of the electrical protection device 100, [Fig. 2] a longitudinal section, i.e. along the XZ axes, of the electrical protection device 100 and [Fig. 3] a transverse section, i.e. along the YZ axes, of the electrical protection device 100.

[0025] The electrical protection device 100 comprises a fixed part including two power terminals 101, 102 and a movable part 120. The movable part 120 comprises a lower surface 120b and an upper surface 120a on which a plate 130 is fixed. The fixed part is opposite the lower surface 120b of the movable part 120.

[0026] The plate 130 is a metal plate, for example made of iron or low alloy steel.

[0027] The movable part 120 can move between an open position and a closed position of the electrical protection device 100. When the electrical protection device 100 is closed, as shown in Figures 2 and 3, the fixed and movable parts 120 are in contact at the contact points 121, 122, and an electric current can flow between the fixed and movable parts 120. Two springs 151, 152 are present in the electrical protection device 100 to apply a pressure force to the movable part 120 in the direction of the fixed part. These two springs 151, 152 are, for example, positioned opposite the contact points 121, 122 so that the pressure force is sufficient to maintain contact between the two parts.The pressure force and therefore the pressure efforts applied by the two springs 151, 152 are, in particular, sufficient to ensure a contact pressure at the contact points 121, 122 compatible with the nominal electrical current flowing in the electrical protection device 100 and limiting heating at the contact points 121, 122. .

[0028] Furthermore, the presence of the two springs 151, 152 allows for better balancing of the entire protective element 100 compared to a protective element having only one spring to exert the pressure force on the moving part towards the fixed part.

[0029] The electrical protection device 100 also includes a permanent magnet 131 positioned above the plate 130 opposite the upper surface 120a of the moving part 120. The permanent magnet 131 is particularly positioned between the two contact points 121, 122 and between the two springs 151, 152. It is separated from the plate 130 by a distance or air gap e. The air gap e has a value that can vary between 0.5 mm and 3 mm. Since the permanent magnet 131 exerts an attractive force on the moving part 120, the value of the air gap e is specifically chosen to optimize this attractive force. Indeed, the larger the air gap e, the greater the pressure force exerted by the two springs 151, 152 can be reduced to maintain contact between the fixed and moving parts 120; and the smaller the air gap e is, the greater the pressure force exerted by the two springs 151, 152 must be to move and hold the moving part 120 towards or on the fixed part.

[0030] The electrical protection device 100 also includes two magnetic bars 191, 192 and two magnetic cheeks (or flanges) 190. Each power terminal 101, 102 of the fixed part of the electrical protection device 100 forms a loop 1011, 1022 within the electrical protection device 100 with the contact points 121, 122. The magnetic bar 191 is thus placed in the loop 1011 formed between the first power terminal 101 and the contact point 121; while the magnetic bar 192 is placed in the loop 1022 formed between the second power terminal 102 and the contact point 122.

[0031] The two magnetic cheeks 190 are placed in contact on the two magnetic bars 191, 192. They are positioned on either side of the fixed and moving parts 120. In other words, they surround the moving part 120 of the electrical protection device 100, as well as a portion of the fixed part. Indeed, only a portion of the loops 1011, 1022 is surrounded by the two magnetic cheeks 190.

[0032] The two magnetic bars 191, 192 are, for example, made of iron. They can also be made of low-alloy steel.

[0033] The two magnetic cheeks 190 are, for example, made of iron. They can also be made of low-alloy steel.

[0034] Low alloy means an alloy, known as XC10, in which there is less than 10% of alloying element other than iron.

[0035] Thus, when an electric current I flows in the fixed part, a magnetic field B is generated and is channeled by the two magnetic bars 191, 192 and the two magnetic cheeks 190. This will create a Laplace force F which repels the moving part 120, which is proportional to the square of the current I.

[0036] The assembly of magnetic cheeks 190 and bars 191, 192 thus increases the levitation forces by lowering the levitation current threshold. This allows the electrical protection device 100 to levitate more quickly and break the short circuit more rapidly. For example, the levitation current threshold can be between 1500 A and 3000 A thanks to this assembly.

[0037] A first housing 110 comprising a lower surface 111 can include the electrical protection element 100. The power terminals 101, 102 of the fixed part are placed outside the first housing 110, while the other components of the electrical protection element 100 are placed inside the first housing 110.

[0038] The electrical protection device 100 may include a second housing 112 placed inside the first housing 110 and comprising the permanent magnet 131.

[0039] The electrical protection device 100 may also include a guide system configured so that the opening of the electrical protection device 100 occurs parallel to the fixed part. The guide system comprises, for example, two shafts 161, 162 integral with the moving part 120, i.e., fixed to the moving part 120 or formed as a single piece with the moving part 120. The two shafts 161, 162 each slide within a barrel 141, 142 integral with the first housing 110. This guide system allows, in particular, the moving part to be braced when the current threshold is exceeded, since the opening of the electrical protection device 100 in this case generally occurs initially at a single point of contact.

[0040] The opening threshold of the electrical protection device 100 is thus defined by three parameters: - the forces of the springs 151, 152 which must be sufficient to ensure a contact pressure force between the fixed and moving parts 120 compatible with the nominal current and limiting heating; - the dimensioning of the assembly of magnetic cheeks 190 and bars 191, 192 which produces levitation forces proportional to the square of the current flowing in the electrical protection device 100; and - the value of the air gap e which defines the value of the attractive force exerted by the permanent magnet 131 on the moving part 120.

[0041] In the event of exceeding the current threshold, the electrical protection device 100 begins to open by levitating and the air gap e, which is then reduced compared to the closed position of the electrical protection device 100, produces an imbalance of the overall forces within the electrical protection device 100. The permanent magnet 131 then exerts a stronger attractive force and attracts the movable part 120 which will come to be pressed against the magnet 131 by means of the plate 130. These attractive forces thus overcome the pressure forces exerted by the two springs 161, 162 and make it possible to maintain the electrical protection device 100 in the open position. This eliminates the need to close the electrical protection device 100 and the possibility of fusion bonding between the fixed and moving parts 120 of the electrical protection device 100.The electrical protection device 100 will thus have made it possible to limit the electrical current relative to the predefined threshold and possibly to activate another electrical protection device.

[0042] Furthermore, the separation caused by the attractive force of the permanent magnet 131 helps to limit the short-circuit current. The electric arcs generated at the contact points 121, 122 following the levitation of the electrical protection device 100 create resistances that reduce the current and facilitate current interruption. which follows. This reduction in short-circuit current facilitates the interruption of the subsequent current.

[0043] Furthermore, the electrical protection device 100 independently generates a voltage between its terminals 101, 102 when it opens. This voltage allows the electrical protection device 100 to be used as an ultra-fast threshold trip unit to power, for example, another electrical protection device.

Claims

Demands

1. Electrical protection device (100) comprising: - a fixed part including two power terminals (101, 102); - a movable part (120) adapted to come into contact with the fixed part and to move between an open position and a closed position of the electrical protection device, the movable part comprising an upper surface (120a), a lower surface (120b) opposite the fixed part and two contact points (121, 122) with the fixed part present on the lower surface; - two springs (151, 152) configured to apply a pressure force on the two contact points of the movable part in the direction of the fixed part; - a plate (130) placed on the upper surface of the movable part;- two magnetic bars (191, 192), each magnetic bar being placed in a loop (1011, 1022) formed between a contact point of the moving part and a power terminal of the fixed part; - two magnetic cheeks (190) surrounding the moving part, each magnetic cheek being in contact with the two magnetic bars; characterized in that the electrical protection device also comprises a permanent magnet (131) placed above said plate between the two contact points of the moving part and between the two springs.

2. Electrical protection device according to claim 1, wherein the distance (e) between the plate and the permanent magnet is between 0.5 mm and 3 mm.

3. Electrical protection device according to any one of claims 1 or 2, comprising a first housing (110) of insulating material in which are placed the moving part, said at least one spring, the plate and a second housing (112) of insulating material comprising the permanent magnet, the two power terminals of the fixed part being placed outside the first housing.

4. Electrical protection device according to any one of claims 1 to 3, comprising an opening guidance system for the electrical protection device configured so that the moving part moves parallel to the fixed part between the opening position and the closing position of the electrical protection device.

5. Electrical protection device according to claim 4, wherein the guidance system comprises at least one shaft (161, 162) integral with the moving part sliding in a barrel (141, 142) and placed inside one of the two springs (151, 152).

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