EP1650771B1 - Improved protection device of electric apparatus against overvoltages - Google Patents

Description

The invention relates generally to the field of electrical protection.

More specifically, the invention relates to a device for protecting electrical devices against overvoltages, for example due to lightning, this device comprising at least: first and second connection pads; a thermosensitive switch comprising at least one conductive moving part and a first fusible link; elastic means exerting a permanent stress on the moving part; and a non-linear voltage-current characteristic clipping component, such as a varistor, having a first terminal directly connected to the first connection pad, and a second terminal selectively connected to the second pad via the switch thermosensitive, the moving part being, in normal operation of the device, maintained by the first fuse link in a closed position in which it establishes an electrical contact between first and second conductors, one of which is at the potential of the second connection pad and the other at the potential of the second terminal of the clipping component, and adopting, under the load of the elastic means and in the event of overheating of the clipping component having caused a melting of the first fuse link, an open position in which introduces, between the first and second conductors, a space which isolates them from one another.

Devices of this type, sometimes referred to as "surge arresters", are well known to those skilled in the art and various examples are given in patents. US 3,889,222 , US 4,015,228 or US 4,288,833 .

The clipping component conventionally used in these devices is constituted by a varistor, which is mounted in series, between the two connection pads, with a thermosensitive switch.

Indeed, as indicated in the three aforementioned patents, the varistors are, towards the end of their life, the seat of a significant heating, the thermosensitive switch having precisely the function of disconnecting the varistor before this heating n ' reaches such a value that it creates a risk of explosion or fire.

The realization of the thermosensitive switch can essentially take three known forms.

Firstly, it is possible to use, as a moving part, a rigid part fastened to at least one of the first and second conductors by a fusible link formed by a low melting point weld, this moving part being biased in translation by a spring in a direction to move away from his or her welds.

Such a solution, which is for example described in patents US 3,301,981 , US 3,964,010 , or US 4,015,228 , requires a relatively large stroke of the moving part to ensure the extinction of any electric arc that may be formed, and thus leads to a relatively large size of the final arrangement.

The second possibility is to use, as a moving part, an elastic conductive part whose first end is fixed permanently on the first conductor and whose second end is fixed to the second conductor by a fusible link formed by a low melting point weld, this part being thus movable only at its second end, which is disengaged from the second conductor, by the inherent elasticity of this part, as soon as the heating of the varistor caused fusion of the weld.

Such a solution, which is for example described in the patent US 4,288,833 , requires for the constitution of the moving part the use of a material both conductive and capable of maintaining significant elasticity over a wide range of temperature, leading to choose a very specific material and therefore expensive, and / or requires to give the moving part a long length to obtain sufficient insulating space after tripping.

The third possibility, which is described in the utility certificate DE 93 05 796 is to use, as a moving part, a locally flexible piece biased by a spring.

This moving part then has a first electrical junction area by which it is fixed on the first conductor by means of the first fuse link, and a second electrical junction area by which it is mounted movable relative to the second conductor, the elastic means exerting on this moving part a pair urging the first junction zone at a distance from the first conductor by bending and rotating the moving part around the second junction zone.

Such a solution imposes constraints both on the choice of material constituting the moving part and on the thickness of this part.

In this context, the object of the present invention is to propose a device for protecting electrical devices against overvoltages freed from the aforementioned compromises.

To this end, the device of the invention, furthermore in conformity with the generic definition given in the preamble of claim 1, is essentially characterized in that the moving part is rigid and in that the temperature-sensitive switch comprises a second fusible link fixing, in normal operation of the device, the second electrical junction zone to the second conductor and helping to block the rotation of the moving part, this second fusible link also being merged in case of overheating of the clipping component and allowing the rotation of the moving part.

In a particularly advantageous embodiment of the invention, the first conductor is for example directly formed by the second connection pad, and the second conductor is for example directly formed by the second terminal of the clipping component.

In the case where the clipping component has a flattened shape of which a minimum dimension or thickness extends in a first direction, the second conductor may also have a flattened shape of which a minimum dimension or thickness extends at least substantially along the first direction, the moving part then preferably having an axis of rotation extending itself at least substantially in the first direction.

The axis of rotation of the moving part can for example pass through an eye made in the moving part and / or in the second conductor.

In practice, the device of the invention comprises an insulating casing supporting the connection pads and in which are housed the thermosensitive switch, the elastic means, and the clipping component, the axis of rotation of the movable piece being able to be formed, at least partially, by an internal lug of the housing.

A particularly compact and economical arrangement can be obtained by providing that the second connection pad has a flat portion extending parallel to the axis of rotation of the moving part, and that this moving part is constituted by a cut metal blank having at least a right-angle fold defining, on this moving part, a first branch on which is formed the first junction zone fixed to the flat of the second stud by the first fuse link, and a second branch perpendicular to the first and on which is formed the second junction zone attached to the second terminal of the clipping component by the second fuse link.

The device of the invention may also comprise, in a manner known per se, a tripping indicator mechanically linked to the moving part on the side of the first junction zone of this mobile part and driven in translation during a rotation of the part. mobile.

Furthermore, the elastic means are for example constituted by a spring extending parallel to a large dimension of the clipping component between a fastening point formed in the housing and a point hooking arranged on the moving part on the side of its first junction zone.

• les figures 1A et 1B sont respectivement des vues de face et en perspective d'un dispositif conforme à l'invention représenté, par souci de clarté, sans le boîtier dont il est normalement pourvu, et dans sa configuration de fonctionnement normal;
• les figures 2A et 2B sont respectivement des vues de face et en perspective d'un dispositif conforme à l'invention représenté, par souci de clarté, sans son boîtier ni le ressort de traction de la pièce mobile, et dans la configuration inactive qu'il atteint après ouverture de l'interrupteur thermosensible;
• la figure 3A représente sous un autre angle le dispositif illustré aux figures 1A et 1B;
• la figure 3B représente, à échelle agrandie, le détail repéré par la référence III sur la figure 3A; et
• les figures 4A et 4B sont respectivement des vues de face et en perspective du dispositif illustré aux figures 1A et 1B, représenté avec son boîtier, mais sans le couvercle servant à fermer ce dernier.

Other characteristics and advantages of the invention will emerge clearly from the description which is given hereinafter, by way of indication and in no way limitative, with reference to the appended drawings, in which:

• Figures 1A and 1B are respectively front views and perspective of a device according to the invention shown, for the sake of clarity, without the housing which it is normally provided, and in its normal operating configuration;
• FIGS. 2A and 2B are respectively front views and perspective views of a device according to the invention shown, for the sake of clarity, without its housing or the traction spring of the moving part, and in the inactive configuration that it reaches after opening the thermosensitive switch;
• FIG. 3A represents, from another angle, the device illustrated in FIGS. 1A and 1B;
• FIG. 3B represents, on an enlarged scale, the detail indicated by reference III in FIG. 3A; and
• Figures 4A and 4B are respectively front and perspective views of the device shown in Figures 1A and 1B, shown with its housing, but without the cover for closing the latter.

As previously announced, the invention relates to a device for protecting electrical devices against overvoltages, especially against overvoltages due to lightning.

Such a device comprises, in a manner known per se, two connection pads 11 and 12, a thermosensitive switch 2 associated with elastic means such as a spring 3, and a voltage clamping component 4 with a voltage-current characteristic of linearly connected in series with the thermosensitive switch 2 between the connection pads 11 and 12, this component being in this case represented in the form of a varistor oxide (s) metal (s).

The thermosensitive switch 2 comprises a conductive moving part 21, associated with at least one fusible link 221 typically constituted by a weld with a low melting point, melting at a temperature, for example of the order of 100 to 120 ° C.

The spring 3, whose function is to exert permanently on the movable part 21 a bias in the direction of a break of the fuse link 221, is for example constituted by a coil spring working in tension.

The varistor 4 has two terminals 41 and 42, the first 41 of which is directly connected to the first connection pad 11, and the second 42 of which is selectively connected to the second connection pad 12 through the thermosensitive switch 2.

In normal operation of the device, the moving part 21 is held by the fuse link 221 in a closed position which is illustrated in FIGS. 1A, 1B, and 3A to 4B and in which it establishes an electrical contact between two conductors 12 and 42.

As shown in the figures, these conductors are preferably directly constituted, according to the invention, by the second connection pad 12 and by the second terminal 42 of the varistor 4.

If another arrangement is adopted, it should at least be provided that the first of the two conductors that connects the movable part 21 is at the electrical potential of the connection pad 12, and that the second of these conductors defines the electrical potential of the terminal 42 of the varistor 4, so that the varistor 4 is connected to the pads 11 and 12 in the normal operating configuration of the device.

In case of overheating of the varistor 4 leading to a melting of the fuse link 221, the moving part 21 adopts, under the bias of the spring 3, an open position as illustrated in FIGS. 2A and 2B, and in which it introduced, between the conductors 12 and 42, a space E (Figure 2A) which isolates these conductors from each other, the varistor 4 then ceasing to be connected to the connection pad 12 and therefore no longer traversed by no current.

According to the invention, the movable part 21 is rigid and mounted to rotate about an axis of rotation remote from the fuse link 221.

More precisely, the moving part 21 has in practice two electrical junction zones 211 and 212, in this case comparable to the two end portions of this part 21.

The moving part 21 is firstly fixed on the connection pad 12 by its first electrical junction area 211 by means of the fuse link 221, and secondly rotatably mounted, by its second zone 212 electrical junction, with respect to the terminal 42 of the varistor 4.

The spring 3 thus exerts on the moving part 21 a torque which urges the first junction zone 211 away from the stud 12 by rotation of the moving part 21 around the second junction zone 212.

In addition to the first fuse link 221, the thermosensitive switch 2 preferably comprises a second fuse link 222 fixing, in normal operation of the device, the second electrical junction zone 212 to the second terminal 42 of the varistor 4.

This second fuse link 222, which therefore contributes, with the first fuse link 221, to block the rotation of the moving part 21 in the normal operating configuration of the device, is also merged in the event of abnormal overheating of the varistor 4 and then authorizes the rotation of the moving part 21.

The second fusible link, for example also consisting of a low melting point weld, is particularly advantageous for several reasons.

First, it ensures, between the second terminal 42 of the varistor 4 and the moving part 21 and even after its fusion, an ideal thermal and electrical conduction, and in particular much greater than that which would be obtained by a simple direct contact of this marker 42 and this piece 21.

Correlatively, this second fuse link 222 avoids the formation, between the terminal 42 and the moving part 21, of any electric arc that could have the effect of soldering the piece 21 to this terminal 42.

Moreover, insofar as the second fuse link 222 is the closest to the heat source represented by the varistor 4 in the overheated state, this second link 222 melts before the first fuse link 221, and forms a fluid bearing facilitating the rotation of the part 21, which thus occurs immediately after the melting of the first fuse link 221.

In the case, which corresponds to the situation illustrated, where the varistor 4 has a flattened shape whose minimum dimension, also called thickness, extends in a direction such that D1 in FIGS. 1B and 4B, it is advisable to so, on the one hand that each terminal 41 and 42 of the varistor 4, and at least the second terminal 42, has a flattened shape whose thickness also extends in the direction D1, and secondly that the axis of rotation 5 of the movable part 21 also extends along the same direction D1.

In practice, the device of the invention comprises an insulating housing 7 which supports the connection pads 11 and 12, and in which are housed the thermosensitive switch 2, the spring 3, and the varistor 4.

Under these conditions, it is possible to provide that the axis of rotation 5 of the movable part 21 is formed by an internal lug of the housing 7.

In this case, or in the case where the axis of rotation 5 of the movable part 21 is formed by a rivet, this axis 5 passes for example through an eye 6 made in the moving part 21 and / or in the second terminal 42 of the varistor 4.

Furthermore, the spring 3 can extend parallel to one of the longer sides of the varistor 4, between an attachment point 70 formed in the housing 7 and a hooking point 213 formed on the moving part 21 of the next to its first junction zone 211.

The second connection pad 12 may consist of a metal blank cut and folded at an angle, and advantageously has a flat portion 120 extending parallel to the axis of rotation 5 of the movable part 21.

To limit the thermal leakage through the connection pad 12 and correspondingly prevent any delay of the melting of the first fuse link 221 in case of overheating of the varistor 4, this pad 12 may be made of a metal or a metal alloy less conduct heat than copper, and present holes such as those shown in Figure 2B under reference 121.

The movable part 21 may itself consist of a metal blank cut and folded, but preferably made of copper or any other metal or metal alloy very conducive to heat.

Thus, the movable part 21 may in particular comprise a fold 210 at right angles, defining first and second branches 21A and 21B of this movable part 21.

The first branch 21A, on which is formed the first zone 211 of electrical junction, is fixed to the flat portion 120 of the second stud 12 of the varistor 4 by the first fuse link 221.

The second branch 21B, which is perpendicular to the first branch 21A and on which is formed the second zone 212 of electrical junction, is fixed to the second terminal 42 of the varistor 4 by the second fuse link 222.

The device of the invention may finally comprise a trigger indicator 8 mechanically connected to the movable part 21 and able to provide, in particular through a window 71 of the housing 7, an indication of the position of the moving part 21.

To do this, the movable part 21 may for example have, on the side of its first junction zone 211, a lateral flange in which is formed a light 214 (FIG. 3B) slidably receiving a lug 80 of the trigger indicator 8 , the latter being thus driven in translation when the moving part 21 passes from its closed position to its open position by rotation about its axis 5.

Claims (9)

1. Device for protecting electrical appliances against overvoltages, this device comprising: first and second connection tabs (11, 12); a heat-sensitive switch (2) comprising at least one moving conductive part (21) and a first fusible link (221); elastic means (3) exerting a permanent strain on the moving part (21); and a voltage limiting component (4) with non-linear voltage-current characteristic, such as a varistor, presenting a first terminal (41) directly linked to the first connection tab (11), and a second terminal (42) selectively linked to the second connection tab (12) via the heat-sensitive switch (2), the moving part (21) being, when the device is operating normally, maintained by the first fusible link (221) in a closed position in which it establishes an electrical contact between first and second conductors, of which one is at the potential of the second connection tab (12) and the other is at the potential of the second terminal (42) of the limiting component (4), and adopting, under the strain of the elastic means (3) and in the case of overheating of the limiting component (4) having caused the first fusible link (221) to blow, an open position in which it introduces, between the first and second conductors, a space (E) which insulates them from each other, the moving part (21) presenting a first electrical junction zone (211) by which it is fixed to the first conductor by means of the first fusible link (221), and a second electrical junction zone (212) by which this moving part (21) is mounted so as to move relative to the second conductor, the elastic means (3) exerting on the moving part (21) a torque straining the first junction zone (211) away from the first conductor by rotation of the moving part (21) about the second junction zone (212), characterized in that the moving part (21) is rigid and in that the heat-sensitive switch (2) comprises a second fusible link (222) fixing, when the device is operating normally, the second electrical junction zone (212) to the second conductor and helping to block the rotation of the moving part (21), this second fusible link (222) also being subject to blowing in case of overheating of the limiting component (4) and then allowing the moving part (21) to rotate.
2. Protection device according to Claim 1, characterized in that the first conductor is directly formed by the second connection tab (12).
3. Protection device according to any one of the preceding claims, characterized in that the second conductor is directly formed by the second terminal (42) of the limiting component (4).
4. Protection device according to any one of the preceding claims, characterized in that the limiting component (4) presents a flattened shape, a minimum dimension or thickness of which extends in a first direction (D1), and in that the second conductor (42) presents a flattened shape, a minimum dimension or thickness of which extends at least roughly in the first direction (D1), and in that the moving part (21) is provided with an axis of rotation (5) itself extending at least roughly in the first direction (D1).
5. Protection device according to Claim 4,
   characterized in that the axis of rotation (5) of the moving part (21) passes through an eye (6) formed in the moving part (21) and/or in the second conductor (42).
6. Protection device according to Claim 4 or 5,
   characterized in that it also comprises an insulating case (7) supporting the connection tabs (11, 12) and in which are housed the heat-sensitive switch (2), the elastic means (3), and the limiting component (4), and in that the axis of rotation (5) of the moving part (21) is at least partially formed by a stub inside the case (7).
7. Protection device according to any one of the preceding claims combined with Claims 2 to 4, characterized in that the second connection tab (12) has a flat (120) extending parallel to the axis of rotation (5) of the moving part (21), and in that this moving part (21) is formed by a cut metal blank presenting at least one right-angled fold (210) defining, on this moving part, a first branch (21A) on which is formed the first junction zone (211) fixed to the flat (120) of the second tab (12) via the first fusible link (221), and a second branch (21B) perpendicular to the first (21A) and on which is formed the second junction zone (212) fixed to the second terminal (42) of the limiting component (4) by the second fusible link (222).
8. Protection device according to any one of the preceding claims, characterized in that it comprises a trip indicator (8) mechanically linked to the moving part (21) alongside the first junction zone (211) of this moving part and driven horizontally when the moving part (21) rotates.
9. Protection device according to any one of the preceding claims, characterized in that it comprises an insulating case (7) supporting the connection tabs (11, 12) and in which are housed the heat-sensitive switch (2), the elastic means (3), and the limiting component (4), and in that the elastic means (3) are formed by a spring (3) extending parallel to a major dimension of the limiting component (4) between a hooking point (70) provided in the case (7) and a hooking point (213) provided on the moving part (21) alongside its first junction zone (211).

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