EP3185275B1 - Device for joining a bimetal strip and a component forming a support for said bimetal strip, and electrical protection unit comprising same - Google Patents

Description

TECHNICAL AREA

The present invention relates generally to bimetallic thermal trip units for current-breaking devices, in particular circuit breakers. It relates more particularly to a device for assembling a bimetallic strip and a part serving to support this bimetallic strip in a current-breaking device, said bimetallic strip being electrically connected by a first end, said free end, to a first connection range. said input, and another end by which the bimetallic is fixed to said support, to a second so-called output connection range.

STATE OF THE PRIOR ART

Documents are known EP 0 291 835 and EP 0 831 510 that a bimetallic thermal release of a current cut-off device provides protection against overloads, the heating of the bimetallic strip being representative of the heating of the device or of the protected electrical installation, so as to trigger the switching device when this heating exceeds a predetermined threshold. The heating of the bimetal can be achieved either directly by passing the current through the bimetallic strip, or in a more usual manner, indirectly by passing the current through an insulated electric heater in thermal contact with the bimetallic strip.

It is also known to assemble this bimetallic strip with a support piece made of electrically conductive material.

For example, the document is known FR 2,669,144 describing such an assembly. This document describes the assembly in two perpendicular planes of a bimetallic strip and a conductive flat part serving as a support, this assembly being made by embedding the part lower bimetallic shaped tenon in a recess serving as mortise provided in the support piece.

In such a device, the current flows from an input terminal, through a ribbon surrounding the bimetallic strip, then from the free end of the bimetallic strip, through the length of the bimetallic strip, then through the support of bimetal, then in the winding of an electromagnetic coil which is electrically connected to an output terminal of the apparatus.

In such a device, the bimetallic foot, corresponding to the point of attachment of the bimetallic strip on the support, has a reduced section corresponding to the section of the aforementioned tenon. This weak section of the bimetal results in a large power generated by the subset including the bimetallic strip and the support. This section of reduced passage is thus interesting for the weak currents but penalizing for the strong currents.

However, the problem currently arises of passing a larger current at constant volume.

SUMMARY OF THE INVENTION

The present invention solves this problem and proposes a device for assembling a bimetallic strip on its support making it possible to increase the operating current of the apparatus which comprises it while keeping the same size of this apparatus, as well as an apparatus power failure device comprising such an assembly device.

For this purpose, the subject of the present invention is an assembly device of the kind mentioned above, this device being characterized in that this bimetal is mounted through the aforementioned support so that it can be fixed at different points along the length of the this bimetallic strip, said bimetallic strip thus having a first and a second part situated respectively on one side and the other side of the aforementioned support, the first part situated on the side of the free end of the bimetallic strip, corresponding to the so-called useful surface of this bimetal, the length of this useful surface being variable depending on the length of installation of this bimetallic strip in the support, this embedding length being determined according to the caliber of the apparatus in order to obtain a constant thermal stroke, whatever the caliber.

According to a particular characteristic, the so-called output electrical connection range is electrically connected to the second part of the aforementioned bimetallic strip.

According to another characteristic, the fixation of the bimetallic strip on the support is carried out by welding.

The present invention also relates to an electrical protection apparatus comprising a thermal release device comprising a bimetallic strip, this device comprising a device for assembling the bimetallic strip on its support comprising the previously mentioned characteristics taken alone or in combination.

According to another characteristic, this apparatus comprises an electromagnetic tripping device comprising a coil, this coil having a first end electrically connected to the second bimetal portion and a second end electrically connected to the aforementioned output range.

According to one characteristic, this device is a low voltage circuit breaker.

• La figure 1 est une vue en perspective éclatée d'un dispositif de déclenchement magnétothermique selon l'invention,
• Les figures 2 et 3 sont deux vues en perspective illustrant ce même dispositif selon deux orientations différentes de manière à montrer deux faces opposées de ce dispositif, et
• Les figures 4 et 5 illustrent respectivement la déflexion du bilame pour deux appareils présentant respectivement un faible calibre et un fort calibre, lesdits appareils comportant un dispositif d'assemblage selon l'invention.

But other advantages and features of the invention will become more apparent in the detailed description which follows and refers to the accompanying drawings given solely by way of example and in which:

• The figure 1 is an exploded perspective view of a magnetothermic trip device according to the invention,
• The Figures 2 and 3 are two perspective views illustrating the same device in two different orientations so as to show two opposite faces of this device, and
• The Figures 4 and 5 illustrate respectively the deflection of the bimetallic strip for two devices having respectively a low caliber and a high caliber, said devices comprising an assembly device according to the invention.

On the Figures 1 to 3 , there is shown said thermal-thermal trigger device D belonging to a low-voltage circuit breaker, this device comprising, in a manner known per se, a thermal tripping device T comprising a bimetallic strip 1, and a magnetic tripping device M comprising a coil 2 said triggering devices being connected in series between a so-called input 3 or upstream connection pad connected to the input terminal of the apparatus and a so-called output or downstream connection pad 4 electrically connected to the output terminal of the device.
As illustrated on the figure 1 , this magnetothermic assembly comprises a thermal assembly T and a magnetic assembly M. This thermal assembly comprises a bimetallic strip 1 supported by a bimetallic support 5, whereas the magnetic assembly M comprises a coil 2 supported by a bead 6, these two sets being supported by an insulating support 7 intended to isolate the different parts to each other.
Such a bimetallic thermal release T is intended to provide protection against overloads, the heating of the bimetallic strip 1 being representative of the heating of the device or the protected electrical installation, so as to trigger the switchgear device. when this heating exceeds a predetermined threshold.
This heating of the bimetallic strip is achieved by passing the current through the bimetallic strip 1, and indirectly by passing the current through an insulated electric heater 8 in electrical contact with the bimetallic strip 1. This strip-shaped heater 8 is made of a material having a resistivity appropriate and is applied against a thin insulating sleeve 9 surrounding the bimetallic strip 1, approximately between the two ends of the latter.
The ribbon 8 has a first end 8a which is electrically connected to a so-called input 3 or upstream connection zone leading to an input terminal (not represented) of current and a second end 8b which is connected to the bimetallic strip 1, by example by electric welding, at a particular point of the bimetallic strip located near the free end 1a thereof.
This bimetallic strip is intended to be fixed on the abovementioned bimetallic support 5, which support is intended to be fixed in the housing of the apparatus. This fixation of the bimetal is advantageously carried out by soldering or brazing.
This coil 2 is constituted by a winding comprising a first end 2a electrically connected to the bimetallic strip 1, and a second end 2b electrically connected to a so-called downstream connection zone 10 said output connected to an output terminal of the device.

According to the invention, the bimetallic strip 1 is mounted through an opening 5a provided in the abovementioned bimetallic support 5 so as to be fixed to said support 5 at different points of the bimetallic strip selected along the length of the bimetallic strip 1. The bimetallic strip and a first portion 1c located above the support 5 and located on the side of its free end 1a, and a second portion 1d located below the support 5. This gives a position of embedding the bimetallic variable to obtain a useful surface 1b bimetallic also variable. It should be noted that this useful surface of the bimetallic strip corresponds to its first part 1a situated above the support 5. The user will thus be able to choose the length of this useful surface according to the size of the apparatus, as this is more particularly illustrated. on the Figures 4 and 5 .
The first end 2a of the coil 2 is electrically connected to the bimetallic strip 1 in an area under the attachment zone z of the bimetallic strip 1 on the aforementioned support 5 as illustrated in FIGS. Figures 2 and 3 .
On the figure 4 bimetallic strip 1 corresponds to that used in a device having a small size. In this figure, the embedding length 1 of the bimetallic strip 1 with respect to the support 5 is minimal, the zone of the bimetallic strip located under the support corresponding substantially to the area necessary for fixing the coil on the bimetallic strip. In this configuration, the deflection of bimetallic strip 1 in the event of an electrical fault of thermal origin results in a curvature of its free end 1a that can be measured by a length x corresponding to a component of this deflection, this component corresponding to the length between the point of attachment f of the bimetallic strip 1 on the support 5 and a point p corresponding to the projection of the free end 1a of the bimetallic strip on an axis X, this axis X being substantially perpendicular to the longitudinal direction of the bimetallic strip. This component x corresponds to the thermal path of the bimetallic strip. At this thermal stroke of the bimetallic strip corresponds to a mechanical stroke of the actuator intended to cooperate with this bimetallic strip in such a way as to trigger the breaking device. On the figure 5 bimetallic strip 1 corresponds to that used in a device with a high rating. In this figure, the embedding length l is increased by a value Y relative to that of the bimetallic strip of the preceding figure so as to reduce the effective area 1b of the bimetallic strip 1. The invention therefore proposes to extend the bimetal strip 1 to through the part of the bimetallic support 5 called the sole, while retaining a weld for example laser between the two parts, then directly solder the end 2a of the winding of the coil 2 on the non-functional part 1d bimetal, under said sole.
Thus, thanks to the invention, the bimetallic embedding and current conduction functions are separated.
Thus, the current line no longer passes through the end portion of the bimetallic having a reduced section, as is the case in the prior art. Thus, the power generated by this subset is decreased.
The embedding height of the bimetallic strip can therefore be adjusted so as to obtain the desired thermal stroke. On strong currents, the point of attachment of the bimetallic strip on its support is raised towards the free end of the bimetallic strip in order to shorten the useful length of the bimetallic strip. On weak currents, this fixing point will be lowered in order to lengthen the useful length of the bimetal and increase its thermal stroke.

Thus, an adaptation according to the current is then possible in order to obtain a constant thermal stroke, this making it possible to obtain a constant mechanical stroke over the entire range of the same product.
Due to this decrease in the power generated, it is possible to manufacture a protection device having a larger size at a constant volume.

Of course, the invention is not limited to the embodiments described and illustrated which have been given by way of example.

Claims (6)

1. Device for joining a bimetal strip (1) and a component (5) that acts as a support for this bimetal strip (1) in a current switching unit, said bimetal strip (1) being electrically connected by a first end, known as the free end, to a first connection area known as the input connection area (3), and by another end, by way of which this bimetal strip is fixed to the abovementioned support (5), to a second connection area known as the output connection area (4), this bimetal strip (1) being mounted so as to pass through the abovementioned support (5), said bimetal strip thus having a first (1c) and a second (1d) part that are situated respectively on one side and the other of the abovementioned support (5), the first part being situated on the side of the free end (1a) of the bimetal strip (1), corresponding to the surface known as the usable surface (1b) of this bimetal strip (1), the length of this usable surface (1b) being variable depending on the insertion length (I) of this bimetal strip (1) in the support (5), characterized in that the bimetal strip (1) is mounted so as to pass through the abovementioned support (5) so as to be able to be fixed at different locations along the length of this bimetal strip (1) and in that said insertion length (I) is determined depending on the calibre of the unit so as to obtain a constant thermal profile (x), regardless of the calibre.
2. Joining device according to Claim 1, characterized in that the electrical connection area (4) known as the output connection area, is electrically connected to the second part (1d) of the bimetal strip (1).
3. Joining device according to Claim 1 or 2, characterized in that the bimetal strip (1) is fixed to the support (5) by welding.
4. Electrical protection unit comprising a thermal trip comprising a bimetal strip (1), characterized in that it comprises a device for joining the bimetal strip (1) to its support (5) according to any one of Claims 1 to 3.
5. Electrical protection unit according to Claim 4, characterized in that it comprises an electromagnetic trip comprising a coil (2), characterized in that this coil (2) comprises a first end (2a) electrically connected to the abovementioned second part (1d) of the bimetal strip and a second end (2b) electrically connected to the abovementioned output area (4).
6. Electrical protection unit according to Claim 4 or 5, characterized in that it is a low voltage circuit breaker.

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