Heat-sensitive material for an overheat detection element, detection element, associated electrical equipment and electrical cabinet

Abstract

Thermosensitive material for an overheat detection element, detection element, associated electrical equipment and electrical cabinet. This thermosensitive material is a hot injectable and electrically insulating material, the thermosensitive material including a polymer matrix, made of a thermoplastic polymer material or thermoplastic elastomer, a plasticizer, having a molar mass (M), and a charge in the form of particles, in particular carbon black.The molar mass (M) of the plasticizer is chosen based on a predetermined first temperature threshold (Ti), so that the heat-sensitive material is configured to release volatile species from the heated plasticizer and charge particles carried by the plasticizer when the material is subjected to a temperature above the first temperature threshold (Ti). These volatile species from the plasticizer and charge particles are detectable by a detection device. See Figure 3 for the abbreviation.

Description

Title of the invention: Thermosensitive material for an overheat detection element, detection element, associated electrical equipment and electrical cabinet

[0001] The present invention relates to a heat-sensitive material for overheat detection, particularly for detecting overheating in electrical equipment. It also relates to an overheat detection element made of such a heat-sensitive material, electrical equipment comprising such a detection element, and an electrical cabinet comprising such electrical equipment.

[0002] In the field of power electrical equipment in an electrical installation, the electrical devices are generally located in an electrical cabinet, which forms a protective enclosure. The electrical devices are generally mounted on an electrical panel, which is itself housed within the electrical cabinet. Each electrical device generally comprises one or more connection points, to which electrical conductors, such as cables or busbars, are respectively connected. Typically, each electrical conductor is, at one end, connected and secured to one of the connection points by means of a screw tightened into a nut.

[0003] In the assembled state, the screw passes through the electrically conductive member and the connection plate and is screwed into the nut, pressing the electrically conductive member against the connection plate to ensure the connection. If the connection between the electrically conductive member and the connection plate is not tight, the electrical resistance of the connection increases, and when a current flows through this connection, localized heating occurs at the connection point. This is a potential source of malfunction, or even an accident if the heating exceeds a certain threshold and causes, for example, a fire. For regulatory and / or safety reasons, it is necessary to monitor the quality of electrical connections, in particular by monitoring the heating of these connections and / or the conductive members.

[0004] It is also known to perform thermal imaging during inspection visits to detect hot spots in an electrical panel. However, the electrical enclosure housing the panel must be opened to take the images, and for safety reasons the electrical panel is often de-energized; therefore, the images do not accurately reflect the normal operation of the electrical equipment and do not allow for continuous monitoring.

[0005] It is also known to install temperature probes, for example thermocouples or electronic temperature detectors, within the electrical panel for continuous monitoring of electrical connections. However, these temperature probes, their installation, and the use of their measurements are costly.

[0006] Another approach to continuously monitoring an electrical cabinet involves using a detection device capable of detecting gas emissions, microparticles, and volatile organic compounds emitted when cable sheaths overheat. EP-3 512 056-A1 describes such an approach, which does not allow for the specific monitoring of a particular point in the electrical cabinet, especially connections that may become loose.

[0007] It is also known, notably from EP-3 336 813-A2, to manufacture labels by incorporating microcapsules into a polymer film having a predetermined melting temperature. The microcapsules contain a specific gas, designed to be detected by a specific detection device. However, the microcapsules are relatively fragile, and their implementation remains delicate and limited to the manufacture of labels, which cannot be placed directly on electrical connections, for example, on screw terminals. Furthermore, the labels must be placed one by one on the conductive elements to be monitored.

[0008] It is these problems that the invention particularly intends to remedy, by proposing a thermosensitive material for the detection of overheating, the thermosensitive material allowing continuous monitoring, being easy to implement and being able to adapt to different part designs.

[0009] To this end, the invention relates to a heat-sensitive material for an overheat detection element, in which: - The thermosensitive material is a hot-injection, electrically insulating material, including: • a polymer matrix, made of a thermoplastic polymer material or a thermoplastic elastomer with a first melting point, • a plasticizer, having a molar mass and a second melting point, the second melting point being lower than the first melting point, and • a charge in the form of particles, notably carbon black, - the molar mass of the plasticizer is chosen according to a first predetermined temperature threshold, the first threshold being strictly lower than the first melting temperature, so that the heat-sensitive material is configured to release volatile species from the heated plasticizer and charge particles carried along by the plasticizer when the heat-sensitive material is subjected to a temperature above the first temperature threshold, said volatile species from the plasticizer and charge particles being detectable by a detection device.

[0010] Thanks to the invention, the heat-sensitive material is a homogeneous material that can be produced by conventional means without risk of deterioration, in particular by hot injection molding, extrusion, etc. Implementation is particularly easy. It is thus possible to shape the heat-sensitive material as needed, whether as a flat, flexible plastic part to be attached to busbars, a nut cover, etc. Electrical equipment can therefore be fitted with parts made of the heat-sensitive material during factory assembly, without requiring any additional operations during the assembly of the electrical panel, making continuous monitoring of the electrical equipment possible from the moment it is installed in the electrical cabinet.Of course, parts made of heat-sensitive material in all shapes can be produced to facilitate their installation on the various electrical components of an existing electrical cabinet, whether they are conductive elements or electrical devices.

[0011] According to advantageous but not mandatory aspects of the invention, such a heat-sensitive material may incorporate one or more of the following characteristics taken individually or in any technically permissible combination: - The first temperature threshold is chosen between 125°C ±10°C and 160°C ± 10°C, - for each initial temperature threshold, the molar mass of the plasticizer is between a minimum and a maximum value, - on a graph linking the first temperature threshold on an x-axis to the molar mass of the plasticizer on an y-axis, the first temperature threshold and the molar mass define a coordinate system, the first threshold and the molar mass being located inside a quadrilateral delimited by four points, respectively: • a first point with coordinates {115; 150], • a second point with coordinates {115; 300], • a third point with coordinates {170; 525], and • a fourth point with coordinates {170 ; 400}. - In graphical representation, the first threshold and the molar mass are located within a quadrilateral delimited by four points, respectively: • a fifth point with coordinates {115; 190}, • the second point with coordinates {115; 300}, • the third point having coordinates {170; 525}, and • a sixth point with coordinates {170 ; 450}. - In graphical representation, the first temperature threshold and the molar mass are located in a band bordered, at the bottom, by an intermediate segment connecting the fifth point to the sixth point, the band having a width, measured parallel to the ordinate axis, equal to 75#g / mol. - The plasticizer addition rate is between 4% and 15% by weight relative to the weight of the thermoplastic polymer matrix. - The filler is added between 2 and 3% by weight relative to the complete formulation of the main body material. - The filler is carbon black. - The polymer matrix is ​​polyethylene terephthalate, while the plasticizer is DINCH, added between 4% and 15% by weight relative to the polymer matrix. - The polymer matrix is ​​polyamide 6 / 6, while the plasticizer is N-Ethyl o / p-toluene sulfonamide, which is added between 4 and 15% by weight of the polymer matrix. - The polymer matrix is ​​polybutylene terephthalate, while the plasticizer is N-Ethyl o / p-toluene sulfonamide, which is added between 4 and 15% by weight of the polymer matrix.

[0012] The invention also relates to an overheating detection element, comprising a body made of the thermosensitive material as described above.

[0013] The invention also relates to electrical equipment, which includes an electrical conductor configured to carry an electric current, in which: - The electrical equipment also includes an overheat detection element as described previously, - The overheat detection element is fixed to the electrical conductor.

[0014] The invention also relates to an electrical cabinet, in which: - The electrical cabinet defines an enclosure and includes: • electrical equipment as described above; • a detection device, configured to detect the flow of plasticizer and / or fillers released by the heat-sensitive material around the overheat detection element when the temperature of the heat-sensitive material exceeds the first temperature threshold, - The overheating detection element and the detection device are located within the electrical cabinet enclosure.

[0015] According to another aspect, the invention relates to a method for detecting overheating in an electrical cabinet, the detection method comprising: - provide an electrical cabinet as described above, - to circulate an electric current through the electrical equipment, so as to cause the overheating detection element to heat up beyond the first temperature threshold and to release, around the body made of the heat-sensitive material, a flow of plasticizer and / or volatile species from the heated plasticizer and / or charge particles carried by the plasticizer, - detect the flow of plasticizer and / or volatile species from the heated plasticizer and / or charge particles carried by the plasticizer by means of the detection device.

[0016] This method induces the same advantages as those mentioned above concerning materials for overheat detection of the invention.

[0017] The invention will be better understood, and other advantages thereof will become more apparent from the following description of several embodiments of a heat-sensitive material for overheat detection, a detection element, electrical equipment, an electrical cabinet, and a detection method, in accordance with its principle, given solely by way of example and with reference to the accompanying drawings, in which:

[0018] - [Fig. 1] [Fig. 1] is a schematic perspective view of an electrical cabinet in accordance with the invention, the electrical cabinet comprising electrical equipment, also in accordance with the invention;

[0019] - [Fig.2] [Fig.2] represents, on three inserts a), b) and c), a connection terminal including an overheat detection element belonging to the electrical equipment of [Fig.1], the overheat detection element also conforming to the invention;

[0020] - [Fig.3] [Fig.3] is a graph illustrating certain properties of a material thermosensitive material used for manufacturing the overheat detection element of [Fig. 2], the thermosensitive material also conforming to the invention, and

[0021] - [Fig.4] [Fig.4] represents, on three inserts a), b), and c), detection elements overheating according to alternative embodiments of the invention.

[0022] An electrical cabinet 10 is shown in [Fig. 1]. The electrical cabinet 10 is schematically represented by a parallelepiped and delimits an enclosure V10. The electrical cabinet 10 comprises at least one electrical device 20 and a detection device 30. The electrical device 20 and the detection device 30 are located in the same enclosure—here, the enclosure V10—of the electrical cabinet 10. The electrical device 20 and the detection device 30 are fixed to a panel 12, which forms the bottom of the enclosure V10.

[0023] The electrical device 20 includes at least one connection range 22, which is configured to be connected to another element of the electrical cabinet 10, by For example, another electrical device of the same type as electrical device 20, or another electrical device of a different type, or a conductive element such as a cable or a set of metal busbars. In the example shown, electrical device 20 is a three-phase circuit breaker, and the connection ranges 22 include four input ranges, labeled 22A, 22B, 22C, and 22D, and four output ranges, which are not shown in the figures.

[0024] One of the connection points 22, here the input point 22C, is shown connected to a conductive element 24, here a cable. What is valid for one of the connection points 22 is applicable to the other connection points. The assembly of the conductive element 24 to the connection point 22C is explained with reference to Figure 2a). The mounting point 22C is part of a metal component of the electrical device 20, the mounting point 22C protruding outside a housing of the electrical device 20. Only the mounting point is shown in Figure 2a), the rest of the electrical device 20 being hidden so as not to clutter the figure.

[0025] The mounting surface 22C is here drilled with an orifice 23. The conductive element 24 includes a mounting tab 25A, which is drilled with a hole 25B. The assembly between the mounting surface 22C and the tab 25A is here achieved by means of a nut 98 and a screw 99. The nut 98 is formed here by a parallelepiped-shaped metal plate, which has a threaded orifice configured to cooperate with the screw 99.

[0026] The nut 98 is here part of an overheating detection element 100. The overheating detection element 100 is also referred to simply as the "detection element 100" in this description. In the first embodiment of the invention, the detection element 100 comprises, in addition to the nut 98, a main body 102 and a core 104.

[0027] The nut 98 is configured to cooperate with the screw so as to clamp the connection range 22C to the tab 25A. The nut 98 is made of a thermally conductive material. Thus, if the connection between the connection range 22C and the tab 25A heats up, for example if the screw 99 is not tightened correctly, the nut 98 transmits some of the heat generated to the rest of the sensing element 100.

[0028] The core 104 is made of a material which is thermally conductive and electrically insulating, for example ceramic.

[0029] The main body 102 provides a first cavity 106, in which the core 104 is received, and a second cavity 108, which adjoins the first cavity 106, in which the nut 98 is received, so that the core 104 is in contact with the nut 98. The core 104 serves to transmit the heat from the nut 98 to the main body 102. Thus, when the nut 98 heats up, for example due to a faulty electrical connection, then the entire sensing element 100 tends to heat up.

[0030] The main body 102 is made of a heat-sensitive material 110. The heat-sensitive material 110 is hot-injection moldable and electrically insulating. The heat-sensitive material 110 includes the following ingredients: - a matrix, which is made of a first thermoplastic polymer material having a first melting temperature T1, - a plasticizer, which has a given molar mass and a second melting temperature T2, the second melting temperature T2 being lower than the first melting temperature T1, and - a filler in the form of particles, particularly in powder form.

[0031] The thermoplastic polymer material used for the matrix is, for example, polyamide 66, denoted PA66, polyamide 6, denoted PA6, polybutylene terephthalate, denoted PBT, a thermoplastic elastomer, denoted TPE, etc. In general, the type of thermoplastic polymer or thermoplastic elastomer used is not limited for the implementation of the invention, as long as the characteristics of rigidity, melting temperature, resistance to aging, heat, electrical insulation, etc., necessary for the intended application are achieved.

[0032] Generally, in the field of plastics processing, fillers are added to the polymer or elastomer matrix to modify the material's properties, either during manufacturing, for example to facilitate demolding, reduce shrinkage, etc., or for the final part, for example to modify its density, hardness, rigidity, color, etc. In the context of the present invention, the fillers used are particles, in other words, powders, preferably electrically insulating. Preferably, the filler particles used have a diameter between 0.1 µm and 100 µm. Preferably, the filler used in the context of the present invention comprises carbon black.

[0033] Plasticizers are also added to the thermoplastic polymer matrix to modify its properties, particularly its mechanical properties. For each thermoplastic polymer, there are generally several types of compatible plasticizers, the known selection criteria including the polarity of the plasticizer and that of the thermoplastic matrix, the chemical functionalities present on the plasticizer and the thermoplastic that can generate chemical bonds... Compatibility can notably be estimated using Hildebrand solubility parameters.

[0034] In the context of the invention, the heat-sensitive material as a whole, and in particular the plasticizer, complies with the European RoHS Directive – an acronym for Restriction of Hazardous Substances – aimed at limiting the use of hazardous substances in electrical and electronic equipment, with the European REACH Regulation – an acronym for Registration, Evaluation, Authorisation and Restriction of Chemicals – and is halogen-free – in accordance to the IEC63355:2022 standard - nor persistent organic pollutant, in accordance with European regulation EU 2019 / 1021 - known as the POPs regulation.

[0035] During the manufacture of the main body 102, the ingredients of the main body material are first mixed together by hot mixing, for example using an extrusion screw, to prepare a homogeneous mixture, preferably in the form of granules. This yields the heat-sensitive material 110. This step of preparing the heat-sensitive material 110 by mixing is also called "compounding." During the preparation step of the heat-sensitive material 110, the mixing temperature is advantageously 30°C to 50°C higher than the first melting temperature T1. Preferably, the plasticizer is liquid at the mixing temperature, so as to promote its integration into the polymer matrix.

[0036] After the preparation step of the heat-sensitive material 110, the heat-sensitive material 110 is considered homogeneous. The heat-sensitive material 110 is then used as raw material for manufacturing the main body 102, which is manufactured here by hot injection molding. Thus, the material of the main body 102 is considered homogeneous.

[0037] Schematically, after injection and cooling, the thermoplastic polymer forms a matrix that contains the plasticizer and fillers. When the sensing element 100 heats up, the plasticizer releases volatile substances. If the temperature reached is sufficient, this can be considered the beginning of decomposition, generating volatiles or gases. Furthermore, these releases can even carry particles from the filler added to the material. This is a progressive process beginning with the migration of the plasticizer and filler particles towards the surface of the main body 102, generating bleeding, followed by the release of volatiles, gases, and filler particles. The volatiles or gases, and the particles from the fillers, carried by the flow of plasticizer, end up suspended in the enclosure V10 of the electrical cabinet 10.

[0038] Surprisingly, it was found that the bleeding of the plasticizer and / or volatile compounds generated by the plasticizer and / or filler particles was not a linear function of temperature, but that the amount of plasticizer and / or volatile compounds and / or particles bleeding increased sharply when the material temperature exceeded a predetermined first temperature threshold. Surprisingly, it was also found that the first temperature threshold varied depending on the molar mass of the plasticizer. The molar mass, denoted M, is expressed in g / mol – grams per mole. In other words, the higher the desired first temperature threshold, the higher the molar mass of the plasticizer must be.

[0039] Thus, within the framework of the invention, the molar mass M of the plasticizer is chosen according to the first temperature threshold, the first temperature threshold being predetermined, during the design of the detection element 100, by the user according to the intended application. Preferably, the first temperature threshold is chosen between 125°C ±10°C and 160°C ±10°C, which corresponds to typical temperatures for monitoring overheating in the field of electrical equipment and electrical cabinets.

[0040] In practice, the thermoplastic polymer material of the matrix is ​​chosen first, particularly according to the technical constraints (mechanical, thermal, fire resistance, etc.) of the part to be manufactured. Then, one or more plasticizers, whose molar mass corresponds to the envisaged temperature threshold, are selected from among those compatible with the selected polymer material, notably according to the aforementioned criteria of polarity, solubility, etc. Preferably, the degradation temperature of the plasticizer is higher than the processing temperature of the material.

[0041] The first temperature threshold is strictly lower than a first melting temperature Tl of the thermoplastic polymer matrix. The heat-sensitive material 110 is thus configured to release a flow of plasticizer and particles from the filler around the main body 102, the filler particles being carried along by the plasticizer, when the heat-sensitive material 110 is subjected to a temperature above the first temperature threshold. The flow of plasticizer and filler thus released by heating beyond the first temperature threshold is detectable by the detection device 30. In particular, volatile species, such as gases, released by the bleeding of plasticizer, and / or the particles carried along by the flow of plasticizer will be detected.

[0042] The detection device 30 is configured to detect a flow of plasticizer and / or fillers in the enclosure V10 of the electrical cabinet 10, and is configured to send an alert signal when a concentration of the plasticizer and / or fillers exceeds a predetermined concentration threshold, indicating that the temperature of the main body 102 exceeds the first temperature threshold. The alert signal is, for example, an audible signal, and / or a visual signal, and / or a signal transmitted as an electronic message via a dedicated wired or wireless interface.

[0043] The technology used for the detection device 30 is not particularly limited. According to a first example, the detection device 30 includes a detector of volatile organic compounds, also known as VOCs. Advantageously, the detection device 30 is configured to detect plasticizer molecules, which includes the molecules of the plasticizer itself and / or volatile species molecules released by the plasticizer. In a second example, the detection device 30 includes an opacimeter to detect opaque particles suspended in the chamber, in other words, to detect the charges carried along during the plasticizer's bleeding. Of course, several technologies can be combined within the detection device 30 to improve detection reliability.

[0044] According to a first example of application of the invention, for a first temperature threshold between 115°C and 135°C, in other words for a first temperature threshold equal to 125°C ±10°C, the molar mass M of the plasticizer is chosen between 150 g / mol and 300 g / mol.

[0045] According to a first formulation of the heat-sensitive material 110 of the main body 102 illustrating the first application example: - The thermoplastic polymer matrix is ​​polybutylene terephthalate - PBT - the plasticizer is N-ethyl o / p-toluene sulfonamide, this plasticizer having a molar mass M of 199 g / mol and being added at a rate of 6.75% by weight of the polymer matrix, and - the fillers are carbon black, which is added at a rate of 2% by weight of the complete formulation.

[0046] Glass fibers were also added at a rate of 30% by weight of the polymer matrix, as well as a halogen-free flame retardant. This addition did not hinder the implementation of the invention. The complete formulation includes the polymer matrix, the plasticizer, fillers including carbon black, and any other optional elements that are not necessary but contribute to the implementation of the invention, in particular reinforcements such as glass fibers, other additives such as a flame retardant, etc.

[0047] The heat-sensitive material 110 is then produced by mixing the aforementioned ingredients using a heated extruder, in the form of granules. The granules of heat-sensitive material 110 are then used in a hot injection molding machine to manufacture the main body 102 from heat-sensitive material 110.

[0048] The main body 102 is then assembled to a core 104 and the nut 98, so as to obtain an overheating detection element of the type of overheating detection element 100, which is then mounted on an electrical connection between two conductive elements. An electric current of controlled intensity flows through said electrical connection, so as to cause the connection to heat up, the temperature of the electrical connection being monitored by an infrared detector. It was verified that the detection device 30 emitted a alarm signal when the temperature of the electrical connection reached the first temperature threshold, here equal to 125°C ±10°C.

[0049] According to a second formulation of the thermosensitive material 110 of the main body 102 illustrating the first application example, the following range of formulations makes it possible to manufacture the thermosensitive material 110 particularly suitable for the detection of heating with a first temperature threshold equal to 125°C ±10°C: - the polymer matrix is ​​a polyamide 6 - PA6 - the plasticizer is N-ethyl o / p-toluene sulfonamide, this plasticizer having a molar mass M of 199 g / mol and being added at a rate of 6.75% by weight of the polymer matrix, and - the fillers are carbon black, which is added at a rate of 2% by weight of the complete formulation.

[0050] Glass fibers were also added at a rate of 30% by weight of the polymer matrix as well as a halogen-free flame retardant, this addition not having hindered the implementation of the invention.

[0051] More generally, the following range of formulations makes it possible to manufacture a thermosensitive material 110 particularly suitable for heating detection with a first temperature threshold of 125°C ±10°C: - the polymer matrix is ​​PBT or PA6, - the plasticizer is N-ethyl o / p-toluene sulfonamide added between 4% and 15% by weight relative to the polymer matrix, - Carbon black fillers are added at between 2 and 3% by weight of the complete formulation.

[0052] According to a second application example of the invention, for a first temperature threshold between 150°C and 170°C, in other words for a first temperature threshold equal to 160°C ±10°C, the molar mass M of the plasticizer is chosen between 400 g / mol and 500 g / mol.

[0053] According to a third formulation of the heat-sensitive material 110 illustrating the second application example: - the matrix is ​​a thermoplastic polyester elastomer - TPE-E -, - the plasticizer is the diisononyl ester of 1,2-cyclohexane dicarboxylic acid (in English, 1,2-Cyclohexane dicarboxylic acid diisononyl ester), denoted DINCH, this plasticizer having a molar mass M of 425 g / mol and being added at a rate of 5% by weight of the polymer matrix, and - the fillers are carbon black, which is added at a rate of 2% by weight of the complete formulation.

[0054] The same test protocol as for the first application example described above was implemented. It was verified that the detection device 30 emitted an alarm signal when the temperature of the electrical connection - in other words the temperature of the heat-sensitive material 110 - reached the first temperature threshold, here equal to 160°C ±10°C.

[0055] According to a fourth formulation of the heat-sensitive material 110 illustrating the second application example: - The polymer matrix is ​​a thermoplastic polyester elastomer - TPE-E, - The plasticizer is DINCH, this plasticizer having a molar mass M of 425 g / mol and being added at a rate of 15% by weight of the polymer matrix, and - carbon black as fillers, with carbon black being added at a rate of 2% by weight of the complete formulation.

[0056] The same test protocol as above was implemented. It was verified that the detection device 30 emitted an alarm signal when the temperature of the heat-sensitive material 110 reached the first temperature threshold, here equal to 160°C ±10°C.

[0057] More generally, the following range of formulations makes it possible to manufacture a thermosensitive material 110 particularly suitable for heating detection with a first temperature threshold of 160°C ±10°C: - The polymer matrix is ​​a thermoplastic polyester elastomer - TPE-E, - the plasticizer is DINCH, added between 4% and 15% by weight relative to the polymer matrix. - Carbon black fillers are added at between 2 and 3% by weight of the complete formulation.

[0058] Figure 3 is a graph 180 illustrating, within the scope of the invention, a range of molar masses of the plasticizer, said range of molar masses being given as a function of the first temperature threshold chosen for the heat-sensitive material 110. The first temperature threshold is thus plotted on an x-axis, and the molar mass of the plasticizer on a y-axis. The first temperature threshold and the molar mass define a coordinate system on the graph 180.

[0059] Thus, according to the invention, the first threshold and the molar mass are advantageously located within a quadrilateral delimited by four points, respectively: • a first point PI having coordinates {115 ; 150], • a second point P2 having coordinates {115; 300], • a third point P3 with coordinates {170; 525], and • a fourth point P4 having coordinates {170 ; 400}.

[0060] The quadrilateral is thus delimited by a lower segment Sinf, which connects point P4 to point PI, and by an upper segment Ssup, which connects point P2 to point P3.

[0061] For every first intermediate temperature threshold, denoted Ti, between 115 and 170°C, there corresponds a single lower molar mass Minf, which is read on the lower segment Sinf, and a single upper molar mass Msup, which is read on the upper segment Ssup. In other words, when the first temperature threshold is equal to the intermediate temperature Ti, the acceptable molar mass range is between the lower molar mass Minf and the upper molar mass Msup.

[0062] Surprisingly, it was found that, for an acceptable range of molar masses associated with a given first intermediate temperature threshold Ti, the higher the molar mass, the less sensitive the overheating detection element 100 was to aging.

[0063] Thus, preferably, in graphical representation, the first temperature threshold and the molar mass are located within a quadrilateral delimited by four points, respectively: • a fifth P5 point having coordinates {115 ; 190], • the second point P2 having coordinates {115; 300], • the third point P3 having coordinates {170; 525], and • a sixth point P6 having coordinates {170 ; 450}.

[0064] An intermediate segment Sint is defined that connects the fifth point P5 to the sixth point P6. To each first intermediate temperature threshold Ti corresponds a unique intermediate molar mass Mint, which is read on the intermediate segment Sint. Thus, preferably, when the first temperature threshold is equal to the intermediate temperature Ti, the preferred range of molar masses is between the intermediate molar mass Mint and the upper molar mass Msup.

[0065] Preferably, in graphical representation, the first intermediate temperature threshold Ti and the molar mass are located in a band bordered at the bottom by the intermediate segment Sint connecting the fifth point P5 to the sixth point P2, the band having a width, measured parallel to the ordinate axis, equal to 75 g / mol. In [Fig. 3], the band is represented by a grey area Zl.

[0066] The invention also relates to a method for detecting overheating in the electrical cabinet 10, the detection method comprising: - provide electrical cabinet 10, - to circulate an electric current through the electrical equipment, so as to cause the heat-sensitive material 110 of the overheating detection element 100 to heat up beyond the first temperature threshold Ti and to release, around the detection element 100, a flow of plasticizer and / or volatile species from the heated plasticizer and / or charge particles carried along by the plasticizer, - detect, using the detection device 30, the flow of plasticizer and / or volatile species from the heated plasticizer and / or the charge particles carried along by the plasticizer.

[0067] The overheating detection elements 100 according to the invention are particularly advantageous because they allow continuous monitoring of the electrical equipment received in the electrical cabinet 10, while remaining inexpensive to install or manufacture, here by conventional means of hot injection of the main body 102.

[0068] An overheating detection element 200 according to a second embodiment of the invention is shown in Figure 4a). In the second embodiment, the elements analogous to those of the first embodiment bear the same reference numerals and function in the same way. The following mainly describes the differences between the first and second embodiments.

[0069] The overheating detection element 200 comprises a main body 202, which is made of a heat-sensitive material similar to the heat-sensitive material 110 of the main body 102 of the overheating detection element 100 according to the first embodiment of the invention, i.e. including: - a polymer matrix, made from a first thermoplastic polymer material with a first melting point, and - a plasticizer, having a molar mass and a second melting point, the second melting point being lower than the first melting point, and - a charge in powder form,

[0070] in which the molar mass of the plasticizer is chosen as a function of the first temperature threshold.

[0071] The main body 202 is in the form of a flattened parallelepiped and is configured to be placed against a conductive element 224, here a conductive bus. The overheating detection element 200 includes a ligature 204, which serves to fix the main body 202 to the conductive element 224.

[0072] An overheating detection element 300 according to a third embodiment of the invention is shown in Figures 4b) and 4c). In the third embodiment, the elements analogous to those of the preceding embodiments bear the same reference numerals and function in the same way. The following primarily describes the differences between the third embodiment and the preceding embodiments.

[0073] The overheating detection element 300 comprises a main body 302, which is made of a heat-sensitive material similar to the heat-sensitive material 110 of the main body 102 of the overheating detection element 100 according to the first embodiment of the invention, i.e. including: - a polymer matrix, made of a first thermoplastic polymer material having a first melting point, and - a plasticizer, having a molar mass and a second melting point, the second melting point being lower than the first melting point, and - a charge in powder form,

[0074] in which the molar mass of the plasticizer is chosen as a function of the first temperature threshold.

[0075] The overheating detection element 300 is configured here to be mounted on a bolt 350, the bolt comprising a screw 352 and a nut 354. The bolt 350 is used, for example, for assembling two conductor buses, or for assembling a cable to an electrical device, etc. The overheating detection element 300 is here made in one piece by hot injection, the main body 302 comprising a wall 303, which is generally ring-shaped with a central orifice, the main body 302 comprising a skirt 304, which extends from one side of the wall 303, and a chimney 306, which extends from the other side of the wall 303, opposite the skirt 304.

[0076] The skirt 304 has a cylindrical shape with a hexagonal cross-section, the skirt 304 being configured to cooperate, in particular by complementary shapes, with the nut 354, so as to fix the overheating detection element 300 to the nut 354, while one end of a rod of the screw 352 passes through the central orifice of the wall 303 and is received in the chimney 306.

[0077] More generally, in view of the three examples of overheating sensors 100, 200 and 300, it is understood that the overheating detection elements according to the invention can be shaped in multiple ways, with multiple forms, so as to facilitate the installation of these overheating detection elements in an electrical cabinet.

[0078] The embodiments and variants mentioned above can be combined with each other to generate new embodiments of the invention.

Claims

1.

2. Demands Heat-sensitive material (110) for an overheat detection element (100; 200; 300), wherein: • the thermosensitive material (110) is a hot-injectable and electrically insulating material, the material including: • a polymer matrix, made of a thermoplastic polymer material or thermoplastic elastomer having a first melting temperature (Tl), • a plasticizer, having a molar mass (M) and a second melting point (T2), the second melting point being lower than the first melting point, and • a charge in the form of particles, notably carbon black, • the molar mass (M) of the plasticizer is chosen according to a predetermined first temperature threshold (Ti), the first threshold being strictly lower than the first melting temperature, so that the thermosensitive material (110) is configured to release volatile species from the heated plasticizer and charge particles carried by the plasticizer when the thermosensitive material is subjected to a temperature above the first temperature threshold (Ti), said volatile species from the plasticizer and charge particles being detectable by a detection device (30). Heat-sensitive material (110) according to claim 1, wherein: • The first temperature threshold is chosen between 125°C ±10°C and 160°C ± 10°C, • for a given first temperature threshold (Ti), the molar mass (M) of the plasticizer is between a minimum value (Sinf) and a maximum value (Ssup), • On a graph linking the first temperature threshold on the x-axis to the molar mass (M) of the plasticizer on the y-axis, the first temperature threshold and the molar mass define a system of coordinates, the first threshold and the molar mass being located inside a quadrilateral delimited by four points, respectively: • a first point (PI) having coordinates {115 ; 150}, • a second point (P2) having coordinates {115 ; 300}, • a third point (P3) having coordinates {170; 525}, and • a fourth point (P4) having coordinates {170 ; 400}.

3. Thermosensitive material (110) according to claim 2, wherein: • in graphical representation, the first threshold and the molar mass are located within a quadrilateral delimited by four points, respectively: • a fifth point having coordinates {115; 190}, • the second point having coordinates {115; 300}, • the third point having coordinates {170; 525}, and • a sixth point having coordinates {170; 450}.

4. Thermosensitive material (110) according to claim 3, wherein: • in graphical representation, the first temperature threshold and the molar mass are located in a band bordered, on the bottom, by an intermediate segment connecting the fifth point to the sixth point, the band having a width, measured parallel to the ordinate axis, equal to 75#g / mol.

5. Thermosensitive material (110) according to any one of claims 1 to 4, wherein: • an addition rate of the plasticizer is between 4% and 15% by weight relative to the weight of the thermoplastic polymer matrix.

6. Thermosensitive material (110) according to any one of claims 1 to 5, wherein: • the filler is added between 2 and 3% by weight relative to the complete formulation of the main body material.

7. Thermosensitive material (110) according to any one of claims 1 to 5, wherein: • the filler is carbon black.

8. Thermosensitive material (110) according to any one of claims 1 to 7, wherein: • the polymer matrix is ​​polyethylene terephthalate, • the plasticizer is DINCH (1,2-Cyclohexane dicarboxylic acid diisononyl ester), added between 4% and 15% by weight relative to the polymer matrix.

9. Thermosensitive material (110) according to any one of claims 1 to 7, wherein: • the polymer matrix is ​​polyamide 6 / 6, • the plasticizer is N-Ethyl o / p-toluene sulfonamide, which is added between 4 and 15% by weight of the polymer matrix.

10. Thermosensitive material (110) according to any one of claims 1 to 7, wherein: • the polymer matrix is ​​polybutylene terephthalate, • the plasticizer is N-Ethyl o / p-toluene sulfonamide, which is added between 4 and 15% by weight of the polymer matrix.

11. Overheating detection element (100; 200; 300), comprising a body (102; 202; 302) made of the thermosensitive material (110) according to any one of claims 1 to 10.

12. Electrical equipment (20), comprising an electrical conductor (22) configured to carry an electric current, wherein: • the electrical equipment also comprises an overheat detection element (100) according to claim 11, • the overheat detection element is fixed to the electrical conductor.

13. Electrical cabinet (10), in which: • The electrical cabinet delimits an enclosure (V10), and includes: • electrical equipment (20) according to claim 12; • a detection device (30), configured to detect the flow of plasticizer and / or charges released by the heat-sensitive material (110) around the overheat detection element (100) when the temperature of the heat-sensitive material (110) exceeds the first temperature threshold (Ti), • the overheat detection element (100) and the detection device (30) are located in the enclosure (V10) of the electrical cabinet.

14. Method for detecting overheating in an electrical cabinet (10), the detection method comprising: • providing an electrical cabinet (10) conforming to claim 13, • passing an electric current through the electrical equipment (20), so as to cause the overheating detection element (100) to heat up beyond the first temperature threshold (Ti) and to release, around the body (102) made of the heat-sensitive material (110), a flow of plasticizer and / or volatile species from the heated plasticizer and / or charge particles carried along by the plasticizer, • detecting the flow of plasticizer and / or volatile species from the heated plasticizer and / or charge particles carried along by the plasticizer by means of the detection device (30).

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