EP2927928B1 - Method for determining an overheating of at least one connection terminal of an electrical device, associated auxiliary apparatus, and electrical system including such an electrical device and such an auxiliary apparatus - Google Patents

Description

The present invention relates to a method for determining, with the aid of an auxiliary apparatus, an overheating of at least one connection terminal of an electrical device, such an auxiliary apparatus and an electrical system comprising such an electrical device. and such an auxiliary apparatus.

A persistent problem in the field of electrical connection terminals is the safety of such terminals, by monitoring their temperature. Indeed, a too high temperature of the connection terminals is able to lead to their destruction, and the decommissioning of an electrical device comprising these connection terminals. More particularly, a too high temperature of the connection terminals is apt to cause a fire.

It is thus known from the documents US Patent 7501926 and respectively US Patent 5188542 to check the temperature of a connection terminal using a bimetallic strip and respectively a thermistor. In such embodiments, the temperature of the connection terminal is compared with a predetermined temperature threshold, beyond which overheating of the terminal is detected. However, such detections are not very accurate.

It is also known from the document US-2009/0167537 measuring the temperature of a connection terminal and comparing this temperature with first and second predetermined temperature thresholds. Such a system makes it possible to switch off an electrical device comprising the connection terminal when the temperature is higher than the second temperature threshold. However, the values chosen for the first and second temperature thresholds do not always make it possible to take into account the different possible conditions of the environment of the connection terminal, which implies errors in the determination of the overheating of the terminal of connection.

The object of the invention is therefore to propose a method for determining, with the aid of an auxiliary apparatus, an overheating of at least one connection terminal of an electrical device, making it possible to determine the overheating in a manner more precise.

• a) la mesure, à un instant temporel donné (tn), d'une première température correspondant à la température de la plage de connexion correspondante, via un premier capteur de température,
• b) le calcul d'une valeur thermique de la plage de connexion en fonction de la première température mesurée,
• c) la comparaison de la valeur thermique de la plage de connexion avec un seuil de température, et
• d) la détection d'une surchauffe de la borne de connexion correspondante lorsque la valeur thermique de la plage de connexion est supérieure au seuil de température,

le procédé étant caractérisé en ce qu'il comprend précédemment à l'étape de comparaison c) et pour chaque borne de connexion, l'étape suivante :

• - b') le calcul du seuil de température à l'instant donné en fonction de la valeur du seuil de température à un instant précédent, la valeur du seuil de température étant variable entre l'instant précédent et l'instant donné, et

lors de l'étape c) de comparaison, la valeur thermique est comparée avec la valeur du seuil de température à l'instant donné.For this purpose, the invention relates to a method for determining, with the aid of an auxiliary device, an overheating of at least one connection terminal of an electrical device, the connection terminal or terminals each comprising at least one connection pad suitable for being connected to a corresponding electrical conductor,
the method comprising for each connection terminal the following steps:

• a) measuring, at a given time instant (tn), a first temperature corresponding to the temperature of the corresponding connection range, via a first temperature sensor,
• b) calculating a thermal value of the connection range as a function of the first temperature measured,
• c) comparing the thermal value of the connection range with a temperature threshold, and
• d) the detection of an overheating of the corresponding connection terminal when the thermal value of the connection range is greater than the temperature threshold,

the method being characterized in that it comprises previously in the comparison step c) and for each connection terminal, the following step:

• - b ') calculating the temperature threshold at the given instant as a function of the value of the temperature threshold at a previous instant, the value of the temperature threshold being variable between the previous instant and the given instant, and

during the comparison step c), the thermal value is compared with the value of the temperature threshold at the given instant.

Thanks to the invention, the value of the temperature threshold for detecting overheating of the connection terminal or terminals is variable between the previous instant and the given instant, which makes it possible to determine more precisely the superheat. The fact that the value of the temperature threshold is variable makes it possible, for example, to better take into account the environment in which the connection terminal or terminals are located.

• Le procédé comprend précédemment à l'étape b') de calcul du seuil de température, une étape b") de mesure de l'intensité du courant circulant dans le conducteur électrique correspondant, et lors de l'étape de calcul b'), le seuil de température est calculée en outre en fonction de l'intensité du courant circulant dans le conducteur électrique correspondant.
• La ou les bornes de connexion comprennent chacune un élément de serrage propre à maintenir la connexion entre le conducteur électrique et la plage de connexion correspondants, via l'application d'une force de serrage sur le conducteur électrique, et lors de l'étape de détection d), un desserrage d'au moins un conducteur électrique par rapport à la borne de connexion correspondante est détecté, lorsque la valeur thermique de la plage de connexion est supérieure au seuil de température, le desserrage correspondant à une valeur d'impédance entre la plage de connexion 66 et le conducteur électrique de sortie correspondant supérieure à une valeur prédéterminée.
• Lors de l'étape b) de calcul de la valeur thermique de la plage de connexion, la valeur thermique est fixée égale à la première température.
• Le procédé comprend précédemment à l'étape b) de calcul de la valeur thermique, une étape a') de mesure d'une deuxième température ambiante au voisinage du dispositif électrique, via un deuxième capteur de température disposé à une distance inférieure à 3 mètres, de préférence à 1 mètre, du dispositif électrique, et lors de l'étape b) de calcul de la valeur thermique, la valeur thermique est égale à la différence entre la première température et la deuxième température.
• Lors de l'étape b') de calcul du seuil de température, le seuil de température est calculé avec la formule suivante : $$\mathrm{S}1\left(\mathrm{n}\right)=\mathit{dt}*\frac{\left(R*Z*{\left(\mathit{<figure-callout\; id="2"\; label="Irms\; n"\; filenames="imgf0005.png"\; state="\{\{state\}\}">Irms</figure-callout>}\left(n\right)\left(\right)\right)}^2-S1\left(n-1\right)\right)}{\mathit{RC}}+S1\left(n-1\right),$$
  
  avec S1(0) correspondant à la valeur du seuil de température à l'instant initial de référence, S1(0) dépendant de la valeur de la première température mesurée à l'instant initial de référence, S1(n) et S1(n-1) correspondant respectivement à la valeur du seuil de température à l'instant donné et à l'instant précédent, avec n supérieur ou égal à 1, dt correspondant à une période de calcul du seuil de température, suivant laquelle le seuil de température est calculé, Irms(n) correspondant à la valeur efficace du courant traversant le conducteur électrique de sortie correspondant à l'instant donné, Z correspondant à l'impédance entre la plage de connexion et le conducteur électrique correspondant, R et C correspondant respectivement à la résistance thermique et à la capacité thermique entre le premier et le deuxième capteurs de température.

According to various aspects of the invention, the method comprises one or more of the following features, taken alone or in any technically permissible combination:

• The method comprises previously in step b ') of calculating the temperature threshold, a step b ") of measuring the intensity of the current flowing in the corresponding electrical conductor, and during the calculation step b'), the temperature threshold is further calculated as a function of the intensity of the current flowing in the corresponding electrical conductor.
• The connection terminal or terminals each comprise a clamping element adapted to maintain the connection between the electrical conductor and the corresponding connection pad, by applying a clamping force on the electrical conductor, and during the step of detection d), a loosening of at least one electrical conductor relative to the corresponding connection terminal is detected, when the thermal value of the connection pad is greater than the temperature threshold, the loosening corresponding to an impedance value between the connection pad 66 and the corresponding output electrical conductor greater than a predetermined value.
• During step b) of calculating the thermal value of the connection range, the thermal value is set equal to the first temperature.
• The method comprises previously in step b) of calculating the thermal value, a step a ') of measuring a second ambient temperature in the vicinity of the electrical device, via a second temperature sensor disposed at a distance of less than 3 meters preferably at 1 meter, the electrical device, and during step b) of calculating the thermal value, the thermal value is equal to the difference between the first temperature and the second temperature.
• During step b ') of calculating the temperature threshold, the temperature threshold is calculated with the following formula: $$\mathrm{S}1\left(\mathrm{not}\right)=\mathit{dt}*\frac{\left(R*Z*{\left(\mathit{Irms}\left(\mathrm{not}\right)\right)}^2-S1\left(\mathrm{not}-1\right)\right)}{\mathit{RC}}+S1\left(\mathrm{not}-1\right),$$
  
  with S1 (0) corresponding to the value of the temperature threshold at the initial reference instant, S1 (0) depending on the value of the first temperature measured at the initial reference instant, S1 (n) and S1 (n -1) respectively corresponding to the value of the temperature threshold at the given instant and the previous instant, with n greater than or equal to 1, dt corresponding to a calculation period of the temperature threshold, according to which the temperature threshold is calculated, Irms (n) corresponding to the rms value of the current flowing through the output electrical conductor corresponding to the given instant, Z corresponding to the impedance between the connection pad and the corresponding electrical conductor, R and C respectively corresponding to the thermal resistance and the thermal capacity between the first and the second temperature sensors.

• un premier capteur de température propre à mesurer, à un instant temporel donné, une première température correspondant à la température de la plage de connexion correspondante,
• des premiers moyens de calcul d'une valeur thermique de la plage de connexion en fonction de la première température mesurée,
• des moyens de comparaison propres à comparer la valeur thermique de la plage de connexion avec un seuil de température, et
• des moyens de détection d'une surchauffe de la borne de connexion correspondante lorsque la valeur thermique de la plage de connexion correspondante est supérieure au seuil de température.

Conformément à l'invention, l'appareil auxiliaire comprend pour chaque borne de connexion des deuxièmes moyens de calcul du seuil de température à l'instant donné en fonction de la valeur du seuil de température à un instant précédent, la valeur du seuil de température étant variable entre l'instant précédent et l'instant donné, et les moyens de comparaison sont propres à comparer la valeur thermique avec la valeur du seuil de température à l'instant donné.The invention also relates to an auxiliary device for an electrical device, the electrical device comprising at least one connection terminal having a connection pad suitable for being connected to a corresponding electrical conductor, the auxiliary device comprising, for each terminal of connection:

• a first temperature sensor capable of measuring, at a given time instant, a first temperature corresponding to the temperature of the corresponding connection range,
• first means for calculating a thermal value of the connection range as a function of the first measured temperature,
• comparison means for comparing the thermal value of the connection range with a temperature threshold, and
• means for detecting an overheating of the corresponding connection terminal when the thermal value of the corresponding connection range is greater than the temperature threshold.

According to the invention, the auxiliary apparatus comprises, for each connection terminal, second means for calculating the temperature threshold at the given instant as a function of the value of the temperature threshold at a previous instant, the value of the temperature threshold. being variable between the previous instant and the given instant, and the comparison means are suitable for comparing the thermal value with the value of the temperature threshold at the given instant.

• L'appareil auxiliaire comprend, pour chaque borne de connexion, un capteur de courant propre à mesurer l'intensité du courant circulant dans le conducteur électrique correspondant, les deuxièmes moyens de calcul étant propres, pour chaque borne de connexion, à calculer le seuil de température en fonction en outre de l'intensité du courant circulant dans le conducteur électrique correspondant.
• L'appareil auxiliaire comprend pour chaque borne de connexion, un organe de liaison électrique à la plage de connexion correspondante, l'organe de liaison comportant un matériau thermiquement conducteur, la différence de température entre la plage de connexion correspondante et l'organe de liaison étant de préférence inférieure à 10°C, pour des températures de la plage de connexion comprises entre 100°C et 400°C, le premier capteur de température étant propre à mesurer la température de l'organe de liaison,
• L'appareil auxiliaire comprend un deuxième capteur de température, disposé à une distance inférieure à 3 mètres, de préférence à 1 mètre, du dispositif électrique et propre à mesurer une deuxième température ambiante au voisinage du dispositif électrique, et les premiers moyens de calcul sont propres à fixer la valeur thermique à une valeur égale à la différence entre la première température et la deuxième température.

According to other advantageous aspects of the invention, the auxiliary apparatus further comprises one or more of the following features, taken individually or in any technically permissible combination:

• The auxiliary apparatus comprises, for each connection terminal, a clean current sensor for measuring the intensity of the current flowing in the corresponding electrical conductor, the second calculation means being clean, for each connection terminal, for calculating the threshold of temperature in addition to the intensity of the current flowing in the corresponding electrical conductor.
• The auxiliary device comprises for each connection terminal, an electrical connecting member to the corresponding connection pad, the connecting member comprising a thermally conductive material, the temperature difference between the corresponding connection pad and the connecting member. being preferably lower than 10 ° C, for connection range temperatures of between 100 ° C and 400 ° C, the first temperature sensor being suitable for measuring the temperature of the connecting member,
• The auxiliary device comprises a second temperature sensor, disposed at a distance of less than 3 meters, preferably at 1 meter, from the electrical device and capable of measuring a second ambient temperature in the vicinity of the device electrical, and the first calculation means are adapted to set the thermal value to a value equal to the difference between the first temperature and the second temperature.

The invention also relates to an electrical system comprising an electrical device and an auxiliary device associated with the electrical device, the electrical device comprising at least one connection terminal having a connection range capable of being connected to an electrical conductor. According to the invention, the auxiliary apparatus is as shown above.

According to another advantageous aspect of the invention, the electrical device is a switching device comprising for each electrical conductor a current input terminal and a current output terminal, and, in an open position, to let current through the corresponding electrical conductor or conductors, and in a closed position to interrupt the flow of current through the corresponding electrical conductor (s), the auxiliary device being connected via the electrical connection member (s) to the or each terminal of current output.

• la figure 1 est une représentation schématique d'un système électrique selon un premier mode de réalisation de l'invention, comprenant un disjoncteur électrique et un appareil auxiliaire couplé électriquement au disjoncteur électrique ;
• la figure 2 est une représentation schématique de l'appareil auxiliaire de la figure 1 et de sa connexion à des bornes de connexion aval du disjoncteur de la figure 1 ;
• la figure 3 est une coupe schématique et partielle d'une borne de connexion aval du disjoncteur, suivant le plan III de la figure 1 ;
• la figure 4 est une représentation schématique d'un modèle thermique simplifié de la liaison entre l'une des bornes de connexion aval et l'appareil auxiliaire de la figure 2;
• la figure 5 est un organigramme d'un procédé de détermination d'une surchauffe des bornes de connexion, conforme à l'invention ;
• la figure 6 est une ensemble de quatre courbes, parmi lesquelles des première, deuxième et troisième courbes représentent l'échauffement, en fonction du temps, d'une borne de connexion du disjoncteur de la figure 1 pour différentes valeurs d'un couple de serrage appliquée à un élément de serrage de la borne et une quatrième courbe représente la valeur d'un seuil de température en fonction du temps ;
• la figure 7 est un ensemble de deux courbes représentant, pour différentes valeurs de courant traversant l'une des bornes de connexion aval du disjoncteur de la figure 1, respectivement, la valeur d'un seuil de température, en fonction du temps, et une valeur thermique de la borne de connexion aval, en fonction du temps ; et
• la figure 8 est une vue analogue à celle de la figure 1 selon un deuxième mode de réalisation de l'invention.

The invention will be better understood and other advantages thereof will appear more clearly in the light of the description which follows, given solely by way of nonlimiting example, and with reference to the appended drawings in which:

• the figure 1 is a schematic representation of an electrical system according to a first embodiment of the invention, comprising an electric circuit breaker and an auxiliary device electrically coupled to the electric circuit breaker;
• the figure 2 is a schematic representation of the auxiliary apparatus of the figure 1 and its connection to the downstream connection terminals of the circuit breaker of the figure 1 ;
• the figure 3 is a schematic and partial section of a connection terminal downstream of the circuit breaker, according to the plane III of the figure 1 ;
• the figure 4 is a schematic representation of a simplified thermal model of the connection between one of the downstream connection terminals and the auxiliary apparatus of the figure 2 ;
• the figure 5 is a flowchart of a method for determining an overheating of the connection terminals, according to the invention;
• the figure 6 is a set of four curves, among which first, second and third curves represent the heating, as a function of time, of a connection terminal of the circuit breaker of the figure 1 for different values of a tightening torque applied to a clamping element of the terminal and a fourth curve representing the value of a temperature threshold as a function of time;
• the figure 7 is a set of two curves representing, for different current values passing through one of the downstream connection terminals of the circuit breaker of the figure 1 respectively, the value of a temperature threshold, as a function of time, and a thermal value of the downstream connection terminal, as a function of time; and
• the figure 8 is a view similar to that of the figure 1 according to a second embodiment of the invention.

On the figure 1 , an electrical system 10 is connected, on the one hand, to a first 12 and a second 14 electrical input conductors and, secondly, to a first 12 'and a second 14' electrical conductors output. The electrical input conductors 12, 14 belonging to an electrical distribution network 16 and being intended to supply via the electrical system 10 and the electrical output conductors 12 ', 14' an electric charge 18.

The electrical system 10 is able to communicate via a wireless link with electronic equipment 20, such as a computer server, for centralizing data. The equipment 20 is also called data concentrator.

The electrical system 10 comprises an electric circuit breaker 22, such as an electromechanical circuit breaker, and an auxiliary device 24 electrically coupled to the circuit breaker 22. The auxiliary device 24 is, for example, fixed under the circuit breaker 22.

The electrical system 10 comprises a rail 25, such as a DIN rail, on which is mechanically fixed the circuit breaker 22.

The first input 12 and output 12 'conductors are, for example, phase conductors or positive positive potential conductors. The second input 14 and output 14 'conductors are, for example, neutral conductors or reference potential conductors. The first and second input electrical conductors 12, 14 and output 12 ', 14' form an electrical connection 26.

The data concentrator 20 is connected, via a data link, such as a radio link, to a display device 27, in order notably to display information relating to the operation of the circuit breaker 22 and transmitted by the auxiliary device 24. The concentrator 20 comprises a first communication element 28 and a first radio antenna 30.

The electric circuit breaker 22 is known per se, and is capable of interrupting the flow of an electric current passing through the first electrical input and output conductors 12 'and / or the second electrical input leads 14 and output 14 ', in particular in the presence of an electrical fault on the first input conductor 12 and / or on the second input conductor 14.

The circuit breaker 22 comprises a first 34 and a second 36 current input terminals, also called first and second upstream connection terminals, to which are connected the first 12 and second 14 electrical input conductors. The circuit breaker 22 also comprises a first 38 and a second 40 current output terminals, also called first and second downstream connection terminals, respectively connected to the first 12 'and second 14' electrical output conductors.

More specifically, the electric circuit breaker 22 makes the connection between the first 12 and second 14 electrical input conductors and respectively the first 12 'and second 14' electrical output conductors, via the upstream connection terminals 34, 36 and the terminals of FIG. downstream connection 38, 40.

The circuit breaker 22 is in the open position capable of interrupting the flow of an electric current through the electrical connection 26. The circuit breaker 22 is in the closed position capable of allowing the current to flow through the electrical connection 26, in order to supply the load 18.

The auxiliary apparatus 24 comprises for each downstream connection terminal 38, 40, a connecting member 42, 44 to the corresponding downstream connection terminal 38, 40, as shown in FIG. figure 2 . The auxiliary apparatus 24 comprises, for each downstream connection terminal 38, 40, a first temperature sensor 46 and a current sensor 50, 51. The auxiliary device 24 also comprises a processing unit 52, a power supply unit electrical 54 and a voltage regulator 56. The auxiliary device 24 comprises a member 58 for storing electrical energy and a second communication member 60, and a second radio antenna 62 able to communicate by radio waves with the first antenna 30. Advantageously, the auxiliary device 24 comprises a voltage sensor 64.

The display device 27, visible on the figure 1 , in particular comprises a display screen, not shown, and means, not shown, of display on the screen of data received from the data concentrator 20.

The first communication device 28 is able to transmit data to the auxiliary device 24 via the first antenna 30 and to establish a radio link with the auxiliary device 24.

Each downstream connection terminal 38, 40 comprises a connection pad 66 capable of being connected respectively to the first 12 'and second 14' conductors respectively. electrical output, as shown on the figure 2 . Each downstream connection terminal 38, 40 also comprises a clamping element 68 able to maintain the connection between the corresponding output electrical conductor 12 ', 14' and the corresponding connection pad 66, by applying a clamping force F on the corresponding output electrical conductor 12 ', 14'.

In the exemplary embodiment of the figure 3 , each downstream connection terminal 38, 40 comprises a movable member 70 adapted to be displaced via the clamping element 68 in order to clamp together, between the connection pad 66 and the movable member 70, the electrical output conductor 12 ' , 14 'corresponding, and the connecting member 42, 44 corresponding.

For example, the clamping force F is induced by a tightening torque C applied to the clamping element 68. figure 3 , the clamping member 68 is a screw.

As a variant, the output terminals differ from the downstream connection terminals 38, 40 presented in the first embodiment, while still including a clamping element adapted to maintain the connection between the corresponding output electrical conductor 12 ', 14' and the corresponding connection pad 66.

The connecting member 42 is in contact with the first electrical output conductor 12 'and the connection pad 66 of the first output terminal 38. The connecting member 42 comprises a thermally and electrically conductive material, such as copper . The temperature difference between the connection pad 66 and the connecting member 42 is preferably less than 10 ° C for temperatures of the connection pad 66 of between 100 ° C and 400 ° C.

Similarly, the connecting member 44 is in contact with the second electrical output conductor 14 'and the connection pad 66 of the second output terminal 40. The connecting member 44 comprises a thermally and electrically conductive material, such as only copper. The temperature difference between the connection pad 66 and the connecting member 44 is preferably less than 10 ° C for temperatures of the connection pad 66 of between 100 ° C and 400 ° C.

Each first temperature sensor 46 is able to measure, at a given time instant t _n , a first temperature corresponding to the temperature of the corresponding connection pad 66, that is to say at the temperature of the downstream connection terminal. 38, 40 corresponding. More specifically, the first temperature sensor 46 is, for example, positioned on the connecting member 42, 44 corresponding and is adapted to measure the temperature of the connecting member 42, 44. Each first temperature sensor is for example , thermocouple or resistance thermometer etc. Each first sensor is suitable for temperature measurement between 25 ° C and 400 ° C.

The current sensors 50, 51 are able to measure the intensity of the current flowing respectively in the first 12 'and second 14' electrical output conductors, that is to say also the intensity of the current flowing through the range of connection 66 and the corresponding downstream connection terminal 38, 40.

The current sensors 50, 51 comprise, for example, a Rogowski toroid, a current transformer, a shunt or a Hall effect sensor.

In a variant, the auxiliary device 24 comprises a current sensor 50 only for one of the downstream connection terminals 38, which is capable of measuring the current flowing in a single of the electrical output conductors, for example the first electrical conductor of the exit 12 '. The current flowing in the second output electrical conductor 14 'is then calculated from the value of the current flowing in the first output electrical conductor 12'. More precisely, the current flowing in the second electrical output conductor 14 'is equal to the opposite of the current flowing in the first electrical conductor 12'.

The processing unit 52 includes a second temperature sensor 71, a processor 72, and a memory 76 associated with the processor 72, as shown in FIG. figure 2 . The processing unit 52 is able to generate a message M1 comprising data calculated via the processor 72 and the memory 76.

The power supply member 54 is clean, via the connecting members 42, 44, to recover a part of the electrical energy transmitted on the electrical output conductors 12 ', 14' and to supply electrical energy to the apparatus auxiliary 24.

The voltage regulator 56 makes it possible to adapt the voltage delivered by the power supply 54 to a voltage value acceptable by the processing unit 52 and by the second communication element 60. The voltage regulator 56 is for example a converter DC / DC, which delivers a DC voltage of 3.3 volts.

The storage member 58 of electrical energy is able to store a portion of the electrical energy delivered by the power supply 54 when the circuit breaker 22 is closed, and to restore the stored electrical energy during a loss of voltage downstream of the circuit breaker 22.

On the figure 2 , the storage member 58 is a capacitor whose capacity value is a function, among other things, of the average power consumption of the auxiliary device 24 of the supply voltage delivered to the second communication element 60 and to the processing unit 52.

The second communication element 60 is able to receive data coming from the data concentrator 20, and more precisely from the first communication element 28 and the first antenna 30, and to establish a radio link with the concentrator 20. second communication member 60 is able to transmit, via the second antenna 62, the message M1 to the data concentrator 20. Advantageously, the communication members 28, 60 and the antennas 30, 62 are in accordance with the communication protocols ZIGBEE or ZIGBEE GREEN POWER, based on the IEE-802.15.4 standard.

Alternatively, the communication member 60 is able to communicate with the data concentrator 20 via a wire link, not shown.

The voltage sensor 64 is known per se, and is capable of measuring a first voltage V1 delivered between the first downstream connection terminal 38 and the second downstream connection terminal 40. The voltage sensor 64 makes it possible, more precisely, to measure the first voltage V1 at the output of the circuit breaker 22, at the first electrical output conductor 12 '.

The second temperature sensor 71 is able to measure a second temperature, corresponding to an ambient temperature in the vicinity of the circuit breaker 22. The second temperature sensor 71 is disposed at a distance of less than 3 m, preferably less than 1 m from the circuit breaker 22. The second temperature sensor 71 is integrated in the processing unit 52.

The figure 4 represents a thermal model of the connection between the auxiliary device 24 and one of the corresponding downstream connection terminals 38, 40. More specifically, the figure 4 corresponds to the thermal model of the connection between one of the connection pads 66 and the second temperature sensor 71. The model corresponds to an electrical circuit 77 comprising a current generator G, a thermal resistor R and a thermal capacitor C connected in parallel. parallel to each other. Thus, the thermal resistance R and the thermal capacitor C represent the thermal relation between the corresponding connection pad 66 and the second temperature sensor 71.

The memory 76 is able to store a first software 78 for calculating a thermal value of each connection pad 66, a second software 80 for calculating, for each connection pad 66, a temperature threshold S1, a software 82 for comparing the thermal value of each connection pad 66 with the temperature threshold S1, a software 83 for detecting an overheating of the downstream connection terminals 38, 40. In addition, the memory 76 is able to store a third software 84 of calculating a power and an electrical energy passing through each output electrical conductor 12 ', 14' as a function of the intensity and voltage values measured by the current sensors 50, 51 and the voltage sensors 64.

The memory 76 is able to store a software 88 for sampling the intensity of the current and the voltage measured by the current sensors 50, 51 and the voltage sensors 64. In a variant, the first calculation means 78, the second means 80, the comparison means 82, the detection means 83, the third calculation means 84 and the sampling means 88 are made in the form of programmable logic components or in the form of dedicated integrated circuits.

The first calculation software 78 is able to calculate the thermal value of each connection pad 66, as a function of the corresponding first measured temperature. More precisely, the first calculation software 78 is able to calculate the difference between the first temperature and the second temperature for each downstream connection terminal 38, 40. Thus, the thermal value corresponds, for example, to a temperature variation, such as the difference between the first temperature and the second temperature, and in particular to a heating of the connection pad 66.

Alternatively, the second temperature is considered equal to a predetermined constant value and the first calculation software 78 sets the thermal value equal to the difference between the first temperature and the predetermined constant value.

The second calculation software 80 is able to calculate the temperature threshold S1 at the given instant t _n as a function of the value of the temperature threshold calculated at a previous instant t _n-1 and the value of the temperature threshold S 1 is variable. between the given instant t _n and the previous instant t _n-1 . The second calculation software 80 is more precisely able to calculate the value of the next temperature threshold S1, a sampling period dt, also called the calculation period dt. The preceding instant t _n-1 corresponds, for example, to an instant preceding the given instant t _n of a duration equal to the calculation period dt.

In a variant, the previous instant t0 corresponds to an initial reference time t0. The initial reference time t0 corresponds, for example, to the instant of a first measurement made by the auxiliary device chosen from the measurement of the first temperature, the measurement of the second temperature and the measurement of the intensity of the current flowing in the corresponding output electrical conductor 12 ', 14', that is to say for example at the moment of powering on the circuit breaker 22.

The second calculation software 80 is also preferably able to calculate the temperature threshold S1 as a function of the intensity of the current flowing in the corresponding output electrical conductor 12 ', 14'. The temperature threshold S1 corresponds, by for example, at a limit temperature rise of the corresponding connection pad 66, that is to say at a temperature variation. The electrical circuit 77 presented above makes it possible to obtain an equation giving the value of the first temperature threshold S1.

avec S1(0) correspondant à la valeur du seuil de température à l'instant initial de référence t0, c'est-à-dire à un échantillon initial, appelé échantillon 0, de la valeur du seuil de température S1, S1(0) dépendant de la valeur de la première et de la deuxième température mesurées à l'instant initial de référence t0, c'est-à-dire par exemple égale à l'écart de la première température mesurée à l'instant initial de référence t0 par rapport à la deuxième température mesurée à l'instant initial de référence t0 et avec S1(n) et S1(n-1) correspondant respectivement à la valeur du seuil de température à l'instant donné t_n=t0+n*dt et à l'instant précédent t_n-1=t0+(n-1)*dt, avec n supérieur ou égal à 1 et correspondant au numéro d'échantillon de la valeur de seuil S1, dt correspondant, par exemple, également à une période suivant laquelle les premier 46 et deuxième 71 capteurs de température et le capteur de courant 50, 51 mesurent respectivement la première température, la deuxième température et le courant circulant dans le conducteur électrique de sortie 12', 14' correspondant, Irms(n) correspondant à la valeur efficace du courant traversant le conducteur électrique de sortie 12', 14' correspondant à l'instant donné t_n, Z correspondant à l'impédance entre la plage de connexion 66 et le conducteur électrique de sortie 12', 14' correspondant, R et C correspondant respectivement à la résistance thermique et à la capacité thermique entre la plage de connexion 66 et le deuxième capteur de température 71, et plus précisément entre le premier capteur de température 46 et le deuxième capteur de température 71.More precisely, the temperature threshold S1 is calculated according to the sampling period dt with the following equation: $$\mathrm{S}1\left(\mathrm{not}\right)=\mathit{dt}*\frac{\left(R*Z*{\left(\mathit{Irms}\left(\mathrm{not}\right)\right)}^2-S1\left(\mathrm{not}-1\right)\right)}{\mathit{RC}}+S1\left(\mathrm{not}-1\right),$$

with S1 (0) corresponding to the value of the temperature threshold at the initial reference time t0, that is to say to an initial sample, called sample 0, of the value of the temperature threshold S1, S1 (0 ) dependent on the value of the first and the second temperature measured at the initial reference time t0, that is to say for example equal to the difference of the first temperature measured at the initial reference time t0 with respect to the second temperature measured at the initial reference time t0 and with S1 (n) and S1 (n-1) respectively corresponding to the value of the temperature threshold at the given instant t _n = t0 + n * dt and at the preceding instant t _n-1 = t0 + (n-1) * dt, with n greater than or equal to 1 and corresponding to the sample number of the threshold value S1, dt corresponding, for example, also to a period in which the first 46 and second 71 temperature sensors and the current sensor 50, 51 measure respectively ectively the first temperature, the second temperature and the current flowing in the corresponding output electrical conductor 12 ', 14', Irms (n) corresponding to the rms value of the current flowing through the output electrical conductor 12 ', 14' corresponding to the given instant t _n , Z corresponding to the impedance between the connection pad 66 and the corresponding output electrical conductor 12 ', 14', R and C respectively corresponding to the thermal resistance and the thermal capacitance between the connection pad 66 and the second temperature sensor 71, and more precisely between the first temperature sensor 46 and the second temperature sensor 71.

Alternatively, the value of the temperature threshold S1 (0) at the initial reference time t0 is a predetermined value.

In the variant where the first calculation software 78 sets the thermal value equal to the difference between the first temperature and the predetermined constant value, the first temperature threshold S1 is calculated with an equation similar to equation (1) presented above, but the values of the parameters R and C of the equation would be different and correspond for example respectively to the thermal resistance and to the thermal capacitance between the connection pad 66 and a predetermined reference point.

The comparison software 82 is able to compare the thermal value of each connection pad 66, calculated by the first calculation software 78, with the corresponding temperature threshold S1. The comparison between the thermal value and the temperature threshold is performed at each multiple of the sampling period dt after the initial reference time t0. The temperature threshold S1 is calculated from the recursive equation (1) making it possible to calculate the value of the first threshold S1 at the given instant t _n , from the knowledge of the value of the first threshold S1 at the instant preceding t _n-1 and in particular from the knowledge of the value of the temperature threshold S1 (0) at the initial reference time t0.

More precisely, the comparison software 82 is able to compare the thermal value calculated from the first temperature measured at the given instant t _n with the value of the temperature threshold S1 (n) at the given instant t _n . Indeed, the comparison is effective if one compares the value of the temperature threshold S1 and the thermal value at the same instant, that is to say at the time of measurement of the first temperature corresponding to the calculated thermal value. . Thus, the given instant t _n corresponds to the measurement instant of the first temperature.

The detection software 83 is, more specifically, able to detect the loosening of at least one corresponding downstream connection terminal 38, 40, that is to say the loosening of at least one electrical output conductor 12 ', 14 'with respect to the corresponding downstream connection terminal 38, 40, when the thermal value of the connection pad 66 is greater than the temperature threshold S1. The loosening corresponds to a value of the tightening torque C less than a first predetermined reference value, that is to say to a value of the clamping force F less than a second predetermined reference value and therefore to a the value of the impedance Z greater than a predetermined value, that is to say, for example, greater than 0.004 Ω, preferably greater than 0.005 Ω.

The operation of the electrical system 10 according to the invention will now be explained using the figure 5 .

The method is presented below in the case of a single downstream connection terminal 38, 40, that is to say for the connection between only one of the downstream connection terminals 38, 40 and the auxiliary device 24. The method generally applies to each downstream connection terminal 38, 40.

During an initial step 100, the first temperature sensor 46 measures, at the instant given t _n , the first temperature. In addition, during the first measurement of the first temperature, that is to say at the initial reference time t0, the first measured temperature is saved and the temperature threshold S1 (0) at the initial reference time t0, that is to say the value of the initial sample of the temperature threshold S1, is calculated and then saved. Then, during a following 102, the second temperature sensor 71 measures the second temperature.

Then, during a step 104, the thermal value of the corresponding connection range 66 is calculated, for example with the difference between the first temperature and the second temperature, that is to say that the value of the second temperature at the first temperature.

Alternatively, in step 104, the thermal value is set equal to the first temperature and step 102 is not performed.

During a step 106, the intensity of the current flowing in the corresponding output electrical conductor 12 ', 14' is measured. Then, during a step 108, the value of the temperature threshold S1 at the given instant t _n is calculated as a function of the value of the temperature threshold S1 (n-1) at the previous instant t _n-1 and preferably also as a function of the intensity of the current measured in step 106. The temperature threshold S1 is thus calculated, for example, from equation (1) presented above. During a first calculation of the temperature threshold S1, after the initial reference time t0, the value of the temperature threshold at the initial reference time t0 is used. In addition, during the calculation of the temperature threshold S1, the values chosen for the thermal resistance R, the thermal capacitor C and the impedance Z between the connection pad 66 and the corresponding output electrical conductor 12 ', 14' are values corresponding to a maximum temperature rise of the corresponding connection pad 66 and therefore to a maximum temperature threshold S1. Thus, the value chosen for the impedance Z corresponds to the minimum permissible impedance to prevent a fire.

Then, during a step 110, the thermal value of the corresponding connection area 66 is compared with the value of the calculated temperature threshold S1, at the given instant t _n , during step 108.

If, during the comparison step 110, the thermal value is less than or equal to the temperature threshold S1, then the process returns to step 100 for measuring the first temperature after a predetermined duration, corresponding, for example , at the sampling period dt.

If, during the comparison step 110, the thermal value is strictly greater than the temperature threshold S1, then, during a step 112, an overheating of the connection pad 66 and the corresponding downstream connection terminal 38, 40 is detected. In step 112, the loosening of the electrical output conductor 12 ', 14' corresponding, with respect to the corresponding downstream connection terminal 38, 40, is then for example detected.

In a next step 114, the first message M1 is generated and includes a data item specifying the looseness detection or, more generally, the overheating of the corresponding downstream connection terminal 38, 40. Finally, during a next step 116, the first message M1 is transmitted to the concentrator 20. The concentrator 20 is then able to indicate to an operator, via the display device 27, an overheating or loosening of the connection terminal downstream 38, 40 corresponding.

Advantageously, during the generation of the first message M1, the electrical power and electrical energy values calculated by the third calculation software 84 are included in the first message M1.

To the figure 6 one observes first, second, and third 204 204 curves corresponding to the thermal values, and more precisely to the heating values of one of the connection pads 66, calculated by the first calculation software 78. The first 200, second 202 and third 204 curves are plotted as a function of time T, and more precisely according to the time elapsed since the initial reference time t0. The initial reference moment corresponds to the abscissa 0 to the figure 6 . The first 200, second 202 and third 204 curves each correspond to a respective tightening torque C, applied to the clamping element 68 in order to maintain the electrical connection between the electrical conductor and the connection pad 66, respectively equal to 2 Nm , 0.2 Nm and 0.1 Nm, for a current measured by the current sensor 50, 51 corresponding to 20 A. figure 6 also shows a fourth curve 206 corresponding to the value of the temperature threshold S1 calculated by the second calculation software 80, as a function of time, and more precisely according to the time elapsed since the initial reference time t0.

On the figure 6 it is observed that the thermal value calculated for the first 200, second 202 and third 204 curves is always lower than the value of the temperature threshold S1, presented on the fourth curve 206. In fact, for the first 200, second 202 and third 204 curves, the value of the tightening torque C and therefore the clamping force F is such that the corresponding downstream connection terminal 38, 40 is not considered loosened, the value of the temperature threshold is never reached. . However, it should be noted that when the value of the tightening torque C, and hence of the clamping force F, decreases, the thermal value corresponding here to a heating value of the connection pad 66 increases. Furthermore, it clearly appears on the fourth curve 206 that the value of the temperature threshold S1 varies according to the time elapsed with respect to the initial reference time t0, and more generally with respect to the previous instant. The shape of the fourth curve 206 is globally similar to that of the other three curves 200, 202, 204. The evolution of the temperature threshold therefore follows that of the thermal value, which makes it possible to determine the overheating of the downstream connection terminal. 38, 40 more precisely, without risk of error.

To the figure 7 a fifth curve 208 corresponding to the thermal value of one of the connection pads 66, calculated by the first calculation software 78, as a function of time, and more precisely according to the time elapsed since the initial instant, is observed. reference t0, and more generally since the previous instant t _n-1 , and a sixth curve 210 corresponding to the value of the temperature threshold S1 calculated by the second calculation software 80, as a function of time. On the figure 7 , the initial reference time corresponds to the abscissa 0. The fifth 208 and sixth 210 curves are obtained for a value of the current flowing through the connection pad 66 and the corresponding output electrical conductor 12 ', 14', which varies with course of time. The current flowing through the corresponding connection pad 66 is equal to 10 A between 0 seconds (s) and 600 s, then 40 A between 600 s and 1500 s and at 20 A between 1500 s and 2800 s.

Concerning the fifth curve 208, a loosening of the clamping element 68, that is to say of the corresponding downstream connection terminal 38, 40, has been performed for a time equal to 2400 s. Thus, between 0 s and 2400 s the tightening torque is equal to 0.2 Nm and after 2400 s the tightening torque is equal to 0 Nm which corresponds to a complete loosening of the clamping element 68.

It is then observed that before a time equal to 2400s, the thermal value is below the temperature threshold S1 and the evolution of the sixth curve 210 follows that of the fifth curve 208. Then, after loosening of the connection terminal corresponding downstream 38, 40, the thermal value increases sharply and becomes greater than the value of the temperature threshold S1. The overheating of the corresponding downstream connection terminal 38, 40 is then detected.

The fact that the value of the temperature threshold S1 varies as a function of time and more precisely between the given instant t _n and the previous instant t _n-1 makes it possible to determine the superheating more precisely. Indeed, this makes it possible to consider, for example, different operating phases of the circuit breaker 22, and more specifically the downstream connection terminals 38, 40. The method of calculating the temperature threshold S1 as a function of time makes it possible, for example, to take better account is taken of the environment in which the downstream connection terminal (s) 38, 40 are located.

It is observed on the fifth 208 and sixth 210 curves, that when the current increases or decreases, the thermal value and the value of the temperature threshold S1 respectively increase or decrease. The evolution of the temperature threshold S1 follows that of the thermal value, which makes it possible to more precisely determine the overheating of the corresponding downstream connection terminal 38, 40. On the figure 7 it is observed that the overheating here due to loosening is detected after 80 s, which makes it possible to quickly detect an anomaly and, for example, to quickly control the power down of the circuit breaker 22 or the intervention of an operator . The fact that the temperature threshold S1 is calculated as a function of the intensity of the current makes it possible, in addition, to improve the detection of the superheating since the evolution of the temperature threshold S1 follows that of the thermal value with precision.

In addition, the auxiliary device 24 makes it possible to detect overheating, ie a terminal loosening even for an intensity of the current flowing through the corresponding output electrical conductor 12 ', 14' of less than 10 A and even when the value overheating is low, for example, of the order of 25 ° C, since the value of the temperature threshold generally changes in a similar way to that of the thermal value when it is preferably further calculated as a function of the measured current through the corresponding output electrical conductor 12 ', 14'.

The connecting members 42, 44 allow improved heat conduction between the corresponding connection pad 66 and each temperature sensor 46.

Advantageously, the auxiliary device 24 comprises means for detecting a loss of voltage downstream of the circuit breaker and is able to determine a cause of loss of voltage downstream of the circuit breaker 22, said cause being preferably chosen from the group consisting of : an electrical overload, a short circuit, and a voltage drop. More specifically, the auxiliary device 24 is in accordance with the auxiliary device described in the patent application filed under the number FR 13 58776 on pages 9 to 11.

The figure 8 illustrates a second embodiment of the invention for which the elements similar to the first embodiment, described above, are identified by identical references, and are not described again.

According to the second embodiment, the current flowing in the electrical conductors 12, 12 ', 14, 14' is a three-phase current, and the electrical connection 26 comprises three first electrical output conductors 12 'and three first electrical input conductors 12, corresponding to phase conductors and a second output electrical conductor 14 'and a second input electrical conductor 14, corresponding to neutral conductors.

The electrical system 10 then comprises four circuit breakers 22 each provided with a single downstream connection terminal 38, 40 and a single upstream connection terminal 34, 36 and forming a four-pole circuit breaker, coupled to the auxiliary device 24.

The auxiliary apparatus 24 then comprises four connecting members and four current sensors.

The second calculation software 80 of the temperature threshold S1 is then adapted to calculate the temperature threshold S1 (n) at the given instant t _n , for each connection terminal, as a function of the value of the temperature threshold S1 (n -1) at the previous instant t _n-1 and the current flowing through the corresponding downstream connection terminal 38, 40.

The operation of this second embodiment for each first electrical output conductor 12 'and the second output electrical conductor 14' is similar to that of the first embodiment, described for a first output conductor 12 'and a second output conductor. output 14 ', and is not described again.

The advantages of this second embodiment are identical to those of the first embodiment.

Alternatively, in this second embodiment, the auxiliary device 24 comprises three current sensors each associated with a respective first output electrical conductor 12 '. The current flowing in the second electrical output conductor 14 'is then calculated from the currents measured in the first electrical output conductors 12'.

More generally, the invention applies equally well to a single-phase circuit breaker adapted to be connected to a phase conductor and a neutral conductor, as shown in the first embodiment, to a three-phase circuit breaker suitable for connection. with three phase conductors, or a four-pole circuit breaker connected to three phase conductors and a neutral conductor, as shown in the second embodiment. For single-phase and four-pole circuit-breakers, when opening the circuit-breaker, depending on the application in question, the neutral conductor is cut and the current flowing through it is interrupted, or the neutral conductor is not cut and the current crossing is not interrupted.

More generally, the auxiliary device 24 is adapted to be associated with any type of electrical device comprising a connection terminal.

According to another variant, the communication elements 28, 60 and the antennas 30, 62 conform to any type of wireless communication protocol, such as the WIFI protocol or the BLUETOOTH protocol.

Claims (12)

1. Method for determining, using an auxiliary unit (24), an overheating of at least one connection terminal (38, 40) of an electrical device (22), the one or more connection terminals (38, 40) each comprising at least one connection area (66) that is capable of being connected to a corresponding electrical conductor (12', 14'),
   the method comprising, for each connection terminal (38, 40), the following steps:

   - a) measuring (100), at a given instant in time (t_n), a first temperature corresponding to the temperature of the corresponding connection area (66), via a first temperature sensor (46);

   - b) computing (104) a thermal value of the connection area (66) as a function of the first measured temperature;

   - c) comparing (110) the thermal value of the connection area (66) with a temperature threshold (S1), and

   - d) detecting (112) an overheating of the corresponding connection terminal (38, 40) when the thermal value of the connection area (66) is above the temperature threshold (S1),

   the method being characterized in that it comprises, prior to comparison step c) and for each connection terminal (38, 40), the following step:

   - b') computing (108) the temperature threshold (S1(n)) at the given instant (t_n) as a function of the value of the temperature threshold (S1(n-1)) at a preceding instant (t_n-1, t0), the value of the temperature threshold (S1) varying between the preceding instant (t_n-1, tO), and the given instant (t_n), and

   in comparison step c), the thermal value is compared with the value of the temperature threshold (S1 (n)) at the given instant (t_n).
2. Method according to Claim 1, characterized in that it comprises, prior to step b') of computing the temperature threshold (S1), the following step:

   - b") measuring (106) the intensity of the current flowing through the corresponding electrical conductor (12', 14'),

   and in that in computation step b'), the temperature threshold (S1) is additionally computed as a function of the intensity of the current flowing through the corresponding electrical conductor (12', 14'),
3. Method according to one of the preceding claims, characterized in that the one or more connection terminals (38, 40) each comprise a clamping element (68) that is capable of maintaining the connection between the corresponding electrical conductor (12', 14') and the corresponding connection area (38, 40) via the application of a clamping force (C) on the electrical conductor (12', 14'), and in that in detection step d), a loosening of at least one electrical conductor (12', 14') with respect to the corresponding connection terminal (38, 40) is detected when the thermal value of the connection area is above the temperature threshold (S1), the loosening corresponding to an impedance value (Z) between the connection area 66 and the corresponding electrical output conductor (12', 14') that is higher than a predetermined value.
4. Method according to one of the preceding claims, characterized in that in step b) of computing the thermal value of the connection area (66), the thermal value is fixed so as to be equal to the first temperature.
5. Method according to one of Claims 1 to 3, characterized in that it comprises, prior to step b) of computing the thermal value, the following step:

   - a') measuring (102) a second ambient temperature in the vicinity of the electrical device (22) via a second temperature sensor (71) that is positioned at a distance of less than 3 metres away, preferably 1 metre away, from the electrical device (22),

   in that, in step b) of computing the thermal value, the thermal value is equal to the difference between the first temperature and the second temperature.
6. Method according to Claim 5, characterized in that in step b') of computing the temperature threshold (S1), the temperature threshold (S1) is computed using the following formula: $$\mathrm{S}1\left(\mathrm{n}\right)=\mathit{dt}*\frac{\left(R*Z*{\left(\mathit{Irms}\left(n\right)\right)}^2-S1\left(n-1\right)\right)}{\mathit{RC}}+S1\left(n-1\right),$$

   

   where S1(0) corresponds to the value of the temperature threshold at the initial reference instant (tO), S1(0) is dependent on the value of the first temperature measured at the initial reference instant,

   S1 (n) and S1 (n-1) correspond, respectively, to the value of the temperature threshold at the given instant (t_n) and at the preceding instant (t_n-1), where n is greater than or equal to 1, dt corresponds to a period of computing the temperature threshold, in which the temperature threshold (S1) is computed, Irms(n) corresponds to the root mean square value of the current flowing through the electrical output conductor (12', 14') corresponding to the given instant (t_n), Z corresponds to the impedance between the connection area (66) and the corresponding electrical conductor (12', 14'), R and C correspond, respectively, to the thermal resistance and to the thermal capacitance between the first (46) and the second (71) temperature sensors.
7. Auxiliary unit (24) for an electrical device (22), the electrical device (22) comprising at least one connection terminal (38, 40) comprising a connection area (66) that is capable of being connected to a corresponding electrical conductor (12', 14'), the auxiliary unit (24) comprising, for each connection terminal (38, 40):

   - a first temperature sensor (46) that is capable of measuring, at a given instant in time (t_n), a first temperature corresponding to the temperature of the corresponding connection area (66);

   - first computation means (78) for computing a thermal value of the connection area (66) as a function of the first measured temperature;

   - comparison means (82) that are capable of comparing the thermal value of the connection area (66) with a temperature threshold (S1), and

   - detection means (83) for detecting an overheating of the corresponding connection terminal (38, 40) when the corresponding thermal value of the connection area (66) is above the temperature threshold (S1),

   characterized in that the auxiliary unit (24) comprises, for each connection terminal (38, 40):

   - second computation means (80) for computing the temperature threshold (S1) at the given instant (t_n) as a function of the value of the temperature threshold (S1(n-1)) at a preceding instant (t_n-1, t0), the value of the temperature threshold (S1) varying between the preceding instant (t_n-1), and the given instant (t_n), and the comparison means (82) are capable of comparing the thermal value with the value of the temperature threshold (S1(n)) at the given instant (t_n).
8. Unit according to Claim 7, characterized in that it comprises, for each connection terminal (38, 40), a current sensor (50, 51) that is capable of measuring the intensity of the current flowing through the corresponding electrical conductor (12', 14'), the second computation means (80) being capable, for each connection terminal (38, 40), of computing the temperature threshold (S1) additionally as a function of the intensity of the current flowing through the corresponding electrical conductor (12', 14').
9. Unit according to Claim 7 or 8, characterized in that it comprises, for each connection terminal (38, 40), a member (42, 44) for making an electrical connection to the corresponding connection area (66), the connection member (42, 44) comprising a thermally conductive material, the difference in temperature between the corresponding connection area (66) and the connection member (42, 44) preferably being less than 10°C for temperatures of the connection area (66) of between 100°C and 400°C, the first temperature sensor (46) being capable of measuring the temperature of the connection member (42, 44).
10. Unit according to one of Claims 7 to 9, characterized in that it comprises a second temperature sensor (71) that is positioned at a distance of less than 3 metres away, preferably 1 metre away, from the electrical device (22) and is capable of measuring a second ambient temperature in the vicinity of the electrical device (22), and in that the first computation means (78) are capable of fixing the thermal value at a value that is equal to the difference between the first temperature and the second temperature.
11. Electrical system (10) comprising an electrical device (22) and an auxiliary unit (24) associated with the electrical device, the electrical device (22) comprising at least one connection terminal (38, 40) comprising a connection area (66) that is capable of being connected to an electrical conductor (12', 14'), characterized in that the auxiliary unit (24) is in accordance with one of Claims 7 to 10.
12. System according to Claim 11, characterized in that the electrical device (22) is a switching device comprising, for each electrical conductor (12, 12', 14, 14'), a current input terminal (34, 36) and a current output terminal (38, 40) and is capable, in an open position, of allowing the current to flow through the one or more corresponding electrical conductors (12', 14') and, in a closed position, of interrupting the flow of the current through the one or more corresponding electrical conductors (12', 14'), the auxiliary unit being connected via the one or more electrical connection members (42, 44) to the or each current output terminal (38, 40).

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