System for non-invasive determination of the temperature of a conductor of an electric cable

Abstract

The invention relates to a system for non-invasively determining (100) a temperature of a conductor of an electric cable, comprising:- an electric cable (10) comprising at least one electric conductor (12) and at least one layer of material (14, 16) surrounding said at least one conductor, said at least one layer having a layer thermal resistance T1,- at least one temperature sensor (20) arranged on an external surface (18) of said at least one layer of material for measuring a peripheral temperature Θb1 at the external surface of said at least one layer of material,- a determination unit (22) configured to determine a conductor temperature Θcond as a function of the measured peripheral temperature Θb1, the layer thermal resistance T1 and the heat flux Wc generated by the flow of an electric current in the electric conductor. Figure for abstract: Figure 2

Description

Title of the invention: System for non-invasive determination of the temperature of a conductor of an electric cable Technical field

[0001] The present invention relates to a system for determining the temperature of an electrical conductor of an electrical cable.

[0002] More specifically, the invention relates to a non-invasive determination system. Technological background

[0003] During the testing phase or the use of an electric cable, it is important to know the temperature of the conductor of the electric cable so as to be able to monitor the correct operation of this same cable as well as to size it correctly.

[0004] One difficulty lies in the fact that placing a temperature sensor directly near the conductor results in the presence of a hole or space within the cable which can generate electric arcs within this space.

[0005] To overcome this difficulty, it is known to connect a portion of the electrical cable to a test loop formed by a cable of the same nature as the electrical cable. No voltage is applied in the test loop and a temperature sensor is placed in contact with the conductor. This makes it possible to monitor the temperature variation of the conductor of the test loop so as to estimate the temperature of the conductor of the portion of electrical cable in which a current flows. The disadvantage of this method is that it can only be carried out in a test phase and not on an electrical cable installed in situ.

[0006] Another method consists of placing an optical fiber inside an electrical cable along the electrical conductor during the manufacture of this electrical cable. This optical fiber makes it possible to measure the temperature of the conductor. The disadvantage of this method is that it is invasive because the presence of the optical fiber requires adaptation of the electrical cable. In addition, the optical fiber must be inserted along the entire length of the cable, which generates a significant cost.

[0007] There is therefore a need for a system for non-invasively determining the temperature of a conductor of an electric cable. Summary of the invention

[0008] For this, the invention proposes a system for non-invasively determining the temperature of a conductor of an electric cable, comprising: - an electrical cable comprising at least one electrical conductor and at least one layer of material surrounding said at least one conductor, said at least one layer having a thermal resistance of layer Tb - at least one temperature sensor arranged on an external surface of said at least one layer of material to measure a peripheral temperature 0M at the external surface of said at least one layer of material, - a determination unit configured to determine a conductor temperature 0cond as a function of the measured peripheral temperature 0bi, the layer thermal resistance Ti and the thermal flux Wc generated by the circulation of an electric current in the electric conductor.

[0009] The determination of the conductor temperature 0cond is done here by means of a physical model using the measured peripheral temperature 0bi, the layer thermal resistance Ti and the thermal flux Wc generated by the circulation of an electric current in the electric conductor.

[0010] The use of this physical model makes it possible to avoid the use of an internal temperature in the electric cable, i.e. measured via a component placed close to the conductor, or more generally inside the external sheath of the electric cable.

[0011] The physical model used makes it possible to estimate the conductor temperature 0cond by means of the measured peripheral temperature 0b[, the layer thermal resistance Ti and the thermal flux Wc generated by the circulation of an electric current in the electric conductor.

[0012] According to one embodiment of the determination system, the determination unit is configured to determine the conductor temperature 0cond based on the following equation: ©cond = ©bl + WC*T!

[0013] The determination unit can be arranged near the electric cable or at a distance from it.

[0014] According to one embodiment of the determination system, said at least one layer of material comprises an external sheath forming said external surface, said at least one temperature sensor being arranged on said external sheath.

[0015] According to one embodiment of the determination system, the latter further comprises a device for measuring the electrical intensity Icond of an electrical current flowing in said at least one electrical conductor, the determination unit being configured to determine said conductor temperature 0cond furthermore as a function of this electrical intensity Icond.

[0016] According to one embodiment of the determination system, the measuring device is a non-invasive device, in particular of the Rogowski coil type.

[0017] According to one embodiment of the determination system, the temperature of the conductor 0cond is determined as follows: ©cond = 0b 1 + Re*Lond2*Ti Rc being the electrical resistance of the conductor

[0018] According to one embodiment of the determination system, the latter further comprising: - an additional layer of material arranged around said at least one layer of material and covering said at least one temperature sensor, said additional layer of material having an additional thermal resistance Tb - at least one additional temperature sensor arranged on an external surface of said additional layer of material for measuring an additional peripheral temperature 0b2 at the external surface of said at least one additional layer of material.

[0019] According to one embodiment of the determination system, said additional layer of material extends around said at least one layer of material only over a portion of the length of the electrical cable.

[0020] According to one embodiment of the determination system, the determination unit is configured to determine the conductor temperature 0cond based on the following equation: a — û ivt is the peripheral temperature measured by said at ^cond ~ Ubl+ Tb X 1 minus one temperature sensor, 0b2 is the additional peripheral temperature measured by said at least one additional temperature sensor, Tb being the additional thermal resistance of the additional layer of material, Ti being the thermal resistance of said at least one layer of material.

[0021] According to one embodiment of the determination system, the determination unit is configured to determine the conductor temperature 0cond furthermore as a function of a heating Wd originating from a dielectric loss in said at least one layer of material.

[0022] According to one embodiment of the determination system, the determination unit is configured to determine the conductor temperature 0cond based on the following equation: Wd being heating from a dielectric loss in said at least one layer of material.

[0023] According to one embodiment of the determination system, the determination unit is configured to determine the conductor temperature 0cond based on the following equation: g _ g + x / _ wd \ Wd being heating from a di- loss electrical in said at least one layer of material.

[0024] According to one embodiment of the determination system, the latter further comprises a determination housing comprising one or more of said at least one temperature sensor and the determination unit, the housing being configured to be removably mounted to the electrical cable.

[0025] According to one embodiment of the determination system, said at least one additional layer of material and said at least one additional temperature sensor are carried by the determination housing.

[0026] This determination box is for example removable from the electric cable so as to carry out a punctual and localized measurement on the electric cable. This box is for example a measuring accessory.

[0027] The determination housing has a dimension along the longitudinal axis such that it extends only over a portion of the length of the electric cable. Brief description of the figures

[0028] The description which follows with reference to the appended drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be implemented. In the appended figures:

[0029] [Fig-1] [Fig.l] represents a sectional view of an electric cable according to a first configuration comprising an electrical conductor and at least one layer of material, the electrical cable belonging to a determination system;

[0030] [Fig.2] [Fig.2] shows a sectional view of the electrical cable of [Fig.l] comprising a plurality of sensors on an outer surface of said at least one layer of material;

[0031] [Fig.3] [Fig.3] represents a diagram of a first modeling of the electric cable, according to a first determination mode comprising a determination of the electrical intensity of the electric current flowing in the electric conductor;

[0032] [Fig.4] [Fig.4] represents a sectional view of the electric cable of [Fig.l] according to a second determination mode in which the determination system comprises an additional layer of material around the electric cable and a plurality of additional sensors arranged on an external surface of this additional layer of material;

[0033] [Fig.5] [Fig.5] represents a diagram of a second modeling of the electric cable according to the second determination mode;

[0034] [Fig.6] [Fig.6] represents a third modeling of the electric cable in which the dielectric losses in said at least one layer of material are taken into account, according to the first method of determination;

[0035] [Fig.7] [Fig.7] represents a fourth modeling of the electric cable in in which the dielectric losses in said at least one layer of material are taken into account, according to the second method of determination;

[0036] [Fig-8] [Fig.8] shows a sectional view of the electrical cable according to a second configuration comprising an electrical conductor, one or more layers of material surrounding the electrical conductor and a screen surrounding said layers of material;

[0037] [Fig.9] [Fig.9] a fifth modeling of the electric cable in which the dielectric losses in said at least one layer of material are taken into account as well as the dielectric losses in the screen;

[0038] [Fig. 10] [Fig. 10] a sixth modeling of the electric cable to determine the conductor temperature 0condde independently of the surrounding environment;

[0039] [Fig. 11] [Fig. 11] shows a perspective view of an embodiment of the determination system of [Fig.l] comprising a determination housing mounted on the electrical cable, the determination housing comprising a temperature sensor and / or a temperature unit. Description of embodiment(s)

[0040] For the sake of clarity, the same references designating the same elements according to the state of the art and according to the invention are used for all the figures.

[0041] The inventive concept is described more fully below with reference to the accompanying drawings, in which embodiments of the inventive concept are shown. In the drawings, the size and relative sizes of elements may be exaggerated for clarity. Like numerals refer to like elements throughout the drawings. However, this inventive concept may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Instead, these embodiments are provided so that this description is complete, and communicates the scope of the inventive concept to those skilled in the art.

[0042] A reference throughout the specification to "an embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, the occurrence of the phrase "in an embodiment" at various locations throughout the specification does not necessarily refer to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Furthermore, the term "comprising" does not exclude other elements or steps.

[0043] Referring to [Fig.l], an electrical cable 10 comprises an electrical conductor 12, a first layer of material 14 around the electrical conductor 12 and a second layer of material 16 around the first layer of material 14.

[0044] The electrical conductor 12 extends along a longitudinal axis A.

[0045] The first 14 and second 16 layers of material extend along the longitudinal axis A, around the electrical conductor 12.

[0046] The first layer of material 14 is for example a layer formed from an electrically insulating material. The first layer of material 14 can therefore be considered as an insulating layer.

[0047] The second layer of material 16 here forms an external layer of the electric cable 10. The second layer of material 16 forms an external surface 18 of the electric cable 10.

[0048] The second layer of material 16 is for example an external sheath.

[0049] More generally, the electrical cable 10 may comprise one or more layers of material surrounding the electrical conductor 12. The electrical cable 10 may in particular comprise one or more of: a screen, a semi-conducting layer, an insulating layer, an external sheath.

[0050] In a preferred configuration, the electrical cable 10 comprises around the conductor, in order of arrangement from the center to the periphery: a semi-conducting layer, an insulating layer, a screen and an external sheath. This configuration corresponds for example to an electrical cable configured for a medium voltage network (between 1 and 52 kV).

[0051] With reference to [Fig.2], a determination system 100 comprises the electrical cable 10, at least one temperature sensor 20 and a determination unit 22.

[0052] The determination system 100 may comprise a plurality of temperature sensors 20 distributed around the longitudinal axis A in the same plane transverse to this longitudinal axis A. In the example of [Fig.2], the determination system 100 comprises 9 temperature sensors 20.

[0053] The temperature sensor(s) 20 are configured to measure a peripheral temperature 0M. In this configuration where the temperature sensors 20 are arranged at the external surface 18 of the electrical cable, the peripheral temperature 0bi corresponds to the surface temperature of the electrical cable 10.

[0054] The temperature sensor(s) 20 are connected to the determination unit 22 so as to communicate the peripheral temperature 0M to this determination unit 22.

[0055] Preferably, the temperature sensors 20 are equally distributed around the longitudinal axis A. The determination system 100 may provide one or more temperature sensors 20 further distributed along the longitudinal axis A so as to measure the peripheral temperature 0bi at different locations along the electrical cable 10.

[0056] This determination unit 22 is configured to determine the conductor temperature 0cond, i.e. the temperature of the electrical conductor 12.

[0057] This determination is carried out in a non-invasive and non-destructive manner. Thus, no component is inserted under the layers of material or near the electrical conductor 12 to determine its conductor temperature 0cond. In addition, no layer of material of the electrical cable 10 is damaged or pierced to carry out this determination. No third-party component is integrated into the manufacture of the electrical cable 10 such as an optical fiber or a sensor in one of the layers of the electrical cable 10 or between these layers of material.

[0058] More generally, the term "non-invasive" or "non-destructive" means that the initial structure of the cable is not modified. This initial structure of the cable corresponds to the structure of the cable without a temperature determination unit or, more generally, a device for determining the temperature of the electrical conductor.

[0059] This makes it possible to determine the conductor temperature on an existing electrical cable, for example one already installed in situ, without having to damage it or insert any measuring tool into it.

[0060] It is considered here that the addition of additional measuring components or layers of material is not invasive or destructive.

[0061] The determination unit 22 uses a physical model making it possible to determine the conductor temperature 0cond as a function of the peripheral temperature 0bi measured by the temperature sensor(s) 20.

[0062] With reference to [Fig. 3], the diffusion of heat through the electric cable 10 is represented in the form of a diagram to illustrate the physical model used by the determination unit 22.

[0063] This physical model is based on the fact that the diffusion of heat through the layers of an electric cable follows a behavior close to that of the circulation of a current within an electric circuit comprising an electric resistance.

[0064] Thus, the physical model establishes a relationship between the thermal resistance T1 of said at least one layer of material. The thermal resistance T1 may correspond to the thermal resistance of one or more of the layers of material. In the example of [Fig.2], the thermal resistance ^represents the thermal resistance of all of the first 14 and second 16 layers of material. For this physical model, the first 14 and second 16 layers of material therefore form a single layer of material having a layer thermal resistance, called Ti

[0065] The passage of current inside the conductor generates heating inducing a thermal flux Wc.

[0066] In this physical model, the voltage difference AU across an electrical resistor is compared to a temperature difference A0 between the internal and external surfaces of said at least one layer of material (i.e. across this layer of material).

[0067] In the application of the electric cable 10, the temperatures at the terminals of the thermal resistance Tl are on the one hand the temperature of the conductor 0cond and on the other hand the peripheral temperature 0M. Thus, the temperature difference A0 is expressed as follows: A0 = 0cond- 0m •

[0068] According to this physical model, a mathematical relationship is established between heat flow Wc, thermal resistance Tl and the temperature difference A0 across this thermal resistance. This relationship is as follows: A0 = Tj*Wc with A0 being the temperature difference A0 between the inner and outer surfaces of the layer of said at least one layer of material, Ti being the thermal resistance of said at least one layer of material, Wc being the thermal flux generated by heating of the conductor.

[0069] The conductor temperature 0cond can therefore be expressed as follows: 0eond= ©bl + WC*T! with 0cond being the conductor temperature, ©bi being the peripheral temperature.

[0070] The thermal resistance Ti of said at least one layer of material is determined as follows: i 2x?r \ a, / pT being the thermal conductivity of said at least one layer of material, dc being the internal diameter of said at least one layer of material, T being the thickness of said at least one layer of material.

[0071] The physical model includes two modes of determining the conductor temperature 0cond.

[0072] In the first determination mode, the determination system 100 comprises a device for measuring the electrical intensity Lond of an electric current flowing in said at least one electrical conductor 12.

[0073] The measuring device is a non-invasive device, in particular of the Rogowski coil type.

[0074] In the second determination mode, the determination system 100 comprises at least one additional layer 24 of material and at least one sensor additional temperature 26.

[0075] This second method of determination makes it possible to avoid using the electrical intensity Icond of the current flowing in the conductor.

[0076] Said at least one additional layer of material 24 is arranged around said at least one layer of material. The additional layer(s) of material 24 covers said at least one temperature sensor 22, as visible in [Fig.4].

[0077] These two determination modes can be used for determining the conductor temperature 0cond according to different models of an electric cable 10. These different models can involve different hypotheses (e.g. taking into account or not dielectric losses) or different configurations of the electric cable 10.

[0078] The determination unit 22 is configured to implement the first and / or the second determination modes. The determination unit 22 is configured to determine the conductor temperature 0cond according to one or more models, in particular one or more of the models presented below.

[0079] Electrical cable without screen and without taking into account dielectric losses

[0080] The determination unit 22 is configured to determine the conductor temperature 0cond according to a first and a second modeling respectively illustrated in FIGS. 3 and 5.

[0081] More specifically, the determination unit 22 is configured for the conductor temperature 0cond according to the first modeling by means of the first determination mode. The determination unit 22 is configured for the conductor temperature 0cond according to the second modeling by means of the second determination mode.

[0082] In the first and second models, the dielectric losses in said at least one layer of material are not taken into account or considered to be minimal.

[0083] In these first and second models, the electric cable 10 is without a screen.

[0084] The first modeling applies to an electrical cable 10 comprising an electrical conductor 12 and one or more layers of material surrounding the electrical conductor 12. One or more temperature sensors 20 are arranged on the external surface 18 of said at least one layer of material.

[0085] The electric cable 10 according to [Fig.2] is an example compatible with this first modeling.

[0086] As indicated above, the conductor temperature 0cond can be expressed as follows: 0eond= ©bl + WC*T! with 0cond being the conductor temperature, 0bi being the peripheral temperature, T i being the thermal resistance of said at least one layer of material, Wc being the thermal flux generated by heating the conductor.

[0087] According to the first method of determination, the heat flux Wc due to heating of the electrical conductor 12 is expressed as follows: W = R *1 a2 ' ' c xvc -tcond Rc being the electrical resistance of the electrical conductor, Icond being the intensity of the current flowing along the electrical conductor.

[0088] The conductor temperature 0cond according to the first method of determination, i.e. a function of the intensity of the electrical conductor, is therefore expressed as follows: 0cond= ©bl + Rc*Icond2*T 1

[0089] The electrical resistance Rc of the electrical conductor is expressed as follows: RC = ROX ( l + a20x (0„,„;-2O)) X ( 1 + v +y(,)with Ro being the direct current resistance of the conductor at 20°C, in Ohm, Ys being the skin effect factor, without unit, Yp being the proximity effect factor, without unit, a20 being the coefficient of electrical resistivity, in K 1 (i.e. per kelvin).

[0090] The parameters R0,Ys,Yp and a20 are values ​​linked to the structure and nature of the electrical conductor.

[0091] The conductor temperature 0cond can thus be expressed as follows: „ 0h j -ÆqXT" jX ( l-20x«2f) ) cond l-Ri^ <I"rmtiXa2oXTi

[0092] According to the second determination mode, i.e. without the intensity of the conductor Icond, the determination unit 100 comprises an additional structure illustrated in [Fig.4]. Thus, the determination system 100 comprises at least one additional layer 24 of material and at least one additional temperature sensor 26.

[0093] Said at least one additional layer of material 24 has an additional thermal resistance Tb.

[0094] Said at least one additional layer of material 24 is for example at least one electrically insulating layer.

[0095] The material of said at least one additional layer of material 24 preferably has a thermal resistance between 0.001 m2.K / W and 0.1 m2.K / W. In this range of thermal resistance, said at least one layer of material 24 makes it possible to prevent overheating of the conductor while allowing a temperature difference large enough to be measured.

[0096] Said at least one additional temperature sensor 26 makes it possible to measure an additional peripheral temperature 0b2 at the level of the external surface 28 of said at least one additional layer of material 24.

[0097] The determination system 100 may comprise a plurality of additional temperature sensors 26 distributed around the longitudinal axis A in the same plane transverse to the longitudinal axis A. In the example of [Fig.4], the determination system 100 comprises 9 additional temperature sensors 26.

[0098] The additional temperature sensor(s) 26 are connected to the determination unit 22 so as to communicate the additional peripheral temperature 0b2 to this determination unit 22.

[0099] Preferably, the additional temperature sensors 26 are equally distributed around the longitudinal axis A. The determination system 100 may provide one or more additional temperature sensors 26 further distributed along the longitudinal axis A so as to measure the additional peripheral temperature 0b2 at different locations along the electrical cable 10.

[0100] Preferably, the number and / or the angular position and / or the longitudinal position of the temperature sensors 20 are respectively identical to the number and / or the angular position and / or the longitudinal position of the additional temperature sensors 26.

[0101] The electrical cable 10 equipped with said at least one additional layer of material 24 and said at least one additional temperature sensor 26 is modeled by a second modeling in [Fig.5]. Said at least one additional layer of material 24 is considered as a resistor of value Tb in series with the resistor of value Ti corresponding to said at least one layer of material.

[0102] According to this second method of determination, the heat flux Wc is expressed as follows: (4 / „ (®tr®h2) Tb

[0103] The conductor temperature can thus be expressed as follows: 2 b

[0104] The determination of the conductor temperature 0cond can thus be determined without requiring the value of the intensity of the current flowing in the electrical conductor 12. This determination is made possible by the addition of an additional layer and an additional sensor.

[0105] Electrical cable without screen and taking into account dielectric losses

[0106] The determination unit 22 is configured to determine the temperature of 0cond conductor according to a third and a fourth modeling respectively illustrated in figures 6 and 7.

[0107] More specifically, the determination unit 22 is configured to determine the conductor temperature 0cond according to the third modeling by means of the first determination mode. The determination unit 22 is configured for the conductor temperature 0cond according to the fourth modeling by means of the second determination mode.

[0108] In the third and fourth models, the dielectric losses in said at least one layer of material are taken into account.

[0109] In these third and fourth models, the electric cable 10 is without a screen.

[0110] In these third and fourth models, the dielectric losses in said at least one layer of material are considered as a heat loss flux Wd at the level of the resistance of value Ti corresponding to said at least one layer of material. This heat loss flux Wd is visible in Figures 6 and 7.

[0111] The third modeling applies to an electrical cable 10 comprising an electrical conductor 12 and one or more layers of material surrounding the electrical conductor 12. One or more temperature sensors 20 are arranged on the external surface 18 of said at least one layer of material.

[0112] The electric cable 10 according to [Fig.2] is an example compatible with this third modeling.

[0113] According to the first method of determination, the conductor temperature 0cond can be expressed as follows as a function of the electrical intensity Icond: e.- <w=eM+rix(wc-^)

[0114] This conductor temperature 0cond can also be expressed as follows by decomposing Rc as described above: e 0^( / ^,)7,(1-2(^

[0115] According to the second determination mode, i.e. without the intensity of the conductor Icond, the determination unit 100 comprises an additional structure as illustrated in [Fig.4]. Thus, the determination system 100 comprises at least one additional layer 24 of material and at least one additional temperature sensor 26.

[0116] The electric cable 10 equipped with said at least one additional layer of material 24 and said at least one additional temperature sensor 26 is modeled by a fourth modeling in [Fig.7].

[0117] Said at least one additional layer of material 24 is considered as a resistance of value Tb in series with the resistance of value T, corresponding to said at least one additional layer of material 24.

[0118]

[0119]

[0120]

[0121]

[0122]

[0123]

[0124]

[0125]

[0126]

[0127]

[0128]

[0129] less one layer of material. According to this second method of determination, the conductor temperature 0cond is expressed as follows: / (0,,-¾ J iv, \ A, = f), + T <x LèkJd - "cond + 1 l T, ? / \ * b ' The previous equation is obtained by considering the following equations: (w,;+£i)and ^e^+T^Wj+w,,) The loss heat flux Wd is determined as a function of the voltage applied to the electrical conductor 12, the frequency of the voltage applied to the electrical conductor 12 and the dielectric characteristics of said at least one layer of material. Electrical cable with screen and consideration of dielectric losses The determination unit 22 is further configured to determine the conductor temperature 0cond in a configuration of the electrical cable 10 comprising a screen 17. As illustrated in [Fig.8], the electrical cable 10 comprises an electrical conductor 12, one or more layers of material surrounding the electrical conductor 12 and a screen 17 surrounding said layers of material. Said layers of material are for example a dielectric layer 30 surrounding the electrical conductor 12 and an insulating layer 32 arranged between the dielectric layer 30 and the screen 17. The electrical cable 10 also includes an outer layer 34, for example an outer sheath, defining an outer surface 38 of the outer layer 34. The outer layer 34 may include a plurality of layers of material. The outer layer 34 has a thermal resistance T3. One or more temperature sensors 20 are disposed on the outer surface 38 of the outer layer 34. Losses in the screen 17 are modeled by a screen heat flux Ws. These losses are due to Joule heating in the screen 17. Determining the screen heat flux Ws requires an invasive measurement on the electrical cable 10. To avoid expressing the conductor temperature 0cond as a function of the heat flux Ws, it is proposed here to combine the first and second determination modes seen previously. In other words, it is provided here to express the conductor temperature 0cond as a function of the intensity Icond of the voltage circulating in the electrical conductor 12 and to use an additional structure comprising at least one additional layer of material 24 and at least one additional temperature sensor 26, as seen in [Fig.8].

[0130] Said at least one additional layer of material 24 has a thermal resistance Tb.

[0131] A fifth modeling is illustrated in [Fig.9] taking into account the screen losses (heat flux Ws) as well as the dielectric losses in said at least one layer (heat flux Wd) and comprising three resistors in series to model the thermal resistances of said at least one layer of material (TJ, of the external sheath 34 (T3) and of said at least one additional layer of material 24 (Tb).

[0132] In this fifth modeling, the conductor temperature 0cond is expressed as follows: l-20xtt20) 0bietant the peripheral temperature Qeond = measured by said at least one temperature sensor 20, 0b2 being the additional peripheral temperature measured by said at least one additional temperature sensor 26, A0 being the temperature difference 0br 0b2, Ti being the thermal resistance of said at least one layer of material, Tb being the thermal resistance of said at least one additional layer of material 24, T3 being the thermal resistance of outer layer 34, Ro being the direct current resistance of the conductor at 20°C, in Ohm, Ys being the skin effect factor, without unit, Yp being the proximity effect factor, without unit, a20 being the coefficient of electrical resistivity, in K 1 (i.e. per kelvin).

[0133] The determination unit 22 is thus capable of determining the conductor temperature 0cond independently of the screen heat flux Ws.

[0134] This expression for the conductor temperature 0cond is obtained by considering that: 0C(W = + Wd ) T3 + ( Wc + ) T xn ( Wc + W, + Wd ) = QC(„,duetei„. = + + r.with Osurf being the peripheral temperature at the level of the external surface of the electric cable 10, and n being the number of electrical conductors 12.

[0135] As detailed previously, the thermal resistance Ti is determined as follows: T i 1 2x~ \ d, /

[0136] The thermal resistance T3 of the outer layer 34 is determined as follows: ^=&^i+2*ïè)with t3 being the thickness of the outer layer 34, Da being the internal diameter of the outer layer 34.

[0137] According to a sixth model illustrated in [Fig.10], the determination unit is also configured to determine the conductor temperature 0condde independently of the surrounding environment, in particular the temperature of this surrounding environment.

[0138] This sixth modeling applies to the same configuration of electric cable 10 as the fifth modeling. In other words, the sixth modeling applies to an electric cable of the type of that of [Fig.8] with an additional structure and a screen 17.

[0139] Depending on the surrounding environment, the heat will be more or less well evacuated from the electric cable 10. The surrounding environment is modeled by a layer of material with a certain thermal resistance T5 and a temperature 0a corresponding to the ambient temperature of the surrounding environment.

[0140] The conductor temperature 0cond can be expressed as follows: 0C(W = 0, + ( ) T ! + n ( WC + Wd + )T3+n(Wc+ Wd + W, ) Tb + n ( + Wd + ) T5

[0141] The temperature difference 0M- 0b2 on either side of the additional layer of material 24 makes it possible to express the conductor temperature 0cond as follows: + ( w, +'^']Tl+n(w,.+wdi- w, ) 2 = ''(Wc+W,l+Ws)Tb

[0142] The conductor temperature 0cond can thus be determined by the determination unit 22 independently of the surrounding environment.

[0143] With reference to [Fig. 11], the determination system 100 may comprise a determination housing 50 in which one or more of said at least one temperature sensor 20 are housed.

[0144] The determination unit 22 is preferably carried by the determination housing 50. If the determination unit is remote from the determination housing 50, the determination housing 50 is configured to communicate information, in particular sensor measurements, to the determination unit 22.

[0145] This determination box 50 is for example removable relative to the electric cable 10 so as to carry out a punctual and localized measurement on the electric cable 10. This box is for example a portable measuring accessory.

[0146] The determination box 50 has a dimension along the longitudinal axis A such that it extends only over a portion of the length of the electric cable 10.

[0147] The determination housing 50 may also comprise the additional structure. In other words, the determination housing 50 may also comprise said at least one additional layer of material 24 and said at least one additional temperature sensor 26.

Claims

Claims

1. System for non-invasively determining (100) a temperature of a conductor of an electric cable, comprising: - an electric cable (10) comprising at least one electric conductor (12) and at least one layer of material (14, 16, 17, 30, 32, 34) surrounding said at least one conductor, said at least one layer having a layer thermal resistance Tb - at least one temperature sensor (20) arranged on an external surface (18) of said at least one layer of material for measuring a peripheral temperature 0M at the external surface of said at least one layer of material, - a determination unit (22) configured to determine a conductor temperature 0cond as a function of the measured peripheral temperature 0bi, the layer thermal resistance Ti and the heat flux Wc generated by the flow of an electric current in the electric conductor.

2. The determination system (100) of claim 1, wherein the determination unit is configured to determine the conductor temperature 0cond based on the following equation: 0eond= ©bl + WC*T!

3. A determination system (100) according to claim 1 or 2, wherein said at least one layer of material comprises an outer sheath forming said outer surface, said at least one temperature sensor being disposed on said outer sheath.

4. Determination system (100) according to one of claims 1 to 3, further comprising a device for measuring the electrical intensity Icond of an electric current flowing in said at least one electrical conductor, the determination unit being configured to determine said conductor temperature 0condenser furthermore as a function of this electrical intensity Icond.

5. Determination system (100) according to the preceding claim, in which the measuring device is a non-invasive device, in particular of the Rogowski coil type.

6. Determination system (100) according to claim 4 or 5, wherein the temperature of the conductor 0cond is determined as follows: 0cond= ©bl + Rc*Icond2*Ti Rc being the electrical resistance of the conductor

7. Determination system (100) according to one of claims 1 to 3, further comprising: - an additional layer of material arranged around said at least one layer of material and covering said at least one temperature sensor, said additional layer of material having an additional thermal resistance Tb, - at least one additional temperature sensor arranged on an external surface of said additional layer of material for measuring an additional peripheral temperature 0b2 at the external surface of said at least one additional layer of material.

8. A determination system (100) according to the preceding claim, wherein said additional layer of material extends around said at least one layer of material only over a portion of the length of the electrical cable.

9. Determination system (100) according to claim 7 or 8, wherein the determination unit is configured to determine the conductor temperature 0cond based on the following equation: n — a < ((-bt^h2) T 0bi is the peripheral temperature measured Umnd ~ Ubl H 7~~ X 1 1 by said at least one temperature sensor, 0b2 is the additional peripheral temperature measured by said at least one additional temperature sensor, Tb being the additional thermal resistance of the additional layer of material, T i being the thermal resistance of said at least one layer of material.

10. Determination system (100) according to any one of the preceding claims, wherein the determination unit is configured to determine the conductor temperature 0cond further as a function of a heating Wd originating from a dielectric loss in said at least one layer of material.

11. Determination system (100) according to the preceding claim in combination with any one of claims 4 to 6, wherein the determination unit is configured to determine the conductor temperature 0cond on the basis of the following equation: g 1 + x ( W + j Wd being heating from a dielectric loss in said at least one layer of material.

12. A determination system (100) according to claim 10 in com- combination with any one of claims 7 to 9, wherein the determining unit is configured to determine the conductor temperature 0cond on the basis of the following equation: a — n wd \ Wd being heating from ucond ~ ' \ -1 b a dielectric loss in said at least one layer of material.

13. A determination system (100) according to any preceding claim, further comprising a determination housing comprising one or more of said at least one temperature sensor and the determination unit, the housing being configured to be removably mounted to the electrical cable.

14. Determination system (100) according to the preceding claim in combination with claim 7, wherein said at least one additional layer of material and said at least one additional temperature sensor are carried by the determination housing.

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