METHOD AND DEVICE FOR SIMULTANEOUSLY MEASURING THE CURRENT INTENSITY IN EACH PHASE OF A POLYPHASE ELECTRICAL CABLE

Abstract

To measure the current intensity in a multi-conductor electrical cable, this intensity is measured simultaneously in all conductors: magnetic field sensors are placed (E1) around the cable; at least one component of the magnetic field produced by the current flowing in each conductor is measured simultaneously (E2); the angle between each conductor and the nearest sensor is determined (E3); since the current intensities are related to the components of the magnetic field by B = kMI, where B is the matrix of magnetic field components, I is the matrix of current intensities, M is a matrix containing proportionality coefficients depending on the angles between conductors and sensors, and k is a predetermined coefficient, the inverse M⁻¹ of M is calculated (E4) in order to deduce the current values ​​I = (µ₀ / 2π)M⁻¹B, where µ₀ is an equivalent magnetic permeability that takes into account the presence of insulating materials in the cable. Figure for the abbreviation: Fig. 1

Description

Title of the invention: METHOD AND DEVICE FOR SIMULTANEOUSLY MEASURING THE CURRENT INTENSITY IN EACH PHASE OF A POLYPHASE ELECTRIC CABLE

[0001] The present invention relates to a method and a device for simultaneously measuring the intensity of the instantaneous current in each phase of a polyphase electric cable, alternating or direct current.

[0002] The invention belongs to the field of electrical cables intended for the transport of energy and / or the transmission of data. It finds application in particular in the field of optimizing the distribution of energy in buildings.

[0003] Currently, to measure the intensity of the instantaneous current in each conductor of a polyphase or multi-conductor cable, most often, the intensity of the current in each of the conductors is measured successively using an ammeter clamp.

[0004] However, these operations are time-consuming and generally provide imprecise results.

[0005] There is no practical technical solution on the market that allows the current intensity in all the conductors of a polyphase cable to be measured simultaneously, quickly and accurately.

[0006] The present invention aims to remedy the aforementioned drawbacks of the prior art.

[0007] For this purpose, the present invention proposes a method for measuring the current intensity in an electric cable comprising a plurality of conductors, remarkable in that it consists of simultaneously measuring the current intensity in the conductors of the plurality of conductors by carrying out steps consisting of: placing a plurality of magnetic field sensors around the cable, at at least one location of the cable; simultaneously measuring, for each of the conductors, at least one component of the magnetic field produced by the current flowing in the conductor, by means of the plurality of magnetic field sensors; for each of the conductors, determining the angle between the conductor and the nearest magnetic field sensor of the plurality of magnetic field sensors, this angle being defined relative to the center of the cable and by treating the conductors and the sensors as points; the intensities of the currents in the conductors being linked to the components of the magnetic field measured by the relation B = kMI where B is the matrix of the com magnetic field components, I is the matrix of current intensities, M is a matrix comprising a plurality of proportionality coefficients depending on the angles between the conductors and the magnetic field sensors and k is a predetermined coefficient, calculate the inverse M 1 of the matrix M, so as to deduce the values ​​of the current intensities I = (po / 2ir).M *.B, where po is an equivalent magnetic permeability which takes into account the presence of insulating materials in the cable.

[0008] Thus, the invention makes it possible to measure the current intensity in all the conductors of the cable in a single operation and to quickly obtain extremely precise results, without having to remove the cable sheath. Furthermore, the installation of the magnetic field sensors around the cables is easy and does not cause any damage, marks or deformation to the cables. Furthermore, since the position of the magnetic field sensors relative to the conductors of the cable is unknown, taking into account the angular offset between sensors and conductors makes it possible to increase the accuracy of the intensity values ​​obtained.

[0009] The invention offers numerous applications, such as the identification of unbalanced current distributions which sometimes reveal a faulty power supply, the anticipation of cable failures when a conductor reaches an excessive temperature or even the reduction of electrical energy consumption in an installation.

[0010] In a particular embodiment, the measuring step consists of simultaneously measuring, for each of the conductors, the tangential component and the radial component of the magnetic field produced by the current flowing in the conductor, by means of the plurality of magnetic field sensors.

[0011] This makes it possible to minimize the error in the intensity values ​​obtained, i.e. to further increase the precision of these values.

[0012] For the same purpose as that indicated above, the present invention also proposes a device for measuring the intensity of the current in an electric cable comprising a plurality of conductors, remarkable in that it comprises: the aforementioned plurality of magnetic field sensors; a processing means adapted to receive the values ​​of the components of the magnetic field and to apply the steps of determining the angle and calculating the inverse matrix of a method as described briefly above to deduce therefrom the intensity of the current flowing in each of the conductors.

[0013] In a particular embodiment, the device further comprises a housing containing the plurality of magnetic field sensors.

[0014] This makes it easier to install the device around the cable, as it is not necessary to install each sensor individually.

[0015] In a particular embodiment, the housing is surrounded by electromagnetic shielding.

[0016] This makes it possible to prevent the penetration of electromagnetic disturbances due, for example, to the Earth's permanent magnetic field and to possible sources of electromagnetic field located near the cable and the sensors.

[0017] In a particular embodiment, the housing has a section formed of two half-rings, suitable for positioning the device around the cable.

[0018] This configuration allows rapid installation of the device around the cable, which is therefore housed in the center of the circular opening formed by the meeting of the two half-rings.

[0019] In a particular embodiment, the device further comprises at least one additional magnetic field sensor adapted to measure the Earth's magnetic field.

[0020] This makes it possible to take into account the value of the Earth's magnetic field, which can thus be subtracted when processing the magnetic field values ​​collected by the sensors.

[0021] In a particular embodiment, the at least one additional sensor is arranged inside the housing and / or outside the housing.

[0022] Still with the same aim as that indicated above, the present invention also proposes an electric cable arrangement comprising an electric cable comprising a plurality of conductors, this arrangement being remarkable in that it further comprises at least one device as succinctly described above placed around the cable.

[0023] In a particular embodiment, the electrical cable arrangement comprises a plurality of devices as briefly described above, placed around the cable at predetermined intervals from each other.

[0024] This makes it possible to ensure adequate measurement of the current intensities in the conductors of the cable in the event that these conductors are twisted in such a way that they are likely to influence the sensitivity of the measurement of the intensities.

[0025] The other particular characteristics and advantages of the device and of the electric cable arrangement being similar to those of the method, they are not repeated here. Brief description of the drawings

[0026] Other aspects and advantages of the invention will appear on reading the detailed description below of particular embodiments, given as non-limiting examples, with reference to the appended drawings, in which:

[0027] [Fig. 1] is a flowchart illustrating steps of a method according to the present invention, in a particular embodiment.

[0028] [Fig.2] is a geometric representation illustrating different parameters used in a method according to the present invention, in a non-limiting example where the electric cable considered comprises five conductors.

[0029] [Fig.3] is a schematic representation of an electrical cable device and arrangement according to the present invention, in a particular embodiment.

[0030] [Fig.4] is a schematic representation of an electrical cable arrangement according to the present invention, in another particular embodiment. Description of embodiment(s)

[0031] The present invention considers a polyphase, or multi-conductor, alternating or direct current cable. N denotes the number of conductors in the cable. These conductors are not necessarily identical.

[0032] The invention is based on the local measurement of at least one component of the magnetic field emitted by the current sources, which are here the N conductors, by means of magnetic field sensors.

[0033] In short, given that a polyphase cable has several current densities coming from its N conductors, we can first calculate the magnetic field produced by the current using the Biot-Savart law, then invert all the local measurements of the magnetic field components by determining an inverse matrix, in order to obtain the current intensities coming from the N current sources.

[0034] Thus, as shown in the flowchart of [Fig.l], the method, in accordance with the invention, for measuring the intensity of the current in an electric cable comprising a plurality of conductors, consists of simultaneously measuring the intensity of the current in the conductors of the plurality of conductors by carrying out a first step E1 consisting of placing a plurality of magnetic field sensors around the cable, at at least one location of the cable.

[0035] Step E1 may for example consist of fixing around the cable one or more devices according to the invention containing the plurality of sensors. The device according to the invention is described further with reference to Figures 3 and 4.

[0036] Then a step E2 consists of simultaneously measuring, for each of the conductors of the cable, at least one component of the magnetic field produced by the current flowing in this conductor.

[0037] These simultaneous measurements are carried out by means of the plurality of magnetic field sensors.

[0038] In a particular embodiment, the plurality of magnetic field sensors can measure for each conductor only the tangential component or only the radial component of the magnetic field.

[0039] Alternatively, for greater accuracy, the plurality of magnetic field sensors may measure for each conductor both the tangential component and the radial component of the magnetic field.

[0040] Then, during a step E3, for each of the conductors, the angle a is determined between this conductor and the nearest magnetic field sensor of the plurality of magnetic field sensors. The angle a is defined relative to the center of the section of the cable and by assimilating the conductors and the sensors to points. Indeed, for simplicity, it is assumed that each conductor has an infinitely small section and that the magnetic field captured by each sensor is located at a point corresponding to the location of the sensor.

[0041] [Fig.2] schematically illustrates, by way of non-limiting example, a cable of circular section comprising five conductors regularly distributed inside the cable, which are assimilated to five points Cl to C5 equidistant from each other on the circumference of a circle T. Only the magnetic field sensor closest to the conductor Cl has been represented and is symbolized by point A. The radius of the circle T is designated by r, the distance between the conductor Cl and the sensor A is designated by db the straight line segment connecting the sensor A and the center of the circle T is designated by d'b the angle at point A between the straight line segment d'i and the straight line segment connecting the conductor Cl and point A is designated by [3. The magnetic field captured by the sensor A is represented by the vector Bb which is orthogonal to the straight line segment connecting the conductor Cl and point A.

[0042] For a cable comprising N conductors each producing a magnetic field B; , i = 1, ..., N, the component BA of the magnetic field at point A coming from the N conductors is defined as follows:

[0043] [Math.l] #4 = E .Bj = ,B Ü ■ cos( / L) - E Arcsini ] • Z A t=l K*! / ^i—Mnd, y \ d; JJ lm

[0044] where: Bim is the component of the magnetic field coming from the ith conductor captured by the mth sensor; the angles a; and [3; are defined for the ith conductor similarly to the angles a and [3 defined above, respectively; d; denotes the distance between the ith conductor and the nearest sensor; Po is an equivalent magnetic permeability which takes into account the presence of insulating materials in the cable; r is as defined above the radius of the circle T; and Iim is the value of the current intensity flowing in the ith conductor and deduced from the magnetic field measurement carried out by the mth sensor.

[0045] The number of magnetic field sensors is at least equal to the total number N of cable conductors.

[0046] Thus, the intensities of the currents in the conductors are linked to the components of the magnetic field measured, by the relation B = kMI where B is the matrix of the components of the magnetic field measured in all the conductors by all the sensors, I is the matrix of the intensities of the currents circulating in all the conductors, M is a matrix comprising a plurality of proportionality coefficients depending on the angles between the conductors and the magnetic field sensors and k is a predetermined coefficient.

[0047] It follows that I = (po / 2ir).M *.B, where M 1 is the inverse matrix of M.

[0048] Thus, as shown in [Fig.l], following step E3 of determining the angle a between each conductor and the nearest sensor, we carry out a step E4 consisting of calculating the inverse matrix M1, so as to deduce the values ​​of the intensities I of the currents in all the conductors of the cable.

[0049] As a non-limiting example, for N = 5 conductors and five magnetic field sensors placed respectively at points A, B, C, D and E, the analytical expression allowing the intensities of the currents in the conductors to be deduced is as follows:

[0050] [Math.2] i ■COS^) 1 A i A <m^4) 1 d^ ■cosm\ • cos ( 3^ i dt ■cos^) a 3^) d, ■cos(fi4) i-cosm ^5 d. ■cos(j3}) ^ d:i ■cos i ■cos[04) ■cos( 35) cos(j3} ■cos^^ d3 cos(n3) â ■cos(04) ■cos(0^ 'BA\ Bc Bd .beI

[0051] where h, i = 1, ..., 5 denotes the intensity of the current flowing in the ith conductor and BA, Bb, Bc, Bd and Be denote the components of the magnetic field respectively measured by the five sensors.

[0052] The equivalent magnetic permeability po is a macroscopic permeability, which makes the calculation simpler than if we considered the local magnetic permeability.

[0053] In a particular embodiment, the angle a between this conductor and the nearest magnetic field sensor of the plurality of magnetic field sensors is determined so as to maximize the following function F:

[0054] [Math.3]

[0055] where F denotes the intensity of the current flowing in the ith conductor.

[0056] There are various known mathematical convergence methods for maximizing F, such as the Levenberg-Marquardt algorithm (also called the LM algorithm) or the Nelder-Mead method.

[0057] As shown in [Fig. 3], a device 30 according to the present invention, for measuring the intensity of the current in an electric cable 32 comprising a plurality of conductors 34, comprises a plurality of magnetic field sensors 36 (five in the non-limiting example illustrated) and a processing means 38 adapted to receive the values ​​of the components of the magnetic field measured by the plurality of sensors 36 and to apply the steps E3 of angle determination and E4 of inverse matrix calculation of the method described above, to deduce therefrom the intensity of the current flowing in each of the conductors 34.

[0058] The processing means 38 may be located either in the device 30 or at a distance from the latter, a communication means then being provided to transmit the values ​​of the measured components of the magnetic field from the sensors 36 to the processing means 38. When it is located at a distance from the device 30, the processing means 38 may be located in a laptop or other computer, a tablet, a smartphone or other mobile means of communication, or even be located in the cloud.

[0059] In the particular embodiment illustrated, the device 30 further comprises a housing 31 containing the plurality of magnetic field sensors 36. Such a housing is optional, the sensors 36 being able to be placed around the cable without being contained in any enclosure.

[0060] In the particular embodiment illustrated, the housing 31 has a section formed by two half-rings 311 and 312, adapted to the positioning of the device 30 around the cable 32, the two half-rings 311 and 312 defining by their assembly an opening in which the cable 32 passes. In the particular embodiment illustrated, the cable 32 has a circular section and the opening formed by the two half-rings 311 and 312 is also circular and of diameter slightly greater than that of the section of the cable.

[0061] Once the device 30 is placed around the cable 32, the two half-rings 311 and 312 can be connected to each other for example by means of a hinge-type joint, or be secured to each other for example by means of screws or nuts or other preferably removable fixing means.

[0062] Also optionally, the housing 31 may be surrounded by electromagnetic shielding preventing disturbance of the sensors by possible sources of surrounding electromagnetic waves as well as by the Earth's permanent magnetic field. This shielding may be made, for example, of a specific steel.

[0063] Whether such shielding is present or not, the device 30 may further be equipped with one or more additional magnetic field sensors 37 adapted to measure in particular the Earth's magnetic field, in order to subtract the value thereof when processing the values ​​of the components of the magnetic field measured by the magnetic field sensors 36. The additional sensor(s) 37 may be arranged inside and / or outside the housing 31, or even directly around the cable when there is no housing.

[0064] Thus, an electrical cable arrangement according to the present invention comprises the cable 32 and at least one device 30 placed around the cable 32.

[0065] As shown in the particular embodiment of [Fig.4], the electrical cable arrangement may comprise a plurality of devices 30, placed around the cable 32 at predetermined intervals from each other.

[0066] The processing means 38 may be unique and common to all the devices 30. As a variant, a processing means 38 may be provided for each device 30 and communication means adapted to communication between the various processing means 38 may possibly be provided.

[0067] In the particular embodiment illustrated, the devices 30 are all identical, each comprise five magnetic field sensors 36 and are arranged at regular intervals along the cable 32.

[0068] Such a configuration makes it possible to guarantee a high-quality measurement of the current intensities, even in the case where the conductors 34 are twisted, for example due to manufacturing conditions and / or specific constraints, which could influence the sensitivity of the measurement of the magnetic fields.

[0069] The number of devices 30 to be placed around the cable 32 and the distance between each device 30 are of course to be defined according to the type of cable 32 considered.

[0070] The invention can be applied to many types of cables, such as cables used in buildings, which are designed for voltages generally lower than 1000 V, and distribution cables, which are designed for voltages generally equal to or greater than 1000 V.

Claims

Claims

1. Method for measuring the current intensity in an electric cable comprising a plurality of conductors, characterized in that it consists in simultaneously measuring the current intensity in the conductors of said plurality of conductors by carrying out steps consisting in: placing (El) a plurality of magnetic field sensors around said cable, at at least one location of said cable; measuring (E2) simultaneously, for each of said conductors, at least one component of the magnetic field produced by the current flowing in said conductor, by means of said plurality of magnetic field sensors; for each of said conductors, determining (E3) the angle between said conductor and the nearest magnetic field sensor of said plurality of magnetic field sensors, said angle being defined with respect to the center of said cable and by assimilating said conductors and said sensors to points;the intensities of the currents in said conductors being linked to the components of the magnetic field measured by the relation B = kMI where B is the matrix of said components of the magnetic field, I is the matrix of said intensities of the currents, M is a matrix comprising a plurality of coefficients of proportionality depending on said angles between said conductors and said magnetic field sensors and k is a predetermined coefficient, calculating (E4) the inverse M 1 of the matrix M, so as to deduce therefrom the values ​​of said intensities of the currents I = (po / 2ir).M *.B, where po is an equivalent magnetic permeability which takes into account the presence of insulating materials in said cable.;

2. Method according to claim 1, characterized in that the measuring step (E2) consists of simultaneously measuring, for each of said conductors, the tangential component and the radial component of the magnetic field produced by the current flowing in said conductor, by means of said plurality of magnetic field sensors.

3. Device (30) for measuring the intensity of the current in an electric cable (32) comprising a plurality of conductors (34), characterized in that it comprises: said plurality of magnetic field sensors (36); a processing means (38) adapted to receive the values ​​of said components of the magnetic field and to apply the steps (E3, E4) of determining the angle and calculating the inverse matrix of a method according to any one of the preceding claims to deduce therefrom the intensity of the current flowing in each of said conductors (34).

4. Device (30) according to claim 3, characterized in that it further comprises a housing (31) containing said plurality of magnetic field sensors (36).

5. Device (30) according to claim 4, characterized in that said housing (31) is surrounded by electromagnetic shielding.

6. Device (30) according to claim 3, 4 or 5, characterized in that said housing (31) has a section formed of two half-rings (311, 312), adapted to the positioning of said device (30) around said cable (32).

7. Device (30) according to any one of claims 3 to 6, characterized in that it further comprises at least one additional magnetic field sensor (37) adapted to measure the Earth's magnetic field.

8. Device (30) according to claim 7, characterized in that said at least one additional sensor (37) is arranged inside said housing and / or outside said housing (31).

9. An electrical cable arrangement comprising an electrical cable (32) comprising a plurality of conductors (34), characterized in that it further comprises at least one device (30) according to any one of claims 3 to 8 placed around said cable (32).

10. An electrical cable arrangement according to claim 9, characterized in that it comprises a plurality of devices (30) according to any one of claims 3 to 8, placed around said cable (32) at predetermined intervals from each other.

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