Current sensor for measuring an alternating current

A current sensor provided with an electrical coil (5) made in the form of a printed circuit. Its closed contour is inscribed within a rectangle delimiting a through window (9) for passing a primary conductor (2). It comprises four rectilinear segments (TR) connected two by two by a circular sector (SC), delimited by an interior arc (10) and an exterior arc (11). It comprises, in its circular sectors (SC), additional turns (13), which extend from exterior arc (11) towards an intermediate arc (14) located between interior arc (10) and exterior arc (11). They are inserted between the main turns (12) in such a way that the spacing between two consecutive turns (12, 13) on the exterior arc (11) is equal to spacing (P) of the main turns (12) in rectilinear segments (TR) and that the average turns density is almost constant in electrical coil (5).

TECHNICAL SCOPE

The present invention relates to a current sensor for measuring an alternating current, said sensor comprising at least one electrical coil made in the form of a printed circuit provided on at least one electronic board, an electronic unit for conditioning the signal of said electrical coil and an electrical terminal block, said electrical coil having a closed contour inscribed within a polygon and delimiting in its center a through window for an electrical conductor crossed by the alternating current to be measured, this conductor being called primary conductor, said electrical coil comprising N rectilinear segments of width L and N circular sectors of the same width L delimited each by an interior arc of interior radius Ri and an exterior arc of exterior radius Re, said rectilinear segments being connected two by two by a circular sector, said rectilinear segments being made of turns separated from each other by a constant spacing P, and said circular sectors being made of turns separated from each other on said interior arc by a constant spacing equal to spacing P and on said exterior arc by a constant spacing larger than spacing P.

PRIOR ART

Alternating currents are measured by means of current sensors based on various operating principles. A well known and widely used technology for industrial applications is based on the Rogowski principle. This principle consists of a winding in the air placed around an electrical conductor crossed by the alternating current to be measured, commonly called a primary conductor. This winding can be made of one or several serially connected electrical coils. The advantages of this type of current sensor lie in its high linearity and in extended measuring dynamics, which allow measuring currents ranging from a few hundred milliamperes to some thousands of amperes, at frequencies starting from a few tens of hertz. These advantages are mainly due to the absence of a magnetic core to saturate. However, the industrial manufacture of good quality Rogowski coils by means of the classical winding techniques is very complex, expensive and difficult to reproduce, as these coils require a constant turns density per unit length and a constant turn cross-section. Several embodiment examples are illustrated in publication WO 2013/037986.

The solution consists in realizing the Rogowski coils in the form of a printed circuit. This technology allows achieving a high accuracy of the path of the winding and an industrial reproducibility particularly suitable for the compliance with the regularity of the winding. However, the Rogowski coils obtained with this printed circuit technology have a low measuring sensitivity, for example in the order of 10 μV/A for a current to measure with a frequency of 50 Hz, as turns density is low, of the order of 1 to 1.2 turns per mm for the classical printed circuit technologies, and as the turns cannot be superimposed.

Rogowski coils are most often circular, as those described for example in publications FR 2 845 197, DE 10 2007 046 054 and US 2008/0106253. The use of polygonal coils, as those described for example in publications EP 1 923 709 and US 2014/0167786, presents winding regularity problems in the corners and affects coil quality.

The sensitivity of the current sensor then varies according to the relative position of the primary conductor in the through window delimited by the current sensor. The winding irregularities in the corners of the coil also entail lower immunity against external magnetic fields, in particular those who might be generated by a neighboring primary conductor positioned close to the coil, which is always the case in the targeted industrial installations. In fact, there are generally three close phase conductors separated by a distance that is generally in the same order of size as the dimensions of the conductors. For example, if the primary conductors are made of 63 mm wide bars separated by an axis distance of 85 mm, the free space between two consecutive bars is equal to 22 mm. Furthermore, in case of high currents, several rectangular bars parallel to each other are commonly used for each phase. Thus the passage cross-section for every phase has necessarily a rectangular shape. Therefore, the use of circular coils leads to a size of the current sensor that is much larger than with rectangular coils, sometimes to such an extent that the installation of the current sensor becomes impossible because of the proximity of the primary conductors of the other phases.

Publication WO 2013/037986 suggests to add additional tuns in the circular sectors of its polygonal coils to correct partly the defects introduced by the presence of corners in these polygonal coils. But this solution is not optimal in terms of sensitivity. In fact, this publication suggests to split each circular sector of the coil in at least two theoretical adjacent bands by adding additional turns with a width lower than the total width of the coil, to create in each of the theoretical bands an average turns density substantially equal to that of the corresponding rectilinear segment. Due to this construction mode of the coil, the spacing between two consecutive turns is not equal on the interior arc and on the exterior arc of the coil, for a same average turns density, this spacing is reduced on the interior arc of the interior theoretical band of a circular sector while it is larger in the corresponding rectilinear segment, which generates an average turns density in the rectilinear segments that is necessarily lower than the average turns density in an area close to the interior edge of the circular sectors. Now the sensitivity of such a sensor is mainly determined by the turns density in its rectilinear segments, which in this case is insufficient, having a negative impact on measurement accuracy.

Therefore these existing solutions are not satisfactory.

DESCRIPTION OF THE INVENTION

The present invention aims to overcome this problem by offering a new design of the Rogowski-type coils for a current sensor, these coils being made in the form of a printed circuit, having a substantially polygonal shape, whose measuring sensitivity is maximized while ensuring good immunity against the position variations of the primary conductor with respect to the current sensor, and a good immunity against the currents flowing through the neighboring primary conductors, comparable to those of circular coils with a similar technology, and offering a reduced size that allows installing the current sensors on primary conductors very close to each other, as well as ease of integration in any measuring appliance configuration.

To that purpose, the invention relates to a current sensor of the kind described in the preamble, characterized in that said electrical coil moreover comprises in its circular sectors additional turns with a width lower than the width of the other turns, called main turns, and extending from said exterior arc towards at least one intermediate arc located between said interior arc and said exterior arc, said additional turns being inserted between said main turns so that the spacing between two consecutive turns on said exterior arc is substantially equal to spacing P and that the average turns density is almost constant in said electrical coil.

So, the regularity of spacing P between turns, on the interior periphery as well as on the exterior periphery of the electrical coil, and the regularity of the average turns density in the whole width of the electrical coil, as well in the rectilinear segments as in the circular sectors, allow both maximizing the measuring sensitivity of the measuring sensor and minimizing the sensitivity of the measuring sensor to the position of the primary conductor and to the presence of neighboring conductors.

In a first embodiment variant, the electrical coil can comprise, in its circular sectors, first additional turns with a width extending from said exterior arc towards respectively a first intermediate arc located between said interior arc and said exterior arc.

In a second embodiment variant, the electrical coil can comprise, in its circular sectors, first additional turns and second additional turns with different respective widths extending from said exterior arc towards respectively a first intermediate arc and a second intermediate arc located between said interior arc and said exterior arc.

In a preferred embodiment of the invention, the electrical coil is made in the form of a printed circuit comprising at least a first conductive layer and a second conductive layer, superimposed on each other, separated from each other by an insulating core of a substrate of said electronic board, said first and second conductive layers being connected to each other by means of connecting holes passing through said substrate to form the turns of said electrical coil.

The current sensor can comprise a return conductor having a flat surface substantially equal to that of said electrical coil to cancel interference fields, said return conductor being made in the form of a printed circuit comprising at least a third conductive layer, superimposed on said electrical coil and separated from it by an insulating layer of said substrate, said return conductor being serially connected to said electrical coil by means of connecting holes passing through said substrate.

In the preferred embodiment, the current sensor comprises two electrical coils made in the form of a printed circuit comprising at least four conductive layers, said electrical coils being identical, opposite to and superimposed on each other, separated from each other by a central insulating layer of the substrate, and serially connected by means of connecting holes passing through said substrate.

This current sensor according to the invention can advantageously comprise an electrical shield including at least one upper exterior conductive layer and one lower exterior conductive layer covering said electrical coil and its return conductor, or said electrical coils, and separated from the electrical coil(s) and/or from the return conductor by means of an additional insulating layer of said substrate.

The electrical shield can moreover comprise at least one lateral conductive layer covering the edge of said substrate and a conductive housing arranged around said electronic conditioning unit.

In another embodiment, the current sensor according to the invention can comprise a voltage measuring circuit arranged for measuring the voltage applied to the primary conductor. This voltage measuring circuit can comprise at least one detection electrode surrounding the through window provided in said electrical coil, said detection electrode being connected to a reference potential by a RC circuit and being made of at least one lateral conductive layer covering the edge of the substrate surrounding said through window.

Depending on the considered application, the current sensor can be single-phase and comprise a through window for a primary conductor, said through window being surrounded by at least one electrical coil, or be polyphase and comprise N through windows for N primary conductors, each through window being surrounded by at least one electrical coil.

The current sensor can comprise only one single electronic board provided with N through windows, the corresponding electrical coils being arranged on said electronic board. It can also comprise at least two superimposed electronic boards, comprising each N through windows, said corresponding electrical coils being distributed alternately on said electronic boards.

In this case, the electronic conditioning unit associated to every electrical coil can advantageously be arranged between the two electronic boards, forming intrinsically an electrical shield protecting the electronic conditioning units, which allows doing without the conductive housing forming the shield, which is indispensable in a current sensor comprising one single electronic board.

ILLUSTRATIONS OF THE INVENTION AND VARIOUS WAYS OF REALIZING IT

Referring toFIG. 1, current sensor1is a single-phase sensor intended for measuring an alternating current flowing through an electrical conductor. This electrical conductor corresponds to a phase of an electrical installation and is commonly called a primary conductor. In the represented example, primary conductor2is made of two conductive bars2a,2bhaving each the shape of a rectangle parallelepiped, and being parallel to each other. This example is not limiting. Primary conductor2can be made of one single conductive bar with a square or rectangular cross-section, of more than two parallel conductive bars, of a conductive cable or of a harness of conductive cables with a circular cross-section, or of any other type of a known conductor, whatever its cross-section. The composition and cross-section of the primary conductor are determined by the alternating current it must transport.

This current sensor1comprises a housing3of which only the lower section is represented to show the inside of current sensor1. This housing3contains an electronic board4carrying at least one electrical coil5made in the form of a printed circuit, an electronic unit6conditioning the signal of electrical coil5, commonly called an integrator, and an electrical terminal block7for connecting current sensor1to peripheral equipment, such as for example a supervision station for the parameters of the electrical installation. Current sensor1can be integral part of a measuring device or be independent and mounted directly on primary conductor2. Application examples are for example described in publications WO 2015/150670 A1 and WO 2015/150671 A1 of the same applicant.

In the represented example, electronic board4moreover comprises a memory unit8in which the calibration data of current sensor1is stored. The composition of current sensor1as described and illustrated can of course vary depending on the needs, on the configuration of the electrical installation to be monitored and on the measuring and/or supervision devices. Units6and8and terminal7are integrated in electronic board4, which carries electrical coil5, but they can be separated and connected to electrical coil5by means of any suitable connection system.

In the illustrated example, electrical coil5has a closed contour inscribed within a polygon, which here is rectangular. This substantially polygonal contour with rounded corners has the advantage of being smaller than a circular contour, especially when primary conductor2is polygonal. Electrical coil5delimits in its center a through window9, having also a substantially polygonal contour, crossed by primary conductor2positioned preferably in the central section of through window9and perpendicularly to the plane of electrical coil5. However, the constructive features of electrical coil5, which will be described later, allow rendering current sensor1insensitive to the relative position of primary conductor2with respect to electrical coil5, and to the proximity of the neighboring primary conductors, as well as to the induced interference fields if primary conductor2is not perpendicular to the plane of electrical coil5.

Referring more specifically toFIG. 2, electrical coil5comprises N rectilinear segments TR of width L and N circular sectors SC of the same width L, the rectilinear segments TR being connected two by two by a circular sector SC. In the figures, the number N of rectilinear segments TR and of circular sectors SC is equal to four since the polygon within which electrical coil5is inscribed is a rectangle.

This example is not limiting and number N of rectilinear segments TR and of circular sectors SC can be higher or lower than four. Each circular sector SC is delimited by an interior arc10of interior radius Ri and an exterior arc11of exterior radius Re where Re=Ri+L. The rectilinear segments TR are made of turns12regularly separated by a constant spacing P, and the circular sectors SC are made of turns12separated on interior arc10by a constant spacing equal to spacing P and on exterior arc11by a constant spacing P1larger than spacing P. In fact, they are separated from each other by an angle depending on spacing P and on interior radius Ri. InFIG. 2, spacing P1is substantially equal to 2P.

The fact of maintaining a constant spacing P between two consecutive turns12on the interior edge of electrical coil5, as well in its rectilinear segments TR as in its circular sectors SC, allows ensuring a constant turns density in the area close to this interior edge, which provides an undeniable advantage from the point of view of the immunity of the measurement against the position variations of primary conductor2with respect to electrical coil5. In fact, when a primary conductor2comes closer to circular sectors SC of electrical coil5, in which the turns density cannot be constant on the whole width of the coil, it is particularly important to maintain this turns density constant in the area close to the interior edge, where the magnetic field gradients are the strongest, since this is the area where the bad approximations of Ampere's integral will have the most influence.

In the example ofFIG. 2, electrical coil5comprises, in its circular sectors SC, first additional turns13of width L1smaller than width L of the other turns12called main turns12. These first additional turns13extend from exterior arc11towards a first intermediate arc14of radius R1located between interior arc10and exterior arc11. They are inserted between main turns12so that an additional turn13is positioned between two main turns12, reducing the spacing between two consecutive turns12,13on exterior arc11to a value substantially equal to spacing P. So, the average density of turns12,13in circular sectors SC is substantially equal to the density of turns12in rectilinear segments TR. The average turns density is the average value, taken on whole width L of electrical coil5, of the number of turns per length unit. The fact of reducing the spacing between two consecutive turns12,13on exterior arc11to a value substantially equal to spacing P between two consecutive turns12on interior arc10provides an undeniable advantage from the point of view of the immunity of the measurement against the presence of external primary conductors neighboring electrical coil5for the same reasons as described previously. So, the regularity of the winding obtained by the invention allows minimizing the sensitivity variation of current sensor1according to the relative position of primary conductor2, and increasing its immunity against external and neighboring primary conductors.FIG. 4illustrates another electrical coil50of current sensor1which is an embodiment variant of electrical coil5ofFIG. 2. The identical parts have the same alphanumerical references. As circular sectors SC are defined by an interior arc10and an exterior arc11with radii Ri and Re smaller than those of electrical coil5ofFIG. 2, spacing P2of main turns12on exterior arc11is larger then spacing P1and substantially equal to 4P. In this embodiment variant, electrical coil50comprises in its circular sectors SC, first additional turns13of width L1and second additional turns15of width L2, the two widths L1and L2being different and smaller than width L of main turns12. First additional turns13extend from exterior arc11towards a first intermediate arc14and second intermediate turns15extend from exterior arc11towards a second intermediate arc16, the two intermediate arcs14,16being located between interior arc10and exterior arc11. The first and second additional turns13,15are inserted between main turns12so that a first additional turn13surrounded by two second additional turns15are positioned between two main turns12, reducing the spacing between two consecutive turns12,13,15on exterior arc11to a value substantially equal to spacing P.

The two embodiment examples of electrical coils5and50according toFIGS. 2 and 4are not limiting and the number of additional turns, as well as their width L1, L2and/or the number of intermediate arcs14,16in circular sectors SC of said electrical coils are not restrictive. The more intermediate arcs are added in circular sectors SC, the more the freedom of arrangement of the additional turns is large to achieve a constant average turns density.

In a general way, the different widths L, L1, L2of turns12,13,15are determined in order to minimize the sensitivity of current sensor1to the position of primary conductor2and to interference signals produced by a neighboring external conductor. The exact determination of the different widths L, L1, L2is obtained by calculating the response of electrical coil5,50according to the position of a primary conductor2placed in all expected positions, and to the response of said coil to a neighboring external conductor placed in contact with current sensor1in all expected positions and minimizing both the sensitivity gap with respect to a reference position of primary conductor2and with respect to an external conductor. In the case of electrical coils5,50located in the air with a rectangular cross-section and for a circular primary conductor2, the calculation of the response of electrical coil5,50can be performed analytically and very accurately, which makes possible the use of optimization algorithms for the search for the best choice for the different widths of turns L, L1, L2. In a general way, the optimum thus obtained is close to a configuration in which the average turns density taken on the whole width of electrical coil5,50in circular sectors SC is identical to the turns density in rectilinear segments TR.

The electrical coils5and50as represented inFIGS. 2 and 4comprising additional turns13,15of variable width L1, L2in circular sectors SC can only be realized in the form of a printed circuit and can in no case be realized with the classic winding technologies. As a non limiting example, for electrical coils5,50using this configuration with additional turns13,15, the optimal values for widths L1and L2are close to L1=0.113×L et L2=0.31×L in these examples.

FIGS. 5 and 6illustrate an embodiment of current sensor1comprising two identical and superimposed electrical coils5,50, as explained later. These figures are used to describe the manufacture of one of electrical coils5,50, which comprises two conductive layers17,18, called first conductive layer17and second conductive layer18, superimposed and separated from each other by a thick insulating core19made of a substrate20, which is integral part of electronic board4. Substrate20forms a support for conductive layers17,18. It is therefore made of an insulating material such as, for example, an epoxy resin, a polyimid resin or teflon-based materials. The first and second conductive layers17,18, which are commonly made out of copper, are connected with each other by first connection holes21passing through insulating core19to form turns12,13,15of electrical coil5,50, these connecting holes21being conductive. To that purpose, connecting holes21are covered inside with a conductive sleeve21aand surrounded outside with a conductive crown21b, in particular out of copper.

The forming of turns12,13,15is illustrated more in detail inFIG. 3, which shows an example of the winding of electrical coil5in one of its circular sectors SC without representing substrate20of electronic board4to facilitate the understanding of the drawing. Each turn12,13, which corresponds to a turn of the winding, comprises a first rectilinear section B1provided in one of conductive layers17,18, a first return loop B2passing through substrate20with a first connection hole21perpendicular to substrate20, a second rectilinear section B3provided in the other of conductive layers17,18, substantially parallel to first rectilinear section B1, and a second return loop B4passing through substrate20with another first connection hole21perpendicular to substrate20, then an end section B5inclined with respect to first rectilinear section B1of the following turn12,13separated by a spacing P from the previous turn12,13. Of course, any other embodiment of the winding of electrical coil5can be suitable. The advantages of such an embodiment in the form of a printed circuit are, as seen previously, the regularity of the turns12,13,15obtained, the possibility of adding additional turns13,15with different widths, the serial reproducibility of said winding, the optimization of this winding and the immunity of electrical coil5,50obtained against the variation of the position of primary conductor2and against the parasitic currents generated by the neighboring conductors. It is thus possible to choose the smallest spacing P possible for a given printed circuit technology in circular sectors SC, which is implemented in rectilinear segments TR in order to maximize the measuring sensitivity of current sensor1,1′ obtained. As a non-limiting example, for conductive tracks with a width of 150 m forming turns12and additional turns13,15, and connection holes21with a minimum diameter of 0.4 mm provided with a conductive crown21barranged around connection holes21with a minimum width of 175 μm, minimum spacing P is equal to 0.9 mm.

As in all Rogowski coils, if one simply taps the output voltage directly between the input of the first turn and the output of the last turn of electrical coil5,50, current sensor1will operate correctly only for primary conductors2orthogonal to the plane of the coil. Any other configuration will create fields orthogonal to electrical coil5,50, which will be captured by the whole flat surface of the coil. To solve this problem, one can use a return conductor (not represented) having the same flat surface as electrical coil5,50to cancel this response by differential effect. In a simplified embodiment variant (not represented), one can use a return conductor having exactly the path of the projection of electrical coil5,50on the plane of the printed circuit. Such configuration can be obtained with a printed circuit with three conductive layers, the return conductor being realized on a third conductive layer. But, as such configuration is relatively rare, one will rather realize it in four conductive layers. In this case, thick insulating core19of substrate20carries the first and second conductive layers17,18of electrical coil5,50and the third and fourth external conductive layers form the return conductor. These third and fourth external conductive layers are separated from electrical coil5,50respectively by a thin insulating layer of substrate20. This return conductor is then connected serially to electrical coil5,50by connection holes passing through the insulating core and the insulating layers. The terms “thick” and “thin” are relative, but they allow identifying insulating core19, which carries electrical coil5,50of current sensor1and is usually thicker than the other thinner insulating layers used for other purposes. The thickness of the insulants in electrical coils5,50is chosen according to the required sensitivity. The thicker the insulant, the better the signal obtained. On the other hand, the thickness of the insulants between the electrical coils or between the electrical coils and the electrical shield is chosen as small as possible to limit the global dimensions of current sensor1,1′.

However, this simple return conductor is fully efficient only for homogeneous interference fields. The immunity against orthogonal interference fields can be improved by coupling two identical electrical coils5,50in opposition, that is to say whose winding is wound in opposite directions. In this case, the useful fields add and, since the two coils have the same sensitivity to the orthogonal fields and are coupled in opposition, these interference fields are eliminated almost perfectly. Such configuration is advantageously obtained by means of a printed circuit with four conductive layers17,18according toFIG. 5. Each electrical coil5,50is realized by a first conductive layer17and a second conductive layer18located on either side of a thick insulating core19crossed by first connection holes21. The two electrical coils5,50are superimposed and separated from each other by a thin central insulating layer22and they are connected serially by second connecting holes23passing through insulating core19and insulating central layer22.

As in all Rogowski coils, electrical coil5,50is also sensitive to interferences due to capacitive coupling between live primary conductor2carrying the alternating current to be measured and electrical coil5,50. To eliminate this effect, current sensor1is provided with an electrical shield24. Referring more specifically toFIG. 6, this electrical shield24can consist in an upper external conductive layer25and a lower external conductive layer26covering electrical coil(s)5,50, and/or the return conductor, and separated from electrical coil(s)5,50, and/or from electrical return conductor respectively by an additional thin insulating layer27,28of substrate20. This electrical shield can be complemented with at least one lateral conductive layer29covering the edges of substrate20. Electrical coil5,50is then entirely enclosed in a Faraday cage and is therefore totally protected against capacitive couplings.

FIG. 8illustrates another embodiment of substrate20ofFIG. 6that allows complementing current sensor1,1′ of the invention with a voltage measuring circuit40arranged for measuring the voltage V(t) applied to primary conductor2. In this embodiment, lateral conductive layer29of substrate20ofFIG. 6, which surrounds through window9provided in electrical coil5,50for primary conductor2, can form a detection electrode41for the voltage applied to said primary conductor2. This detection electrode41, instead of being connected to a reference potential as that of the rest of electrical shield24, is insulated from the rest of electrical shield24and connected to a reference potential, which can be the same as that of electrical shield24or any other reference potential not necessarily connected to the shield, via a capacitor42connected in parallel to a resistor43. The electrical insulation of detection electrode41from the rest of electrical shield24is achieved by an interruption zone44in the corresponding conductive layers17,18,25,26provided on substrate20, or by any equivalent means performing the same function. Capacitor42can have a typical value from some hundred picofarads (pF) to some tens of nanofarads (nF), and resistor43can have a typical value comprised between some tens of kilo-ohms (kΩ) to some mega-ohms (MΩ). Detection electrode41and primary conductor2thus form a capacitance illustrated by a capacitor45represented by dotted lines inFIG. 8and having a value comprised between a fraction of a picofarad and some picofarads (pF). The set formed by detection electrode41and the RC assembly (capacitor42+capacitor45+resistor43) forms a high-pass filter with a cut-off frequency that can range from some tenths of a hertz to some hundred of hertz, according to the processing type chose for the output signal. This high-pass filter also forms a voltage divider that generates an output voltage V(t) at the terminals of resistor43that is an image of the voltage applied to said primary conductor2and that can be interpreted by a processing unit. Application examples are illustrated in publications WO 2015/150670 A1 and WO 2015/150671 A1 of the same applicant. The values of capacitors42,45and of resistor43are only given on an indicative basis and are not limiting.

As this Rogowski coil shows low sensitivity, typically 10 μV/A for a current to measure with a frequency of 50 Hz, electronic conditioning unit6, which generally includes a 1st-order low-pass amplifier circuit, must be located close to electrical coil5,50to limit the influences of the interfering magnetic fields in the connections between electrical coil5,50and said electronic conditioning unit6. A consequence of this proximity is the proximity of primary conductor2, which can generate a capacitive coupling between primary conductor2and said electronic conditioning unit6. It is therefore indispensable to protect this electronic conditioning unit6by means of an electrical shield, which can be made in the form of a conductive housing30containing said electronic conditioning unit6.

Current sensor1′ can also be a polyphase sensor, that is to say a sensor suitable for measuring the alternating current in an electrical installation comprising more than one phase, and thus more than one primary conductor2.FIGS. 7A and 7Billustrate an embodiment example of a three-phase current sensor1′. In function of the axis distance of primary conductors2and of the size of electrical coils5,50, it can be interesting to provide a current sensor1′ provided with two electronic boards4a,4bsuperimposed, parallel and separated by an interval I wherein electrical coils5,50are arranged in an alternating manner. For example, electrical coil5,50corresponding to the central primary conductor can be mounted on rear electronic board4b, while the two other electrical coils5,50corresponding to the end electrical conductors can be mounted on front electronic board4a. This way, the size of electrical coils5,50is no longer a barrier and current sensor1′ can be adapted to all configurations of a device for polyphase measurement and/or for multiphase electrical installations. In this embodiment example, the electronic conditioning units6arranged close to their electrical coils5,50will be positioned in interval I existing between the two electronic boards4a,4b. This particular circuit has the advantage of forming intrinsically an electrical shield protecting said electronic conditioning units6, allowing to do without conductive housing30necessary in single-phase current sensor1illustrated in figure land comprising one single electronic board4.

Other configurations can be considered to realize a polyphase current sensor1′ according to the invention. Electrical coils5and corresponding through windows9can be arranged on a same electronic board4. In this case, they can be aligned, staggered or arranged according to any other layout.

Possibilities for Industrial Application:

Current sensor1,1′ as described can therefore be realized with well-known printed circuit manufacturing techniques that allow realizing Rogowski-type electrical coils with a substantially polygonal shape and optimizing the quality of these coils, ensuring them an immunity against interference fields and currents equivalent to that of circular coils, with the advantages of the polygonal shape in terms of size and ease of implantation. This description shows clearly that the invention allows reaching the goals defined.

The present invention is however not restricted to the examples of embodiment described, but extends to any modification and variant which is obvious to a person skilled in the art.