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 ).
1. A current sensor ( 1 , 1 ′) for measuring an alternating current, the sensor comprising:
at least one electrical coil ( 5 , 50 ),
an electronic unit ( 6 ) for conditioning a signal of the at least one electrical coil,
an electrical terminal block ( 7 ),
the at least one electrical coil ( 5 , 50 ) having a closed contour inscribed within a polygon and delimiting in its center a through window ( 9 ) for an electrical conductor crossed by the alternating current to be measured, this conductor being called a primary conductor ( 2 ),
the at least one electrical coil ( 5 , 50 ) comprising N rectilinear segments (TR) of width L and N circular sectors (SC) delimited each by an interior arc ( 10 ) of interior radius Ri and an exterior arc ( 11 ) of exterior radius Re,
the rectilinear segments (TR) being connected two by two by a circular sector (SC),
the rectilinear segments (TR) being made of turns ( 12 ) separated from each other by a constant spacing P, separated from each other on the interior arc ( 10 ) by a constant spacing equal to spacing P,
wherein the at least one electrical coil ( 5 , 50 ) is made in a form of a printed circuit provided on at least one electronic board ( 4 ) comprising additional turns ( 13 , 15 ) in its circular sectors (SC) with a width (L 1 , L 2 ) lower than the width (L) of other turns, called main turns ( 12 ), and extending from the exterior arc ( 11 ) towards at least one intermediate arc ( 14 , 16 ) located between the interior arc ( 10 ) and the exterior arc ( 11 ), the additional turns ( 13 , 15 ) being inserted between the main turns ( 12 ) so that the spacing between two consecutive turns ( 12 , 13 , 15 ) on the exterior arc ( 11 ) is substantially equal to spacing P, the N rectilinear segments (TR) and the N circular sectors (SC) have a same width L, in the circular sectors (SC), main turns ( 12 ) being separated from each other on the interior arc ( 10 ) by a constant spacing equal to spacing P, of rectilinear segments (TR), and main turns ( 12 ) and additional turns ( 13 , 15 ) being separated from each other on the exterior arc ( 11 ) by rectilinear segments (TR), so that an average turns density is almost constant in all of the electrical coil ( 5 , 50 ), and the constant spacing P is chosen the smallest spacing P possible for a given printed circuit technology in circuit sectors (SC) which is implemented in rectilinear segments (TR) in order to maximize the measuring sensitivity of the current sensor ( 1 , 11 ).
2. The current sensor according to claim 1 , wherein the electrical coil ( 5 ) comprises, in its circular sectors (SC), first additional turns ( 13 ) with a width (L 1 ) extending from the exterior arc ( 11 ) towards respectively a first intermediate arc ( 14 ) located between the interior arc ( 10 ) and the exterior arc ( 11 ).
3. The current sensor according to claim 1 , wherein the electrical coil ( 50 ) comprises, in the circular sectors (SC), first additional turns ( 13 ) and second additional turns ( 15 ) with different respective widths (L 1 ) and (L 2 ) extending from the exterior arc ( 11 ) towards respectively a first intermediate arc ( 14 ) and a second intermediate arc ( 16 ) located between the interior arc ( 10 ) and the exterior arc ( 11 ).
4. The current sensor according to claim 1 , wherein the electrical coil ( 5 , 50 ) is made in the form of a printed circuit comprising at least a first conductive layer ( 17 ) and a second conductive layer ( 18 ), superimposed on each other, separated from each other by an insulating core ( 19 ) of a substrate ( 20 ) of the electronic board ( 4 ), and the first and second conductive layers ( 17 , 18 ) are connected to each other by connecting holes ( 21 ) passing through the substrate ( 20 ) to form the turns ( 12 , 13 , 15 ) of the electrical coil ( 5 , 50 ).
5. The current sensor according to claim 4 , wherein the current sensor comprises a return conductor having a flat surface substantially equal to that of the electrical coil ( 5 , 50 ) to cancel interference fields, the return conductor is made in the form of a printed circuit comprising at least a third conductive layer, superimposed on the electrical coil ( 5 , 50 ) and separated from the electrical coil ( 5 , 50 ) by an insulating layer of the substrate ( 20 ), and the return conductor is serially connected to the electrical coil ( 5 , 50 ) by connecting holes passing through the substrate ( 20 ).
6. The current sensor according to claim 4 , wherein the current sensor comprises two electrical coils ( 5 , 50 ) made in the form of a printed circuit comprising at least four conductive layers ( 17 , 18 ), the two electrical coils ( 5 , 50 ) are identical, opposite to and superimposed on each other, separated from each other by a central insulating layer ( 22 ) of the substrate, and are serially connected by connecting holes ( 23 ) passing through the substrate ( 20 ).
7. The current sensor according to claim 1 , wherein the current sensor comprises an electrical shield ( 24 ).
8. The current sensor according to claim 7 , wherein the electrical shield ( 24 ) includes at least one upper exterior conductive layer ( 25 ) and one lower exterior conductive layer ( 26 ) covering the electrical coil ( 5 , 50 ) and a return conductor, or the electrical coils ( 5 , 50 ), and separated from the electrical coil(s) ( 5 , 50 ) and/or from the return conductor by an additional insulating layer ( 27 , 28 ) of a substrate ( 20 ).
9. The current sensor according to claim 7 , wherein the electrical shield ( 24 ) comprises at least one lateral conductive layer ( 29 ) covering an edge of the substrate ( 20 ).
10. The current sensor according to claim 7 , wherein the electrical shield ( 24 ) comprises a conductive housing ( 30 ) arranged around the electronic conditioning unit ( 6 ).
11. The current sensor according to claim 1 , wherein the current sensor is a single-phase current sensor and comprises the through window ( 9 ) for the primary conductor ( 2 ), and the through window ( 9 ) is surrounded by the at least one electrical coil ( 5 , 50 ).
12. The current sensor according to claim 1 , wherein the current sensor is a polyphase current sensor and comprises N through windows ( 9 ) for N primary conductors ( 2 ), and each through window ( 9 ) is surrounded by a corresponding one of the at least one electrical coil ( 5 , 50 ).
13. The current sensor according to claim 12 , wherein the current sensor comprises one electronic board ( 4 ) provided with N through windows ( 9 ), and the corresponding electrical coils ( 5 , 50 ) are arranged on the electronic board ( 4 ).
14. The current sensor according to claim 12 , wherein the current sensor comprises at least two superimposed electronic boards ( 4 a , 4 b ), comprising each N through windows ( 9 ), and the corresponding electrical coils ( 5 , 50 ) are distributed alternately on the electronic boards ( 4 a , 4 b ).
15. The current sensor according to claim 14 , wherein an electronic conditioning unit ( 6 ) being associated to each electrical coil ( 5 , 50 ) is arranged in an interval (I) located between the at least two electronic boards ( 4 ), forming intrinsically an electrical shield protecting the electronic conditioning units ( 6 ).
16. The current sensor according to claim 1 , wherein the current sensor comprises a voltage measuring circuit ( 40 ) arranged for measuring a voltage applied to the primary conductor ( 2 ).
17. The current sensor according to claim 16 , wherein the voltage measuring circuit ( 40 ) comprises at least one detection electrode ( 41 ) surrounding the through window ( 9 ) provided in the electrical coil ( 5 , 50 ), and the at least one detection electrode ( 41 ) is connected to a reference potential by a RC circuit ( 42 , 43 , 45 ) and is made of at least one lateral conductive layer ( 29 ) covering an edge of substrate ( 20 ) surrounding the through window ( 9 ).