Current transformer with magnetic core on primary conductor bar

Abstract

The open-loop current transducer (2) includes a primary conductor bar (4, 104, 104') for carrying the current to be measured, a magnetic core (6) having a U-shape formed by end branches (6a) and transverse branches (6b) rising therefrom to free ends, a magnetic circuit gap (5) formed at the free ends of the transverse branches between the inner surfaces (18b) of the transverse branches (6b), a magnetic field detector (8) positioned within the magnetic circuit gap (5), and a housing enclosing the magnetic core (6) and sections of the primary conductor bar extending through and beyond the magnetic core (6) on both sides. The primary conductor bar includes a central portion (14, 114, 114') having a width (Wc) equal to the width (Wg) of the magnetic field gap, the central portion being clamped between the transverse branches with an interference fit.

Description

Content of disclosure

[0001] The present invention relates to a current transducer for measuring a current flowing in a primary conductor, the current transducer including a magnetic core and a magnetic field detector in an air gap of the magnetic core.

[0002] Current sensors are used in a wide variety of applications for monitoring or controlling electrical devices and systems, and in many applications offer important advantages in reducing the size and manufacturing costs of the sensor.

[0003] Many open loop current transducers include a magnetic core configured to surround a primary conductor through which the current to be measured flows, the magnetic core having an air gap in which a magnetic field detector is positioned to measure a portion of the magnetic flux circulating in the magnetic core due to the magnetic field generated by the primary conductor. The magnetic field detector is most often a Hall effect detector, typically provided in the form of an application specific integrated circuit (ASIC) having terminals for connection to a circuit board. The circuit board interconnects the magnetic field detector to a connector of the transducer for connection to an external circuit or provides terminals for connection to an external circuit board to which the transducer is mounted.

[0004] In certain applications, the primary conductor bar is directly integrated into the current transducer, providing connection ends for coupling to the conductor carrying the current to be measured. Such a primary conductor bar may essentially be in the form of a rigid metal bar with connection ends configured according to the application and implementation of the current transducer in the electrical system. The magnetic core, the magnetic field detector, and the primary conductor are often assembled in an electrically insulated housing, in which the magnetic core, the primary conductor, the magnetic field detector, and other components such as conductors and circuit boards may be mounted as separate components. In some applications, the inside of the insulated housing may be filled with a potting material that provides better insulation and stability to the various components assembled inside the housing. The primary conductor bar is typically overmolded by a plastic housing around which the magnetic core is mounted, or is inserted into a cavity of the insulating housing, in which the magnetic core is assembled or overmolded.

[0005] While such open loop current transformers are very economical, they are very bulky, limiting their use in applications where space is limited. Many other current transformers exist that do not use a magnetic core or are of a closed loop type that can be implemented to meet limited space requirements, but such current transformers are typically more costly to manufacture and use than the types of open loop current transformers previously described.

[0006] SUMMARY OF THE PRESENT EMBODIMENT It is an object of the present invention to provide an open loop current converter which is compact, reliable and economical.

[0007] It would be advantageous to provide a current transducer that is cost effective to construct.

[0008] It would be advantageous to provide a current transducer that is robust and can be implemented in harsh environments.

[0009] The object of the present invention is achieved by providing a current transducer as claimed in claim 1.

[0010] The object of the present invention is achieved by providing a current transducer as claimed in claim 12.

[0011] Disclosed herein is an open loop current transducer including a primary conductor bar for carrying a current to be measured, a magnetic core having a U-shape formed by an end branch and a lateral branch rising therefrom to a free end, a magnetic circuit gap formed between inner surfaces of the lateral branches at the free ends of the lateral branches, a magnetic field detector positioned within the magnetic circuit gap, and a housing enclosing the magnetic core and a section of the primary conductor bar extending through the magnetic core.

[0012] According to a first aspect of the invention, the primary conductor bar comprises a central portion having a width equal to the width of the magnetic field gap, configured to be clamped with a non-null clamping force between said lateral branches with an interference force fit. To obtain an interference force fit, some material deformation must be present, which essentially involves some elastic deformation in such a way that a clamping effect is present. This means that before assembly the width of the magnetic field gap is slightly smaller than the width of the central portion, thus requiring a forced insertion, which generates stresses and provides a clamping effect between them.

[0013] According to a second aspect of the invention, a conductor primary conductor bar central portion includes a base layer and one or more folded over conductor layers, and has an overall width equal to the width of the air gap in the core.

[0014] The layer folded over the conductor may advantageously be formed from a tongue integrally formed with and extending laterally from an edge of the primary conductor bar, the folding direction being perpendicular to the direction of primary current flow through the air gap.

[0015] In an advantageous embodiment, the lateral branches of the magnetic core are substantially parallel to one another.

[0016] In one embodiment, the primary conductor bar central portion has a width less than the width of the sections of the primary conductor bar located on either side of the magnetic core, and the central portion is formed by a pair of recesses from opposing outer edges of the primary conductor bar, each recess receiving a lateral branch of the magnetic core therein in a close fit.

[0017] In an advantageous embodiment, the length of the recess in the direction of primary current flow is essentially equal to the length of the magnetic core.

[0018] In an advantageous embodiment, the width of each lateral branch is equal to + / - 20% of the width of the recess.

[0019] In an advantageous embodiment, the cross section of the portion of the primary conductor bar mounted inside the housing has an essentially flat rectangular shape.

[0020] In an advantageous embodiment, the housing includes a base that is inserted into the magnetic circuit gap and includes a magnetic field detector accommodating portion that includes a slot that receives the magnetic field detector therein, the magnetic field detector being retained within the magnetic circuit gap and separated from the lateral branches of the magnetic core by an insulating layer.

[0021] In an advantageous embodiment, the housing base includes a magnetic field sensing unit accommodating portion that allows for translational insertion of the magnetic field sensing unit within the housing base, and the housing further includes a cover mounted over the magnetic field sensing unit accommodating portion.

[0022] In an advantageous embodiment, the current converter includes a connector, the connector including a shroud integrally formed with the housing base, overmolded by the housing base, and including a terminal having a connection portion that connects to a circuit board of the magnetic field sensing unit.

[0023] In an advantageous embodiment, the central portion has a rectangular cross section and the inner surface of the magnetic core which fits closely around the central portion also has a rectangular shape.

[0024] Further objects and advantageous features of the present invention will be apparent from the appended claims, detailed description and accompanying drawings. [Brief description of the drawings]

[0025] [Figure 1a] FIG. 1 is a perspective view of a current transducer according to an embodiment of the present invention. [Figure 1b] FIG. 1 is a perspective view of a current transducer according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a perspective view of a current transducer according to another embodiment of the present invention. [Diagram 3] 1 is a perspective view of a plurality of current transformers according to an embodiment of the present invention; [Figure 4] 1 is a perspective cross-sectional view of a current transducer according to an embodiment of the present invention; [Figure 5a] FIG. 2 is a perspective view of components of a current transformer according to one embodiment of the present invention with the housing removed, showing a magnetic core and a magnetic field detector mounted around a primary conductor. [Figure 5b] FIG. 5b is a perspective view of a magnetic core of the embodiment of FIG. 5a. [Figure 5c] FIG. 5b is a perspective view of a primary conductor bar of the embodiment of FIG. 5a. [Figure 6] FIG. 5b is a perspective view similar to FIG. 5a of a variant; [Figure 7] FIG. 5b is a perspective view similar to FIG. 5a of a variant; [Figure 8] FIG. 5b is a perspective view similar to FIG. 5a of a variant; [Figure 9a] 2 is a perspective partial cross-sectional view of a current transducer according to another embodiment of the present invention. [Figure 9b] FIG. 9b is a perspective view of a portion of the embodiment of FIG. 9a with the housing removed. [Figure 9c] FIG. 9b is a perspective view of a primary conductor bar of the embodiment of FIG. 9a. [Figure 10a] 2 is a perspective partial cross-sectional view of a current transducer according to another embodiment of the present invention. [Figure 10b] FIG. 10b is a perspective view of a portion of the embodiment of FIG. 10a with the housing removed. [Figure 10c] FIG. 10b is a perspective view of a primary conductor bar of the embodiment of FIG.

[0026] Referring to the drawings, a current transducer 2 according to an embodiment of the present invention includes a magnetic core 6 , a magnetic field detector 8 and a primary conductor 4 , 104 , 104 ′ carrying a primary current that is measured by the current transducer 2 .

[0027] The magnetic core 6 has a generally U-shaped configuration including end branches 6a and lateral branches 6b extending from the ends of the end branches 6a to their respective free ends. In a preferred embodiment, the lateral branches 6b are substantially parallel to one another. In a preferred embodiment, the lateral branches are substantially perpendicular to the end branches 6a.

[0028] The magnetic field detector 8 may be in the form of an application specific integrated circuit (ASIC) including a Hall effect detector packaged inside an insulating housing and providing electrical terminals 21 for connection to a circuit board or flexible circuit board having conductive traces thereon. Such magnetic field detectors are well known per se and need not be described further herein. Other magnetic field detectors may be used instead of the Hall effect detector, for example fluxgate detectors or magnetoresistive magnetic field detectors.

[0029] The magnetic field detector 8 may be interconnected by its terminals 21 to a circuit board or flexible circuit 20 to form the magnetic field sensing unit 7 .

[0030] In the embodiment shown in Fig. 4, the magnetic field sensing unit comprises a rigid circuit board 20 to which the magnetic field detector 8 is connected, which circuit board extends to a connector portion to which terminals 22 of the connector 12 are mounted. The connector 12 allows the current transducer to be connected to an external circuit via a pluggable connector. However, the connector 12 may also exhibit other forms, for example having electrical terminals for connection to an external circuit board, for example by soldering or welding. Such connection systems between the current transducer and the external circuit are known per se.

[0031] The magnetic field detector 8 is positioned in a magnetic circuit gap 5 (often referred to as an "air gap" even though the gap is not necessarily filled with air) formed between the free ends of the lateral branches 6b of the magnetic core 6. Each lateral branch 6b presents an essentially flat inner surface 18b which extends from the end branch 6a to form the air gap 5.

[0032] The primary conductor bars 4, 104, 104' may typically be extruded and / or stamped and formed from a substantially rigid, self-supporting metallic material such as a copper alloy.

[0033] 1-8, the primary conductor bar includes a central portion 14 formed by recesses 14a, 14b extending into the primary conductor bar from an outer edge 17 that defines a width W of the primary conductor bar extending from the magnetic core 6. Thus, the central portion 14 has a smaller width W than the primary conductor has on either side of the magnetic core 6. C and the width W of the central portion 14 C is substantially equal to the gap 5 between the inner surfaces 18b of the lateral branches 6b of the magnetic core, allowing the central portion 14 to be inserted between the lateral branches with a tight fit. The depth Wi of the recesses 14a, 14b may be substantially equal to the width Wb of the lateral branches 6a, 6b or may be within plus or minus 20% of the width of the lateral branches (Wi=Wb+ / -0.2×Wb), the width W of the primary conductor bar 4 and the magnetic core 6 being substantially equal within 20%. Thus, the width of the current transducer around the magnetic core and the part of the primary conductor extending from the magnetic core may be very compact without substantially reducing the width W of the connecting part 16a, 16b of the primary conductor that allows it to be coupled to the conductor carrying the current to be measured.

[0034] The length Li of the recesses 14a, 14b of the primary conductor bar 4 may essentially correspond to the length (thickness) Lb of the magnetic core branches 6b interposed between them, with the length of the central portion 14 (as viewed in the direction of primary current flow) being limited to the thickness Lb of the magnetic core. This reduces the resistance to current flow presented by the reduced section of the central portion by minimizing its length in the direction of current flow.

[0035] The term "width" as used herein defines the distance measured in a direction generally perpendicular to the direction of primary current flow measured at the central portion of the conductor bar, and the term "length" as used herein defines the distance measured in a direction generally parallel to the direction of primary current flow measured at the central portion of the conductor bar.

[0036] The magnetic core in the preferred embodiment may include a substantially rectangular inner shape formed by the inner surface 18b of the lateral branch 6b and the inner surface 18a of the end branch 6a, whereby the central portion 14 of the primary conductor bar 4, having a rectangular cross section, may be inserted in close conformity with and fit with the inner wall 18a and a part of the wall 18b rising therefrom, the remaining height of the lateral branch serving to form an air gap 5 therebetween, in which the magnetic field detector 8 is inserted. Thus, in one embodiment, the primary conductor central portion 14 may be slidably fitted between and in direct contact with the lateral branches of the magnetic core, such that the magnetic flux generated by the primary conductor, particularly its central portion 14, is efficiently captured by the magnetic core 6. This reduces the section required by the magnetic core 6 compared to conventional solutions in which an insulating material is located between the magnetic core and the primary conductor.

[0037] The close fit of the magnetic core 6 around the central portion 14 of the primary conductor bar 4 advantageously reduces the magnetic field fringe flux, which makes it possible to optimize and reduce the section of the magnetic core and therefore its size. The three branches 6a, 6b of the magnetic core 6 formed in a simple U-shape are also cost-effective to manufacture and very easy to assemble to the primary conductor bar 4 by translating the primary conductor bar into the magnetic core.

[0038] In an advantageous embodiment, the primary conductor central portion 14 is fitted between the lateral branches of the magnetic core with an interference fit, in which the width Wg of the air gap between the branches 6b is slightly smaller than the width or thickness Wc of the primary conductor central portion 14, 114, 114' before assembly, and some elastic and / or plastic deformation of the primary conductor and / or the magnetic core occurs during assembly of the primary conductor to the magnetic core.

[0039] As best seen in Figures 4, 9a and 10a, the housing 10 surrounds and receives within it the magnetic core 6 and portions of the primary conductor bars positioned on either side of the magnetic core.

[0040] The housing may be a separately formed insulating housing fitted around the magnetic core and primary conductor central portion, or in an advantageous embodiment, may be overmolded around the magnetic core and primary conductor central portion.

[0041] In an advantageous embodiment, the housing can include a magnetic field detector receiving portion 24 that provides an insulating layer between the primary conductor bar central portion 14, 114, 114' and the magnetic field detector 8, as well as between the lateral branch 6b of the magnetic core and the magnetic field detector 8. The magnetic field detector receiving portion 24 includes a slot 26 in which the magnetic field detector 8 is received and positioned.

[0042] The magnetic field detector receiving portion 24 may have a width Wh that is substantially equal to or slightly smaller than the air gap width Wg to provide a snug or close fit within the air gap and to stably position the magnetic field detector within the air gap.

[0043] The housing 10 may further include a portion that forms a connector shroud 27 that surrounds the terminals 22 of the connector 12. The housing also has magnetic field sensor receiving portions 24, 28.

[0044] In the illustrated embodiment, the base 10a may advantageously be formed by overmolding around the magnetic core 6, including the magnetic field detector housing portion 24 and the connector shroud portion 27, which is attached to the central portion 14, 114, 114' of the primary conductor bar 4, 104, 104'.

[0045] In an alternative embodiment, the housing base 10a may be formed of two pieces assembled around the magnetic core and primary conductor bar instead of being overmolded, as shown in Figure 4. The magnetic field sensing unit 7 including the magnetic field detector 8 and the circuit board 20 may be mounted on the base 10a by assembling the cover 10b to the base 10a to cover the magnetic field sensing unit 7 after inserting the magnetic field detector 8 into the slot 26 and connecting the circuit board 20 to the terminals 22 of the connector 12.

[0046] The above-described arrangement thus results in a particularly cost-effective production of the current transducer.

[0047] The magnetic core 6 is advantageously made from a stack of sheets of soft magnetic material as known per se in the field of magnetic cores, as shown in Figures 6, 7 and 9a-10c. The laminated structure of the soft magnetic material described above has a certain compliance that allows the central part 14, 114, 114' of the primary conductor bar 4, 104 to be inserted with an interference fit through the magnetic circuit gap between the transverse branches 6b, assembling the primary conductor with a tight and secure fit to the magnetic core. The latter ensures that the magnetic core and the primary conductor can be fixed together in a simple assembly operation in a fixed and accurate positional arrangement and then fitted in the insulating housing 10 or overmolded with the insulating housing as can be best seen in Figures 9a and 10a.

[0048] In the variation shown in FIG. 8, stacked laminated sheets of soft magnetic material are stacked in a direction parallel to the direction of the magnetic gap to form a U-shaped magnetic core.

[0049] In the embodiment of Figures 9a-10c, the primary conductor central portion 114, 114' includes one or more conductor folded layers 115a, 115b with an overall width (thickness) Wc' that allows the overall width (thickness) Wc' to be adjusted to the width Wg of the air gap in the core. The adjustment can be either by using primary conductor bars with different material thicknesses or by using magnetic cores with air gaps of different widths. The conductor folded layers 115a, 115b can be formed from tongues that are integrally formed with the edges of the primary conductor bars 104, 104' and extend laterally from the edges of the primary conductor bars, with the folding direction perpendicular to the direction of primary current flow through the air gap. In the variant shown in Figures 9a-10c, there is a single folded layer 115a, while in the variant shown in Figures 10a-10c, there are two folded layers 115b.

[0050] In the embodiment of Figures 9a-10c, a recess 114a in the central portion 114 of the primary conductor bar 104, 104' serves to receive the magnetic field detector 8 therein.

[0051] The insertion by interference fit of the primary conductor bar central portions 114, 114' between the core branches 6be ensures stable clamping of the folded layers and a secure, tightly fitted assembly of the magnetic core and the primary conductor bar.

[0052] Advantageously, the open loop current transducer according to the invention is particularly compact and easy to assemble, thus providing a low-cost current transducer that has a large measurement range for its size, yet is robust.

[0053] [List of reference symbols used] Current Transducer 2 Primary conductor bar 4 Outer edge 17 central part 14 Recesses 14a, 14b Connection ends 16a, 16b Primary conductor bars 104, 104' central part 114 Recess 114a Folded tongue 115 Single fold 115a Double fold 115b Connection end 116 Magnetic Core 6 Magnetic circuit gap 5 End branch 6a Inner surface 18a Lateral branch 6b Inner surface 18b Free end chamfer 28 Magnetic Field Sensing Unit 7 Magnetic Field Detector 8 Terminal 21 Circuit Board, Circuit Flex 20 Terminal 22 Housing 10 Base 10a Magnetic field sensing unit receiving cavity 23 Magnetic field detector housing 24 Slot 26 Circuit board housing 28 Cover 10b Connector 12 Terminal 22 Connector Shroud 27

[0054] [Embodiment] (1) An open-loop current converter (2), a primary conductor bar (4, 104, 104') for carrying the current to be measured; a magnetic core (6) having a U-shape formed by an end branch (6a) and a lateral branch (6b) rising therefrom to a free end; a magnetic circuit gap (5) formed between the inner surfaces (18b) of the lateral branches (6b) at the free ends of the lateral branches; a magnetic field detector (8) positioned within the magnetic circuit gap (5); a housing enclosing the magnetic core (6) and a section of the primary conductor bar extending through and beyond the magnetic core (6) on both sides; The primary conductor bar includes a central portion (14, 114, 114') having a width (Wc) equal to a width (Wg) of a magnetic field gap, the central portion being clamped between the lateral branches with an interference fit, an open loop current transformer. (2) A current transformer as described in embodiment 1, wherein the primary conductor bar central portion (14) has a width (Wc) smaller than the width (W) of the sections of the primary conductor bar positioned on either side of the magnetic core, and the central portion (14) is formed by a pair of recesses (14a, 14d) from opposing outer edges (17) of the primary conductor bar, each recess receiving a lateral branch (6b) of the magnetic core in a closely fitting manner therein. (3) A current converter as described in embodiment 2, wherein the length (Li) of the recess (14a) in the direction of flow of the primary current is essentially equal to the length (Lb) of the magnetic core. (4) A current transformer as described in embodiment 2 or 3, wherein the width (Wb) of each lateral branch is equal to the width (Wi) of the recess (14a, 14b) + / - 20%. (5) A current converter according to any one of the first to fourth embodiments, wherein a cross section of a portion of the primary conductor bar mounted inside the housing (10) has an essentially flat rectangular shape.

[0055] (6) A current converter as described in any one of embodiments 1 to 5, wherein the housing (10) includes a base (10a) including a magnetic field detector accommodating portion (24a) that is inserted into the magnetic circuit gap (5) and includes a slot (26) that receives the magnetic field detector (8) therein, and the magnetic field detector is held within the magnetic circuit gap and separated from the lateral branch of the magnetic core by an insulating layer. (7) A current converter as described in any of embodiments 1 to 6, wherein the housing base (10a) includes a magnetic field sensing unit accommodating portion (28) that enables the magnetic field sensing unit to be inserted by translational movement within the housing base, and the housing further includes a cover (10b) attached over the magnetic field sensing unit accommodating portion. (8) A current converter as described in any one of embodiments 1 to 7, wherein the current converter includes a connector (12), the connector including a shroud integrally formed with the housing base (10a), and a terminal (22) overmolded by the housing base and having a connection portion for connecting to a circuit board (20) of the magnetic field sensing unit. (9) A current converter as described in any one of embodiments 1 to 8, wherein the central portion (14) has a rectangular cross section, and the magnetic core inner surfaces (18a, 18b) that fit closely around the central portion also have a rectangular shape. (10) A current converter as described in any one of embodiments 1 to 9, wherein the conductor primary conductor bar central portion (114, 114') includes a base layer and one or more conductor folded layers (115a, 115b), and an overall width (Wc') is equal to the width (Wg) of the air gap in the core.

[0056] (11) A current transformer as described in embodiment 10, wherein the layer folded over the conductor is formed from a tongue-like portion integrally formed with and extending laterally from an edge of the primary conductor bar (104, 104'), the folding direction being perpendicular to the direction of flow of the primary current through the air gap. (12) An open loop current converter (2), a primary conductor bar (4, 104, 104') for carrying the current to be measured; a magnetic core (6) having a U-shape formed by an end branch (6a) and a lateral branch (6b) rising therefrom to a free end; a magnetic circuit gap (5) formed between the inner surfaces (18b) of the lateral branches (6b) at the free ends of the lateral branches; a magnetic field detector (8) positioned within the magnetic circuit gap (5); a housing enclosing the magnetic core (6) and a section of the primary conductor bar extending through and beyond the magnetic core (6) on both sides; An open loop current transformer, comprising a conductor primary conductor bar central portion (114, 114') including a base layer and one or more conductor folded layers (115a, 115b), and having an overall width (Wc') equal to the width (Wg) of the air gap in the core. (13) A current transformer as described in embodiment 12, wherein the primary conductor bar central portion has a width (Wc) equal to a width (Wg) of the magnetic circuit gap, and the central portion is clamped with a non-null force between the lateral branches with an interference force fit. (14) A current transformer as described in embodiment 12 or 13, wherein the primary conductor bar central portion (14) has a width (Wc) smaller than the width (W) of the sections of the primary conductor bar located on either side of the magnetic core, and the central portion (14) is formed by a pair of recesses (14a, 14d) from opposing outer edges (17) of the primary conductor bar, each recess receiving a lateral branch (6b) of the magnetic core in a closely fitting manner therein. (15) A current converter as described in embodiment 14, wherein a length (Li) of the recess (14a) in the direction of flow of the primary current is essentially equal to a length (Lb) of the magnetic core.

[0057] (16) A current transducer as described in embodiment 14 or 15, wherein the width (Wb) of each lateral branch is equal to the width (Wi) of the recess (14a, 14b) + / - 20%. (17) A current converter according to any one of embodiments 12 to 16, wherein a cross section of a portion of the primary conductor bar mounted inside the housing (10) has an essentially flat rectangular shape. (18) A current converter as described in any one of embodiments 12 to 17, wherein the housing (10) includes a base (10a) including a magnetic field detector accommodating portion (24a) that is inserted into the magnetic circuit gap (5) and includes a slot (26) that receives the magnetic field detector (8) therein, and the magnetic field detector is held within the magnetic circuit gap and separated from the lateral branch of the magnetic core by an insulating layer. (19) A current converter as described in any of embodiments 12 to 18, wherein the housing base (10a) includes a magnetic field sensing unit accommodating portion (28) that enables insertion of the magnetic field sensing unit by translational movement within the housing base, and the housing further includes a cover (10b) attached over the magnetic field sensing unit accommodating portion. (20) A current converter as described in any of embodiments 12 to 19, wherein the current converter includes a connector (12), the connector including a shroud formed integrally with the housing base (10a), and a terminal (22) overmolded by the housing base and having a connection portion for connecting to a circuit board (20) of the magnetic field sensing unit.

[0058] (21) A current converter as described in any one of embodiments 12 to 20, wherein the central portion (14) has a rectangular cross section, and the magnetic core inner surfaces (18a, 18b) that fit closely around the central portion also have a rectangular shape. (22) A current transformer as described in any one of embodiments 12 to 21, wherein the layer folded over the conductor is formed from a tongue-like portion integrally formed with and extending laterally from an edge of the primary conductor bar (104, 104'), the folding direction being perpendicular to the direction of flow of the primary current through the air gap.

Claims

1. An open loop current converter (2), a primary conductor bar (4, 104, 104') for carrying the current to be measured; a magnetic core (6) having a U-shape formed by an end branch (6a) and a lateral branch (6b) rising therefrom to a free end; a magnetic circuit gap (5) formed between the inner surfaces (18b) of the lateral branches (6b) at the free ends of the lateral branches; a magnetic field detector (8) positioned within the magnetic circuit gap (5); a housing enclosing the magnetic core (6) and a section of the primary conductor bar extending through and beyond the magnetic core (6) on both sides; An open loop current transformer, wherein a primary conductor bar central portion (114, 114') includes a base layer and one or more conductor folded layers (115a, 115b), and the overall width (Wc') is equal to the width (Wg) of the magnetic circuit gap in the magnetic core.

2. 2. The current transformer of claim 1, wherein the primary conductor bar central portion has a width (Wc) equal to a width (Wg) of the magnetic circuit gap, and the primary conductor bar central portion is clamped with a non-null force between the lateral branches with an interference force fit.

3. 3. A current transformer as claimed in claim 1 or 2, wherein the primary conductor bar central portion has a width (Wc) smaller than the widths (W) of the sections of the primary conductor bar located on either side of the magnetic core, the primary conductor bar central portion being formed by a pair of recesses (14a, 14b) from opposite outer edges (17) of the primary conductor bar, each recess receiving a lateral branch (6b) of the magnetic core therein in a closely fitting manner.

4. 4. A current transducer according to claim 3, wherein the length (Li) of the recess (14a) in the direction of current flow is essentially equal to the length (Lb) of the magnetic core.

5. A current transformer according to claim 3 or 4, wherein the width (Wb) of each lateral branch is equal to + / - 20% of the width (Wi) of said recess (14a, 14b).

6. A current transformer according to any one of the preceding claims, wherein a cross section of the part of the primary conductor bar mounted inside the housing (10) has an essentially flat rectangular shape.

7. The current converter according to any one of claims 1 to 6, wherein the housing (10) includes a housing base (10a) including a magnetic field detector receiving portion (24a) inserted into the magnetic circuit gap (5) and including a slot (26) for receiving the magnetic field detector (8) therein, the magnetic field detector being held in the magnetic circuit gap and separated from the lateral branches of the magnetic core by an insulating layer.

8. A current converter as described in any one of claims 1 to 7, wherein the housing base (10a) includes a magnetic field sensing unit accommodating portion (28) that enables insertion of a magnetic field sensing unit by translational movement within the housing base, and the housing further includes a cover (10b) attached over the magnetic field sensing unit accommodating portion.

9. 9. The current converter of claim 8, wherein the current converter includes a connector (12), the connector including a shroud integrally formed with the housing base (10a), and a terminal (22) overmolded by the housing base and having a connection portion for connecting to a circuit board (20) of the magnetic field sensing unit.

10. 10. A current transformer as claimed in any one of claims 1 to 9, wherein the primary conductor bar central portion has a rectangular cross section and the magnetic core inner surface (18a, 18b) which fits closely around the primary conductor bar central portion also has a rectangular shape.

11. 11. A current transformer as claimed in any one of claims 1 to 10, wherein the layer folded on the conductor is formed from a tongue integrally formed with and extending laterally from an edge of the primary conductor bar (104, 104'), the folding direction being perpendicular to the direction of current flow through the magnetic circuit gap.

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