Current Transducer

Abstract

1. A current converter (1), comprising: a housing (2), a magnetic core, and a magnetic field detection system, the magnetic core enclosing a primary conductor passage (4) for receiving a primary conductor (30) therethrough, the magnetic core including a first part (15) and a second part (16) assembled within the housing to form a first magnetic circuit gap (17a) and a second magnetic circuit gap (17b), the magnetic field detection system including a first magnetic field detector (18a) positioned in the first magnetic circuit gap (17a) and a second magnetic field detector (18b) positioned in the second magnetic circuit gap (17b), the first and second magnetic circuit gaps being disposed on opposite sides of the magnetic core, each of the first and second parts including a pair of side branches (15a, 16a) joined by a bridging branch (15b, 16b). The side branches of the first and second magnetic core parts overlap such that the side branch (15a) of the first part (15) of the magnetic core is positioned adjacent to the inside of the side branch (16a) of the second part (16) of the magnetic core, and the first and second magnetic circuit gaps are formed between the outside of the side branch of the first part and the inside of the side branch of the second part.

Description

[Technical field]

[0001] The present invention relates to a current transducer for measuring current flowing in one or more primary conductors, the current transducer comprising a magnetic core surrounding a central passage configured to receive the one or more primary conductors. [Background technology]

[0002] A well-known type of current transducer includes a magnetic core with an air gap in which a magnetic field detector, such as a Hall effect sensor, is positioned to measure the magnetic field generated by the current flowing in the primary conductor. Such transducers may be of the open-loop or closed-loop type, the latter generally having a compensation coil which generates a secondary current which attempts to cancel the magnetic field generated by the primary current being measured.

[0003] In some current transformers, there are two air gaps and two magnetic field detectors, one in each air gap. The air gaps and magnetic field detectors are usually arranged symmetrically on opposite sides of the magnetic circuit. One advantage of having a pair of air gaps is that the magnetic core is provided in two pieces, typically two U-shaped pieces, which can be separated so that the primary conductor can be located in a central passage surrounded by the magnetic core when assembled together.

[0004] Although two-part magnetic cores with only one air gap in which the magnetic field detector is located are also known, higher measurement sensitivity and accuracy with reduced saturation of the magnetic material can be achieved with a two-part magnetic core having two air gaps, each with a magnetic field detector.

[0005] In conventional transducers having a pair of magnetic field detectors and corresponding air gaps, differences in the length of the air gap adversely affect the accuracy of the transducer, particularly in transducer configurations that allow the primary conductor to be inserted and removed from the central passageway due to the amount of play required to open and close the magnetic core. Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above, it is an object of the present invention to provide a current transducer with a two-part magnetic core that is accurate and economically manufacturable, particularly for applications where the magnetic circuit can be opened to allow positioning of the primary conductor within the central passage of the magnetic core.

[0007] It would be advantageous to provide a current transducer of the type described above in which variations in measurement accuracy due to manufacturing tolerances and positional tolerances due to moving parts are reduced.

[0008] It would be advantageous to provide a compact current converter.

[0009] It would be advantageous to provide a current transducer that is easy to install and use. [Means for solving the problem]

[0010] The object of the present invention is achieved by providing a current transducer as claimed in claim 1.

[0011] Disclosed herein is a current converter including a housing, a magnetic core, and a magnetic field detection system, the magnetic core enclosing a primary conductor passage for receiving a primary conductor therethrough. The magnetic core includes a first part and a second part assembled within the housing to form a first magnetic circuit gap and a second magnetic circuit gap, the magnetic field detection system including a first magnetic field detector positioned in the first magnetic circuit gap and a second magnetic field detector positioned in the second magnetic circuit gap. The first and second magnetic circuit gaps are disposed on opposite sides of the magnetic core, the first and second parts each including a pair of side branches joined by a bridging branch. The side branches of the first and second magnetic core parts overlap such that the side branch of the first part of the magnetic core is positioned adjacent to an inner side of the side branch of the second part of the magnetic core, the first and second magnetic circuit gaps being formed between an outer side of the side branch of the first part and an inner side of the side branch of the second part.

[0012] In an advantageous embodiment, both the first part and the second part of the magnetic core are U-shaped.

[0013] In an advantageous embodiment, the housing includes a base housing and a cover housing movable relative to the base housing from an open position in which the primary conductor may be placed within the primary conductor passage, to a closed and locked position in which the magnetic core completely surrounds the primary conductor passage, one of the first and second parts of the magnetic core being attached to the base and the other of the first and second parts of the magnetic core being attached to the cover.

[0014] In an advantageous embodiment, the cover housing is hingedly connected to the base housing.

[0015] In an alternative embodiment, the cover housing is removably coupled to the base housing.

[0016] In an advantageous embodiment, the lateral branch of the first part of the magnetic core is received in a corresponding cavity in the base housing and the magnetic field detector is mounted in said same cavity.

[0017] In an advantageous embodiment, the magnetic core receiving portion includes an outer guide wall for the side branch having an outer surface which guides a complementary guide wall for the side branch on the cover housing in the closed position.

[0018] In an advantageous embodiment, the guide wall is tapered.

[0019] In an advantageous embodiment, a first part of the magnetic core is positioned within the base housing and a second part of the magnetic core is positioned within the cover housing.

[0020] In an advantageous embodiment, the magnetic field detector is in the form of an ASIC mounted on an electronic circuit board mounted within the base housing.

[0021] In an advantageous embodiment, the ASIC is disposed perpendicularly and upright from the circuit board when positioned within a corresponding cavity in the housing adjacent to a corresponding side branch of the first part of the magnetic core.

[0022] Further objects and advantageous features of the present invention will become apparent from the appended claims, detailed description and accompanying drawings. [Brief description of the drawings]

[0023] [Figure 1a] FIG. 2 is a top view of a current transducer according to one embodiment of the present invention. [Figure 1b] FIG. 1b is a cross-sectional view taken along line 1b-1b in FIG. [Figure 1c] FIG. 1b is an enlarged view of a portion of FIG. [Figure 1d] 1c, showing the magnetic core in an open position for insertion of a primary conductor into the central passage of the magnetic core; FIG. [Diagram 2] 1 is a perspective exploded view of a current transducer according to one embodiment of the present invention; [Diagram 3] 2 is a schematic cross-sectional view through a magnetic core and a magnetic field detector of a current transducer according to an embodiment of the present invention; [Figure 4] 4 is a schematic diagram of a magnetic circuit according to an embodiment of the present invention showing the magnetic field lines of the primary conductor at various positions within the central passage; [Diagram 5] 1 is a schematic diagram of a magnetic core according to one embodiment of the present invention, showing (exaggerated) the symmetry of the air gap due to manufacturing and positional tolerances. [Figure 6] 1 is a plot of magnetic field strength in the first and second air gaps as a function of air gap length as a function of the offset of the first magnetic core relative to the second magnetic core. [Figure 7] 7 is a plot illustrating the combined output of the first and second magnetic field detectors due to the offset of FIG. 6; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Referring to the figure, a current transducer 1 for measuring current in one or more primary conductors 3 includes a housing 2, magnetic cores 15, 16, magnetic field detection systems 18a, 18b, and electronic circuitry 21 mounted within the housing. The housing 2 has a primary conductor receiving portion defining a primary conductor passageway 4 for receiving one or more primary conductors therethrough.

[0025] The magnetic core includes a first part 15 and a second part 16 that define a first magnetic circuit gap 17a and a second magnetic circuit gap 17b between the first part 15 and the second part 16 of the magnetic core. The magnetic field detection system includes a first magnetic field detector 18a mounted in the first magnetic circuit gap and a second magnetic field detector 18b mounted in the second magnetic circuit gap 17b. The magnetic circuit gaps are also commonly known as "air gaps", although they may be filled with non-magnetic materials other than air.

[0026] The magnetic field detector may be a Hall effect detector, a fluxgate detector or any other form of magnetic field detector known per se in the art. The magnetic field detector may advantageously be provided in the form of an ASIC (Application Specific Integrated Circuit) mounted on and connected to the circuit board 19 of the electronic circuit 21.

[0027] The electronic circuitry may further include a connector 20 for electrically connecting to an external circuit to which the transducer is connected in use. The electronic circuitry may include further circuit components on a circuit board 19 for processing signals from and providing power to the magnetic field detectors 18a, 18b. Such functions are well known per se and need not be described further here.

[0028] The housing includes a base housing 5 in which the electronic circuitry 21 and the first part of the magnetic core 15 are received. The housing 2 further includes a cover housing 8 in which the second part of the magnetic core 16 is mounted, the cover housing 8 being coupled to the base housing 5.

[0029] The base housing 5 includes a first housing member 5a and a second housing member 5b that are assembled together to form one or more cavities therein for receiving and housing the electronic circuitry and the magnetic core first part 15. The second housing member 5b includes a magnetic core receiving portion 6 having a cavity for receiving and positioning, among other things, the side branch 15a of the magnetic core first part 15. Within the housing cavity, the magnetic field detectors 18a, 18b are also received adjacent the outside of the side branch 15a.

[0030] The first and second parts 15, 16 of the magnetic core may be generally U-shaped and include side branches 15a, 16a interconnected by a bridging branch 15b. The side branches 15a of the first part 15 may be closer together than the side branches 16a of the second part, such that the side branches of the first part are positioned within the space formed between the side branches 16 of the second part. Thus, an air gap 17a is formed between the outside of the side branch 15a of the first part and the inside of the side branch 16a of the second part.

[0031] The U-shapes of the first and second parts are arranged opposite to each other to form a central passage therebetween, and the side branches overlap each other to form an air gap between the outer and inner sides of the respective branches. Thus, when the first part is laterally displaced relative to the second part, one of the air gaps has a shortened length G1 and the other air gap has a lengthened length G2. Thus, the sum of the air gaps G1 and G2 remains constant. An important advantage of this configuration is that the variations in the measurement of the magnetic field when summing the outputs of the first and second magnetic field detectors are reduced compared to conventional transducers in which an air gap is provided between the opposing ends of the mirror-symmetrically arranged side branches. In such prior art configurations, the length of both air gaps may change when the position between the first and second magnetic core parts is displaced. Thus, inaccuracies due to variations in the position of the magnetic core parts exist without any mitigating effect.

[0032] The magnetic core receiving portion 6 of the base housing 5 may advantageously include a guide wall 7 on the outer side of the receiving cavity 22 forming a guide surface 11 on the outer side cooperating with a guide wall on the cover housing 8 for positioning the side branch 16a of the second part 16 outside the side branch 15 of the first part of the magnetic core or with a guide wall on the cover housing 8 for positioning the side branch 16a of the second part 16 outside the side branch 15 of the first part of the magnetic core. The guide wall 7 may advantageously have a tapered guide surface 11 at its upper end for guiding and positioning the cover when it is pivoted into the closed position.

[0033] The cover housing 8 may be coupled to the base housing 5 via a pivot coupling, including, for example, a pin 14 received in a complementary hole in a pivot projection 13 of the cover housing, allowing the cover housing to be pivotally opened to receive the primary conductor in the primary conductor passage 4, as best seen in FIG. 1d. The cover housing can then be pivoted back to a closed position where a latch 12, for example, clips onto the base housing 5 to secure the cover housing to the base housing in the closed position, as best seen in FIG. 1c.

[0034] Various other fastening mechanisms may be provided as known per se for split magnetic cores that allow for positioning of the primary conductor in the central passage. For example, instead of having a pivot mechanism, the cover housing may be completely removable from the base housing and secured together by a pair of latches. Other coupling mechanisms may be provided for disassembly and assembly of the cover housing and base housing to open the central passage for positioning the primary conductor in the central passage.

[0035] An important advantage of the inventive arrangement in which the side branches overlap to form two air gaps is that not only is the effect of inaccuracies in the relative lateral positioning reduced, but also the effect of inaccuracies in the spacing between the core parts is reduced, since there is no change in the size of the air gap whether the bridging branches are close or far apart.

[0036] As best seen in the plot of Figure 6, when the first part of the magnetic core is laterally displaced relative to the second part, the length G1 of one air gap varies inversely with the length G2 of the other air gap, while the sum G1+G2 remains constant. As a result, the effect of inaccuracies in the positioning of the first and second magnetic core parts on the output of the magnetic field detector is reduced. This arrangement also makes it possible to reduce the effect of an off-center primary conductor 30, as shown in Figure 4.

[0037] [List of reference symbols used] Current transducer 1 Housing 2 Primary conductor receiving part 3 Primary conductor passage 4 Base Housing 5 First housing member (base) 5a Second housing member 5b Magnetic core receiving part 6 Guide wall for side branch 7 Guide surface 11 Cover housing 8 Third housing member 8a Magnetic core receiving part 9 Cavity 10 Latch 12 Pivot protrusion 13 Fourth housing member 8b Pivot Connector Pin14 Magnetic Core 1st part 15 Lateral branch 15a Bridge Junction 15b Second part 16 Lateral branch 16a Bridge Junction 16b First magnetic circuit gap (air gap) 17a Second magnetic circuit gap (air gap) 17b Magnetic Field Detection System First magnetic field detector 18a Second magnetic field detector 18b electronic circuit 21 Circuit Board 19 Connector 20 Circuit Components First air gap length G1 Second Air Gap Length G2

[0038] [Embodiment] (1) A current converter (1), The magnetic field detection system includes a housing (2), a magnetic core, and a magnetic field detection system. The magnetic core encloses a primary conductor passage (4) for receiving a primary conductor (30) therethrough; the magnetic core includes a first part (15) and a second part (16) assembled within the housing to form a first magnetic circuit gap (17a) and a second magnetic circuit gap (17b); the magnetic field detection system includes a first magnetic field detector (18a) positioned in the first magnetic circuit gap (17a) and a second magnetic field detector (18b) positioned in the second magnetic circuit gap (17b); the first magnetic circuit gap and the second magnetic circuit gap are disposed on opposite sides of a magnetic core; each of the first and second parts includes a pair of side branches (15a, 16a) joined by a bridge branch (15b, 16b); the side branches of the first and second magnetic core parts overlap such that the side branch (15a) of the first part (15) of the magnetic core is positioned adjacent to the inside of the side branch (16a) of the second part (16) of the magnetic core, and the first and second magnetic circuit gaps are formed between an outside of the side branch of the first part and an inside of the side branch of the second part. (2) A current converter as described in embodiment 1, wherein the first and second parts of the magnetic core are both U-shaped. (3) The current converter of embodiment 1, wherein the housing includes a base housing (5) and a cover housing (8) movable relative to the base housing from an open position in which the primary conductor (30) may be placed in the primary conductor passage (4) to a closed and locked position in which the magnetic core completely surrounds the primary conductor passage (4), one of the first part and the second part of the magnetic core being attached to the base and the other of the first part and the second part of the magnetic core being attached to the cover. (4) A current converter as described in embodiment 1, wherein the cover housing (8) is hingedly connected to the base housing (5). (5) A current converter as described in embodiment 1, wherein the cover housing (8) is removably coupled to the base housing (5).

[0039] (6) A current converter as described in embodiment 1, wherein the side branch (15a) of the first part (15) of the magnetic core is received in a corresponding cavity in the base housing and the magnetic field detector is mounted in the same cavity. (7) A current transducer as described in embodiment 6, wherein the magnetic core receiving portion (6) includes an outer guide wall (7) for a side branch having an outer surface (11) that guides a complementary guide wall for a side branch on the cover housing in the closed position. (8) A current transducer as described in embodiment 7, wherein the guide wall is tapered. (9) A current converter as described in embodiment 1, wherein the first part of the magnetic core is positioned within the base housing (5) and the second part of the magnetic core (16) is positioned within the cover housing (8). (10) A current converter as described in embodiment 9, wherein the magnetic field detectors (18a, 18b) are in the form of an ASIC mounted on an electronic circuit board (19) mounted within the base housing (5).

[0040] (11) A current converter as described in embodiment 10, wherein the ASIC is disposed perpendicularly and upright from the circuit board (19) when positioned within the corresponding cavity of the housing adjacent to the corresponding side branch of the first part of the magnetic core.

Claims

1. A current converter (1), The magnetic field detection system includes a housing (2), a magnetic core, and a magnetic field detection system. The magnetic core encloses a primary conductor passage (4) for receiving a primary conductor (30) therethrough; the magnetic core includes a first part (15) and a second part (16) assembled within the housing to form a first magnetic circuit gap (17a) and a second magnetic circuit gap (17b); the magnetic field detection system includes a first magnetic field detector (18a) positioned in the first magnetic circuit gap (17a) and a second magnetic field detector (18b) positioned in the second magnetic circuit gap (17b); the first magnetic circuit gap and the second magnetic circuit gap are disposed on opposite sides of the magnetic core; each of the first and second parts includes a pair of side branches (15a, 16a) joined by a bridge branch (15b, 16b); a first part having a first magnetic core and a second part having a second magnetic core, the first part having a first magnetic core and a second part having a second magnetic core, the second part having a first magnetic core and a second part having a second magnetic core, the second part having a first magnetic core and a second part having a second magnetic core, the second part having a first magnetic core and a second part having a second magnetic core, the second part having a first magnetic core and a second part having a second magnetic core, the second part having a first magnetic core and a second part having a second magnetic core, the second part having a first magnetic core and a second part having a second magnetic core, the second part having a first magnetic core and a second part having a second magnetic core, the second part having a first magnetic core and a second part having a second magnetic core, the second part having a first magnetic core and a second part having a second magnetic core, the second part having a first magnetic core and a second part having a second magnetic core, the first ...

2. The current transformer of claim 1 , wherein the first and second parts of the magnetic core are both U-shaped.

3. 2. The current converter of claim 1, wherein the housing includes a base housing (5) and a cover housing (8) movable relative to the base housing from an open position in which the primary conductor (30) can be placed in the primary conductor passage (4) to a closed and locked position in which the magnetic core completely surrounds the primary conductor passage (4), one of the first part and the second part of the magnetic core being attached to the base housing and the other of the first part and the second part of the magnetic core being attached to the cover housing.

4. 4. The current transformer according to claim 3, wherein the cover housing (8) is hingedly connected to the base housing (5).

5. 4. The current transformer according to claim 3, wherein the cover housing (8) is removably coupled to the base housing (5).

6. 4. A current converter as claimed in claim 3, wherein the side branch (15a) of the first part (15) of the magnetic core is received in a corresponding cavity in the base housing, and the first magnetic field detector and the second magnetic field detector are mounted in the same cavity.

7. A current converter as described in claim 6, wherein the magnetic core receiving portion (6) of the base housing includes an outer guide wall (7) for a side branch having an outer surface (11) that guides a complementary guide wall for the side branch on the cover housing in the closed and locked position.

8. The current transducer of claim 7 , wherein the guide wall is tapered.

9. 4. The current transformer according to claim 3, wherein the first part of the magnetic core is positioned within the base housing (5) and the second part of the magnetic core (16) is positioned within the cover housing (8).

10. 10. The current converter according to claim 9, wherein the first magnetic field detector (18a) and the second magnetic field detector (18b) are in the form of an ASIC mounted on an electronic circuit board (19) mounted in the base housing (5).

11. 11. The current transformer of claim 10, wherein the ASIC is disposed perpendicularly and upright from the circuit board (19) when positioned in the corresponding cavity of the base housing adjacent to the corresponding side branch of the first part of the magnetic core.

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