Current transformer for measuring residual current
By employing a design with multiple primary conductors and slot structures in the current transformer, combined with lightweight soft magnetic materials and ASIC chips, the problem of insufficient common-mode rejection is solved, enabling economical and accurate residual current measurement and integration for multiphase applications.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- LEM INT SA
- Filing Date
- 2024-03-06
- Publication Date
- 2026-06-16
Smart Images
Figure CN120883064B_ABST
Abstract
Description
[0001] This invention relates to a current transformer for measuring residual current.
[0002] Residual current sensors are commonly used to measure leakage current in conductor systems. Referring to Figures 1 and 2, the conductor system has a set of N primary conductors (three in this example), through which primary currents flow. Each primary current generates a magnetic field concentrated in a core surrounding the primary conductor and controlled by a transducer. This magnetic field is measured by one or more magnetic field transducers in one or more air gaps within the core. The measured magnetic field is a mirror image of the sum of the N currents, which, in a closed circuit with supply and return currents, should be zero amperes (0 A). If the measured sum of currents is not equal to 0 A, this indicates that one or more conductors are experiencing leakage.
[0003] In the absence of leakage current, the sum of the N currents should be 0 A, because the magnetic fields generated by each primary current in each of the N primary conductors should compensate for each other through superposition, and the field is concentrated in the core. However, in reality, this is not the case due to dipole fields and mechanical asymmetry, so the sum of the measured currents is not zero and may reach a magnitude that interferes with the actual measurement of leakage current.
[0004] The ability of a transducer to avoid a non-zero sum due to the aforementioned disturbances is sometimes referred to as common-mode rejection (CMR).
[0005] To mitigate the effects of the aforementioned non-zero sums and increase CMR, it is known to use magnetic cores with very high permeability. However, such cores are expensive and require specific materials with reduced availability.
[0006] In view of the above, the object of the present invention is to provide a current transducer for measuring residual current that is economical yet accurate, and in particular has high common-mode rejection.
[0007] Advantageously, it provides a very compact current transducer for measuring residual current.
[0008] Advantageously, it provides a lightweight current transducer for measuring residual current.
[0009] Advantageously, it provides an easy-to-assemble current transducer for measuring residual current.
[0010] Advantageously, a current transducer for measuring residual current is provided that can be assembled with a circuit board.
[0011] A more specific object of the present invention for certain applications is to provide a current transducer for measuring residual current, which can be integrated with a circuit board for multiphase applications (e.g., multiphase inverter applications).
[0012] The object of the present invention is achieved by providing a system according to claim 1.
[0013] The dependent claims set forth various advantageous features of embodiments of the invention.
[0014] The present invention discloses a current transducer for measuring residual current, comprising: a plurality of primary conductors; a magnetic core having at least one air gap; at least one magnetic field sensor located within the at least one air gap; and a housing surrounding at least a portion of the primary conductors, the magnetic core, and the magnetic field sensor, each primary conductor extending between first and second connection terminals and having a central portion that interconnects the first and second connection terminals, the central portion extending through a primary conductor channel surrounded by the magnetic core, the central portions of the primary conductors being arranged in an overlapping stacked relationship separated by an insulating layer, the central portions extending along a primary conductor centerline (A) extending through the primary conductor channel.
[0015] At least a first primary conductor among the plurality of primary conductors includes a first connecting terminal located at a non-zero distance from the centerline (A), and a second connecting terminal located at a non-zero distance from the centerline (A) on a second side of the centerline opposite to a first side of the centerline. At least a second primary conductor among the plurality of primary conductors has the first connecting terminal separated from the centerline by a non-zero distance on the second side, and has a second connecting terminal separated from the centerline by a non-zero distance on the first side of the centerline.
[0016] In an advantageous embodiment, the current transducer further includes a third primary conductor among the plurality of primary conductors, the third primary conductor having the first connection terminal and the second connection terminal and the central portion, forming a straight primary conductor aligned and centered on a center line (A).
[0017] In an advantageous embodiment, only three primary conductors are used for connection to the three-phase conduction system.
[0018] In an advantageous embodiment, at least the first and second primary conductors include a plurality of slots, the plurality of slots including at least one first slot and at least one second slot, the first slot extending from a first lateral side of the central portion into the central portion, the second slot extending from a second lateral side of the central portion opposite to the first lateral side into the central portion, the plurality of slots being arranged such that primary current flowing between the first and second connection terminals of the at least first and second primary conductors flows through the central portion in a tortuous path.
[0019] In an advantageous embodiment, there is at least a third groove extending laterally from a first lateral side of the central portion into the central portion, the first and third grooves being arranged in a relationship spaced apart from the first groove.
[0020] In an advantageous embodiment, there are three slots, two extending laterally from the first side and one extending laterally from the second side, positioned substantially centrally between the first and third slots.
[0021] In an advantageous embodiment, the groove extends from the respective lateral side along a length (W1, W2) ranging from 40% to 70% of the width (W) of the central portion of the primary conductor between the first lateral side and the second opposing lateral side.
[0022] In an advantageous embodiment, the groove is a substantially thin straight slit.
[0023] In an advantageous embodiment, at least the first and second primary conductors including the slot have the slot arranged in a stacked, overlapping, and aligned relationship.
[0024] In an advantageous embodiment, the current transducer further includes a circuit board, the magnetic field sensor being electrically connected to secondary conductor tracks on the circuit board, and the primary conductor being provided as conductive circuit tracks on different layers of the circuit board.
[0025] In an advantageous embodiment, the magnetic field sensor is provided in the form of an ASIC chip, which is mounted in a hole formed through the circuit board, or the main surface of the ASIC chip is mounted flat against the outer surface of the circuit board.
[0026] In an advantageous embodiment, the connection terminals of the primary conductor and the connection terminals on the circuit board connected to the magnetic field sensor are in the form of conductive pads formed on the circuit board or electroplated through holes to connect to the conductors of the external circuit.
[0027] In an advantageous embodiment, the housing includes a base and a cover assembled around a portion of the magnetic core, magnetic field sensor, and primary conductor, the base and cover being assembled together on opposite sides of the circuit board.
[0028] In an advantageous embodiment, the magnetic core is in the form of a flat strip of soft magnetic material bent to form a magnetic circuit, the ends of the magnetic core strip forming open end extensions that branch and bend from the ends of the magnetic core, such that the open end extensions are arranged parallel to the circuit board and mounted against the opposite side of the circuit board.
[0029] In an advantageous embodiment, the magnetic core is in the form of a flat strip of soft magnetic material that is bent to form a magnetic circuit. The ratio of the thickness T to the width W of the soft magnetic material strip, T / W, is less than 0.3, preferably less than 0.2, and greater than 0.1. The width is measured in a direction orthogonal to the center line (A) of the primary conductor.
[0030] Other advantageous features of the invention will become apparent from the following detailed description and accompanying drawings of embodiments of the invention. Attached Figure Description
[0031] Figure 1 is a simplified schematic diagram of the three-phase primary conductor arrangement of a current transducer for measuring residual current according to the prior art;
[0032] Figure 2 This is a simplified schematic cross-sectional view of a current transducer used for measuring residual current;
[0033] Figure 3a The primary conductor arrangement of a three-phase current transformer for measuring residual current is shown according to an embodiment of the present invention;
[0034] Figure 3b This is a simplified perspective view of a current transducer (without housing) for measuring residual current according to an embodiment of the present invention;
[0035] Figure 3c yes Figure 3b An exploded view of the primary conductor arrangement in an embodiment;
[0036] Figure 4a This is similar to another embodiment of the present invention. Figure 3a The view;
[0037] Figure 4b yes Figure 4a A perspective view of an embodiment, wherein the overmolded housing is schematically shown with transparency;
[0038] Figure 5 a to d schematically illustrate variations of the primary conductor of a current transducer for measuring residual current according to an embodiment of the present invention;
[0039] Figure 6a This is a perspective view of a current transducer for measuring residual current according to an embodiment of the present invention;
[0040] Figure 6b yes Figure 6a Exploded view of an embodiment;
[0041] Figure 6c It is along Figure 6a A cross-sectional view of line 6c-6c;
[0042] Figure 7 It is a graph showing the relationship between common mode suppression and core permeability of a current transducer in the prior art and a current transducer according to an embodiment of the present invention;
[0043] Referring to the accompanying drawings, a current transducer 1 for measuring residual current according to an embodiment of the present invention includes a plurality of primary conductors 2, a magnetic core 3 extending through a primary conductor channel 10 around the primary conductors 2, at least one magnetic field sensor 4 located in at least one air gap 13 formed between the open ends of the magnetic core, and an insulating housing 9 that at least partially houses the primary conductors, the magnetic core and the magnetic field sensor.
[0044] In such Figures 6a to 6c In the illustrated embodiment, the current transducer may further include a circuit board 5 to which the magnetic field sensor is electrically connected. The primary conductor 2 may also be formed as a conductive trace in the circuit board, with different primary conductors formed in different layers of the circuit board separated by an insulating layer. Forming conductive traces in different layers of the circuit board is well known in the field of circuit boards. Additional electrical components may be mounted on the circuit board, for example, for filtering or signal processing of measurement or power signals to and from the magnetic field sensor. The circuit board 5 may advantageously have connection terminals 6 for connecting the primary conductor 2 to external circuitry, and connection terminals 14 for connecting secondary conductors carrying measurement and power signals to and from the magnetic field sensor 4.
[0045] The magnetic core 3 includes branches 11a, 11b, 11c surrounding the primary conductor channel 10, and in the example shown, includes a single air gap 13 formed between open end extensions 12 extending from the end branch 11c.
[0046] Figures 6a to 6c In this embodiment, the magnetic core can advantageously be made of a strip of soft magnetic material stamped from a material sheet and bent into a generally rectangular shape surrounding the primary conductor channel 10, thereby forming an air gap. The open-end extensions 12 of the magnetic core are bent out from the end branches 11c to which they are connected and extend such that the plane of the material sheet of the open-end extensions 12 is substantially parallel to the circuit board 5. This allows the open-end extensions 12 to cover the magnetic field sensor 4 in the form of an ASIC (Application-Specific Integrated Circuit) chip, which is mounted with its main surface parallel to the circuit board. The ASIC chip providing the magnetic field sensor 4 can be mounted on top of and abut against the outer surface of the circuit board, or as... Figure 6b As shown, it is positioned within hole 17 on the circuit board. The latter arrangement allows the air gap 13 to be as small as possible to improve the magnetic coupling between the magnetic field sensor 8 and the magnetic circuit formed by the magnetic core 3.
[0047] In an embodiment, the ASIC chip forming the magnetic field sensor 4 may have a thickness equal to or less than that of the circuit board 5, such that the open end extension 12 of the magnetic core 3 can abut against the opposite outer surface of the circuit board, and the air gap is defined by the thickness of the circuit board.
[0048] The open end extension 12 can be welded, brazed, or clamped to the opposite outer surface of the circuit board 5 to mechanically fix the magnetic core to the circuit board and define the size of the air gap 13.
[0049] The housing 9 may include first and second components, for example in the form of a base 9a and a cover 9b, which are fixed together around a portion of the magnetic core 3 and the circuit board 5 and the magnetic field sensor 4 mounted thereon. The housing 9 has a connection terminal 6 for the primary conductor 2 and a connection terminal 14 for the secondary conductor connected to the magnetic field sensor 4, which can be used to connect to the external circuitry on which the current transducer 1 is mounted and connected.
[0050] However, other arrangements can be provided within the scope of this invention based on known techniques, for example, the connection ends of the primary and secondary conductors can be provided in a connector for pluggable connection to a complementary external connector. In the latter arrangement, the primary conductor, magnetic core, magnetic field sensor, and circuit board can be completely housed and encapsulated within an insulating housing.
[0051] In addition to providing connectors that present terminals for connection to the primary and secondary conductors, the insulating housing may be partially or completely assembled or molded onto the magnetic core, magnetic field sensor 4, and primary conductor.
[0052] In the application shown in the accompanying drawings, a three-phase primary conductor system is illustrated, for example, for use in an inverter, such as for connection to a photovoltaic system.
[0053] However, in embodiments within the scope of this invention, there may be two or more primary conductors stacked and insulated from each other for measuring residual current. Whether there are two, three, four, or more primary conductors stacked and insulated from each other, the principle of this invention remains the same for measuring residual current.
[0054] To describe the invention, a three-phase system, one of the more widely used conduction systems in many applications, is shown and discussed.
[0055] Specific reference Figures 3a to 3cIn addition to 4a and 4b, according to a first aspect of the invention, each of the primary conductors 2a, 2b, 2c has a respective connecting terminal 61a, 61b, 62a, 62b, 63a, 63b, which are in a non-overlapping relationship and interconnected to their respective central portions 7a, 7b, 7c, which are in a stacked overlapping relationship, extending through the primary conductor channel 10 and surrounded by the magnetic core 3.
[0056] The first primary conductor (2a) has a first connecting terminal (61a) and a second connecting terminal (61b). The first connecting terminal is arranged at a distance from the centerline A extending through the center portion of the primary conductor channel (10), and the second connecting terminal is arranged at a distance from the centerline, but on the side of the centerline opposite to the first connecting terminal. The first primary conductor 2b thus extends from one side of the centerline to the other side. The second stacked primary conductor 2b has a similar form to the first primary conductor 2a, but is mirror-symmetrical, such that it has a first connecting terminal 62a arranged at a distance from the centerline A of the primary conductor, and a second connecting terminal 62b arranged at a distance from the centerline, but on the side of the centerline opposite to the first connecting terminal 62a. Thus, the connecting terminals of the second and third conductors are on opposite sides of each other. The second and third primary conductors thus form a generally X-shape.
[0057] In a three-phase conductor system, the third primary conductor 2c can extend in a substantially straight manner parallel to and aligned with the centerline A of the primary conductor.
[0058] In the illustrated embodiment, the central portions 7a, 7b, and 7c of the first, second, and third conductors are aligned with and overlap each other with the center line A.
[0059] The intersection of the first and second primary conductors with the center line and the retention of the third primary conductor on the center line have the effect of increasing common-mode suppression and thus reducing the common-mode signal that affects leakage measurement.
[0060] For more specific reference Figure 4a and 4b According to a second aspect of the invention, the primary conductors 2a, 2b, 2c include transverse grooves 8 extending from the outer transverse side edges 15, 16 of the central portion into the central portions 7a, 7b, 7c.
[0061] exist Figure 4a , 4b In the embodiment shown, there are three slots 8, with a first centrally located slot 8 extending from a first lateral side 15 of the central portion 7, and second and third slots 8 extending from opposite second lateral sides 16 of the central portion 7 of the primary conductor. The slots 8 are spaced apart from each other in the direction of the centerline A of the primary conductor.
[0062] The slot 8 generates a weaving currentflow path through the central portion 7 of each conductor, which has the effect of generating a magnetic field through the central channel 10, which increases common-mode rejection and thus improves leakage measurement of the current transducer by reducing common-mode effects on the stacked primary conductors 2.
[0063] The lengths W1 and W2 of the grooves extending from the lateral edges 15 and 16 are preferably equal to at least 40% of the width W between the lateral edges 15 and 16 of the primary conductor portion 7, preferably in the range of 50% to 70%, to ensure that the primary current detours through the central portions 7a, 7b and 7c.
[0064] In the illustrated embodiment, the slots 8 of the different primary conductors 2a, 2b, 2c are preferably identical and overlap each other in a stacked manner. However, within the scope of the invention, slots can be provided for the different primary conductors that are not stacked and aligned vertically with each other. Furthermore, slots from only some of the different primary conductors can be aligned, and the intermediate or central primary conductor 2b, which extends substantially in a straight line, can be left without any slots, and the primary conductors can be stacked above and below the intermediate primary conductor with slots.
[0065] In variations (e.g.) Figure 5 In the variants a) to d) schematically shown, a greater number of slots 8 arranged in the central portion 7 can be provided to create more turns in the tortuous primary conductor flow path. For example, there can be two slots extending from the first lateral side and two slots extending from the second lateral side offset from each other, or there can be three slots extending from the first lateral side and two slots extending from the second lateral side. In one variant (not shown), there may also be only two slots, one on each side, for creating a tortuous primary conductor current flow path.
[0066] The groove can also be straight or curved, and the groove can have different lengths.
[0067] Figure 7 The diagram illustrates an improvement in dB of the three-phase primary conductor arrangement according to FIG1a (prior art) and the three-phase primary conductor arrangement of a current transducer according to an embodiment of the present invention, wherein... Figure 4a and 4b The configuration demonstrates a significant improvement in common-mode suppression.
[0068] Reference tag list
[0069] Current transducer 1
[0070] Primary conductors 2, 2a, 2b, 2c
[0071] Connecting terminals 6, 61a, 61b, 62a, 62b, 63a, 63b
[0072] First end
[0073] Second end
[0074] Central parts 7, 7a, 7b, 7c
[0075] Slot 8
[0076] First transverse side edge 15
[0077] Second transverse side edge 16
[0078] Magnetic core 3
[0079] Primary conductor channel 10
[0080] Branches 11a, 11b, 11c
[0081] Open end extension 12
[0082] Air gap 13
[0083] Magnetic field sensor 4
[0084] Connection terminal 14
[0085] Circuit board 5
[0086] Hole 17 (for mounting a magnetic field sensor)
[0087] Casing 9
[0088] Base 9a
[0089] Cover 9b
[0090] Primary conductor centerline A
Claims
1. A current transducer (1) for measuring residual current, comprising a plurality of primary conductors (2, 2a, 2b, 2c), a magnetic core (3) having at least one air gap (13), at least one magnetic field sensor (4) located within the at least one air gap (13), and a housing (9) surrounding at least a portion of the primary conductors, the magnetic core, and the magnetic field sensor, each primary conductor extending between first and second connecting terminals (61a, 61b, 62a, 62b, 63a, 63b) and having a central portion (7a, 7b, 7c) interconnecting the first and second connecting terminals, the central portion extending through a primary conductor channel (10) surrounded by the magnetic core (3), the central portions of the primary conductors being arranged in an overlapping stacked relationship separated by an insulating layer, the central portions extending along a primary conductor centerline (A) extending through the primary conductor channel (10), characterized in that, At least a first primary conductor of the plurality of primary conductors includes a first connecting terminal (61a) located at a non-zero distance from the center line (A) and a second connecting terminal (61b) located at a non-zero distance from the center line (A) on a second side of the center line opposite to a first side of the center line, and at least a second primary conductor of the plurality of primary conductors has a first connecting terminal (62a) separated from the center line by a non-zero distance on the second side and a second connecting terminal (62b) separated from the center line by a non-zero distance on the first side of the center line.
2. The current transducer according to claim 1 further includes a third primary conductor (2c) of the plurality of primary conductors, the third primary conductor having the first connecting terminal (63a) and the second connecting terminal (63b) and the central portion (7b), forming a straight primary conductor aligned and centered on the center line (A).
3. The current transducer according to any one of the preceding claims, wherein only three primary conductors are present for connection to a three-phase conduction system.
4. The current transducer of claim 1, wherein at least the first and second primary conductors include a plurality of slots (8), the plurality of slots including at least a first slot extending from a first lateral side (15) of the central portion into the central portion, and at least a second slot extending from a second lateral side (16) of the central portion opposite to the first lateral side into the central portion, the plurality of slots being arranged such that a primary current flowing between the first and second connection terminals of the at least first and second primary conductors flows through the central portion in a tortuous path.
5. The current transducer according to claim 4, wherein, There is at least a third groove extending laterally from the first lateral side of the central portion into the central portion, the first groove and the third groove being arranged in a relationship spaced apart from the first groove.
6. The current transducer of claim 5, wherein there are three slots, two extending laterally from the first lateral side and one extending laterally from the second lateral side and centrally positioned between the first slot and the third slot.
7. The current transducer according to claim 6, wherein, The groove extends from the respective lateral side along a length (W1, W2) ranging from 40% to 70% of the width (W) of the primary conductor center portion (7) between the first lateral side (15) and the second opposite lateral side (16).
8. The current transducer of claim 4, wherein the slot is a substantially thin straight slit.
9. The current transducer of claim 4, wherein at least the first and second primary conductors, including the slots, have the slots arranged in a stacked, overlapping, and aligned relationship.
10. The current transducer according to claim 1 further includes a circuit board (5), wherein the magnetic field sensor (4) is electrically connected to a secondary conductor trace on the circuit board, and the primary conductor is configured as a conductive circuit trace on a different layer of the circuit board.
11. The current transducer according to claim 10, wherein, The magnetic field sensor (4) is provided in the form of an ASIC chip, which is installed in a hole formed through the circuit board, or the main surface of the ASIC chip is mounted flat against the outer surface of the circuit board.
12. The current transducer according to any one of claims 10-11, wherein the connection terminal (6) of the primary conductor and the connection terminal (14) on the circuit board connected to the magnetic field sensor are in the form of conductive pads or electroplated through holes formed on the circuit board for connecting to external circuits.
13. The current transducer according to claim 10, wherein the housing (9) comprises a base (9a) and a cover (9b) assembled around the magnetic core (3), the magnetic field sensor (4) and a portion of the primary conductor, the base (9a) and the cover (9b) being assembled together on opposite sides of the circuit board (5).
14. The current transducer according to claim 10, wherein the magnetic core is in the form of a flat strip of soft magnetic material bent to form a magnetic circuit, and the ends of the magnetic core strip form open end extensions (12) that branch and bend from the ends of the magnetic core, such that the open end extensions (12) are arranged parallel to the circuit board and mounted against the opposite side of the circuit board.
15. The current transducer of claim 1, wherein the magnetic core is in the form of a flat strip of soft magnetic material bent to form a magnetic circuit, the ratio of the thickness T to the width W of the soft magnetic material strip being less than 0.3 and greater than 0.1, the width being measured in a direction orthogonal to the center line (A) of the primary conductor.