Zero-phase converter

Abstract

To provide a zero-phase-sequence current transformer capable of suppressing deterioration in balance characteristic even if a primary conductor is arranged so as to be deviated from an original arrangement position.SOLUTION: A zero-phase-sequence current transformer 1 comprises: a core 11 that has first parts 111a and 111b which are oppositely arranged while having a predetermined gap, and second parts 112a and 112b that are oppositely arranged over between an end part of one of the first parts 111a and 111b and an end part of the other and have a length shorter than that of the first parts 111a and 111b, and are formed of a magnetic material; a plurality of primary conductors 12 that are arranged via a space 16 surrounded by the core 11 in a state of being arranged with the predetermined interval, and cross the core 11; and a plurality of secondary windings 13 that are wound around the first parts 111a and 111b while being shifted, and output a dielectric voltage on the basis of a magnetic flux generated in the core 11 in accordance with a current flowing through the plurality of primary conductors 12.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a zero-phase current transformer.

Background Art

[0002] A zero-phase current transformer has a core made of a magnetic material, a secondary winding wound toroidally around the core, a shield made of a magnetic material for reducing the influence of an external magnetic field, and a primary conductor arranged to penetrate the core, and uses the voltage generated at both ends of the secondary winding to detect an abnormal current. In the case of a balanced current with no abnormality in the current flowing through the primary conductor, the magnetic fluxes generated in the core by the balanced current cancel each other out, so no voltage is generated at both ends of the secondary winding. However, in reality, due to manufacturing errors of the zero-phase current transformer, even when a balanced current is flowing through the primary conductor, a voltage may be generated at both ends of the secondary winding. In this case, the secondary winding outputs a voltage as if leakage current has occurred even though no leakage current has occurred. Also, the magnetic flux distribution in the core provided in the zero-phase current transformer changes due to the magnetic flux generated by the current, and a voltage is generated at both ends of the secondary winding.

[0003] A leakage detection device capable of preventing such false detection of leakage due to a balanced current is disclosed in Patent Document 1. The leakage detection device includes, separately from the leakage detection coil, a balance output suppression coil composed of a pair of coils symmetrically arranged along the core several times, and generates an output that cancels out the magnetic flux in the core generated by the balanced current. Thereby, the leakage detection device suppresses false detection of leakage due to the balanced current.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The ability of a zero-sequence current transformer to prevent voltage from being generated across the secondary winding due to manufacturing tolerances or transient inrush currents that occur when a motor is connected to a ground fault circuit interrupter is called the balance characteristic. If this balance characteristic deteriorates, the zero-sequence current transformer may falsely detect a ground fault when one does not exist.

[0006] The object of the present invention is to provide a zero-sequence current transformer that can suppress deterioration of balance characteristics even when the primary conductor is positioned away from its original position. [Means for solving the problem]

[0007] To achieve the above objective, a zero-sequence current transformer according to one aspect of the present invention comprises a core made of a magnetic material having a pair of first parts arranged opposite to each other with a predetermined gap between them, and a pair of second parts arranged opposite to each other across one end and the other end of the pair of first parts and having a shorter length than the pair of first parts; a plurality of primary conductors arranged at predetermined intervals through a space surrounded by the core and intersecting the core; and a plurality of secondary windings wound around the pair of first parts with a staggered pattern and outputting an induced voltage based on the magnetic flux generated in the core in response to the current flowing through the plurality of primary conductors. [Effects of the Invention]

[0008] According to one aspect of the present invention, even if the primary conductor is positioned away from its original position, deterioration of the equilibrium characteristics can be suppressed. [Brief explanation of the drawing]

[0009] [Figure 1] This figure schematically shows an example of the general configuration of a zero-sequence current transformer according to one embodiment of the present invention. [Figure 2] This figure schematically shows a cross-section (a cross-section cut along line AA in Figure 1) illustrating an example of the general configuration of a zero-sequence current transformer according to one embodiment of the present invention. [Figure 3] This figure illustrates the effects of a zero-phase current transformer according to one embodiment of the present invention, and shows an example of a balanced current flowing through multiple primary conductors. [Figure 4] This figure illustrates the effects of a zero-sequence current transformer according to one embodiment of the present invention, and schematically shows an example of the magnetic flux distribution in the core at time t1 shown in Figure 3. [Figure 5] This figure illustrates the effects of a zero-sequence current transformer according to one embodiment of the present invention, and shows an example of an induced voltage detected at a predetermined location in the core when a plurality of primary conductors are arranged in a reference position and a balanced current flows through the plurality of primary conductors. [Figure 6] This figure illustrates the effects of a zero-sequence current transformer according to one embodiment of the present invention, and shows an example of an induced voltage output from a secondary winding wound around the entire core when a plurality of primary conductors are arranged in a reference position and a balanced current flows through the plurality of primary conductors. [Figure 7] This diagram illustrates the effects of a zero-sequence current transformer according to one embodiment of the present invention, and schematically shows an example of the magnetic flux distribution within the core when the primary conductor is positioned offset from its original position. [Figure 8] This figure illustrates the effects of a zero-sequence current transformer according to one embodiment of the present invention, and shows an example of induced voltage based on the magnetic flux distribution shown in Figure 7. [Figure 9] This diagram illustrates the effects of a zero-sequence current transformer according to one embodiment of the present invention, and shows an example of the voltage output from the secondary winding wound around the entire core when the magnetic flux distribution shown in Figure 7 occurs within the core. [Figure 10] This figure illustrates the effects of a zero-sequence current transformer according to one embodiment of the present invention, and shows an example of the voltage output from each of the multiple secondary windings wound around the first part of the core when the magnetic flux distribution shown in Figure 7 occurs within the core. [Figure 11] This diagram illustrates the effects of a zero-sequence current transformer according to one embodiment of the present invention, comparing the effective value of the voltage output from a selected secondary winding in the zero-sequence current transformer when the primary conductor is positioned off-center from its original position, with the effective value of the voltage output from a secondary winding provided in a comparative zero-sequence current transformer and wound around the entire core. [Modes for carrying out the invention]

[0010] One embodiment of the present invention illustrates an apparatus or method for embodying the technical concept of the present invention, and the technical concept of the present invention does not limit the materials, shapes, structures, arrangements, etc. of the components to those described below. The technical concept of the present invention can be modified in various ways within the technical scope defined by the claims described in the patent claims.

[0011] (Outline configuration of a zero-phase current transformer) A zero-sequence current transformer according to one embodiment of the present invention will be described using Figures 1 to 11. First, the general configuration of the zero-sequence current transformer 1 according to this embodiment will be described using Figures 1 and 2. Figure 1 is a schematic diagram showing an example of the general configuration of the zero-sequence current transformer 1. In Figure 1, the core 11, a plurality of primary conductors 12, a plurality of secondary windings 13, and a shield section 14 provided in the zero-sequence current transformer 1 are shown as viewed in the direction of extension of the plurality of primary conductors 12. Also, in Figure 1, for ease of understanding, the shield section 14 is shown as cut in a plane containing the central axis of the core 11, and a leakage current detection unit 15 connected to the plurality of secondary windings 13 is shown. Figure 2 is a schematic diagram showing a cross-section of the core 11, etc. of the zero-sequence current transformer 1, cut along the central axis of one of the plurality of primary conductors 121 in a plane containing the central axis.

[0012] As shown in Figure 1, the zero-phase current transformer 1 according to this embodiment comprises a core 11 made of a magnetic material, which has a pair of first parts 111a, 111b arranged opposite to each other with a predetermined gap between them, and a pair of second parts 112a, 112b arranged opposite to each other across one end and the other end of the pair of first parts 111a, 111b, and having a shorter length than the pair of first parts 111a, 111b.

[0013] The first part 111a and the first part 111b are arranged substantially parallel to each other. The first part 111a and the first part 111b have substantially the same shape. Each of the first part 111a and the first part 111b has a columnar shape, for example, a prismatic shape. In this embodiment, the first part 111a and the second part 112b each have a cuboid shape, but they may have a cylindrical shape.

[0014] The second part 112a is arranged across one end of the first part 111a and one end of the first part 111b. The second part 112a has a shape that is bent into a curved shape that bulges toward the side where the first part 111a and the first part 111b are not arranged. The cross-section of the second part 112a cut in the extending direction of the second part 112a has substantially the same shape as each of the cross-section of the first part 111a cut in the extending direction of the first part 111a and the cross-section of the first part 111b cut in the extending direction of the first part 111b. The second part 112a is integrally formed with the first part 111a and the first part 111b.

[0015] The second part 112b is arranged across the other end of the first part 111a and the other end of the first part 111b. The second part 112b has a shape that is bent into a curved shape that bulges toward the side where the first part 111a and the first part 111b are not arranged. Therefore, the second part 112a and the second part 112b have a shape that bends toward opposite sides. The cross-section of the second part 112b cut in the extending direction of the second part 112b has substantially the same shape as the cross-section of the second part 112a cut in the extending direction of the first part 111a. The said cross-section of the second part 112b has substantially the same shape as each of the cross-section of the first part 111a cut in the extending direction of the first part 111a and the cross-section of the first part 111b cut in the extending direction of the first part 111b. The second part 112b is integrally formed with the first part 111a and the first part 111b.

[0016] As described above, the core 11 is formed by integrating a pair of first portions 111a and 111b and a pair of second portions 112a and 112b, has a substantially uniform cross-sectional shape, and has a track-like annular shape. In the present embodiment, the pair of first portions 111a and 111b have a linear shape, but may have a curved shape such as an elliptical shape. That is, the core 11 may have a non-circular shape with different dimensions in two orthogonal directions. The core 11 is formed of a soft magnetic material such as permalloy, for example.

[0017] As shown in FIG. 1, the zero-phase current transformer 1 includes a plurality of primary conductors 12 arranged through a space 16 surrounded by the core 11 and intersecting the core 11 while being arranged side by side at a predetermined interval. The plurality of primary conductors 12 include a primary conductor 121 connected to a primary circuit (not shown) through which an R-phase current flows, a primary conductor 122 connected to a primary circuit (not shown) through which an S-phase current flows, and a primary conductor 123 connected to a primary circuit (not shown) through which a T-phase current flows. In the present embodiment, the plurality of primary conductors 12 include the primary conductors 121, 122, and 123, but are not limited to three, and may include two or four or more primary conductors.

[0018] The primary conductor 121, the primary conductor 122, and the primary conductor 123 are symmetrically arranged in the space 16. Specifically, the primary conductor 121 is arranged with its central axis coinciding with the center of the space 16 when viewing the space 16 in the extending direction of the primary conductor 121. The primary conductor 122 and the primary conductor 123 are arranged at equal intervals from the primary conductor 123. The primary conductor 121, the primary conductor 122, and the primary conductor 123 are arranged such that a virtual plane including their respective central axes is parallel to at least one of the pair of first portions 111a and 111b. Although details will be described later, the primary conductor 121, the primary conductor 122, and the primary conductor 123 may not be symmetrically arranged in the space 16 due to manufacturing errors of the zero-phase current transformer 1.

[0019] As shown in Figure 1, the zero-phase current transformer 1 includes a plurality of secondary windings 13 that are wound around a pair of first parts 111a and 111b in a staggered manner and output an induced voltage based on the magnetic flux generated in the core 11 in response to the current flowing through the plurality of primary conductors 12. The plurality of secondary windings 13 are wound toroidally around the core 11. The plurality of secondary windings 13 include at least a first secondary winding 131, a second secondary winding 132, and a third secondary winding 133. In this embodiment, the plurality of secondary windings 13 includes a first secondary winding 131, a second secondary winding 132, and a third secondary winding 133, but is not limited to three; it may have two or four or more secondary windings as long as the number of secondary conductors 12 is greater than or equal to the number of primary conductors 12.

[0020] Adjacent secondary windings among the multiple secondary windings 13 are wound around a pair of first sections 111a and 111b with some overlap. Specifically, in the case of adjacent first secondary windings 131 and second secondary windings 132, the first secondary winding 131 is wound around the first sections 111a and 111b with some overlap with the second secondary winding 132. In Figure 1, for ease of understanding, the first secondary winding 131 is wound around the first sections 111a and 111b with a gap between each turn, and the second secondary winding 132 is also wound around the first sections 111a and 111b with a gap between each turn, and the first secondary windings 131 and second secondary windings 132 are shown as being positioned in the gaps between them. However, in reality, the first secondary winding 131 is wound around the first sections 111a and 111b with adjacent turns in contact without any gaps between each turn. Similarly, in practice, the second secondary winding 132 is wound around the first sections 111a and 111b with adjacent turns in contact without any gaps between each turn. As a result, the first secondary winding 131 is wound around the first sections 111a and 111b, covering a portion of the second secondary winding 132.

[0021] Furthermore, in the adjacent first secondary winding 131 and third secondary winding 133, the third secondary winding 133 is wound around the first sections 111a and 111b, overlapping a portion of the first secondary winding 131. In Figure 1, for ease of understanding, the third secondary winding 133 is shown wound around the first sections 111a and 111b with a gap between each turn, and the third secondary winding 133 and the first secondary winding 131 are shown positioned in the gaps between them. However, in reality, the third secondary winding 133 is wound around the first sections 111a and 111b without a gap between each turn, with adjacent turns in contact. Therefore, the third secondary winding 133 is wound around the first sections 111a and 111b, covering a portion of the first secondary winding 131.

[0022] Furthermore, in the central portions of the first portions 111a and 111b, the first secondary winding 131, the second secondary winding 132, and the third secondary winding 133 are wound around the first portions 111a and 111b in an overlapping manner. In this way, the multiple secondary windings 13 are wound around the core 11, including the central portions of the first portions 111a and 111b in the extending direction of the first portions 111a and 111b. In this embodiment, the first secondary winding 131, the second secondary winding 132, and the third secondary winding 133 are wound around the first portions 111a and 111b with the second secondary winding 132 in contact with the surface of the first portions 111a and 111b, the first secondary winding 131 in contact with the second secondary winding 132, and the third secondary winding 133 in contact with the first secondary winding 131 (see Figure 2). Therefore, in this embodiment, in the multiple secondary windings 13, the second secondary winding 132 is arranged in the bottom layer, the first secondary winding 131 is arranged in the middle layer, and the third secondary winding 133 is arranged in the top layer. However, as long as the first secondary winding 131, the second secondary winding 132, and the third secondary winding 133 are arranged offset from each other, there is no restriction on the stacking order in which they are wound around the first portions 111a and 111b.

[0023] Multiple secondary windings 13 are not wound around a pair of second sections 112a, 112b, but are routed along the pair of second sections 112a, 112b. Specifically, as shown in Figure 1, when multiple secondary windings 13 are wound around the core 11, for example, the second secondary winding 132 is wound around the first section 111a and then routed along the second section 112b to the first section 111b. Furthermore, the second secondary winding 132 that has been routed to the first section 111b is wound around the first section 111b and then routed along the second section 112a to the first section 111a.

[0024] Furthermore, the first secondary winding 131 is wound around the first portion 111a on a portion of the second secondary winding 132 wound around the first portion 111a, and then routed to the first portion 111b along, for example, the second portion 112b. In addition, the first secondary winding 131 routed to the first portion 111b is wound around the first portion 111b on a portion of the second secondary winding 132 wound around the first portion 111b, and then routed to the first portion 111a along, for example, the second portion 112a.

[0025] Furthermore, the third secondary winding 133 is wound around the first portion 111a over the second secondary winding 132 and a portion of the first secondary winding 131 wound around the first portion 111a, and then routed to the first portion 111b, for example along the second portion 112b. Furthermore, the third secondary winding 133, routed to the first portion 111b, is wound around the first portion 111b over a portion of the first secondary winding 131 wound around the first portion 111b, and then routed to the first portion 111a, for example along the second portion 112a.

[0026] Thus, the multiple secondary windings 13 are not wound around the core 11 through the space 16, but rather wound around the core 11 along the shape of the core 11. For this reason, the multiple secondary windings 13 can be arranged inside the shield section 14 (details described later) which surrounds the core 11. Both ends of the multiple secondary windings 13 are led out from the shield section 14 and connected to the leakage current detection section 15 (details described later).

[0027] As shown in Figure 1, the first secondary winding 131 is positioned such that its central portions 131a and 131b coincide with the reference position 161 where the primary conductor 121 (an example of one of several primary conductors) would normally be positioned. The central portion 131a corresponds, for example, to the central part of the portion of the first secondary winding 131 wound around the first portion 111a. The central portion 131b corresponds, for example, to the central part of the portion of the first secondary winding 131 wound around the first portion 111b. The reference position 161 corresponds, for example, to the position that coincides with the center of space 16 when space 16 is viewed in the direction of extension of the primary conductor 121. In the zero-phase current transformer 1, when the primary conductor 121 is positioned at the reference position 161, the central axis of the primary conductor 121 coincides with the reference position 161. For this reason, the first secondary winding 131 is wound in the central range A131 of the entire range of the first portions 111a and 111b.

[0028] The second secondary winding 132 is positioned off-center to the side of the second portion 112a (an example of one of a pair of second portions) by the amount of the maximum possible error that could cause the primary conductor 121 to be positioned off-center from the reference position 161 in the direction of extension of the first portions 111a and 111b. Therefore, the second secondary winding 132 is wound in a range A132 that is off-center to the second portion 112a side of the entire range of the first portions 111a and 111b. The offset range MA12, where the range A132 around the second secondary winding 132 is offset from the range A131 around the first secondary winding 131, corresponds to the maximum error of the primary conductor 121.

[0029] The third secondary winding 133 is positioned off-center to the side of the second portion 112b (an example of the other half of a pair of second portions) by the amount of the maximum error of the primary conductor 121. Therefore, the third secondary winding 133 is wound in a range A133 that is off-center to the second portion 112b side of the entire range of the first portions 111a and 111b. The offset range MA13, where the range A133 around the third secondary winding 133 is offset from the range A131 around the first secondary winding 131, corresponds to the maximum error of the primary conductor 121.

[0030] As will be explained in detail later, each of the multiple primary conductors 12 may be positioned within a predetermined range from its original reference position due to manufacturing errors, etc. The maximum range of this predetermined range from the reference position corresponds to the maximum error. The maximum errors in the primary conductor 121 connected to the R-phase circuit, the primary conductor 122 connected to the S-phase circuit, and the primary conductor 123 connected to the T-phase circuit are approximately the same. For this reason, in this embodiment, the amount of misalignment between adjacent secondary windings in the multiple secondary windings 13 is set based on the maximum error in the primary conductor 121, but it may also be determined based on the maximum error in either the primary conductor 122 or the primary conductor 123.

[0031] Furthermore, as will be explained in more detail later, even if a balanced current flows through multiple primary conductors, if at least one of these primary conductors is positioned misaligned with respect to the reference position, an induced voltage may be generated at both ends of the secondary winding that wraps around the entire core. In this case, a zero-phase current transformer equipped with a secondary winding that wraps around the entire core may mistakenly detect that a leakage current is present in the circuit to which the multiple primary conductors are connected, even though no leakage current is actually occurring in that circuit.

[0032] In contrast, the zero-sequence current transformer 1 is equipped with multiple secondary windings 13 that are offset from each other, and when a balanced current flows through multiple primary conductors 12, the secondary winding with the lowest induced voltage at both ends of the multiple secondary windings 13 is used for detecting leakage current in the circuit to which the multiple primary conductors 12 are connected. As a result, the zero-sequence current transformer 1 can suppress false detection of leakage current based on the offset arrangement of the multiple primary conductors 12 relative to a reference position.

[0033] As shown in Figures 1 and 2, the zero-phase current transformer 1 includes a shield section 14 that covers the core 11 and a plurality of secondary windings 13. The shield section 14 is provided to cover the entire core 11 in a manner aligned with the core 11. For this reason, the shield section 14 has a track shape that is slightly larger than the core 11.

[0034] As shown in Figure 2, the shield portion 14 has an outer peripheral portion 141 that has a shape that leaves one of the four surfaces of the core 11 open and surrounds the remaining surface. The outer peripheral portion 141 has a concave cross-section that leaves one side in the direction of extension of the plurality of primary conductors 12 open. The shield portion 14 has a cover portion 143 that is positioned to close the open side of the inner peripheral portion 142, and an opposing portion 144 that is positioned opposite the cover portion 143 with the inner peripheral portion 142 in between. The ends of the cover portion 143 and the opposing portion 144 on the side where the plurality of primary conductors 12 are not positioned are flush with the inner peripheral portion 142. The ends of the cover portion 143 and the opposing portion 144 on the side where the plurality of primary conductors 12 are positioned so as to protrude beyond the inner peripheral portion 142 toward the plurality of primary conductors 12. The shield portion 14 has an inner circumferential portion 142 that is sandwiched between the cover portion 143 and the opposing portion 144 on the side of the multiple primary conductors 12 and is located on the outer surface of the outer circumferential portion 141.

[0035] The outer periphery 141, inner periphery 142, lid 143, and opposing 144 may be fitted together to form a space 145 that encloses the core 11 and the multiple secondary windings 13. Alternatively, the outer periphery 141, inner periphery 142, lid 143, and opposing 144 may be bonded together with an adhesive or the like to form a space 145 that encloses the core 11 and the multiple secondary windings 13. The outer periphery 141, inner periphery 142, lid 143, and opposing 144 may be fitted together to form a space 145 that encloses the core 11 and the multiple secondary windings 13. The shield portion 14 has an opening (not shown) for drawing the multiple secondary windings 13 out of the space 145 to the outside of the shield portion 14. This allows the multiple secondary windings 13 arranged in the space of the shield portion 14 to be connected to the leakage current detection unit 15 (see Figure 1).

[0036] The outer periphery 141, inner periphery 142, cover 143, and opposing portion 144 are formed of a magnetic material with high saturation magnetic flux density (e.g., high saturation density permalloy, silicon steel, pure iron, etc.). This allows the shield portion 14 to block external noise. The shield portion 14 also reduces the amount of magnetic flux generated by current flowing through the multiple primary conductors 12 that links with the multiple secondary windings 13. However, when comparing the effect of the shield portion 14 in making it difficult for the magnetic flux to link with the multiple secondary windings 13 with its effect in blocking external noise, blocking external noise improves the accuracy of detecting leakage current in the circuit. Therefore, by providing the shield portion 14, the zero-phase current transformer 1 can improve the accuracy of detecting leakage current in the circuit connected to the multiple primary conductors 12.

[0037] Returning to Figure 1, the zero-phase current transformer 1 includes a leakage detection unit (an example of a detection unit) 15 that detects whether or not a leakage current has occurred in at least one of the circuits connected to the multiple primary conductors 12 based on the induced voltages output from the multiple secondary windings 13. The leakage detection unit 15 uses the secondary winding that outputs the lowest induced voltage among the multiple secondary windings 13 when a balanced current is flowing through the multiple primary conductors 12 to detect the leakage current.

[0038] The leakage current detection unit 15 is connected to both ends of each of the multiple secondary windings 13, and the induced voltage detected in each of the multiple secondary windings 13 is input to it. In the zero-phase current transformer 1, a balanced current is passed through the multiple primary conductors 12 during pre-shipment inspection or after shipment but before actual operation, and the induced voltage output from both ends of the multiple secondary windings 13 is measured by the leakage current detection unit 15. The leakage current detection unit 15 calculates the effective value of the induced voltage output from each of the multiple secondary windings 13 and compares the magnitude of these induced voltages. The leakage current detection unit 15 selects the secondary winding that output the induced voltage with the smallest calculated effective value.

[0039] Here, the fact that the induced voltage detected when a balanced current flows through multiple primary conductors 12 is low (i.e., has a small effective value) means that the balance characteristics are less likely to deteriorate even if the multiple primary conductors 12 are positioned offset from their reference positions. For this reason, the zero-phase current transformer 1 uses the secondary winding selected by the leakage detection unit 15 in this way to detect leakage current in the circuit to which multiple primary conductors 12 are connected, thereby suppressing deterioration of the balance characteristics even if the multiple primary conductors 12 are positioned off from their original positions (i.e., reference positions) due to manufacturing errors or the like.

[0040] (Function and effect of zero-phase current transformer) Next, the operation and effects of the zero-phase current transformer 1 according to this embodiment will be explained using Figures 3 to 11 with reference to Figures 1 and 2. In Figures 3 to 11, even if a component is from a comparative example of a zero-phase current transformer used for comparison with the zero-phase current transformer 1, the same reference numerals will be used for components that perform the same operation and function as those provided in the zero-phase current transformer 1.

[0041] Figures 3 to 6 illustrate the case where multiple primary conductors 12 are positioned at a reference location and a balanced current is flowing through them. Figure 3 shows an example of the current waveform of the balanced current flowing through primary conductors 121, 122, and 123 provided on the multiple primary conductors 12. In Figure 3, "Ir" indicates the current flowing through primary conductor 121 connected to the R-phase circuit. In Figure 3, "Is" indicates the current flowing through primary conductor 122 connected to the S-phase circuit. In Figure 3, "It" indicates the current flowing through primary conductor 123 connected to the T-phase circuit.

[0042] Figure 4 schematically shows the analysis results of the magnetic flux distribution generated in the core 11 at time t1 when the balanced current shown in Figure 3 flows through the primary conductors 121, 122, and 123. Figure 5 shows an example of the voltage waveform of the induced voltage based on the magnetic flux distribution shown in Figure 4. In Figure 5, "E111a" indicates the induced voltage output from the secondary winding wound around the first part 111a of the core 11. In Figure 5, "E111b" indicates the induced voltage output from the secondary winding wound around the first part 111b of the core 11. In Figure 5, "E112a" indicates the induced voltage output from the secondary winding wound around the second part 112a of the core 11. In Figure 5, "E112b" indicates the induced voltage output from the secondary winding wound around the second part 112b of the core 11.

[0043] Figure 6 shows an example of the voltage waveform of the induced voltage output from the secondary winding wound around the entire core 11 when multiple primary conductors 12 are positioned at a reference position and balanced currents flow through the multiple primary conductors 12. In Figure 6, "E" indicates the induced voltage output from the secondary winding.

[0044] As shown in Figure 3, the current Ir flowing through the primary conductor 121 provided on the multiple primary conductors 12, the current Is flowing through the primary conductor 122 provided on the multiple primary conductors 12, and the current It flowing through the primary conductor 123 provided on the multiple primary conductors 12 have the same amplitude and current waveforms that are 120° out of phase with respect to each other. At time t1, the current value of Ir is 0, the current Is has a negative current value, and the current It has a positive current value. The absolute values ​​of the currents Is and It are the same.

[0045] At time t1 shown in Figure 4, the current value of Ir is 0, so no magnetic field is generated by Ir. On the other hand, at time t1, current Is generates a concentric magnetic field around primary conductor 122. This magnetic field becomes denser, i.e., stronger, as it approaches primary conductor 122. Similarly, at time t1, current It generates a concentric magnetic field around primary conductor 123. This magnetic field becomes denser, i.e., stronger, as it approaches primary conductor 122. Furthermore, the magnetic fields generated by current Is and current It are in opposite directions and have approximately the same strength.

[0046] Therefore, as shown in Figure 4, a higher density magnetic flux is generated in the second portion 112a near the primary conductor 122 compared to the first portions 111a and 111b. Similarly, a higher density magnetic flux is generated in the second portion 112b near the primary conductor 123 compared to the first portions 111a and 111b. Magnetic fluxes are generated in the second portions 112a and 112b in opposite directions and with approximately the same magnetic flux density.

[0047] As you move away from the primary conductors 122 and 123, the magnetic field based on the currents Is and It weakens, and therefore the magnetic flux generated in the first parts 111a and 111b of the core 11 also weakens. For this reason, in the region 111a-4 on the second part 112a side of the entire region of the first part 111a and the region 111a-5 adjacent to the second part 112b, magnetic flux is generated based on the current Is flowing through the primary conductor 122. On the other hand, in the regions 111a-3 and 111a-5 on the second part 112b side of the entire region of the first part 111a, magnetic flux is generated based on the current It flowing through the primary conductor 123. Furthermore, in the central region 111a-1 of the entire region of the first part 111a, magnetic flux is generated based on both the current Is flowing through the primary conductor 122 and the current It flowing through the primary conductor 123. In the central part in the direction of extension of the first part 111a, the two magnetic fluxes repel each other, so the magnetic flux tends to be sparser compared to other regions.

[0048] Therefore, within the entire region of the first part 111a, the magnetic flux density is highest in region 111a-4, which is adjacent to the second part 112a, and in region 111a-5, which is adjacent to the second part 112b. Also, within the entire region of the first part 111a, the magnetic flux density is lowest in region 111a-1, which is closer to the center. Furthermore, within the entire region of the first part 111a, the magnetic flux density is lower in region 111a-2, which is closer to the second part 112a, and in region 111a-3, which is closer to the second part 112b, than in regions 111a-4 and 111a-5, but higher than in region 111a-1. In addition, the magnetic flux generated in region 111a-2 and the magnetic flux generated in region 111a-3 are in opposite directions and have approximately the same magnetic flux density. The magnetic flux generated in region 111a-4 and the magnetic flux generated in region 111a-5 are in opposite directions and have approximately the same magnetic flux density. In region 111a-1, which is near the primary conductor 121, a magnetic flux with a lower magnetic flux density is generated compared to regions 111a-2, 111a-3, 111a-4, and 111a-5.

[0049] For the same reasons as in the first part 111a, within the entire region of the first part 111b, the magnetic flux density is highest in regions 111b-4 adjacent to the second part 112a and 111b-5 adjacent to the second part 112b. Also, within the entire region of the first part 111b, the magnetic flux density is lowest in the central region 111b-1. Furthermore, within the entire region of the first part 111b, the magnetic flux density is lower in regions 111b-2 adjacent to the second part 112a and 111b-3 adjacent to the second part 112b than in regions 111b-4 and 111b-5, but higher than in region 111b-1. In addition, the magnetic flux generated in region 111b-2 and region 111b-3 are in opposite directions and have approximately the same magnetic flux density. The magnetic flux generated in region 111b-4 and region 111b-5 are in opposite directions and have approximately the same magnetic flux density. In the region 111b-1, which is near the primary conductor 121, a magnetic flux with a lower magnetic flux density is generated compared to regions 111b-2, 111b-3, 111b-4, and 111b-5. Thus, in the core 11, a magnetic flux is generated that has a line-symmetric relationship with respect to a virtual straight line passing through the center in the extension direction of the first parts 111a and 111b as the axis of symmetry.

[0050] Figure 4 illustrates the distribution of magnetic flux in the core 11 when no current flows through the centrally located primary conductor 121. However, when balanced currents flow through multiple primary conductors 12, even if current flows through primary conductor 121, regions where opposing magnetic fluxes repel each other are created in the first sections 111a and 111b. For example, if currents of the same polarity flow through primary conductors 121 and 122, and a current of a different polarity flows through primary conductor 123, regions where magnetic fluxes repel each other are created in the region between primary conductors 121 and 123 in the first sections 111a and 111b. Also, for example, if currents of the same polarity flow through primary conductors 121 and 123, and a current of a different polarity flows through primary conductor 122, regions where magnetic fluxes repel each other are created in the region between primary conductors 121 and 122 in the first sections 111a and 111b. Thus, when a balanced current flows through multiple primary conductors 12, a region with the lowest magnetic flux density is created in the first parts 111a and 111b.

[0051] As explained using Figure 4, when multiple primary conductors 12 are positioned at a reference location and balanced currents flow through them, magnetic fluxes of different densities are generated in the first parts 111a, 111b and the second parts 112a, 112b of the core 11. However, in this case, the magnetic flux generated in the core 11 has a distribution that becomes zero when it goes around the core 11 once. The induced voltage generated in the secondary winding wound around the core 11 due to the magnetic flux generated in the core 11 is obtained by the product of the differential value of the magnetic flux linking the secondary winding and the number of turns of the secondary winding. Therefore, the induced voltages generated in the secondary winding wound in the same direction and the same number of times in each of the first parts 111a, 111b, 112a, and 112b are as shown in Figure 5.

[0052] Specifically, as shown in Figure 5, the induced voltage E111a generated in the secondary winding wound around the first part 111a and the induced voltage E111b generated in the secondary winding wound around the first part 111b have the same maximum value (i.e., amplitude) and opposite polarity. Similarly, the induced voltage E112a generated in the secondary winding wound around the second part 112a and the induced voltage E112b generated in the secondary winding wound around the second part 112b have the same maximum value (i.e., amplitude) and opposite polarity. Furthermore, since the magnetic flux density in the second parts 112a and 112b is higher than that in the first parts 111a and 111b, the induced voltages E112 and E112b have a larger maximum value (i.e., amplitude) than the induced voltages E111a and E111b.

[0053] Thus, when multiple primary conductors 12 are positioned at a reference location and balanced currents flow through them, the induced voltage E111a in the first part 111a and the induced voltage E111b in the first part 111b cancel each other out, and the induced voltage E112a in the second part 112a and the induced voltage E112b in the second part 112b cancel each other out. In other words, when multiple primary conductors 12 are positioned at a reference location and balanced currents flow through them, the induced voltages are in a balanced state throughout the core 11. For this reason, as shown in Figure 6, no induced voltage E is generated at both ends of the secondary winding that is uniformly wound throughout the core 11.

[0054] Incidentally, when a zero-phase current transformer is actually incorporated into equipment and used, due to manufacturing errors and other factors, multiple primary conductors may not be positioned at the reference position but may be positioned asymmetrically with respect to the core. Here, we will explain the case where multiple primary conductors 12 are positioned offset from the reference position and a balanced current is flowing, using Figures 7 to 9. Figure 7 is a schematic diagram showing the analysis results of the magnetic flux distribution generated in the core 11 at time t1 in Figure 3, when primary conductor 121 is positioned offset towards the second part 112b side with respect to the reference position, and the balanced current shown in Figure 3 flows through primary conductors 121, 122, and 123.

[0055] Figure 8 shows an example of the voltage waveform of the induced voltage based on the magnetic flux distribution shown in Figure 7. The terms "E111a," "E111b," "E112a," and "E112b" in Figure 8 have the same meaning as "E111a," "E111b," "E112a," and "E112b" in Figure 5, so no further explanation is provided. Figure 9 shows an example of the voltage waveform of the induced voltage output from the secondary winding wound around the entire core 11 when the primary conductor 121 is positioned offset to the second portion 112b side relative to the reference position, and balanced current flows through the primary conductors 121, 122, and 123. "Ea" in Figure 9 indicates the induced voltage output from the secondary winding. For ease of understanding, the induced voltage E shown in Figure 6 is also shown in Figure 9.

[0056] As shown in Figure 7, when the primary conductor 121 is positioned offset towards the second portion 112b side relative to the reference position, the distance between the primary conductor 121 and the primary conductor 123 becomes shorter than the distance between the primary conductor 121 and the primary conductor 122. Therefore, the magnetic field generated by the current Ir in the primary conductor 121 is stronger near the primary conductor 123 than near the primary conductor 122. As a result, the magnetic field generated by the current Is flowing through the primary conductor 122 is less affected by the magnetic field generated by the current Ir flowing through the primary conductor 121 than the magnetic field generated by the current It flowing through the primary conductor 123. Therefore, when the primary conductor 121 is positioned offset towards the second portion 112b side relative to the reference position, and balanced currents flow through the primary conductors 121, 122, and 123, the range of magnetic flux most affected by the magnetic field based on the current Is flowing through the primary conductor 122 is wider than the range of magnetic flux most affected by the magnetic field based on the current It flowing through the primary conductor 123.

[0057] As a result, as shown in Figure 7, in the region 111a-4 adjacent to the second portion 112a within the entire region of the first portion 111a, magnetic flux is generated based on the current Is flowing through the primary conductor 122, and the magnetic flux density is higher than in other regions of the first portion 111a. In addition, in the region 111a-1 near the primary conductor 121 within the entire region of the first portion 111a, magnetic flux is generated based on both the current Is flowing through the primary conductor 122 and the current It flowing through the primary conductor 123. In the central part of region 111a-1 in the direction of extension of the first portion 111a, the two magnetic fluxes repel each other, so the magnetic flux tends to be sparser compared to other regions. For this reason, a magnetic flux with a lower magnetic flux density is generated in region 111a-1 than in other regions of the first portion 111a. In region 111a-2, between region 111a-1 and region 111a-4, and in region 111a-3, between region 111a-1 and the second part 112b, magnetic flux is generated with opposite directions and approximately the same magnetic flux density. The magnetic flux generated in region 111a-2 has the same direction as the magnetic flux generated in region 111a-4. The magnetic flux generated in region 111a-2 and the magnetic flux generated in region 111a-3 have opposite directions and approximately the same magnetic flux density. The magnetic flux generated in region 111b-4 has the same direction as region 111b-2.

[0058] For the same reasons as in the first part 111a, the region 111b-4 adjacent to the second part 112a has the highest magnetic flux density within the entire region of the first part 111b. Also, within the entire region of the first part 111b, the region 111b-1 near the primary conductor 121 has the lowest magnetic flux density. Furthermore, within the entire region of the first part 111b, the region 111b-2 between region 111b-1 and region 111b-4, and the region 111b-3 between region 111b-1 and the second part 112b, have a lower magnetic flux density than region 111b-4 and a higher magnetic flux density than region 111b-1. In addition, the magnetic flux generated in region 111b-2 and the magnetic flux generated in region 111b-3 are in opposite directions and have approximately the same magnetic flux density. The magnetic flux generated in region 111b-4 has the same direction as the magnetic flux generated in region 111b-2.

[0059] Within the second portion 112a near the primary conductor 122, a magnetic flux is generated based on the magnetic field produced by the current Is flowing through the primary conductor 122. Therefore, a magnetic flux with the same direction and magnetic flux density as the magnetic flux generated in region 111a-4 of the first portion 111a is generated in the second portion 112a.

[0060] In the region 112b-2 of the second part 112b adjacent to the first part 111a, a magnetic flux is generated with the same direction and magnetic flux density as the magnetic flux generated in region 111a-3 of the first part 111a. In the region 112b-3 of the second part 112b adjacent to the first part 111b, a magnetic flux is generated with the same direction and magnetic flux density as the magnetic flux generated in region 111b-3 of the first part 111b. The magnetic flux generated in region 112b-2 and the magnetic flux generated in region 112b-3 are in opposite directions and have approximately the same magnetic flux density.

[0061] In region 112b-1, which is between regions 112b-2 and 112b-3 within the entire region of the second part 112b, a magnetic flux is generated based on the magnetic field produced by the current It flowing through the primary conductor 123. As a result, a magnetic flux is generated in the opposite direction to the magnetic flux generated in regions 112b-2 and 112b-3, and with a higher magnetic flux density than that flux.

[0062] Thus, even if a balanced current flows through multiple primary conductors 12, the distribution of magnetic flux generated in the core 11 becomes asymmetrical when the axis of symmetry is a virtual straight line passing through the center in the extending direction of the first parts 111a and 111b, due to the displacement of the primary conductor 121 relative to the reference position. Figure 7 shows the distribution of magnetic flux generated in the core 11 at time t1 shown in Figure 3, but at other times as well, the distribution of magnetic flux generated in the core 11 becomes asymmetrical when the axis of symmetry is a virtual straight line passing through the center in the extending direction of the first parts 111a and 111b. Furthermore, although not shown in the illustration, if either of the primary conductors 122 or 123 is displacementd relative to the reference position, the distribution of magnetic flux generated in the core 11 becomes asymmetrical when the axis of symmetry is a virtual straight line passing through the center in the extending direction of the first parts 111a and 111b.

[0063] When the distribution of magnetic flux generated in core 11 is asymmetrical, the magnetic flux generated in core 11 does not become zero even after going around core 11 once. Therefore, the induced voltage generated in the secondary windings wound in the same direction and in the same number of turns in each of the first part 111a, first part 111b, second part 112a, and second part 112b is as shown in Figure 8.

[0064] Specifically, as shown in Figure 8, the induced voltage E111a generated in the secondary winding wound around the first part 111a and the induced voltage E111b generated in the secondary winding wound around the first part 111b have the same maximum value (i.e., amplitude) and opposite polarity. Furthermore, the induced voltage E112a generated in the secondary winding wound around the second part 112a has a larger maximum value (i.e., amplitude) and opposite polarity than the induced voltage E112b generated in the secondary winding wound around the second part 112b. Moreover, since the magnetic flux density in the second part 112a is higher than that in the first parts 111a and 111b, the induced voltage E112a has a larger maximum value (i.e., amplitude) than the induced voltages E111a and E111b.

[0065] Thus, when at least one of the multiple primary conductors 12 (primary conductor 121 in this example) is positioned offset from the reference position and a balanced current flows through the multiple primary conductors 12, the induced voltage E112a in the second part 112a and the induced voltage E112b in the second part 112b cancel each other out, but the induced voltage E111a in the first part 111a and the induced voltage E111b in the first part 111b do not cancel each other out. In other words, when at least one of the multiple primary conductors 12 (primary conductor 121 in this example) is positioned offset from the reference position and a balanced current flows through the multiple primary conductors 12, the induced voltage in the entire core 11 is in an unbalanced state. Therefore, as shown in Figure 9, an induced voltage Ea corresponding to the difference between the induced voltages E121a and E121b is generated at both ends of the secondary winding uniformly wound around the entire core 11.

[0066] Thus, even though a balanced current is flowing, if an induced voltage Ea is generated at both ends of the secondary winding, which is uniformly wound around the entire core 11, the zero-sequence current transformer will mistakenly detect that a leakage current has occurred in the circuit that is connected to multiple primary conductors and is the target of leakage detection.

[0067] Therefore, the winding density of the secondary winding wound around the core 11 is varied, and the secondary winding is wound around the core 11 such that the second portion 112a, 112b, where the magnetic flux is concentrated, is less densely wound than the first portion 111a, 111b, where the magnetic flux is not concentrated. As described above, the induced voltage output from both ends of the secondary winding is proportional to the number of turns of the secondary winding. For this reason, the secondary winding is wound such that the first portion 111a, 111b, where the magnetic flux is least concentrated, is the densest, and the second portion 112a, where the magnetic flux is most concentrated, is the least dense. Furthermore, the secondary winding is wound in the second portion 112b, where the magnetic flux is more concentrated than in the first portion 111a, 111b but less concentrated than in the second portion 112a, to be less densely wound than in the first portion 111a, 111b and denser than in the second portion 112a. In this way, by creating density variations in the secondary winding to correspond to the magnetic flux density generated within the core 11 and winding it around the core 11, the induced voltage output from both ends of a single secondary winding wound around the entire core 11 is suppressed. That is, the induced voltage Ea shown in Figure 9 becomes smaller in voltage value (i.e., amplitude).

[0068] However, it is unclear in which direction and to what extent the multiple primary conductors 12 are deviated from the reference position within the maximum error range. Consequently, it is also unclear how the density of magnetic flux occurs within the core 11. Therefore, there is a problem in that it is extremely difficult to create density in the secondary winding and wind it around the core 11 in a way that effectively suppresses the induced voltage.

[0069] Therefore, in this embodiment, the zero-phase current transformer 1 has multiple secondary windings 13 wound around the core 11 with a slight offset from each other, and the secondary winding with the lowest induced voltage output when a balanced current flows through multiple primary conductors 12 is used for leakage detection.

[0070] Figure 10 shows an example of induced voltages output from both ends of multiple secondary windings 13 when the magnetic flux distribution shown in Figure 7 occurs in the core 11 of the zero-phase current transformer 1. "E131" in Figure 5 indicates the induced voltage output from the first secondary winding 131. "E132" in Figure 5 indicates the induced voltage output from the second secondary winding 132. "E133" in Figure 5 indicates the induced voltage output from the third secondary winding 133.

[0071] When the primary conductor 121 is positioned offset to the second portion 112b side relative to the reference position, the magnetic flux density in the region on the second portion 112a side and the magnetic flux density on the second portion 112b side become higher and lower in the first portion 111a,111b side, compared to when the primary conductor 121 is positioned at the reference position (see Figure 7). As a result, as shown in Figure 10, the voltage value (i.e., amplitude) of the induced voltage E132 output from both ends of the second secondary winding 132 positioned on the second portion 112a side is the largest, and the voltage value (i.e., amplitude) of the induced voltage E133 output from both ends of the third secondary winding 133 positioned on the second portion 112b side is the lowest. Furthermore, the induced voltage E131 output from both ends of the first secondary winding 131 positioned closer to the center of the first portion 111a,111b has a voltage value (i.e., amplitude) that is smaller than the induced voltage E132 and larger than the induced voltage E133.

[0072] The induced voltages E131, E132, and E133 are input to the leakage detection unit 15 (see Figure 1). As shown in Figure 10, the voltage values ​​of the induced voltages E131, E132, and E133 change in a period corresponding to the period of the currents Ir, Is, It (see Figure 3) flowing through the multiple primary conductors 12. Therefore, the leakage detection unit 15 calculates, for example, the RMS values ​​of the induced voltage E131 input from the first secondary winding 131, the induced voltage E132 input from the second secondary winding 132, and the induced voltage E133 input from the third secondary winding 133, and determines the level of the induced voltages E131, E132, and E133 based on the calculated RMS values. In the example shown in Figure 10, the RMS value of the induced voltage E133 is the smallest. Therefore, the leakage detection unit 15 selects the third secondary winding 133, which outputs the smallest effective value induced voltage E132, as the secondary winding for detecting leakage current (e.g., ground fault) in the circuit connected to the multiple primary conductors 12.

[0073] Thus, even if the position of the density of magnetic flux generated in the core 11 is unclear due to the displacement of multiple primary conductors 12 relative to the reference position caused by manufacturing errors, the zero-sequence current transformer 1 can ensure a balanced state by selecting the secondary winding that outputs the smallest dielectric voltage.

[0074] Figure 11 is a graph showing the simulation results of the RMS values ​​of the induced voltages in the zero-sequence current transformer according to this embodiment and the zero-sequence current transformer according to the comparative example. The zero-sequence current transformer model used in the simulation is the same in this embodiment and the comparative example, except for the secondary winding. That is, the core and shield models have the same structure as the core 11 and shield 14 provided in the zero-sequence current transformer 1 shown in Figure 1. The secondary winding model in the zero-sequence current transformer according to this embodiment has the same structure as the multiple secondary windings 13 provided in the zero-sequence current transformer 1, with three secondary windings wound around the core at an offset from each other, while the zero-sequence current transformer according to the comparative example has a structure in which the windings are uniformly wound around the entire core. Furthermore, the multiple primary conductor models have the same structure as the multiple primary conductors 12 shown in Figure 7, with the windings arranged in an asymmetrical relationship in the direction of extension of the first part of the core.

[0075] In Figure 11, "This Embodiment" shows the effective values ​​of the induced voltages output from both ends of a secondary winding whose center in the direction of extension of the first portion coincides with the central axis of one of the three primary conductors when viewed in the direction of extension of the multiple primary conductors. In Figure 11, "Comparative Example" shows the effective values ​​of the induced voltages output from both ends of a secondary winding provided in a zero-sequence current transformer according to the comparative example.

[0076] As explained using Figures 3 to 6, the magnetic flux in the core that links with the secondary winding whose center lies on a straight line with the central axis of the primary conductor is small. The zero-sequence current transformer 1 comprises a plurality of secondary windings 13 that are offset in the direction of extension of the first portions 111a and 111b. Therefore, even if at least one of the plurality of primary conductors 12 is offset, there is a secondary winding whose center lies on or near a straight line with the central axis of any of the plurality of primary conductors 12. As a result, as shown in Figure 11, the effective value of the induced voltage in the zero-sequence current transformer according to this embodiment is smaller than the effective value of the induced voltage in the zero-sequence current transformer according to the comparative example (i.e., the effective value of the induced voltage of the secondary winding wound around the entire core).

[0077] In this way, the zero-sequence current transformer 1 can reduce the induced voltage that occurs when at least one of the multiple primary conductors 12 is positioned even if it is misaligned with the reference position, thereby suppressing deterioration of the balance characteristics. As a result, the zero-sequence current transformer 1 can suppress false detection of leakage current based on the misalignment.

[0078] As described above, the zero-phase current transformer 1 according to this embodiment comprises a core 11 made of a magnetic material having a pair of first parts 111a, 111b arranged opposite to each other with a predetermined gap between them, and a pair of second parts 112a, 112b arranged opposite to each other across one end and the other end of the pair of first parts 111a, 111b, and having a shorter length than the pair of first parts 111a, 111b; a plurality of primary conductors 12 arranged at predetermined intervals through a space 16 surrounded by the core 11 and intersecting the core 11; and a plurality of secondary windings 13 wound around the pair of first parts 111a, 111b with a staggered arrangement, and outputting an induced voltage based on the magnetic flux generated in the core 11 in accordance with the current flowing through the plurality of primary conductors 12.

[0079] As a result, the zero-phase current transformer 1 can suppress deterioration of its balance characteristics even if at least one of the multiple primary conductors 12 is positioned outside its original location. Consequently, the zero-phase current transformer 1 can suppress false detection of leakage current.

[0080] The present invention is not limited to the embodiments described above and can be modified in various ways. The zero-sequence current transformer according to the above embodiment has three secondary windings as a plurality of secondary windings, but the present invention is not limited thereto. For example, the zero-sequence current transformer may have four or more secondary windings within a range of deviation amounts smaller than the maximum error. This makes it easier for a secondary winding to have good balance characteristics with respect to deviations within the maximum error range of the plurality of primary conductors, so the zero-sequence current transformer can improve the suppression of false detection of leakage current.

[0081] The technical scope of the present invention is not limited to the illustrative and described embodiments, but also includes all embodiments that produce effects equivalent to those aimed at by the present invention. Furthermore, the technical scope of the present invention is not limited to the combination of features of the invention defined by the claims, but can be defined by any desired combination of specific features from all disclosed features. [Explanation of symbols]

[0082] 1 Zero phase current transformer 11 cores 12 Multiple primary conductors 13 Multiple secondary windings 14 Shield section 15. Leakage current detection unit 16,145 space 111a,111b First part 111a-1,111a-2,111a-3,111a-4,111a-5,111b-1,111b-2,111b-3,111b-4,111b-5,112b-1,112b-2,112b-3 area 112a,112b Second part 121, 122, 123 Primary conductor 131 First secondary winding 131a,131b central part 132 Secondary winding 133 Third secondary winding 141 Outer perimeter 142 Inner circumference 143 Lid 144 Opposite section 161 Reference position

Claims

1. A core made of a magnetic material having a pair of first parts arranged opposite each other with a predetermined gap between them, and a pair of second parts arranged opposite each other across the gap between one end and the other end of the pair of first parts and having a shorter length than the pair of first parts, Multiple primary conductors are arranged at predetermined intervals, passing through a space surrounded by the core and intersecting the core, A plurality of secondary windings are wound around the pair of first parts in a staggered manner and output an induced voltage based on the magnetic flux generated in the core in response to the current flowing through the plurality of primary conductors. A zero-phase current transformer equipped with this feature.

2. The aforementioned plurality of secondary windings include at least a first secondary winding, a second secondary winding, and a third secondary winding. The first secondary winding is positioned such that its center aligns with the reference position where one of the plurality of primary conductors is originally located. The second secondary winding is positioned off-center to one side of the pair of second parts by the maximum error that could cause one of them to be positioned offset from the reference position in the extending direction of the part, The third secondary winding is positioned off-center to the other side of the pair of second parts by the amount of the maximum error. The zero-phase current transformer according to claim 1.

3. Among the multiple secondary windings, adjacent secondary windings are wound around the pair of first parts with a portion of them overlapping. The zero-phase current transformer according to claim 1.

4. The plurality of secondary windings are not wound around the pair of second parts but are routed along the pair of second parts. The zero-phase current transformer according to claim 1.

5. The system includes a shield portion arranged to cover the core and the plurality of secondary windings. The zero-phase current transformer according to claim 1.

6. The system includes a detection unit that detects whether or not a leakage current is occurring in at least one of the circuits connected to the plurality of primary conductors, based on the induced voltages output from the plurality of secondary windings. The detection unit uses the secondary winding that outputs the lowest induced voltage among the plurality of secondary windings when a balanced current is flowing through the plurality of primary conductors to detect the leakage current. A zero-phase current transformer according to any one of claims 1 to 5.

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