JP7321119B2 - zero phase current transformer - Google Patents

Description

The present disclosure relates to zero-phase current transformers that detect zero-phase current.

A ground fault directional relay is generally installed in power receiving equipment for the purpose of ground fault protection, and a zero-phase current transformer is widely used for ground fault detection performed by such a ground fault directional relay. A zero-phase current transformer has an annular core through which U-phase, V-phase, and W-phase primary conductors are inserted.

Then, the zero-phase current transformer outputs a secondary current corresponding to the vector sum of the currents flowing through these primary conductors from the secondary coil as a zero-phase current. The ground-fault direction relay detects leakage current based on the zero-phase current output from the zero-phase current transformer.

A zero-phase current transformer is required to have a wide range of current transformation characteristics from a low current region to an overcurrent region. Patent Literature 1 discloses a current transformer that includes an annular core in which two types of iron core materials having different magnetic permeability are laminated and has a wide range of current transformation characteristics from a low current region to an overcurrent region.

JP-A-60-173814

However, in Patent Document 1, the secondary coil is directly wound around the annular core, and when the secondary coil is wound around the annular core, stress may be applied to the annular core and the annular core may be distorted. When the annular core is distorted, the magnetization properties of the annular core deteriorate. In this regard, by surrounding the annular core with a protective case and winding the secondary coil around the protective case, it is possible to prevent the annular core from being distorted.

However, since the protective case has a high rigidity, various stresses are applied to the secondary coil during the manufacturing process, which may cause deviation in winding intervals of the electric wires forming the secondary coil. If the winding interval of the electric wire forming the secondary coil is uneven, the magnetic characteristics deteriorate, and the current transformation characteristics of the zero-phase current transformer deteriorate.

The present disclosure has been made in view of the above, and an object thereof is to obtain a zero-phase current transformer capable of suppressing deterioration of magnetic characteristics due to stress applied to a secondary coil in a manufacturing process.

In order to solve the above-described problems and achieve the object, a zero-phase current transformer of the present disclosure includes an annular core, elastic resin, and a secondary coil. The annular core has a plurality of annular cores including at least two annular cores with different magnetic permeability and saturation magnetic flux density. An elastic resin covers the annular core. The secondary coil is toroidally wound around elastic resin. The plurality of toroid cores includes a first toroid core, a second toroid core, and a third toroid core, the first toroid core and the second toroid core to be formed of the same core material, and the third toroid core to be the first toroid core. The magnetic permeability is higher than that of the annular core and the second annular core, and the first annular core is arranged on the outer peripheral side or the inner peripheral side of the second annular core and the third annular core. are arranged side by side in a direction perpendicular to the radial direction of the annular core.

Advantageous Effects of Invention According to the present disclosure, it is possible to suppress deterioration of magnetic properties due to stress applied to a secondary coil in a manufacturing process.

Appearance perspective view of the zero-phase current transformer according to the first embodiment 1 is an external perspective view of a zero-phase current transformer in a state in which a three-phase primary conductor is inserted according to the first embodiment; FIG. Front view of the zero-phase current transformer according to the first embodiment Cross-sectional view along the IV-IV line shown in Fig. 3 Front view of the annular core according to the first embodiment Cross-sectional view along the VI-VI line shown in Fig. 5 Appearance perspective view of the first annular core according to the first embodiment Appearance perspective view of the second annular core according to the first embodiment Appearance perspective view of the third annular core according to the first embodiment FIG. 2 is a perspective view showing a lamination state of each of the first toroid core, the second toroid core, and the third toroid core according to the first embodiment; FIG. 4 is a front view showing a work-in-process product of the zero-phase current transformer before being covered with the thermosetting resin according to the first embodiment; Cross-sectional view along line XII-XII shown in FIG. Sectional view along line XIII-XIII shown in FIG. FIG. 4 is a diagram including a cross-sectional view of the annular core and the elastic resin in a partial area of the work-in-progress according to the first embodiment; Enlarged view of area A shown in FIG. FIG. 4 is a front view showing a work-in-process product of the zero-phase current transformer before the secondary coil is wound according to the first embodiment; Sectional view along line XVII-XVII shown in FIG. Sectional view along line XVIII-XVIII shown in FIG. FIG. 4 shows another configuration example of the annular core according to the first embodiment; Sectional view showing another configuration example of the annular core according to the first embodiment

A zero-phase current transformer according to an embodiment will be described in detail below with reference to the drawings.

Embodiment 1.
FIG. 1 is an external perspective view of a zero-phase current transformer according to Embodiment 1. FIG. As shown in FIG. 1, the zero-phase current transformer 1 according to the first embodiment is used when performing a characteristic test of secondary terminals 2 and 3 that output a secondary current and the zero-phase current transformer 1. It has test terminals 4 and 5 . By supplying a current to the test terminals 4 and 5, a secondary current corresponding to the current supplied to the test terminals 4 and 5 is output from the secondary terminals 2 and 3.

FIG. 2 is an external perspective view of the zero-phase current transformer in which three-phase primary conductors are inserted according to the first embodiment. As shown in FIG. 2, a U-phase primary conductor 7, a V-phase primary conductor 8, and a W-phase primary conductor 9, which constitute an electric circuit 6, are inserted through the hollow portion 1a of the zero-phase current transformer 1. . The U-phase primary conductor 7 is a conductor through which a U-phase current of the three-phase alternating current flows, and the V-phase primary conductor 8 is a conductor through which a V-phase current of the three-phase alternating current flows. The conductor 9 is a conductor through which the W-phase current of the three-phase alternating current flows.

The secondary terminals 2 and 3 of the zero-phase current transformer 1 have a current vector flowing through the U-phase primary conductor 7, a current vector flowing through the V-phase primary conductor 8, and a current flowing through the W-phase primary conductor 9. A secondary current corresponding to the sum of the vectors of is output as a zero-phase current. The zero-phase current transformer 1 is provided, for example, in a ground fault relay or an earth leakage alarm. The ground fault relay or earth leakage alarm detects the ground leakage current based on the secondary current output as the zero phase current from the secondary terminals 2 and 3 of the zero phase current transformer 1, and detects the occurrence of the ground fault in the electric circuit 6. to detect

3 is a front view of the zero-phase current transformer according to Embodiment 1, and FIG. 4 is a cross-sectional view taken along line IV-IV shown in FIG. 5 is a front view of the annular core according to the first embodiment, and FIG. 6 is a cross-sectional view along line VI-VI shown in FIG.

As shown in FIG. 4, the zero-phase current transformer 1 includes an annular core 10, an elastic resin 14 covering the surface of the annular core 10, a secondary coil 15 wound around the outer surface of the elastic resin 14, a secondary and a thermosetting resin 16 covering the outer surface of the elastic resin 14 around which the coil 15 is wound.

In addition, the zero-phase current transformer 1 has a test coil (not shown) wound around an elastic resin 14, as will be described later. It is covered with resin 16 . The elastic resin 14 is, for example, silicone resin or fluorine resin, but is not limited to these resins. Also, the thermosetting resin 16 is, for example, an epoxy resin. The thermosetting resin 16 may be phenol resin, melamine resin, urea resin, or bismaleimide resin.

As shown in FIGS. 4 to 6, the annular core 10 is a composite core in which a plurality of annular cores are combined, and includes a first annular core 11, a second annular core 12, and a third annular core 13. First annular core 11 is arranged at a position in contact with each of the outer circumference of second annular core 12 and the outer circumference of third annular core 13 . The first annular core 11 is arranged, for example, in a concentric positional relationship with each of the second annular core 12 and the third annular core 13 .

The second toroidal core 12 and the third toroidal core 13 are arranged in a line in a direction orthogonal to the radial direction of the toroidal core 10 and are adjacent to each other. In the annular core 10 shown in FIGS. 4 and 6, the second annular core 12 and the third annular core 13 have the same inner diameter and outer diameter and the same thickness in the radial direction. The thickness in the directions may be different.

In the annular core 10 , the second annular core 12 and the third annular core 13 may be arranged on either side of the annular core 10 in the direction orthogonal to the radial direction. That is, the second toroidal core 12 and the third toroidal core 13 may be arranged upside down in the direction orthogonal to the radial direction of the toroidal core 10 from the arrangement shown in FIGS. 4 and 6 .

When the first toroid core 11, the second toroid core 12, and the third toroid core 13 are combined, if there is a gap between these toroid cores, in the manufacturing process of the toroid core 10, a press board, a press paper, or the like is used to fill the gap. The toroidal cores are fixed to each other after the gaps are filled by inserting the toroidal cores into each other.

The annular core 10 shown in FIGS. 4 and 6 is composed of the three annular cores described above, and by adjusting the cross-sectional area of the third annular core 13, the characteristics can be optimized. It can be configured so as not to saturate in the range up to the current region. The cross-sectional area of the third toroidal core 13 can be adjusted, for example, by adjusting the width of the hoop material forming the third toroidal core 13 and the number of turns of the hoop material.

7 is an external perspective view of a first toroidal core according to Embodiment 1, FIG. 8 is an external perspective view of a second toroidal core according to Embodiment 1, and FIG. 9 is an external perspective view of Embodiment 1. FIG. Fig. 2 is an external perspective view of a third annular core according to the above; 10 is a perspective view showing a lamination state of each of the first toroid core, the second toroid core, and the third toroid core according to the first embodiment. FIG.

As shown in FIGS. 7 to 9, each of first toroid core 11, second toroid core 12, and third toroid core 13 is a toroidal core. Moreover, as shown in FIG. 10, each of the first toroidal core 11, the second toroidal core 12, and the third toroidal core 13 is configured by laminating core materials.

For each of the first toroid core 11, the second toroid core 12, and the third toroid core 13, for example, a thin rectangular hoop material is used as a core material, and the winding start portion of the hoop material is fixed to a jig. , the hoop material is wound around a jig so as to have a circular shape. The winding end portion of the hoop material to the jig is fixed by, for example, welding.

Each of the first toroidal core 11 and the second toroidal core 12 is made of a first toroidal core material having a lower magnetic permeability in a low magnetic field and a higher saturation magnetic flux density than the third toroidal core 13 . The first core material is, for example, a silicon steel plate such as a grain-oriented silicon steel plate. Each of the first toroidal core 11 and the second toroidal core 12 is formed by winding a hoop material formed of, for example, a silicon steel plate around a jig. A low magnetic field is, for example, a magnetic field of 0.001 Tesla or more and 0.01 Tesla or less. Such a low magnetic field is generated, for example, when a leakage current flows through the electric circuit 6 . Note that the low magnetic field is not limited to a magnetic field of 0.001 Tesla or more and 0.01 Tesla or less.

Also, the third toroidal core 13 is made of a second toroidal core material having a higher magnetic permeability in a low magnetic field and a lower saturation magnetic flux density than the first toroidal core 11 and the second toroidal core 12 . The second core material is permalloy, for example. The third annular core 13 is formed by, for example, winding a plate-shaped hoop material made of permalloy around a jig. The annular core 10 can improve the characteristics of the zero-phase current transformer 1 in a low current region by using the second core material, compared to an annular core composed only of the first core material.

Thus, the annular core 10 is composed of two materials with different magnetic permeability and saturation magnetic flux density. Therefore, the zero-phase current transformer 1 can improve current transformation characteristics in a range from a low current region to an overcurrent region.

Even if the cross-sectional area of the third annular core 13 is the same, the larger the inner diameter of the core, the greater the amount of core material used. 13 is preferably arranged on the inner periphery.

Further, when the third toroidal core 13 forming the toroidal core 10 is distorted by stress or the like, the magnetic properties of the toroidal core 10 deteriorate. Therefore, in the annular core 10, the first annular core 11 is arranged on the outer peripheral side where the influence of thermal stress due to thermosetting of the thermosetting resin 16 is large. protected from In addition, the third annular core 13 is covered with the elastic resin 14 at the inner periphery, which is relatively less affected by thermal stress due to thermosetting of the thermosetting resin 16, and is protected from thermal stress.

11 is a front view of a work-in-process zero-phase current transformer before being covered with a thermosetting resin according to the first embodiment. FIG. 12 is a cross-sectional view taken along line XII-XII shown in FIG. 11. FIG. 13 is a cross-sectional view taken along line XIII-XIII shown in FIG. 12. FIG.

A work-in-progress 20 shown in FIG. 11 is a work-in-progress of the zero-phase current transformer 1 before being covered with a thermosetting resin. 14 is wound in a toroidal shape, and the winding interval α of the electric wire constituting the secondary coil 15 is arranged at equal intervals in the axial direction of the secondary coil 15 . The winding interval α increases from the inner diameter side of the elastic resin 14 toward the outer diameter side of the elastic resin 14 .

The secondary coil 15 is wound with the number of turns suitable for the current transformation ratio of the rated zero-phase current in order to comply with the JEC-1201 "Instrument Transformers (For Protective Relays)" standard. The electric wire forming the secondary coil 15 is, for example, an insulated electric wire having a circular cross-section with a diameter of about 1.0 to 2.0 mm. In the process of winding the electric wire around the elastic resin 14 at equal intervals in the circumferential direction of the annular core 10, the tension applied to the secondary coil 15 is controlled to be constant.

When the secondary coil 15 is wound directly around the annular core 10, if the tension changes, the stress applied to the annular core 10 will not be uniform. It is covered with resin 14 . Therefore, the stress applied to the annular core 10 can be absorbed by the elastic resin 14 and the influence on the annular core 10 can be suppressed.

As shown in FIGS. 11 to 13, a test coil 18 is attached to elastic resin 14 covering the surface of annular core 10 . In order to maintain insulation between the test coil 18 and the secondary coil 15, the test coil 18 is wrapped around the elastic resin 14 while being protected by an insulating tube or the like (not shown).

As shown in FIG. 1, in addition to secondary terminals 2 and 3, the zero-phase current transformer 1 is provided with test terminals 4 and 5 adjacent to the secondary terminals 2 and 3 in the circumferential direction. Therefore, as shown in FIG. 11 , there is a gap β in the axial direction of the secondary coil 15 between the winding start and the winding end of the secondary coil 15 . The winding of the coil 15 becomes uneven. Therefore, in order to suppress the influence of the magnetization characteristics caused by uneven winding of the secondary coil 15, the secondary coil 15 is wound around the elastic resin 14 so that the size of the gap β is as small as possible.

In the manufacturing process of the zero-phase current transformer 1, the work-in-progress 20 is fixed to a mold. Then, the thermosetting resin 16 is injected into the mold to form the zero-phase current transformer 1 shown in FIGS. 1 to 4. FIG. The work-in-progress 20 is fixed to the mold by, for example, attaching insulating spacers to at least one of the side surfaces 15a and 15b of the secondary coil 15 and the inner circumference 15c of the secondary coil 15, thereby This is done so as to secure a gap from the work-in-progress 20 .

In the manufacturing process of the zero-phase current transformer 1, the thermosetting resin 16 is molded by being cast in a mold in a vacuum state and heated and cured. In the manufacturing process of the zero-phase current transformer 1, the secondary terminals 2, 3 and the test terminals 4, 5 are attached to the work-in-process 20 before combining the lower mold and the upper mold.

FIG. 12 shows an axial cross-section of the secondary coil 15 in the work-in-process 20 . Hereinafter, the axial direction of the secondary coil 15 may be simply referred to as the axial direction. The secondary coil 15 is wound along the outer circumference of the cross section of the elastic resin 14, as shown in FIG.

Since the secondary coil 15 is wound around the elastic resin 14 in this way, the stress applied to the annular core 10 during the winding operation of the secondary coil 15 can be relieved. In addition, since the secondary coil 15 is wound around the elastic resin 14, it is possible to prevent insulation deterioration due to thermal stress applied to the secondary coil 15 when the thermosetting resin 16 is cured. It is possible to protect the coating of the electric wire.

Here, the relationship between the elastic resin 14 and the secondary coil 15 in the work-in-process 20 will be described more specifically. FIG. 14 is a diagram including a cross-sectional view of the annular core and the elastic resin in a partial area of the work-in-process according to the first embodiment. 15 is an enlarged view of the area A shown in FIG. 14. FIG.

As shown in FIGS. 14 and 15, since a constant tension is applied to the secondary coil 15 when the secondary coil 15 is wound around the elastic resin 14, the contact portion of the elastic resin 14 with the secondary coil 15 is deformation occurs. Due to the deformation of the elastic resin 14, the secondary coil 15 bites into the elastic resin 14, and the secondary coil 15 is fixed at the wound position. Therefore, since the electric wires forming the secondary coil 15 are held at regular intervals in the axial direction, deterioration of magnetic characteristics in the zero-phase current transformer 1 can be prevented.

When the secondary coil 15 is wound around a highly rigid member such as a protective case, it is wound with a relatively high tension in order to suppress misalignment. Since it is wound, a high holding force can be obtained by biting into the resin. Therefore, in the zero-phase current transformer 1, even if the tension applied to the secondary coil 15 when the secondary coil 15 is wound around the elastic resin 14 is low, positional deviation can be suppressed. Insulation deterioration of the secondary coil 15 due to the influence can be prevented.

Even if the current flowing through the electric circuit 6 does not contain a zero-phase current, a minute secondary current may flow through the secondary coil 15, but the secondary coil 15 is held at a uniform winding interval α by the elastic resin 14. be done. Therefore, in the zero-phase current transformer 1, deterioration of the magnetic characteristics due to the influence of the arrangement of the U-phase primary conductor 7, the V-phase primary conductor 8, the W-phase primary conductor 9, the secondary coil 15, and the annular core 10 is prevented. can be prevented.

In FIG. 15, a boundary line 30 indicating the surface of the elastic resin 14 before the secondary coil 15 is wound with a dashed line, and a boundary line 31 indicating the surface of the elastic resin 14 after the secondary coil 15 is wound with a solid line. is shown. A boundary line 30 indicates the surface of the elastic resin 14 after curing. A boundary line 31 indicates the surface of the elastic resin 14 deformed by winding the secondary coil 15 thereon.

When an electric wire with a diameter of less than 2.0 mm is used in the secondary coil 15, in the step of winding the secondary coil 15 around the elastic resin 14, the wire is 2 mm thick so that the electric wire sinks about 50% of the diameter with respect to the boundary line 30. It is desirable to wind the secondary coil 15 around the elastic resin 14 while managing the tension applied to the secondary coil 15 . Further, when an electric wire having a diameter of 2.0 mm or more is used in the secondary coil 15 , in the step of winding the secondary coil 15 around the elastic resin 14 , the electric wire constituting the secondary coil 15 has a diameter of 2.0 mm or more with respect to the boundary line 30 . It is desirable to manage the tension applied to the secondary coil 15 and wind the secondary coil 15 around the elastic resin 14 so that it sinks about 30 to 50%.

Next, the process of covering the surface of the annular core 10 with the elastic resin 14 will be described. 16 is a front view of a work-in-process zero-phase current transformer before a secondary coil is wound thereon according to the first embodiment; FIG. 17 is a cross-sectional view taken along line XVII-XVII shown in FIG. 16. FIG. 18 is a cross-sectional view taken along line XVIII-XVIII shown in FIG. 17. FIG.

A work-in-process product 21 shown in FIG. 16 is a work-in-process product of the zero-phase current transformer 1 before the secondary coil 15 is wound thereon, and is formed by covering the surface of the annular core 10 with the elastic resin 14 . In the manufacturing process of the zero-phase current transformer 1, the annular core 10 is fixed to a mold, and the elastic resin 14 is injected into the mold to which the annular core 10 is fixed, thereby forming the in-process shown in FIGS. A product 21 is formed.

The annular core 10 is fixed to the mold by attaching insulating spacers to at least one of the side surfaces 10a and 10b of the annular core 10 shown in FIG. , such that a gap between the mold and the annular core 10 is ensured. Also, the elastic resin 14 is molded by being cast in a mold under normal pressure or in a vacuum and cured. Thereby, the resin molding for the annular core 10 is performed.

As shown in FIGS. 16 to 18, in the work-in-process 21, the elastic resin 14 is arranged so as to surround three annular cores of the first annular core 11, the second annular core 12, and the third annular core 13. . The elastic resin 14 fixes the first annular core 11 , the second annular core 12 , and the third annular core 13 . In addition, the elastic resin 14 suppresses distortion of the annular core 10 due to thermal stress during hardening of the thermosetting resin 16, and further suppresses distortion of the annular core 10 due to external force when winding the secondary coil 15. .

As shown in FIG. 18, since the contraction stress of the thermosetting resin 16 is greater on the outer diameter side than on the inner diameter side, the radial thickness of the elastic resin 14 is different from the thickness e1 on the outer diameter side to the thickness e2 on the inner diameter side. Work in progress 21 is formed to be thicker. The thickness e<b>1 on the outer diameter side is the thickness on the outer circumference side of the annular core 10 , and the thickness e<b>2 on the inner diameter side is the thickness on the inner circumference side of the annular core 10 . In order to uniformly wind the secondary coil 15, the elastic resin 14 is desirably a perfect circle, so that the elastic resin 14 can be adjusted after molding, such as by scraping.

19 is a diagram showing another configuration example of the annular core according to the first embodiment; FIG. In the annular core 10 shown in FIG. 19, the usage ratio of the third annular core 13 is reduced compared to the annular core 10 shown in FIG. .

As described above, in the annular core 10 shown in FIG. 19, the manufacturing cost can be reduced by optimizing the usage ratio of the third annular core 13 . In addition, the silicon steel plates used for the first toroidal core 11 and the second toroidal core 12 have large variations in low magnetic field characteristics for each base material. Material loss may occur because it cannot be used in products. In the annular core 10 shown in FIG. 19, by changing and optimizing the use ratio of the third annular core 13, the low magnetic field characteristics of the annular core 10 can be improved and the loss of materials can be reduced.

Moreover, in the above description, the first annular core 11 is arranged on the outer peripheral side of each of the second annular core 12 and the third annular core 13, but the present invention is not limited to such an example. 20 is a cross-sectional view showing another configuration example of the annular core according to the first embodiment, taken along line IV-IV shown in FIG. 3. FIG.

In annular core 10 of zero-phase current transformer 1 shown in FIG. 20 , first annular core 11 is arranged at a position in contact with each of the inner circumference of second annular core 12 and the inner circumference of third annular core 13 . Moreover, the first annular core 11 of the annular core 10 shown in FIG. 20 has the same shape and size as the first annular core 11 of the annular core 10 shown in FIG. Therefore, when manufacturing a zero-phase current transformer 1 having a large outer shape, the first toroidal core 11 can be used without changing the shape and size of the first toroidal core 11 . That is, the first ring core 11 can be shared between the zero-phase current transformer 1 with a small outer shape and the zero-phase current transformer 1 with a large outer shape.

In addition, in manufacturing the second annular core 12 and the third annular core 13 of the annular core 10 shown in FIG. 20, the same hoop as the second annular core 12 and the third annular core 13 of the annular core 10 shown in FIG. material is used to change the inner diameter of the toroidal core. As a result, the annular core 10 shown in FIG. 20 and the annular core 10 shown in FIG. 6 and the like can share the width of the hoop material. It is possible to deal with complicated specifications that could not be dealt with in the conventional case. When the first toroid core 11, the second toroid core 12, and the third toroid core 13 are combined, if there is a gap between these toroid cores, in the manufacturing process of the toroid core 10, a press board, a press paper, or the like is used. is inserted into the gap to fill the gap, and then the annular cores are fixed together.

In the above example, the annular core 10 is composed of three annular cores, but the annular core 10 may be composed of two annular cores, or may be composed of four or more annular cores. For example, the annular core 10 may be composed of the first annular core 11 and the third annular core 13 without the second annular core 12 . In this case, in the annular core 10 , the axial length of the third annular core 13 can be the same as the axial length of the first annular core 11 .

As described above, the zero-phase current transformer 1 according to the first embodiment includes the annular core 10, the elastic resin 14, and the secondary coil 15. Annular core 10 has a plurality of annular cores including at least two annular cores with different magnetic permeability and saturation magnetic flux density. An elastic resin 14 covers the annular core 10 . The secondary coil 15 is toroidally wound around the elastic resin 14 . As a result, it is possible to suppress deterioration of the magnetic characteristics due to the stress applied to the secondary coil in the manufacturing process of the zero-phase current transformer 1 .

The zero-phase current transformer 1 also includes a thermosetting resin 16 covering the secondary coil 15 and the elastic resin 14 . In the radial direction of the annular core 10 , the elastic resin 14 has a thickness e<b>1 on the outer peripheral side that is thicker than a thickness e<b>2 on the inner peripheral side of the annular core 10 . As a result, the zero-phase current transformer 1 can suppress the deterioration of the magnetic characteristics of the zero-phase current transformer 1 even when the secondary coil 15 is subjected to thermal stress due to the thermosetting of the thermosetting resin 16. can.

Annular core 10 also includes first annular core 11 , second annular core 12 , and third annular core 13 . The first toroidal core 11 and the second toroidal core 12 are made of the same core material. The third toroidal core 13 has a higher magnetic permeability in a low magnetic field than the first toroidal core 11 and the second toroidal core 12 . The first annular core 11 is arranged on the outer peripheral side or the inner peripheral side of the second annular core 12 and the third annular core 13 . The second annular core 12 and the third annular core 13 are arranged side by side in a direction perpendicular to the radial direction of the annular core 10 . As a result, the zero-phase current transformer 1 can improve the low magnetic field characteristics in the annular core 10 by changing and optimizing the usage ratio of the third annular core 13, and can reduce material loss. can. Further, for example, when manufacturing a zero-phase current transformer 1 having a large outer shape, the first toroidal core 11 can be used without changing the shape and size of the first toroidal core 11 .

Also, the first annular core 11 and the second annular core 12 are formed by laminating silicon steel plates. The third annular core 13 is formed by laminating plate-shaped permalloys. As a result, the zero-phase current transformer 1 can accurately obtain a wide range of current transformation characteristics from low current to overcurrent.

A press board or press paper is arranged between two annular cores among the first annular core 11 , the second annular core 12 , and the third annular core 13 . Thereby, the gap between the annular cores can be filled, and the annular cores can be easily fixed to each other.

The configuration shown in the above embodiment is an example, and can be combined with another known technique, and part of the configuration can be omitted or changed without departing from the scope of the invention. It is possible.

1 zero-phase current transformer 1a hollow part 2, 3 secondary terminals 4, 5 test terminals 6 electric circuit 7 U-phase primary conductor 8 V-phase primary conductor 9 W-phase primary conductor 10 ring Core 10a, 10b, 15a, 15b side surface 10c, 15c inner circumference 11 first annular core 12 second annular core 13 third annular core 14 elastic resin 15 secondary coil 16 thermosetting resin 18 test coil, 20, 21 work in progress, 30, 31 borderline, 40 pressboard.

Claims (4)

an annular core having a plurality of annular cores including at least two annular cores with different magnetic permeability and saturation magnetic flux density;
an elastic resin covering the annular core;
a secondary coil wound toroidally around the elastic resin ;
The plurality of annular cores are
including a first toroid core, a second toroid core, and a third toroid core;
The first toroidal core and the second toroidal core are
formed by the same core material,
The third annular core is
a magnetic permeability higher than that of the first annular core and the second annular core;
The first annular core is
arranged on the outer peripheral side or the inner peripheral side of the second annular core and the third annular core,
The second annular core and the third annular core are
arranged side by side in a direction perpendicular to the radial direction of the annular core
A zero-phase current transformer characterized by: a thermosetting resin covering the secondary coil and the elastic resin;
The elastic resin is
The zero-phase current transformer according to claim 1, wherein, in the radial direction of the annular core, the thickness on the outer peripheral side of the annular core is thicker than the thickness on the inner peripheral side of the annular core. The first annular core and the second annular core are
It is formed by laminating silicon steel plates,
The third annular core is
3. The zero-phase current transformer according to claim 1, wherein the plate-like permalloy is laminated. 4. The pressboard or press paper according to any one of claims 1 to 3, wherein a press board or press paper is arranged between two annular cores among the first annular core, the second annular core, and the third annular core. The zero-phase current transformer according to .

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