JP2007123625A - Current transformer and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current transformer wherein a measurement error of an exciting voltage in a small current region is enhanced, and to provide a manufacturing method thereof. <P>SOLUTION: An insulation resin member is pressed to exert a pressing force to an internal case 13 to deform the internal case 13 toward an iron core 5. The deforming force moves the iron core 5 in a space 13 to absorb the pressure, and the pressure is hardly exerted to the iron core 5 so as to hardly cause a magnetic stress and magnetic distortion or the like to the iron core 5. The insulation resin member is pressed at an iron core annealing temperature to form an insulation layer 2. Accordingly, the magnetic stress and the magnetic distortion or the like are improved for the iron core 5, the magnetic characteristics of the iron core are improved, the exciting characteristics are enhanced, and the measurement error is reduced in the small current region. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a current transformer having an insulating layer covering an iron core, a winding, and the like, and a method for manufacturing the current transformer.

  Generally, a current transformer is used to operate a measurement or protection relay by transforming a large current in a high-voltage circuit or a low-voltage circuit into a small current proportional to the large current. The current transformer includes an iron core that detects magnetic flux from the primary conductor, a secondary coil that is a winding for converting the magnetic flux into a secondary current, an insulating layer that covers the iron core and the secondary coil, and part of the insulating layer And a secondary terminal drawn from a secondary coil provided in Connect to measuring instrument and protective relay from secondary terminal.

  The range of use such as measurement by a conventional current transformer and operation of a protective relay was a high current region of about 100 to 2000% and a medium current region of 5 to 100% with a rated current of 100%. This further expansion of the high current region results in an increase in the size of the core of the current transformer and an increase in the size of the current transformer.

  In addition, the small current region below the middle current region has a large error and cannot be used, so the measurement usage range is narrow. For this reason, the conventional current transformer always selects the rated current according to the load current situation, and replaces the current transformer according to the rated current.

  The structure of the current transformer will be described. A cushioning material, for example, an insulating tape is wound around an annular core formed of a plurality of silicon steel plates in an annular shape, and a secondary coil is wound around the insulating tape. A current transformer was manufactured by vacuum casting an insulating resin member through a stress buffering means, for example, a sponge, and then forming an insulating layer by a secondary curing process in which heating at about 80 ° C. was applied. The iron core has a strip-shaped iron core other than the ring-shaped iron core, but the other configuration and operation are the same only by changing the shape of the iron core.

  In general, there is a pressure casting method that can be manufactured at a lower cost than the above-mentioned vacuum casting as a method for producing an insulating resin member. It is not used because it gives a large residual stress and the predetermined characteristics as a current transformer cannot be obtained.

In addition, patent document 1 and patent document 2 can be mentioned as a current transformer.
Japanese Patent Publication No. 2001-267158 Japanese Patent Publication No. 2003-51417

  However, in the manufacturing method in which second casting is performed by vacuum casting and then heating at about 80 ° C., even if the pressing force due to shrinkage at the time of cooling of the insulating resin member is about 80 ° C. is buffered with a sponge, the annular core is inevitably formed. As shown in FIG. 3, the excitation characteristic B when the insulating layer is molded is lower than the excitation characteristic A of the annular core before molding the insulating layer, as shown in FIG. As a result, when the excitation voltage value V is smaller than the excitation voltage value V of the excitation characteristic A in the small current region of the excitation characteristic B, the output of the current transformer in the small current region is reduced. This was a cause of increased measurement error.

  An object of the present invention is to provide a current transformer with improved measurement error accuracy in a small current region and a method for manufacturing the current transformer.

  A first aspect of the present invention includes an iron core, a cushion material wound around the iron core, a winding wound around the cushion material, and an insulating layer coated on the winding via a stress buffering means. In the current transformer, the case used as the stress buffer means is provided with a space in which the winding moves due to the pressing force when the insulating layer is formed.

  A second aspect of the present invention is a current transformer in which an iron core and a cushion material wound around the iron core are provided, a winding is wound around the cushion material, and an insulating layer is coated on the winding via a stress buffering means. In the manufacturing method, the winding is housed in the space where the winding moves by the pressing force when forming the insulating layer provided in the case used as the stress buffering means, and the insulating resin member is pressed into the case at the core annealing temperature. It is characterized in that it is molded and covered with an insulating layer.

  In a third aspect of the present invention, an iron core, a cushion material is wound around the iron core, a winding is wound around the cushion material, and an insulating layer is coated by a casting method via the inner case and the stress buffer strengthening means. In the manufacturing method, a high temperature, that is, an annealing temperature is applied to the iron core after the insulating layer is coated.

    A fourth aspect of the present invention is characterized in that a split case is used as the inner case.

  According to the current transformer of the present invention, when pressure is applied to the case when the insulating resin member is pressed by the high-temperature press casting method, the case is deformed to the iron core side. Due to this deformation force, the iron core moves through the space and absorbs pressure, and it becomes difficult for the pressure to be applied to the iron core, making it difficult for magnetic distortion to occur in the iron core, and the excitation current characteristic A (see FIG. 3) can be maintained. When the excitation voltage value V is larger than the excitation voltage value V of the excitation characteristic B in the small current region of the excitation characteristic A, the output of the current transformer increases in the small current region, and the measurement error in the small current region Less.

  In addition, according to the current transformer manufacturing method of the present invention, when the insulating layer is formed and pressed at a high temperature, the iron core is heated to the annealing temperature of the iron core. Therefore, the magnetic distortion of the wound iron core is improved, the iron core magnetic characteristics are improved, and the exciting current characteristic C (see FIG. 3) can be obtained. In the small current region of the excitation current characteristic C, when the excitation voltage value V becomes larger than the excitation voltage value V of the excitation characteristics A and B, the output of the current transformer in the small current region further increases, and the small current region Measurement errors in the region can be further reduced.

  Further reduction of measurement error in these small current areas will expand the current measurement range of the current transformer without increasing its size, and may also reduce the need to replace the current transformer according to the rated current. it can.

Example 1
Embodiments according to the present invention will be described with reference to FIGS. 1, 2, and 3.

  FIG. 1 is a front view showing the entire through current transformer 1, and FIG. 2 is a cross-sectional view taken along line AA in FIG. 1. FIG. 3 is an excitation characteristic diagram obtained from the through-type current transformer 1 of FIGS.

  1 and 2 show a through-type current transformer 1, and an annular insulating layer 2 has a hollow hole 3 formed therein. The primary conductor 4 is inserted into the hollow hole 3. An annular iron core 5 that detects magnetic flux generated by the current flowing through the primary conductor 4, a secondary coil 6 that is a winding for converting the magnetic flux into a secondary current, and the iron core 5 and the secondary coil 6 are formed by the insulating layer 2. Cover. The secondary coil 6 drawn out from a part of the insulating layer 2 is connected to the power source side secondary terminal k2 and the load side secondary terminal l2 of the lower insulating layer 2A.

  The power supply side secondary terminal k2 and the load side secondary terminal l2 are used by being connected to a measuring instrument or a protective relay via a cable 7. The mounting bracket 8 is supported on the lower insulating layer 2A by mounting screws 9. The lower insulating layer 2A is not necessarily required because the power source side secondary terminal k2 and the load side secondary terminal l2 can be provided on the insulating layer 2.

Furthermore, the detailed structure of the penetration type current transformer 1 is demonstrated with reference to FIG.
That is, a plurality of silicon steel plates are laminated to form an iron core 5 in an annular shape, and the iron core 5 is covered with a cushioning material such as an insulating tape and a resin (for example, epoxy resin) coating as shown in FIG. For example, in the case of the insulating tape 11, the insulating tape 11 is wound around the iron core 5 to cover it. The secondary coil 6 is wound around the insulating tape 11 and the secondary coil 6 is fixed to the iron core 5.

  The secondary coil 6 is hermetically stored so as to be surrounded by the inner case 12. The inner case 12 is formed in an annular shape with an insulating member. The annular inner case 12 forms divided cases 12A and 12B so that the secondary coil 6 can be easily housed inside. Further, the inner case 12 is divided into an upper side and a lower side as an inner case 12 that is easy to store, and a divided piece case is formed. After the secondary coil 6 is arranged in the lower divided piece case, the upper divided piece case is lowered. You may comprise the case which contact | abutted to the side division | segmentation piece case and sealed the secondary coil inside.

  A space portion 13 is formed in the inner case 12 so that the secondary coil 6 can freely move in the space portion 13. The inner case 12 is covered with the insulating layer 2. The insulating layer 2 is used to obtain a withstand voltage.

  In order to hot-press the insulating layer 2 on the inner case 12, the inner case 12 is set in a lower press mold heated to about 150 ° C. for high-temperature press casting, and heated to about 150 ° C. With the upper press and the flexible insulating resin member pressed against the lower press, the mold is maintained at about 150 ° C. for several minutes and the insulating resin member is pressed into the inner case 12 to force the inner case 12. Then, the insulating layer 2 and the lower insulating layer 2A are formed. The temperature during heating may be 140 ° C. or higher in consideration of variations. The point is that the temperature is such that the core 5 is annealed and the magnetic distortion of the winding core due to the residual stress applied when winding the winding around the core is improved.

  Thus, in this Example 1, when the pressure at the time of pressing an insulating resin member by high temperature press casting and the pressure at the time of a heating are applied to the inner case 12, the inner case 12 will deform | transform into the iron core 5 side. Due to this deformation force, the iron core 5 and the secondary coil 6 move through the space 13 to absorb the pressure, and it becomes difficult for the pressure to be applied to the iron core 5, and the magnetostriction due to the heat shrinkage stress in the iron core 5 is alleviated. Thus, the exciting current characteristic A can be maintained. When the excitation voltage value V is larger than the excitation voltage value V of the excitation characteristic B in the small current region of the excitation characteristic A, the output of the current transformer increases in the small current region, and the measurement error in the small current region Less. Further, since the iron core 5 and the secondary coil 6 move in the space 13 by this deformation force, the iron core 5 and the secondary coil 6 are protected by the inner case, and there is no damage such as tension due to the pressing force and pressure.

Further, by using the inner case 12 in the divided cases 12A and 12B, after the secondary coil 6 is disposed in the one-side divided case piece, the other-side divided case piece is brought into contact with the one-side divided case piece, Since a case is comprised and the secondary coil 6 can be accommodated in an internal case, there exists an advantage which can perform the arrangement | positioning operation | work which arrange | positions the secondary coil 6 in an internal case easily.
(Example 2)
Further, according to the current transformer manufacturing method of the present invention, when the pressure generated when the insulating layer is formed at a high temperature is applied to the inner case 12, the inner case 12 is deformed to the iron core 5 side. With this deformation force, the iron core 5 and the secondary coil 6 move through the space 13 to absorb the pressure, and it becomes difficult for the pressure to be applied to the iron core 5, and the magnetic stress generated in the iron core 5 can be relaxed.

  Furthermore, since the insulating layer 2 is formed by pressing the insulating resin member against a high-temperature mold, the iron core 5 is heated at a high temperature, so that it is annealed. Thereby, the magnetic distortion of the winding core due to the residual stress applied when winding the winding around the iron core is improved, and the magnetic properties of the core are improved.

As a result, as shown in FIG. 3, the excitation characteristic C of the present invention is better than the excitation characteristics A and B, and in the small current region of the excitation current characteristic C, the excitation voltage value V is the excitation voltage value V of the excitation characteristics A and B. By increasing it, the output of the current transformer in the small current region is further increased, and the measurement error in the small current region can be further reduced. In other words, the measurement usage range has expanded.
(Example 3)
Further, when the insulating layer 2 is formed by press-molding the insulating resin member at the high temperature of the present invention, that is, the temperature at which the iron core 5 can be annealed, by strengthening the known pressure relaxation means, the exciting current characteristic C of FIG. Needless to say, it can be obtained.

Further, it is needless to say that the excitation current characteristic C shown in FIG. 3 can be obtained even when the current transformer is manufactured by the conventional casting method using the inner case and then the iron core 5 is annealed. Absent.
Although the through-type current transformer has been described above, the present invention can also be used for other current transformers that are not the through-type, such as a winding type, a bar type, and a window type.

  As described above, according to the current transformer and the manufacturing method thereof of the present invention, the measurement error of the excitation voltage value in the small current region can be reduced. Further reduction of measurement error in these small current areas will expand the current measurement range of the current transformer without increasing its size, and may also reduce the need to replace the current transformer according to the rated current. it can.

The front view of the penetration type current transformer concerning the embodiment of the present invention. The fragmentary sectional view from the AA line of FIG. The characteristic view which shows the excitation characteristic of the penetration type current transformer of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Through-type current transformer, 2 ... Insulating layer, 3 ... Hollow hole, 4 ... Primary conductor, 5 ... Iron core, 6 ... Secondary coil, 7 ... Cable, 8 ... Mounting bracket, 9 ... Mounting screw, 11 ... Insulating tape, 12 ... inner case, 13 ... space, k2 ... power source side secondary terminal, L2 ... load side secondary terminal.

Claims (4)

In a current transformer comprising an iron core, a cushion material wound around the iron core, a winding wound around the cushion material, and an insulating layer coated on the winding via a stress buffering means, A current transformer, characterized in that a space used for moving a winding by a pressing force at the time of forming an insulating layer is provided in a case used as a stress buffering means. In a method of manufacturing a current transformer, comprising an iron core and a cushion material wound around the iron core, winding a winding around the cushion material, and covering the winding with an insulating layer via a stress buffering means, the stress The winding is housed in a space where the winding moves due to the pressing force at the time of forming the insulating layer provided in the case used as the buffer means, and the insulating resin member is press-molded at the core annealing temperature in the case. The manufacturing method of the current transformer characterized by coat | covering. In a manufacturing method of an iron core and a current transformer in which a cushioning material is wound around the iron core, a winding is wound around the cushioning material, and an insulating layer is coated on the winding via a stress buffering means. A method of manufacturing a current transformer, characterized by applying a high temperature, that is, an annealing temperature to an iron core after layer coating. The current transformer according to claim 1 or 2, wherein the case uses a split case.