Capacitive instrument transformer

Abstract

Provided is a capacitive instrument transformer, in which the distance between a shield and an internal electrode is shorter than the distance between a voltage-dividing electrode and the internal electrode. Flashover between the internal electrode and the shield is more likely to occur than flashover between the internal electrode and the voltage-dividing electrode. Therefore, even under a circumstance in which flashover could occur between the internal electrode and the voltage-dividing electrode, flashover between the internal electrode and the shield is likely to occur, and therefore a situation in which high voltage intrudes into a low-voltage-side circuit can be effectively kept to a minimum.

Description

Capacitor-type voltage transformer

[0001] The present disclosure relates to a capacitor potential transformer.

[0002] Known types of instrument transformers include electromagnetic transformers, in which high-voltage and low-voltage windings are wound around an iron core, and capacitor transformers, which utilize the principle of capacitance voltage division.

[0003] In an electromagnetic transformer, the high-voltage winding and the low-voltage winding are insulated, so even if a flashover occurs on the high-voltage side, the high voltage does not enter the low-voltage circuit. On the other hand, in a capacitor transformer, although the high-voltage conductor and the voltage-dividing electrode are separated from each other, it is possible that a flashover occurring between the high-voltage conductor and the voltage-dividing electrode will cause the high voltage to enter the low-voltage circuit.

[0004] Japanese Patent Application Laid-Open No. 2002-271924

[0005] An object of the present disclosure is to provide a capacitor-type potential transformer that can suppress the effects of flashover.

[0006] A capacitor-type potential transformer according to one aspect of the present disclosure comprises a cylindrical housing extending in a first direction, a first electrode extending in the first direction within the housing, a second electrode having a cylindrical shape extending coaxially with the first electrode within the housing and surrounding the first electrode, the second electrode being connected to a measuring instrument, and a shield made of a conductor and arranged within the housing insulated from the second electrode, wherein the distance between the shield and the first electrode is shorter than the distance between the second electrode and the first electrode.

[0007] According to various aspects of the present disclosure, a capacitor-type potential transformer capable of suppressing the effects of flashover is provided.

[0008] Fig. 1 is a schematic cross-sectional view showing a potential transformer according to an embodiment. Fig. 2 is an enlarged view of a main part of the potential transformer shown in Fig. 1. Fig. 3 is a diagram showing an equivalent circuit of the potential transformer shown in Fig. 1. Fig. 4 is a schematic cross-sectional view showing a potential transformer of a different form. Fig. 5 is a schematic cross-sectional view showing a potential transformer of a different form.

[0009] Hereinafter, embodiments of a capacitor-type potential transformer according to the present disclosure will be described with reference to the drawings. The numerical values, shapes, materials, etc. presented in the following description are merely examples, and various modifications are possible as long as no technical contradictions occur. Furthermore, each embodiment described below is merely an example, and various combinations are possible as long as no technical contradictions occur.

[0010] A potential transformer 1 according to one embodiment is a capacitor-type potential transformer, which is a type of potential transformer. As shown in FIG. 1 , the potential transformer 1 includes an internal electrode 10 (first electrode) extending in one direction (first direction). The internal electrode 10 according to this embodiment has a cylindrical shape and is made of a conductor such as metal. Under normal conditions, a high AC voltage (three-phase AC) of, for example, 22 to 765 / √3 kV is applied to the internal electrode 10 at a frequency of 50 Hz or 60 Hz. The potential transformer 1 is used to measure the voltage of the internal electrode 10.

[0011] As shown in FIG. 1 , the potential transformer 1 further includes a housing 20 that partially or entirely houses the internal electrode 10. The housing 20 has a cylindrical shape extending along the extension direction of the internal electrode 10, and defines a cavity therein in which the internal electrode 10 is housed. The cavity of the housing 20 is kept airtight and filled with an insulating gas. In this embodiment, the housing 20 has a cylindrical shape and is disposed coaxially with the internal electrode 10. That is, the internal electrode 10 and the housing 20 share a common axis Z. In this embodiment, the housing 20 is made of a conductor such as a metal.

[0012] As shown in FIG. 1 , the potential transformer 1 further includes a voltage-dividing electrode 30 (second electrode) housed within the housing 20. The voltage-dividing electrode 30 has a cylindrical shape extending along the extension direction of the internal electrode 10 and is disposed coaxially with the internal electrode 10, surrounding the internal electrode 10. Therefore, the voltage-dividing electrode 30 has a uniform separation distance D1 from the internal electrode 10 at any position along the extension direction of the internal electrode 10. The voltage-dividing electrode 30 can be connected to a measuring device 35 provided outside the potential transformer 1. The measuring device 35 according to this embodiment is a voltmeter, which measures the voltage of the internal electrode 10 by utilizing the principle of capacitance voltage division by measuring the voltage of the voltage-dividing electrode 30. The measuring device 35 is not limited to a voltmeter and may be, for example, a protective relay or a signal converter.

[0013] In this embodiment, the housing 20 accommodates multiple stages of voltage-dividing electrodes 30. More specifically, the housing 20 accommodates two stages of voltage-dividing electrodes 30, each consisting of a first voltage-dividing electrode 30A and a second voltage-dividing electrode 30B. By providing multiple stages of voltage-dividing electrodes 30 in this manner, it is possible to multiplex or provide redundancy to the output to the measuring device 35. The first voltage-dividing electrode 30A and the second voltage-dividing electrode 30B are adjacent to each other and aligned along the extension direction of the internal electrode 10. The first voltage-dividing electrode 30A and the second voltage-dividing electrode 30B have substantially the same shape and dimensions. The first voltage-dividing electrode 30A and the second voltage-dividing electrode 30B also have the same inner diameter, and therefore the first voltage-dividing electrode 30A and the second voltage-dividing electrode 30B are spaced the same distance D1 from the internal electrode 10. When multiple voltage-dividing electrodes 30A, 30B are accommodated in the housing 20, all of the multiple voltage-dividing electrodes 30A, 30B are connected to the measuring device 35.

[0014] In this embodiment, the voltage-dividing electrode 30 is configured to include a cylindrical main body 31 and a flange 32. In this embodiment, the flange 32 is provided on each end of the main body 31 in the extension direction of the internal electrode 10. The flange 32 extends outward in a direction perpendicular to the extension direction of the internal electrode 10. The flange 32 may be formed around the entire circumference of the voltage-dividing electrode 30, in which case it has an annular shape.

[0015] As shown in FIG. 1 , the potential transformer 1 further includes a shield 40 housed within the housing 20. The shield 40 is made of a conductor such as metal. The shield 40 is spaced apart from and insulated from the voltage-dividing electrode 30. In this embodiment, the shield 40 has a mushroom-shaped cross section extending inward in a direction perpendicular to the extension direction of the internal electrode 10. In this embodiment, the shield 40 is disposed adjacent to the voltage-dividing electrode 30 in the extension direction of the internal electrode 10. More specifically, the shield 40 is adjacent to and aligned with the voltage-dividing electrode 30 in the extension direction of the internal electrode 10. The shield 40 can be disposed around the entire circumference of the internal electrode 10 as viewed from the extension direction of the internal electrode 10. The shield 40 may be composed of a single member surrounding the entire circumference of the internal electrode 10 as viewed from the extension direction of the internal electrode 10, or may be composed of multiple members. The multiple members constituting the shield 40 can be disposed at equal angular intervals around the internal electrode 10. In the embodiment shown in FIG. 1, the shield 40 is made up of two members arranged on both sides of the internal electrode 10, but it may be made up of three or more members.

[0016] In this embodiment, the shield 40 is fixed to the voltage-dividing electrode 30. As shown in FIGS. 1 and 2 , the shield 40 and the voltage-dividing electrode 30 can be fixed together with a bolt 51 and a nut 52 that extend along the extension direction of the internal electrode 10. To insulate the shield 40 and the voltage-dividing electrode 30 from each other, an insulator 53 (first insulator) is interposed between the shield 40 and the voltage-dividing electrode 30. In the embodiment shown in FIG. 2 , a bolt 51 inserted from the shield 40 side passes through an insulating pipe 54 that penetrates between the shield 40 and the flange portion 32 of the voltage-dividing electrode 30 and reaches the voltage-dividing electrode 30 side, and a nut 52 is screwed onto the tip of the bolt 51 via an insulating washer 55. Therefore, the bolt 51 is electrically connected to the shield 40 and is insulated from the voltage-dividing electrode 30.

[0017] In this embodiment, three stages of shields 40A to 40C are provided adjacent to two stages of voltage-dividing electrodes 30 in the extension direction of the internal electrode 10. The shields 40A and 40C (first shield and second shield) are provided at positions sandwiching the two stages of voltage-dividing electrodes 30 in the extension direction of the internal electrode 10, and the shield 40B is provided between the two stages of voltage-dividing electrodes 30 in the extension direction of the internal electrode 10. The shields 40A and 40B sandwich the voltage-dividing electrode 30A in the extension direction of the internal electrode 10, and the shields 40A and 40B are fixed to the voltage-dividing electrode 30A in a manner similar to the fixing manner shown in FIG. 2. The shields 40B and 40C sandwich the voltage-dividing electrode 30B in the extension direction of the internal electrode 10, and the shields 40B and 40C are fixed to the voltage-dividing electrode 30B in a manner similar to the fixing manner shown in FIG. 2.

[0018] In this embodiment, of the three stages of shields 40A to 40C, shields 40A and 40C are joined to the housing 20 via joints 56. Joints 56 are, for example, mounting brackets and can be made entirely of a conductor such as metal, in which case electrical continuity is achieved between the housing 20 and shields 40B. Shield 40B may or may not be joined to the housing 20. The three stages of shields 40A to 40C are connected to one another by predetermined electric wires, metal plates, metal foils, etc.

[0019] In this embodiment, each shield 40 is designed to be spaced the same distance D2 from the internal electrode 10. More specifically, each shield 40 is spaced the distance D2 from the internal electrode 10 in a direction perpendicular to the extension direction of the internal electrode 10. The distance D2 between the shield 40 and the internal electrode 10 is shorter than the distance D1 between the voltage-dividing electrode 30 and the internal electrode 10 (D2<D1).

[0020] In this embodiment, a grounded ground electrode 60 (third electrode) is provided on the outer peripheral surface 31a of the main body 31 of each voltage-dividing electrode 30 (i.e., the surface opposite the internal electrode 10). An insulator 61 (second insulator) is interposed between the ground electrode 60 and the voltage-dividing electrode 30. The ground electrode 60 and the voltage-dividing electrode 30 are insulated from each other. For example, a metal foil can be used for the ground electrode 60, and a resin film can be used for the insulator 61. In this case, the ground electrode 60 and the insulator 61 are wrapped around the outer peripheral surface 31a of the main body 31 of the voltage-dividing electrode 30. The ground electrode 60 and the insulator 61 can be provided around the entire circumference of the voltage-dividing electrode 30.

[0021] The potential transformer 1 according to this embodiment can be represented by an equivalent circuit as shown in Fig. 3. In the potential transformer 1, a capacitance C1 is formed between the internal electrode 10 and the voltage-dividing electrode 30, and a capacitance C2 is formed between the voltage-dividing electrode 30 and the ground electrode 60. By employing a thin insulator 61 such as a resin film, the voltage-dividing electrode 30 and the ground electrode 60 can be brought closer together, thereby realizing a relatively large capacitance for the capacitance C2.

[0022] As described above, in the potential transformer 1, the distance D2 between the shield 40 and the internal electrode 10 is shorter than the distance D1 between the voltage-dividing electrode 30 and the internal electrode 10. Therefore, the configuration is such that a flashover is more likely to occur between the internal electrode 10 and the shield 40 than between the internal electrode 10 and the voltage-dividing electrode 30. Therefore, even in a situation where a flashover could occur between the internal electrode 10 and the voltage-dividing electrode 30, a flashover is more likely to occur between the internal electrode 10 and the shield 40. If a flashover occurs between the internal electrode 10 and the voltage-dividing electrode 30, a high voltage may enter a low-voltage circuit (e.g., a measuring instrument 35). However, by causing a flashover between the internal electrode 10 and the shield 40, such a situation can be prevented.

[0023] Furthermore, the voltage transformer 1 can also prevent high-frequency surges of several MHz or more from entering the low-voltage circuit (e.g., the measuring device 35). This is due to the ground electrode 60, which forms a relatively large capacitance C2 between the voltage dividing electrode 30 and the ground electrode 60, reducing the impedance Z between the voltage dividing electrode 30 and the measuring device 35. １ Therefore, the impedance Z associated with the capacitance C2 ２ By reducing (Z ２ <Z １ ), because high frequency surges tend to flow toward the ground electrode 60.

[0024] The potential transformer 1 is not limited to the above-described form, but may take various forms.

[0025] For example, the number of stages of the voltage-dividing electrode 30 may be three or more, or may be one stage as shown in Fig. 4. In this case, the shield 40 may be one stage or two stages as shown in Fig. 4. In Fig. 4, the shields 40A and 40B (first shield and second shield) are provided at positions sandwiching the voltage-dividing electrode 30 in the extension direction of the internal electrode 10, and are fixed to the voltage-dividing electrode 30 in the same fixing manner as that shown in Fig. 2.

[0026] Furthermore, the shield 40 does not necessarily need to be adjacent to the voltage-dividing electrode 30 in the extension direction of the internal electrode 10, and may be provided at a distance from the voltage-dividing electrode 30 as shown in FIG. 5 . In this case, the voltage-dividing electrode 30 is not fixed to the shield 40, but may be joined to the housing 20 via a joint 57 such as a mounting bracket. Because the voltage-dividing electrode 30 is insulated from the shield 40, when electrical continuity is established between the shield 40 and the housing 20, the voltage-dividing electrode 30 and the housing 20 must be insulated from each other. In the embodiment shown in FIG. 5 , the voltage-dividing electrode 30 and the housing 20 are insulated from each other by interposing an insulator 58 between the flange portion 32 of the voltage-dividing electrode 30 and the joint 57.

[0027] As can be understood from the above description, this specification discloses the following. [Supplementary Note 1] A capacitor-type potential transformer comprising: a cylindrical housing extending in a first direction; a first electrode extending in the first direction within the housing; a second electrode extending coaxially with the first electrode within the housing, having a cylindrical shape surrounding the first electrode, and connected to a measuring instrument; and a shield made of a conductor and arranged within the housing insulated from the second electrode, wherein the distance between the shield and the first electrode is shorter than the distance between the second electrode and the first electrode. [Supplementary Note 2] The capacitor-type potential transformer according to Supplementary Note 1, wherein the housing is made of a conductor and the shield is electrically connected to the housing. [Supplementary Note 3] The capacitor-type potential transformer according to Supplementary Note 1 or 2, further comprising a first insulator interposed between the shield and the second electrode, wherein the shield and the second electrode are adjacent to each other in the first direction via the first insulator. [Appendix 4] A capacitor-type potential transformer according to any one of Appendices 1 to 3, wherein the shield includes a first shield located on one end side of the second electrode in the first direction, and a second shield located on the other end side of the second electrode in the first direction. [Appendix 5] A capacitor-type potential transformer according to any one of Appendices 1 to 4, wherein the shield surrounds the first electrode when viewed from the first direction. [Appendix 6] A capacitor-type potential transformer according to Appendices 5, wherein the shield is composed of one shield surrounding the entire circumference of the first electrode when viewed from the first direction, or a plurality of shields arranged at equal angular intervals. [Appendix 7] A capacitor-type potential transformer according to any one of Appendices 1 to 6, comprising a plurality of stages of the second electrodes arranged along the first direction. [Appendix 8] A capacitor-type potential transformer according to any one of Appendices 1 to 7, further comprising a third electrode provided on the outer circumferential surface of the second electrode via a second insulator, and grounded. [Appendix 9] The capacitor-type potential transformer according to Appendix 8, wherein the second insulator is a resin film wrapped around the outer peripheral surface of the second electrode.

[0028] 1...instrument transformer, 10...internal electrode, 20...casing, 30, 30A, 30B...voltage dividing electrode, 40, 40A, 40B, 40C...shield, 53...first insulator, 60...ground electrode, 61...second insulator

Claims

1. A capacitor-type potential transformer comprising: a cylindrical housing extending in a first direction; a first electrode extending in the first direction within the housing; a second electrode extending coaxially with the first electrode within the housing and having a cylindrical shape surrounding the first electrode, the second electrode being connected to a measuring instrument; and a shield made of a conductor and arranged within the housing insulated from the second electrode, wherein the distance between the shield and the first electrode is shorter than the distance between the second electrode and the first electrode.

2. A capacitor-type potential transformer as claimed in claim 1, wherein the housing is made of a conductor and the shield is electrically connected to the housing.

3. A capacitor-type potential transformer as claimed in claim 1, further comprising a first insulator interposed between said shield and said second electrode, said shield and said second electrode being adjacent to each other in said first direction with said first insulator interposed therebetween.

4. A capacitor-type potential transformer as claimed in claim 1, wherein the shield includes a first shield located on one end side of the second electrode in the first direction, and a second shield located on the other end side of the second electrode in the first direction.

5. A capacitor-type potential transformer according to claim 1, wherein said shield surrounds said first electrode when viewed from said first direction.

6. A capacitor-type potential transformer as claimed in claim 5, wherein the shield is composed of one or more shields arranged at equal angular intervals surrounding the entire periphery of the first electrode when viewed from the first direction.

7. A capacitor-type potential transformer according to claim 1, comprising a plurality of stages of the second electrodes arranged along the first direction.

8. A capacitor-type potential transformer as claimed in claim 1, further comprising a third electrode provided on the outer peripheral surface of said second electrode via a second insulator and grounded.

9. A capacitor-type potential transformer according to claim 8, wherein the second insulator is a resin film wrapped around the outer circumferential surface of the second electrode.

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