Capacitor voltage transformer

Abstract

According to the present invention, a capacitor voltage transformer is configured such that elongation of a voltage-dividing electrode in the extension direction of an internal electrode is restricted by a shield that sandwiches and holds the voltage-dividing electrode. As a result, the present invention does not readily experience changes in output voltage caused by thermal deformation of the voltage-dividing electrode, can achieve a more accurate output voltage, and can thereby achieve high measurement accuracy and low ratio error. In addition, the shield, which is joined to a housing, can undergo thermal deformation so as to undergo elongation in the extension direction of the internal electrode. When the shield elongates, force along the extension direction of the internal electrode is applied to the voltage-dividing electrode from the shield, further suppressing elongation of the voltage-dividing electrode in the extension direction of the internal electrode.

Description

Capacitor-type voltage transformer

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

[0002] A well-known type of instrument transformer is a capacitor-type transformer that uses the principle of capacitance voltage division. With a capacitor-type transformer, the voltage of a high-voltage conductor can be measured by measuring the output voltage from the voltage dividing electrode facing the high-voltage conductor.

[0003] Japanese Patent Application Laid-Open No. 2002-271924

[0004] If the voltage dividing electrodes of a capacitor-type transformer are thermally deformed, a change in output voltage may occur due to the thermal deformation. Therefore, suppressing the thermal deformation can improve measurement accuracy.

[0005] An object of the present disclosure is to provide a capacitor-type potential transformer with improved measurement accuracy.

[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, a first shield joined to the housing and positioned on one end side of the second electrode in the first direction, and a second shield joined to the housing and positioned on the other end side of the second electrode in the first direction, the first shield and second shield holding the second electrode so as to sandwich it in the first direction.

[0007] According to various aspects of the present disclosure, a capacitor potential transformer with improved measurement accuracy is provided.

[0008] Fig. 2 is a schematic cross-sectional view showing a potential transformer according to an embodiment. Fig. 3 is an enlarged view of a main part of the potential transformer shown in Fig. 1. Fig. 4 is a diagram showing an equivalent circuit of the potential transformer shown in Fig. 1. Fig. 5 is a diagram showing a schematic thermal deformation of a voltage dividing electrode. Fig. 6 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 in the extension direction of the internal electrode 10, and is disposed coaxially with the internal electrode 10 to surround it. 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, and 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 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.

[0014] 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. Specifically, as shown in the cross section of FIG. 2 , the shield 40 has a stem portion 41 extending perpendicular to the extension direction of the internal electrode 10 and an umbrella portion 42 located at the inner end and wider than the stem portion 41. The shield 40 is disposed adjacent to the voltage-dividing electrode 30 in the extension direction of the internal electrode 10, and the umbrella portion 42 partially covers the voltage-dividing electrode 30 in the extension direction of the stem portion 41 (the left-right direction in FIG. 2 ). 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 arranged around the entire periphery of the internal electrode 10 when viewed from the extension direction of the internal electrode 10. The shield 40 may be composed of one member that surrounds the entire periphery of the internal electrode 10 when viewed from the extension direction of the internal electrode 10, or may be composed of multiple members. The multiple members that make up the shield 40 can be arranged at equal angular intervals around the internal electrode 10. In the embodiment shown in FIG. 1 , the shield 40 is composed of two members arranged on both sides of the internal electrode 10, but it may also be composed of three or more members.

[0015] In this embodiment, two stages of shields 40A and 40B are provided adjacent to the voltage-dividing electrode 30 in the extension direction of the internal electrode 10. The shield 40A (first shield) is arranged on one end side (upper side in the embodiment shown in FIG. 1 ) of the voltage-dividing electrode 30 in the extension direction of the internal electrode 10, and the shield 40B (second shield) is arranged on the other end side (lower side in the embodiment shown in FIG. 1 ) of the voltage-dividing electrode 30 in the extension direction of the internal electrode 10. The shields 40A and 40B hold the voltage-dividing electrode 30 so as to sandwich it therebetween in the extension direction of the internal electrode 10.

[0016] In this embodiment, both shields 40A and 40B are fixed to the voltage-dividing electrode 30. Taking the shield 40A as an example, the shield 40A and the voltage-dividing electrode 30 can be fixed with a bolt 51 and a nut 52 extending along the extension direction of the internal electrode 10, as shown in FIGS. 1 and 2 . To insulate the shield 40A from the voltage-dividing electrode 30, an insulator 53 (first insulator) is interposed between the shield 40A and the voltage-dividing electrode 30. In the embodiment shown in FIG. 2 , a bolt 51 inserted from the shield 40A side passes through an insulating pipe 54 that penetrates between the shield 40A 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 40A and is insulated from the voltage-dividing electrode 30. The shield 40B is also fixed to the voltage-dividing electrode 30 in the same manner as the shield 40A.

[0017] In this embodiment, both shields 40A and 40B 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 the shields 40A and 40B. The two-stage shields 40A and 40B are connected to each other by a predetermined electric wire, metal plate, metal foil, or the like.

[0018] In this embodiment, a grounded ground electrode 60 (third electrode) is provided on the outer peripheral surface 31a of the main body 31 of the 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 periphery of the voltage-dividing electrode 30.

[0019] 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.

[0020] Here, thermal deformation of the voltage-dividing electrode 30 will be described. The voltage-dividing electrode 30 may undergo thermal deformation (expansion) as the temperature rises. In the cylindrical voltage-dividing electrode 30, thermal deformation such as expansion in the extension direction of the internal electrode 10 may occur, as shown in FIG. 4. When such thermal deformation occurs, the area facing the internal electrode 10 expands, causing changes in the electric field and capacitance C1, and as a result, the output voltage output from the voltage-dividing electrode 30 to the measuring instrument 35 changes.

[0021] In the potential transformer 1 according to this embodiment, the shields 40A and 40B that hold the voltage dividing electrode 30 in a sandwiched manner limit the extension of the voltage dividing electrode 30 in the extension direction of the internal electrode 10. As a result, in the potential transformer 1, changes in the output voltage due to thermal deformation of the voltage dividing electrode 30 are less likely to occur, and a more accurate output voltage can be obtained, thereby achieving high measurement accuracy and low ratio error.

[0022] In addition, the shields 40A, 40B joined to the housing 20 may also undergo thermal deformation such that they expand in the extension direction of the internal electrode 10, as shown in FIG. 4 . In this case, a force is applied from the shields 40A, 40B to the voltage-dividing electrode 30 along the extension direction of the internal electrode 10, further suppressing the expansion of the voltage-dividing electrode 30 in the extension direction of the internal electrode 10. The umbrella portions 42 located at the inner ends of the shields 40A, 40B may also undergo thermal deformation such that they expand in the extension direction of the internal electrode 10. In this case, the area of ​​the voltage-dividing electrode 30 exposed from the shields 40A, 40B to the internal electrode 10 is reduced, thereby reducing the area of ​​the voltage-dividing electrode 30 that is capacitively coupled to the internal electrode 10. Due to the expansion of the umbrella portions 42 of the shields 40A, 40B, an expansion of the area of ​​the voltage-dividing electrode 30 that is capacitively coupled to the internal electrode 10 is suppressed, even when the voltage-dividing electrode 30 expands in the extension direction of the internal electrode 10.

[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 voltage-dividing electrode 30 may have multiple stages, as shown in FIG. 5 . In the embodiment shown in FIG. 5 , the voltage-dividing electrode 30 is configured with two stages: a first voltage-dividing electrode 30A and a second voltage-dividing electrode 30B. By configuring the voltage-dividing electrode 30 in multiple stages, it is possible to multiplex or make redundant 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. When multiple voltage-dividing electrodes 30A, 30B are housed in the housing 20, all of the multiple voltage-dividing electrodes 30A, 30B are connected to the measuring device 35.

[0026] In the embodiment shown in Fig. 5, 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.

[0027] 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. Shield 40B may or may not be joined to the housing 20. The three stages of shields 40A to 40C are electrically connected to one another by predetermined electric wires, metal plates, metal foils, etc.

[0028] 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 and having a cylindrical shape surrounding the first electrode, the second electrode being connected to a measuring instrument; a first shield joined to the housing and arranged on one end side of the second electrode in the first direction; and a second shield joined to the housing and arranged on the other end side of the second electrode in the first direction, the first shield and the second shield holding the second electrode so as to sandwich the second electrode in the first direction. [Supplementary Note 2] The capacitor-type potential transformer according to Supplementary Note 1, wherein the housing, the first shield, and the second shield are made of conductors, and the first shield and the second shield are electrically connected to the housing. [Supplementary Note 3] The capacitor-type potential transformer according to Supplementary Note 2, further comprising a first insulator interposed between the first shield and the second shield and the second electrode, wherein the first shield and the second shield and the second electrode are adjacent to each other in the first direction via the first insulator. [Supplementary Note 4] The capacitor-type potential transformer according to any one of Supplements 1 to 3, wherein both the first shield and the second shield surround the first electrode when viewed from the first direction. [Supplementary Note 5] The capacitor-type potential transformer according to Supplementary Note 4, wherein both the first shield and the second shield are composed of one shield surrounding the entire circumference of the first electrode or a plurality of shields arranged at equal angular intervals when viewed from the first direction. [Supplementary Note 6] The capacitor-type potential transformer according to any one of Supplements 1 to 5, comprising the second electrode in a plurality of stages lined up along the first direction. [Appendix 7] The capacitor-type potential transformer according to any one of Appendices 1 to 6, further comprising a third electrode that is provided on an outer peripheral surface of the second electrode via a second insulator and is grounded. [Appendix 8] The capacitor-type potential transformer according to Appendices 7, wherein the second insulator is a resin film wrapped around the outer peripheral surface of the second electrode.

[0029] 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 within the housing in the first direction; 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; a first shield joined to the housing and positioned on one end side of the second electrode in the first direction; and a second shield joined to the housing and positioned on the other end side of the second electrode in the first direction, the first shield and the second shield holding the second electrode in such a way that they sandwich the second electrode in the first direction.

2. A capacitor-type potential transformer as claimed in claim 1, wherein the housing, the first shield and the second shield are constructed of conductors, and the first shield and the second shield are electrically connected to the housing.

3. A capacitor-type potential transformer as described in claim 2, further comprising a first insulator interposed between the first and second shields and the second electrode, and the first and second shields and the second electrode are adjacent to each other in the first direction via the first insulator.

4. A capacitor-type potential transformer as claimed in claim 1, wherein said first shield and said second shield both surround said first electrode when viewed from said first direction.

5. A capacitor-type potential transformer as described in claim 4, wherein the first shield and the second shield are each 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.

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

7. 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.

8. A capacitor-type potential transformer according to claim 7, wherein the second insulator is a resin film wrapped around the outer circumferential surface of the second electrode.