Vacuum circuit breaker

Abstract

This vacuum circuit breaker comprises: a fixed electrode (22); a movable electrode (24); a cylindrical first insulating container (26) that covers the fixed electrode (22) and a fixed electrode rod (21), and that has a protruding part on the entire outer periphery thereof; a cylindrical second insulating container (27) that covers the movable electrode (24) and a movable electrode rod (23), and that has a protruding part on the entire outer periphery thereof; a first metal shield (28) that joins the first insulating container (26) and the second insulating container (27), and that captures a metal vapor generated between the fixed electrode (22) and the movable electrode (24) during current interruption; a second metal shield (29) that is joined to a first side surface of the protruding part of the first insulating container (26) and to a first side surface of the protruding part of the second insulating container (27), and that has the same potential as that of the first metal shield (28); a third metal shield (31) that is joined to a second side surface of the protruding part of the first insulating container (26) and to the bottom surface of the first insulating container (26); and a fourth metal shield (30) that is joined to a second side surface of the protruding part of the second insulating container (27) and to the bottom surface of the second insulating container (27).

Description

Vacuum circuit breaker

[0001] The present disclosure relates to a vacuum interrupter.

[0002] A vacuum circuit breaker has a vacuum valve mounted inside a grounded tank as a current switching unit. The vacuum valve includes a ceramic insulating container, an intermediate shield, a fixed electrode, a movable electrode, and a bellows. A pair of electrodes is provided inside the cylindrical ceramic insulating container, and the fixed electrode and movable electrode are opened and closed by the expansion and contraction of the bellows while maintaining internal airtightness.

[0003] In recent years, development of higher voltage vacuum circuit breakers has progressed. To accommodate this trend, the configuration of vacuum interrupters has also been studied. For example, from the perspective of ease of manufacture, a vacuum interrupter has been commercialized in which the ceramic insulating vessel inside the vacuum interrupter is divided into two axially, with an electrically floating cylindrical metal (middle shield) placed between the two ceramic insulating vessels.

[0004] When a fault current is interrupted, the ideal potential distribution within a vacuum interrupter is 100% on the application side electrode, 50% on the middle shield, and 0% on the ground side electrode. However, when considering the influence of the grounded tank located around the vacuum interrupter, which has a potential of 0%, and the stray capacitance that exists between the vacuum interrupter and the grounded tank, the potential of the middle shield of the vacuum interrupter drops to about 30%. As a result, the potential inside the vacuum interrupter is biased toward the application side electrode, and the electric field strength inside the vacuum interrupter increases, which causes the vacuum interrupter and vacuum circuit breaker to become larger.

[0005] In order to miniaturize the vacuum interrupter, Patent Document 1 connects two capacitors with the same capacitance in series and then connects them in parallel to a pair of electrodes. By arranging the two capacitors, the stray capacitance between the application electrode and the middle shield, and between the middle shield and the ground electrode, is controlled, and the middle shield potential approaches the ideal 50%, thereby alleviating the electric field inside the vacuum interrupter and achieving miniaturization.

[0006] Patent No. 836239

[0007] When applying a capacitor to improve the potential distribution of the middle shield to a vacuum interrupter compatible with high voltage, multiple capacitors are connected in series to a pair of electrodes external to the vacuum interrupter. Since attaching capacitors to the vacuum interrupter increases the number of parts and complicates the manufacturing process, a vacuum circuit breaker is desired that is equipped with a vacuum interrupter in which the potential distribution of the middle shield approaches the ideal middle shield potential of 50% while optimizing the number of parts and simplifying the manufacturing process.

[0008] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a vacuum circuit breaker equipped with a vacuum valve in which the potential distribution of the middle shield approaches the ideal middle shield potential of 50%, while optimizing the number of parts and simplifying the manufacturing process.

[0009] The present disclosure comprises a cylindrical first insulating container that covers the fixed electrode and the fixed electrode rod and has a convex portion on the entire outer periphery; a cylindrical second insulating container that covers the movable electrode and the movable electrode rod and has a convex portion on the entire outer periphery; a first metal shield that joins the first insulating container and the second insulating container and captures metal vapor generated between the fixed electrode and the movable electrode when current is interrupted; a second metal shield that is joined to a first side surface of the convex portion of the first insulating container and to the first side surface of the convex portion of the second insulating container and has the same potential as the first metal shield; a third metal shield that is joined to a second side surface of the convex portion of the first insulating container and to the bottom surface of the first insulating container; and a fourth metal shield that is joined to a second side surface of the convex portion of the second insulating container and to the bottom surface of the second insulating container.

[0010] According to the present disclosure, by forming a convex portion on the outer peripheral surface of the insulating container of the vacuum interrupter and joining the middle shield to two side surfaces of the convex portion, it is possible to provide a vacuum interrupter in which the middle shield's potential distribution approaches the ideal middle shield potential of 50%. Furthermore, because no capacitor is used, the number of parts is optimized and manufacturing work is simplified.

[0011] Fig. 3 is an external view of a vacuum circuit breaker according to a first embodiment. Fig. 4 is a cross-sectional view showing the configuration of a vacuum interrupter stored in a tank constituting the vacuum circuit breaker according to the first embodiment. Fig. 5 is a cross-sectional schematic view of the AA cross section of Fig. 2 according to the first embodiment. Fig. 6 is an equivalent circuit diagram of the vacuum interrupter according to the first embodiment. Fig. 7 is a distribution diagram of the potential sharing of a metal shield in the vacuum interrupter according to the first embodiment.

[0012] First Embodiment. Figure 1 is an external view of a vacuum circuit breaker 100 according to a first embodiment. The vacuum circuit breaker 100 includes a cylindrical tank 10, two porcelain tubes 11 and 12 standing vertically at the top of the tank 10, an operating device 13, two pipes 14 and 15 standing vertically at the bottom of the tank 10, and two current transformers 16 and 17. The tank 10 is supported by a stand 18 standing on an installation surface. The X-axis, Y-axis, and Z-axis in the figure are three axes perpendicular to each other, and the X-axis and Y-axis are horizontal axes. The Z-axis is a vertical axis.

[0013] 2 is a cross-sectional view of a vacuum interrupter 20 housed in a tank 10 constituting a vacuum circuit breaker 100 according to a first embodiment. The vacuum interrupter 20 includes a fixed electrode rod 21, a fixed electrode 22, a movable electrode rod 23, a movable electrode 24, a bellows 25, insulating containers 26 and 27, and metal shields 28, 29, 30, and 31. In the coordinate axes in the figure, the direction of the X-axis arrow represents the positive side of the X-axis, and the direction 180° opposite to the X-axis arrow represents the negative side of the X-axis. The direction of the Z-axis arrow represents the positive side of the Z-axis, and the direction 180° opposite to the Z-axis arrow represents the negative side of the Z-axis. A vacuum is maintained inside the insulating containers 26 and 27. The opening and closing operation of the fixed electrode 22 and the movable electrode 24 is performed in a vacuum-tight state via bellows 25. When the movable electrode rod 23 moves to the negative side in the X-axis direction, the movable electrode 24 is pulled away from the fixed electrode 22, and when the movable electrode rod 23 moves to the positive side in the X-axis direction, the movable electrode 24 comes into contact with the fixed electrode 22.

[0014] FIG. 3 is a schematic cross-sectional view of the AA section of FIG. 2 as viewed from the negative side in the X-axis direction.

[0015] The insulating container 26 is a cylinder that covers the movable electrode rod 23 and the movable electrode 24 and has a convex portion integrally formed around the entire outer periphery. The convex portion rises in the Z-axis direction from the outer periphery of the insulating container 26, and the upper surface of the convex portion is a curved surface that is parallel to the outer periphery of the insulating container 26. The rising position of the convex portion is not limited, as it depends on the shapes of the metal shield 28 and the bellows 25. The insulating container 26 is made of an insulating material such as ceramic.

[0016] The insulating container 27 covers the fixed electrode rod 21 and the fixed electrode 22, and is a cylinder with a convex portion integrally formed around the entire outer periphery on its outer periphery, and has the same shape as the insulating container 26. The convex portion rises in the Z-axis direction from the outer periphery of the insulating container 27, and the upper surface of the convex portion is a curved surface parallel to the outer periphery of the insulating container 27. The rising position of the convex portion is not limited, as it depends on the shapes of the metal shield 28 and the bellows 25. The insulating container 27 is made of an insulating material such as ceramic.

[0017] The metal shield 28 is a metal tube that joins the insulating containers 26 and 27 and covers the fixed electrode 22 and the movable electrode 24. It captures metal vapor that is generated between the fixed electrode 22 and the movable electrode 24 when a fault current is interrupted, and prevents a deterioration in the insulating performance of the inner surfaces of the insulating containers 26 and 27.

[0018] The metal shield 29 is disposed outside the outer peripheral surface of the metal shield 28. The metal shield 29 is joined to the convex side surface 26a of the insulating container 26, the outer peripheral surface 26c of the insulating container 26, the outer peripheral surface 27c of the insulating container 27, and the convex side surface 27b of the insulating container 27. As shown by the dotted square in Figure 2, in order to reduce the possibility of discharge due to electric field concentration at the end of the metal shield 29, the metal shield 29 covers the convex ends of the insulating containers 26 and 27, and the shape of the end of the metal shield 29 covering the convex ends of the insulating containers 26 and 27 is rounded. The metal shield 29 is at the same potential as the metal shield 28.

[0019] The metal shield 30 joins the side surface 27a of the convex portion of the insulating container 27, the outer peripheral surface 27d of the insulating container 27, and the bottom surface 27e of the insulating container 27. In order to reduce the possibility of discharge due to electric field concentration at the end of the metal shield 30, the metal shield 30 covers the end of the convex portion of the insulating container 27 on the + side in the X-axis direction, and the shape of the end of the metal shield 30 covering the end of the convex portion of the insulating container 27 is rounded.

[0020] The metal shield 31 joins the side surface 26b of the convex portion of the insulating container 26, the outer peripheral surface 26d of the insulating container 26, and the bottom surface 26e of the insulating container 26. In order to reduce the possibility of discharge due to electric field concentration at the end of the metal shield 31, the metal shield 31 covers the end of the convex portion of the insulating container 26 on the negative side in the X-axis direction, and the end of the metal shield 31 covering the end of the convex portion of the insulating container 26 is rounded.

[0021] Fig. 4 is an equivalent circuit diagram of the vacuum interrupter 20 according to the first embodiment. In Fig. 4, Cg is the capacitance between the fixed electrode 22 and the movable electrode 24 when the electrodes are open, Cm is the capacitance between the metal shield 28 and the movable electrode 24, Cs is the capacitance between the metal shield 28 and the fixed electrode 22, Cf is the capacitance between the metal shield 28 and the tank 10, Cr1 is the capacitance in a structure in which the insulating container 26 is sandwiched between the metal shields 29 and 31, and Cr2 is the capacitance in a structure in which the insulating container 27 is sandwiched between the metal shields 29 and 30. The capacitances of Cm and Cs are equal, and the capacitances of Cr1 and Cr2 are equal.

[0022] Based on FIG. 4 , the potential distribution of the metal shield 28 is expressed by the following equation (1). Since the capacitances of Cr1 and Cr2 are equal, and the capacitances of Cm and Cs are equal, we can rewrite them as Cr1 = Cr2 = Cr and Cm = Cs = Cms, and the first term on the right-hand side of equation (1) can be rewritten as the second term on the right-hand side. Cr on the right-hand side of equation (1) is expressed by the following equation (2). ε0 is the dielectric constant of a vacuum, εr is the relative dielectric constant of the insulating container 26 sandwiched between the metal shields 29 and 31, r1 is the distance from the central axis of the electrode to the top surface of the convex portion of the insulating container 26 as shown in FIG. 3 , r2 is the distance from the central axis of the electrode to the outer peripheral surface of the insulating container 26 as shown in FIG. 3 , and d is the distance in the X-axis direction from the top surface of the convex portion of the insulating container 26 as shown in FIG. 2 .

[0023]

[0024]

[0025] A conventional vacuum interrupter has a pair of electrodes disposed inside a cylindrical insulating container, with a metal shield surrounding the pair of electrodes. The structure of the conventional vacuum interrupter differs from vacuum interrupter 20 according to the first embodiment in that it does not include the protrusions on insulating containers 26 and 27 and the metal shields 29-31. Therefore, the potential distribution of metal shield 28 in the conventional vacuum interrupter structure is expressed by the following equation (3). As in equation (1), since the electrostatic capacitances of Cm and Cs are equal, we can rewrite it as Cm = Cs = Cms, and the first term on the right-hand side of equation (3) can be rewritten as the second term on the right-hand side:

[0026]

[0027] The magnitude relationship between V1 and V2 is expressed by the following equation (4): Vacuum interrupter 20 differs from conventional vacuum interrupters in that the two side surfaces of the convex portion of insulating container 26 are joined by metal shields 29, 31, and the two side surfaces of the convex portion of insulating container 27 are joined by metal shields 29, 30. Therefore, the potential share V1 of metal shield 28 in the structure of vacuum interrupter 20 is greater than the potential share V2 of metal shield 28 in the structure of conventional vacuum interrupters, and approaches the ideal middle shield potential of 50%.

[0028]

[0029] 5 shows the relationship between the potential distribution of the metal shield 28 and the relative dielectric constant εr of the insulating container. The solid line shows the potential distribution of the metal shield 28 in the vacuum interrupter 20, and the dotted line shows the potential distribution of the metal shield 28 in a conventional vacuum interrupter. When the insulating container is made of ceramic and Cms, Cf, r1, r2, and d are arbitrarily entered into equation (1), the potential distribution of the metal shield 28 in the vacuum interrupter 20 becomes greater than the potential distribution of the metal shield 28 in the conventional vacuum interrupter structure, approaching the ideal middle shield potential of 50%.

[0030] The vacuum interrupter 20 according to the first embodiment differs from the conventional vacuum interrupter in that the two side surfaces of the convex portion of the insulating container 26 are joined by metal shields 29 and 31, and the two side surfaces of the convex portion of the insulating container 27 are joined by metal shields 29 and 30. By adopting the structure of the vacuum interrupter 20, the ideal intermediate shield potential of 50% can be achieved without the need for the capacitor described in Patent Document 1. Furthermore, because the insulating containers 26 and 27 are made of the same material as the insulating containers used in conventional vacuum interrupters, the metal shields 29 to 31 are made of the same material as the metal shield 28, and the vacuum interrupter 20 does not use a capacitor, the number of parts is optimized and assembly is simplified.

[0031] 10 tank, 11, 12 porcelain tube, 13 operating device, 14, 15 tube, 16, 17 variable coil, 100 vacuum circuit breaker.

Claims

1. A fixed electrode connected to a fixed electrode rod serving as a current-carrying medium; a movable electrode that can be separated from and brought into contact with the fixed electrode by movement of a movable electrode rod serving as a current-carrying medium in the direction of the central axis of the fixed electrode; a first insulating container that covers the fixed electrode rod and the fixed electrode and has a convex portion along the entire outer periphery on its outer periphery; a second insulating container that covers the movable electrode rod and the movable electrode and has a convex portion along the entire outer periphery on its outer periphery, and is arranged side by side with the first insulating container in the direction of the central axis; a first metal shield that joins the first insulating container and the second insulating container, covers the fixed electrode and the movable electrode, and captures metal vapor that is generated when current is interrupted; a second metal shield that is arranged outside the outer periphery of the first metal shield and joins a first side surface of the convex portion of the first insulating container and a first side surface of the convex portion of the second insulating container that face the convex portions of the first insulating container and the second insulating container, and has the same potential as the first metal shield; a third metal shield joined to the second side surface of the protrusion of the first insulating container and to the bottom surface of the first insulating container; and a fourth metal shield joined to the second side surface of the protrusion of the second insulating container and to the bottom surface of the second insulating container.

2. A vacuum circuit breaker as described in claim 1, wherein the convex portion of the first insulating container and the convex portion of the second insulating container rise vertically from the outer peripheral surface, and the upper surfaces of the convex portions are curved surfaces parallel to the outer peripheral surface.

3. A vacuum circuit breaker as described in claim 1, wherein the second metal shield covers the convex end of the first insulating container and the convex end of the second insulating container, and the two ends of the second metal shield covering the two convex ends are rounded.

4. A vacuum circuit breaker as claimed in claim 1, wherein the third metal shield covers the end of the convex portion of the first insulating container, and the end of the third metal shield covering the end of the convex portion is rounded.

5. A vacuum circuit breaker as described in claim 1, wherein the fourth metal shield covers the end of the convex portion of the second insulating container, and the end of the fourth metal shield covering the end of the convex portion is rounded.

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