Surge protective element

Abstract

To provide a surge protective element capable of reducing damage caused by surges and suppressing fluctuation in discharge start voltage.SOLUTION: A surge protective element includes: an insulating tube 2; a pair of sealing electrodes 3 that close off both end openings of the insulating tube to seal a discharge control gas in the interior thereof; a pair of discharge electrodes 4 in which base ends are in contact with inner surfaces of the sealing electrodes and tips protrude into the insulating tube and face each other; and an insulating member 5 sandwiched between tip surfaces of the pair of discharge electrodes and accommodated inside the insulating tube. The insulating member has a columnar shape having an axial line orthogonal to an axial line of the insulating tube, and groove portions 5a extending along the axial line of the insulating member are formed in an outer circumferential surface exposed between the pair of discharge electrodes.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a surge protection element used to protect various devices from surges generated by lightning strikes and the like, and to prevent accidents before they occur. [Background technology]

[0002] Surge protection elements are connected to parts of electronic equipment for communication devices such as telephones, facsimiles, and modems that are susceptible to electrical shock from abnormal voltages (surge voltages) such as lightning surges and static electricity, such as where they connect to communication lines, power lines, antennas, or CRT drive circuits, in order to prevent destruction by thermal damage or fire of the electronic equipment or the printed circuit boards on which it is mounted due to abnormal voltages.

[0003] Conventionally, a surge absorber has been known as a surge protection element, in which a discharge element is made up of a ceramic insulator in which a conductive film formed on the surface is divided in the middle to provide one or more discharge gaps (microgaps), and a pair of cap electrodes (discharge electrodes) provided at both ends of the insulator, and the discharge element is sealed in a glass tube with a pair of sealing electrodes (see, for example, Patent Document 1). In such surge protection elements, a conductive film is formed as an electrode film, and the thin conductive film locally enhances the surrounding electric field, thereby working in favor of a response voltage to a surge. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-153565 Summary of the Invention [Problem to be solved by the invention]

[0005] The above conventional techniques still have the following problems. In the above-mentioned conventional surge protection elements, the electrode film is formed by forming a conductive film several to several tens of micrometers using film-forming techniques such as thick-film printing or sputtering. However, because the thickness is thin, there is a risk that the conductive film will melt and shatter, making it unable to maintain its function when a high-intensity surge or repeated surges are applied. Furthermore, conductive debris such as metals scattered from the discharge electrode and adhering to the outer surface of the insulator significantly disrupts the electric field distribution, causing fluctuations in the discharge inception voltage Vs, making it impossible to maintain a stable discharge inception voltage Vs.

[0006] The present invention has been made in view of the above-mentioned problems, and has as its object to provide a surge protection element that can reduce damage caused by surges and suppress fluctuations in discharge start voltage. [Means for solving the problem]

[0007] The present invention employs the following configuration to solve the above problems: That is, a surge protection element of a first invention includes an insulating tube, a pair of sealed electrodes that close open ends of the insulating tube to seal a discharge control gas inside, a pair of discharge electrodes whose base ends contact the inner surface of the sealed electrodes and whose tip ends protrude into the insulating tube and face each other, and an insulating member that is sandwiched between tip surfaces of the pair of discharge electrodes and housed in the insulating tube, wherein the insulating member is columnar with an axis perpendicular to the axis of the insulating tube, and has a groove that extends along the axis of the insulating member on its outer peripheral surface exposed between the pair of discharge electrodes.

[0008] In this surge protection device, the insulating member is columnar with an axis perpendicular to the axis of the insulating tube, and a groove extending along its axis is formed on the outer peripheral surface exposed between the pair of discharge electrodes. Therefore, even if conductive debris from the discharge electrodes generated by surge discharge adheres to the outer peripheral surface of the insulating member, it is less likely to adhere to the groove and is separated and divided by the groove. Therefore, the conductive debris adheres to the dispersed area, which is separated and divided into smaller areas, resulting in less disturbance of the electric field distribution and suppressing fluctuations in the discharge start voltage Vs after surge life testing. Furthermore, the use of a conductive discharge electrode increases heat capacity and reduces thermal resistance compared to a thin conductive film, improving surge durability and suppressing fluctuations in the discharge start voltage.

[0009] A surge protection element according to a second invention is the surge protection element of the first invention, characterized in that the insulating member has a plurality of the grooves. In other words, in this surge protection element, the insulating member has multiple grooves, so even if conductive debris adheres to the outer surface of the insulating member, the multiple grooves divide and separate the scattering area into multiple areas, making each scattering area even smaller.

[0010] The surge protection element according to the third invention is the second invention, characterized in that the insulating member has a gear-shaped cross section with a plurality of the grooves equally spaced circumferentially. In other words, in this surge protection element, the insulating member is formed in a gear-like cross section with multiple grooves equally spaced circumferentially, so that when the insulating member is inserted between a pair of discharge electrodes inside the insulating tube, it is easy to expose the multiple grooves between the pair of discharge electrodes, eliminating the need for positioning during assembly.

[0011] The surge protection element according to the fourth invention is characterized in that, in the third invention, the insulating member is formed in a gear-like cross section with eight of the groove portions equally spaced circumferentially. That is, in this surge protection device, the insulating member has a gear-shaped cross section with eight grooves evenly spaced around the circumference, and therefore has eight teeth on its outer circumferential surface, and two adjacent teeth of the eight teeth abut against the opposing discharge electrodes, thereby stably positioning the insulating member between the pair of discharge electrodes. Also, three grooves are exposed on each side of the outer circumferential surface exposed between the pair of discharge electrodes, which makes it possible to divide and separate the scattering region into three.

[0012] The surge protection element of the fifth invention is characterized in that, in the first or second invention, the outer diameter of the insulating member is smaller than the outer diameter of the discharge electrodes, and areas are formed on both sides of the insulating member where the tip surfaces of the pair of discharge electrodes directly face each other. That is, in this surge protection element, the outer diameter of the insulating member is made smaller than the outer diameter of the discharge electrodes, and an area is formed on both sides of the insulating member where the tip faces of a pair of discharge electrodes directly face each other, so that a discharge path is formed on both sides of the insulating member, making it easier for arc discharge to propagate between the pair of discharge electrodes. [Effects of the Invention]

[0013] According to the present invention, the following effects are achieved. That is, in the surge protection element according to the present invention, the insulating member is columnar with an axis perpendicular to the axis of the insulating tube, and a groove extending along its own axis is formed on the outer surface exposed between the pair of discharge electrodes, so that there is little disturbance in the electric field distribution, fluctuations in the discharge inception voltage Vs after a surge life test can be suppressed, and durability against surges is improved. Therefore, the surge protection element of the present invention can improve the surge breakdown resistance and surge characteristic resistance. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a front view showing a surge protection element with a portion broken away in one embodiment of the surge protection element according to the present invention. [Figure 2]10 is an explanatory diagram showing a scattering region of conductive debris on an insulating member disposed between a pair of discharge electrodes in the present embodiment. FIG. [Figure 3] 2 is a side view showing a surge protection element with a portion broken away in the present embodiment. FIG. [Figure 4] FIG. 2 is a perspective view showing an insulating member disposed between a pair of discharge electrodes in the present embodiment. [Figure 5] 10 is a graph showing the change in discharge start voltage Vs with respect to the number of life tests in an example of a surge protection element according to the present invention. [Figure 6] 10 is a graph showing the change in discharge start voltage Vs with respect to the number of life tests in a comparative example of a surge protection element according to the present invention. [Figure 7] 4A and 4B are images showing the outer circumferential surface of the insulating member after a life test in an example (a) of the surge protection element according to the present invention and a comparative example (b). DETAILED DESCRIPTION OF THE INVENTION

[0015] An embodiment of a surge protection element according to the present invention will be described below with reference to Figures 1 to 4. Note that the scale of each drawing used in the following description has been changed appropriately so that each component can be recognized or easily recognized.

[0016] As shown in Figures 1 to 4, the surge protection element 1 of this embodiment comprises an insulating tube 2, a pair of sealed electrodes 3 that close the openings at both ends of the insulating tube 2 and seal the discharge control gas inside, a pair of discharge electrodes 4 whose base ends contact the inner surface of the sealed electrodes 3 and whose tips protrude into the insulating tube 2 and face each other, and an insulating member 5 that is sandwiched between the tip surfaces 4a of the pair of discharge electrodes 4 and housed in the insulating tube 2.

[0017] As shown in FIG. 3, the insulating member 5 is columnar and has an axis AX2 perpendicular to the axis AX1 of the insulating tube 2, and has a groove 5a extending along its own axis AX2 formed on the outer surface exposed between the pair of discharge electrodes 4. The insulating member 5 also has a plurality of grooves 5a. Furthermore, as shown in FIGS. 1 and 2, the insulating member 5 is formed in a gear-like cross section with a plurality of grooves 5a at equal intervals in the circumferential direction.

[0018] That is, the insulating member 5 is formed in a gear-like cross section having eight grooves 5a and eight teeth 5b equally spaced in the circumferential direction. The groove depth of the grooves 5a is preferably set within a range of, for example, 10 to 20% of the radius of the insulating member 5. In this embodiment, the grooves 5a have a depth of 150 μm for an insulating member 5 with a radius of 1 mm.

[0019] The outer diameter of the insulating member 5 is smaller than the outer diameter of the discharge electrodes 4, and regions A1 are formed on both sides of the insulating member 5 where the tip surfaces 4a of the pair of discharge electrodes 4 directly face each other. The pair of discharge electrodes 4 are formed at their tip ends with annular protrusions 4b that protrude in the axial direction along the outer periphery. The discharge electrode 4 is formed in a cylindrical shape with a circular hole 4c at the tip end thereof, the hole 4c being centered on the axis AX1. That is, at the tip of the discharge electrode 4, an annular protrusion 4b is formed on the outer periphery of a hole 4c. The discharge electrode 4 of this embodiment is made of, for example, copper.

[0020] In this embodiment, one end of a lead wire 7 is connected to the outside of the sealed electrode 3 by welding, soldering, embedding, or the like. The sealing electrode 3 is formed of a metal, for example, an Fe (iron)-Ni (nickel) alloy whose surface is coated with copper oxide, and has a disk or cylindrical shape. For example, the sealing electrode 3 is made from dumet wire.

[0021] The insulating tube 2 is a glass tube made of, for example, lead glass and formed into a substantially cylindrical shape. The pair of sealed electrodes 3 are fitted into the openings at both ends of the insulating tube 2 of the glass tube and fused by heat treatment, so that the insulating tube 2 is fixed in a tight contact state.

[0022] The discharge control gas sealed in the insulating tube 2 is an inert gas such as He, Ar, Ne, Xe, Kr, SF6, CO2, C3F8, C2F6, CF4, H2, air, or a mixture thereof. The insulating member 5 is made of a ceramic material such as alumina, mullite, corundum-mullite, etc. The insulating member 5 of this embodiment is made of alumina.

[0023] As described above, in the surge protection element 1 of this embodiment, the insulating member 5 is columnar with an axis AX2 perpendicular to the axis AX1 of the insulating tube 2, and has grooves 5a extending along its own axis AX2 formed on its outer surface exposed between the pair of discharge electrodes 4. Therefore, as shown in the right part of Figure 2, even if conductive debris from the discharge electrodes 4 generated by surge discharge TB scatters in the direction of arrow M1 and adheres to the outer surface of the insulating member 5, it is unlikely to adhere within the grooves 5a, but is cut off and divided by the grooves 5a.

[0024] As a result, the scattering area M where the conductive debris adheres is separated and divided, and each of these becomes smaller, which reduces the disturbance in the electric field distribution and makes it possible to suppress fluctuations in the discharge start voltage Vs after the surge life test. Furthermore, by using the discharge electrode 4 which is a conductive material, the heat capacity increases and the thermal resistance decreases compared to a thin conductive film, improving durability against surges and suppressing fluctuations in the discharge start voltage Vs.

[0025] In the case of a surge protection element using, for example, a cylindrical insulating member 15 (hereinafter also referred to as a round insulator) without a groove portion 5a, as shown in the left part of Figure 2, conductive debris from the discharge electrode 4 scatters in the direction of arrow M2 and adheres widely to the outer peripheral surface of the insulating member 15, and the scattering area M becomes large without being divided, which makes it easy for the electric field distribution to become disturbed.

[0026] Furthermore, since the insulating member 5 has multiple groove portions 5a, even if conductive debris adheres to the outer peripheral surface of the insulating member 5, the multiple groove portions 5a divide and separate the scattering area M into multiple areas, making each scattering area M even smaller. Furthermore, since the insulating member 5 is formed in a gear-like cross section with a plurality of grooves 5a equally spaced circumferentially, when the insulating member 5 is inserted between the pair of discharge electrodes 4 inside the insulating tube 2, the plurality of grooves 5a can be easily exposed between the pair of discharge electrodes 4, eliminating the need for positioning during assembly.

[0027] In particular, the insulating member 5 has a gear-shaped cross section with eight grooves 5a equally spaced in the circumferential direction, and therefore has eight teeth 5b on its outer peripheral surface, and two adjacent teeth 5b of the eight teeth 5b come into contact with the opposing discharge electrodes 4, thereby stably positioning the insulating member 5 between the pair of discharge electrodes 4. Furthermore, three grooves 5a are exposed on each of the outer peripheral surface portions on both sides exposed between the pair of discharge electrodes 4, making it possible to divide and separate the scattering region M into three.

[0028] Furthermore, the outer diameter of the insulating member 5 is smaller than the outer diameter of the discharge electrodes 4, and an area A1 is formed on both sides of the insulating member 5 where the tip surfaces 4a of the pair of discharge electrodes 4 directly face each other. Therefore, a discharge path is formed on both sides of the insulating member 5, and the arc discharge TB can be easily transmitted between the pair of discharge electrodes 4. [Example]

[0029] FIG. 5 shows the results of investigating the change in discharge inception voltage Vs when a life test was conducted in which surges were repeatedly applied to a surge protection element using an insulating member (gear insulator) with grooves formed therein according to the above embodiment as an example of the present invention (referred to as gear insulator in the figure). As a comparative example, the change in discharge inception voltage Vs after the life test was also investigated for a surge protection element using an insulating material (round insulator) without a groove, and the results are shown in Figure 6 (referred to as round insulator in the figure).

[0030] These results show that in the comparative example using a round insulator without grooves, the discharge inception voltage Vs drops significantly after 100 life tests, whereas in the example of the present invention using a gear insulator with grooves, the drop in discharge inception voltage Vs is suppressed even after 300 life tests.

[0031] 7(a) shows an image of the outer surface of the insulating member of the example of the present invention taken out after 300 cycles of the life test. Also, FIG. 7(b) shows an image of the outer surface of the insulating member of the comparative example taken out in the same manner. In the round insulator of the comparative example, the scattering area where the conductive debris adheres is distributed widely over the entire outer surface, whereas in the gear insulator of the embodiment of the present invention, the scattering area where the conductive debris adheres is divided by grooves on the outer surface and becomes smaller.

[0032] The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. [Explanation of symbols]

[0033] 1...surge protection element, 2...insulating tube, 3...sealed electrode, 4...discharge electrode, 4a...tip surface of discharge electrode, 5...insulating member, 5a...groove portion, AX1...axis line of insulating tube, AX2...axis line of insulating member, A1...area directly opposed to the tip surface of the discharge electrode

Claims

1. an insulating tube; a pair of sealing electrodes that close both end openings of the insulating tube to seal a discharge control gas inside; a pair of discharge electrodes whose base ends are in contact with the inner surface of the sealed electrode and whose tip ends protrude into the insulating tube and face each other; an insulating member sandwiched between the tip surfaces of the pair of discharge electrodes and housed in the insulating tube, A surge protection element characterized in that the insulating member is columnar with an axis perpendicular to the axis of the insulating tube, and a groove extending along the axis of the insulating member is formed on the outer surface exposed between the pair of discharge electrodes.

2. 2. The surge protection device according to claim 1, A surge protection element, characterized in that the insulating member has a plurality of the grooves.

3. 3. The surge protection device according to claim 2, A surge protection element, characterized in that the insulating member is formed in a gear-like cross section with a plurality of the grooves equally spaced in the circumferential direction.

4. 4. The surge protection device according to claim 3, A surge protection element, characterized in that the insulating member is formed in a gear-like cross section with eight of the grooves equally spaced in the circumferential direction.

5. The surge protection device according to claim 1 or 2, A surge protection element characterized in that the outer diameter of the insulating member is smaller than the outer diameter of the discharge electrodes, and areas are formed on both sides of the insulating member where the tip surfaces of the pair of discharge electrodes directly face each other.

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