Surge protection element

Abstract

Provided is a surge protection element capable of reducing damage caused by surges and suppressing fluctuation in discharge start voltage. A surge protection element according to the present invention comprises: an insulating tube (2); a pair of sealing electrodes (3) that close off both end openings of the insulating tube and 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 tip ends protrude into the insulating tube and face each other; and an insulating member (5) sandwiched between tip end 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 is such that 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.

Description

Surge Protection Device

[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.

[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 due to abnormal voltages (surge voltages) such as lightning surges and static electricity, such as where the equipment is connected to communication lines, power lines, antennas, or CRT drive circuits, in order to prevent damage such as thermal damage or fire to the electronic equipment or the printed circuit board on which it is mounted due to abnormal voltages.

[0003] A known surge protection element is a surge absorber in which a discharge element is made up of a ceramic insulator with a conductive film formed on its surface 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 favoring the response voltage to a surge.

[0004] Japanese Unexamined Patent Publication No. 8-153565

[0005] The above-mentioned conventional technologies have the following problems remaining. In the above-mentioned conventional surge protection elements, a conductive film of several to several tens of micrometers is formed as an electrode film 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 functionality, when a high-intensity surge or repeated surges are applied. In addition, conductive debris such as metal that is scattered from the discharge electrode and adheres to the outer surface of the insulator significantly disrupts the electric field distribution, causing fluctuations in the discharge start voltage Vs, making it impossible to maintain a stable discharge start 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.

[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 is 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 element, 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-adhering scattering area is separated and divided, becoming smaller, thereby minimizing the disturbance of the electric field distribution and suppressing fluctuations in the discharge start voltage Vs after surge life testing. Furthermore, by using a discharge electrode made of a conductive material, the heat capacity is increased and thermal resistance is reduced compared to a thin conductive film, improving durability against surges and suppressing fluctuations in the discharge start voltage.

[0009] A surge protection element according to a second aspect of the present invention is the surge protection element according to the first aspect of the present invention, characterized in that the insulating member has a plurality of grooves. That is, in this surge protection element, even if conductive debris adheres to the outer peripheral surface of the insulating member, the grooves divide and separate the scattering region into a plurality of smaller regions, thereby making each scattering region even smaller.

[0010] A surge protection element according to a third invention is the surge protection element of the second invention, characterized in that the insulating member has a gear-shaped cross section with a plurality of the grooves equally spaced circumferentially. That is, in this surge protection element, the insulating member has a gear-shaped cross section with a plurality of grooves equally spaced circumferentially, so that when the insulating member is inserted between a pair of discharge electrodes in an insulating tube, the plurality of grooves can be easily exposed between the pair of discharge electrodes, eliminating the need for positioning during assembly.

[0011] A surge protection element according to a fourth aspect of the present invention is the surge protection element according to the third aspect, characterized in that the insulating member has a gear-shaped cross section with eight grooves equally spaced circumferentially. In other words, in this surge protection element, the insulating member has a gear-shaped cross section with eight grooves equally spaced circumferentially, so that the insulating member 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. Furthermore, three grooves are exposed on each of the outer circumferential surface portions on both sides exposed between the pair of discharge electrodes, so that the scattering region can be divided and separated into three.

[0012] A surge protection element according to a fifth aspect of the present invention is the surge protection element of the first or second aspect, characterized in that the outer diameter of the insulating member is smaller than the outer diameter of the discharge electrodes, and regions where the tip faces of the pair of discharge electrodes directly face each other are formed on both sides of the insulating member. That is, in this surge protection element, the outer diameter of the insulating member is smaller than the outer diameter of the discharge electrodes, and regions where the tip faces of the pair of discharge electrodes directly face each other are formed on both sides of the insulating member, so that discharge paths are formed on both sides of the insulating member, making it easier for arc discharge to propagate between the pair of discharge electrodes.

[0013] The present invention has the following advantages. Specifically, in the surge protection element of the present invention, the insulating member is columnar with an axis perpendicular to the axis of the insulating tube, and a groove extending along the axis is formed on the outer peripheral surface exposed between the pair of discharge electrodes. This reduces the disturbance of the electric field distribution, suppresses fluctuations in the discharge inception voltage Vs after a surge life test, and improves surge durability. Therefore, the surge protection element of the present invention can improve surge breakdown resistance and surge characteristic resistance.

[0014] FIG. 1 is a front view showing a partially broken surge protection element in one embodiment of the surge protection element according to the present invention. FIG. 2 is an explanatory diagram showing a scattering region of conductive debris in an insulating member arranged between a pair of discharge electrodes in the present embodiment. FIG. 3 is a side view showing a partially broken surge protection element in the present embodiment. FIG. 4 is a perspective view showing an insulating member arranged between a pair of discharge electrodes in the present embodiment. FIG. 5 is a graph showing changes in discharge inception voltage Vs with respect to the number of times of life test in an example of a surge protection element according to the present invention. FIG. 6 is a graph showing changes in discharge inception voltage Vs with respect to the number of times of life test in a comparative example of a surge protection element according to the present invention. FIG. 7 is an image showing the outer surface of the insulating member after a life test in example (a) and comparative example (b) of a surge protection element according to the present invention.

[0015] An embodiment of a surge protection device 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 that have their base ends in contact with the inner surface of the sealed electrodes 3 and their tips that 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 within 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 grooves 5a extending along its own axis AX2 formed on the outer peripheral 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 has a gear-like cross section with a plurality of grooves 5a equally spaced circumferentially.

[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 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 insulating member 5 has a radius of 1 mm and the grooves 5a have a depth of 150 μm.

[0019] The outer diameter of the insulating member 5 is smaller than the outer diameter of the discharge electrode 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. An annular protrusion 4b that protrudes in the axial direction along the outer periphery is formed at the tip of the pair of discharge electrodes 4. The discharge electrode 4 is formed in a cylindrical shape with a circular hole 4c centered on the axis AX1 formed at the tip. In other words, the tip of the discharge electrode 4 has an annular protrusion 4b formed on the outer periphery of the hole 4c. The discharge electrode 4 in 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 sealed 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 sealed electrode 3 is made of a 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, or SF ６ , CO ２ , C ３ F ８ , C ２ F ６ , C.F. ４ , H ２ , air, or a mixture thereof. The insulating member 5 is made of a ceramic material such as alumina, mullite, or corundum-mullite. The insulating member 5 in 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 a groove 5a extending along its own axis AX2 is formed on the outer surface exposed between the pair of discharge electrodes 4. Therefore, as shown in the right part of Figure 2, even if conductive debris generated from the discharge electrodes 4 by the surge discharge TB scatters as indicated by arrow M1 and adheres to the outer surface of the insulating member 5, it is unlikely to adhere within the groove 5a, but is instead separated and divided by the groove 5a.

[0024] Therefore, the scattering region 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 employing 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 making it possible to suppress 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 grooves 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, because the insulating member 5 has a plurality of grooves 5a, even if conductive debris adheres to the outer peripheral surface of the insulating member 5, the plurality of grooves 5a divide and separate the scattering region M into a plurality of smaller regions, thereby further reducing the size of each scattering region M. Furthermore, because the insulating member 5 has a gear-shaped 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-like cross section with eight grooves 5a equally spaced in the circumferential direction, and therefore has eight teeth 5b on its outer circumferential 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 circumferential 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 4 a 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.

[0029] The change in discharge inception voltage Vs of a surge protection element using an insulating member (gear insulator) with grooves formed therein according to the above embodiment was examined during a life test in which surges were repeatedly applied, and the results are shown in Figure 5 (referred to as "gear insulator" in the figure). As a comparative example, the change in discharge inception voltage Vs of a surge protection element using an insulating member (round insulator) without grooves was also examined after a life test, 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] 7A shows an image of the outer circumferential surface of an insulating member according to an example of the present invention, which was removed after 300 cycles of the life test. Also, FIG. 7B shows an image of the outer circumferential surface of an insulating member similarly removed from the comparative example. It can be seen that, in the round insulator of the comparative example, the scattered area with the conductive debris attached is widely distributed over the entire outer circumferential surface, whereas, in the gear insulator according to the example of the present invention, the scattered area with the conductive debris attached is divided by grooves on the outer circumferential 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.

[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 of insulating tube, AX2... axis of insulating member, A1... region directly facing tip surface of discharge electrode

Claims

1. A surge protection element comprising: an insulating tube; a pair of sealing electrodes that close off openings at both 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 sealing electrodes and whose tips protrude into the insulating tube and face each other; and an insulating member that is sandwiched between the tip surfaces of the pair of discharge electrodes and is contained within the insulating tube, wherein the insulating member is columnar with an axis that is perpendicular to the axis of the insulating tube, and a groove that extends along the axis of the insulating member is formed on the outer surface exposed between the pair of discharge electrodes.

2. A surge protection element according to claim 1, wherein the insulating member has a plurality of the grooves.

3. A surge protection element according to claim 2, wherein the insulating member has a gear-shaped cross section with a plurality of the grooves at equal intervals in the circumferential direction.

4. A surge protection element according to claim 3, wherein the insulating member has a gear-shaped cross section with eight of the grooves equally spaced circumferentially.

5. A surge protection element as claimed in claim 1, 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 faces of the pair of discharge electrodes directly face each other.

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