Surge Protection Device

Abstract

To provide a surge protective element capable of reducing heat and shock damage caused by discharge and suppressing fluctuations in a discharge starting voltage.SOLUTION: A surge protective element includes an insulating tube 2, a pair of sealing electrodes 3 that close the openings at both ends of the insulating tube to seal discharge control gas therein, a columnar or cylindrical insulating member 4 housed in the insulating tube, and a pair of cap electrodes 5 which are placed over both ends of the insulating member and whose base ends contact the inner surfaces of the pair of sealing electrodes, and the pair of cap electrodes have their tip ends 5a facing each other with a space between them, and the outer diameter of the tip ends gradually increases toward the tips.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, as a surge protection element, for example, as shown in FIG. 5, a surge absorber has been known in which a discharge element consisting of a ceramic insulator 104 in which a conductive film 104a formed on the surface is divided in the middle to provide a discharge gap (microgap) 104b, and a pair of cap electrodes 105 provided on both ends of the insulator 104 is sealed in a glass tube 102 by a pair of sealing electrodes 103 (see Patent Document 1). [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 conventional surge protection device described above, an electric field is generated by applying a voltage between the pair of conductive films 104a or the pair of cap electrodes 105 that face each other via the discharge gap 104b, and the discharge is affected by the electric field. As shown in Fig. 6, the electric field is generated not only at the tips of the pair of opposing cylindrical conductive films 104a, but also in other parts, in a direction that goes in and out of the cylindrical conductive film 104a. In other words, the electric field is not only concentrated at the part where the tips of the pair of conductive films 104a face each other linearly, but also generated in large amounts on the outer peripheral surface outside that part. Therefore, when a large current discharge occurs, the discharge reaches the envelope (glass tube 102), which is a sealed housing, and the hermetic seal with the envelope, causing the plasma sputtering to cause thermal and shock damage to the structural body, which has significant strength, leading to destruction.In addition, since the conductive film 104a is located in the surge discharge path, it is easily affected by heat and sputtering, which causes the disadvantage of changing the discharge start voltage after the surge.

[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 heat and shock due to discharge and also 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 columnar or cylindrical insulating member housed in the insulating tube, and a pair of cap electrodes that cover both ends of the insulating member and have base ends in contact with the inner surfaces of the pair of sealed electrodes, wherein tip ends of the pair of cap electrodes face each other with a gap between them, and the outer diameters of the tip ends gradually increase toward the tip.

[0008] In this surge protection element, the tips of a pair of cap electrodes face each other with a gap between them, and the outer diameter of the tips gradually increases toward the tips. This allows the electric field to be concentrated in the space between the pair of tapered tips that face each other, thereby reducing damage from heat and shock.

[0009] That is, the electric field is concentrated between the pair of widened and facing tips, and the electric field is less likely to enter or exit the outer peripheral surface of the tapered tips, reducing thermal and shock damage caused by discharge to the outer peripheral surface and other structures, such as insulating tubes. Because the tips are tapered, the electric field is concentrated in the space between the opposing surfaces, rather than in a linear fashion, making it less likely to be generated on the outer peripheral surface. Furthermore, the sharp cross-sectional shape of the tips makes it easier for the electric field to concentrate at the tips. In this way, by eliminating the conductive film and providing the cap electrode with the function of determining the discharge inception voltage, fluctuations in the discharge inception voltage after a surge can also be suppressed. In conventional surge protection elements, the gap between a pair of conductive films (microgap) determines the discharge start voltage, but in the present invention, the gap between a pair of tip portions determines the discharge start voltage.

[0010] The surge protection element of the second invention is characterized in that, in the first invention, the inner diameter of the tip portion also gradually increases toward the tip, and a space is formed between the tip portion and the outer peripheral surface of the insulating member. In other words, in this surge protection element, the inner diameter of the tip portion also gradually increases toward the tip, and a space is formed between the tip portion and the outer surface of the insulating member.As a result, an electric field is likely to be generated on the insulating member side, which is a dielectric, and therefore an electric field is likely to be generated in the space formed between the tip portion and the outer surface of the insulating member, and further, the electric field generated on the outer surface side is reduced.

[0011] The surge protection element of the third invention is the surge protection element of the first or second invention, characterized in that the tip portion is formed in a trumpet shape that is curved radially outward as it approaches the tip. In other words, in this surge protection element, the tip is formed in a trumpet shape that curves radially outward as it approaches the tip, so that the outer surface of the tip is a concave curved surface.Compared to when the tip is uniformly expanded in diameter, this allows for a larger distance and space to be secured between the outer surface of the tip and the insulating tube, thereby further reducing the impact of discharge on the insulating tube. [Effects of the Invention]

[0012] According to the present invention, the following effects are achieved. In other words, according to the surge protection element of the present invention, the tip ends of a pair of cap electrodes face each other with a gap between them, and the outer diameter of the tip ends gradually increases toward the tip, thereby reducing damage caused by heat and shock due to discharge and suppressing fluctuations in the discharge start voltage. Therefore, the surge protection element of the present invention can improve the surge breakdown resistance and surge characteristic resistance. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a perspective view showing an embodiment of a surge protection element according to the present invention; [Figure 2] FIG. 2 is a cross-sectional view showing an insulating member to which a pair of cap electrodes are attached in the present embodiment. [Figure 3] FIG. 2 is a front view showing the surge protection element in the present embodiment. [Figure 4] 1A is an overall view showing the distribution of an electric field generated between a pair of cap electrodes in this embodiment, and FIG. 1B is an enlarged view of a main part thereof. [Figure 5] FIG. 10 is a front view showing a surge protection element in a comparative example of the surge protection element according to the present invention. [Figure 6] 1A is an overall view showing the distribution of an electric field generated between a pair of cap electrodes in a comparative example of this embodiment, and FIG. 1B is an enlarged view of a main part thereof. DETAILED DESCRIPTION OF THE INVENTION

[0014] 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.

[0015] As shown in Figures 1 to 3, 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 columnar or cylindrical insulating member 4 housed within the insulating tube 2, and a pair of cap electrodes 5 that cover both ends of the insulating member 4 and have their base ends in contact with the inner surfaces of the pair of sealed electrodes 3. The pair of cap electrodes 5 have tip portions 5a that face each other with a gap therebetween, and the outer diameter of the tip portions 5a gradually increases toward the tip. The insulating member 4 is formed in a cylindrical shape.

[0016] In this embodiment, the inner diameter of the tip portion 5a also gradually increases toward the tip, and a space S is formed between the tip portion 5a and the outer circumferential surface of the insulating member 4. That is, the tip portion 5a gradually expands in diameter toward the tip and is gradually spaced radially outward from the outer circumferential surface of the insulating member 4a, thereby forming a space S. The tip portion 5a is formed in a trumpet shape that curves radially outward toward the tip.

[0017] 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.

[0018] The insulating tube 2 is a glass tube made of, for example, lead glass and formed into a substantially cylindrical shape, with the central portion bulging outward in the radial direction. 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.

[0019] 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 4 is made of a ceramic material such as alumina, mullite, corundum-mullite, etc. The insulating member 4 of this embodiment is made of alumina.

[0020] The cap electrode 5 is made of, for example, copper. The cap electrode 5 is formed in a cylindrical shape with a bottom, and is composed of a bottom surface portion 5c which is the base end, a straight body portion 5d whose base end side is connected to the bottom surface portion 5c and has a constant outer diameter, and the tip portion 5a connected to the tip side of the straight body portion 5c.

[0021] Incidentally, a conductive film such as SnO2 may be formed on the outer peripheral surface of the cap electrode 5 by a thin film forming technique such as physical vapor deposition (PVD) or chemical vapor deposition (CVD). The gap between the pair of cap electrodes 5 is set appropriately depending on the application, etc., and may be set to the same gap as the microgap formed between conventional conductive films.

[0022] The results of a simulation of the electric field distribution between the pair of cap electrodes 5 in the surge protection device 1 of this embodiment will be described with reference to FIG. As can be seen from Fig. 4, the electric field between the pair of cap electrodes 5 is concentrated in the space between the pair of expanded tip portions 5a. In particular, the electric field is concentrated in the space S between the expanded tip portions 5a and the insulating member 4, i.e., in the space S inside the tip portions 5a. On the other hand, it can be seen that the electric field generated on the outer peripheral surface side of the tip portions 5a is small. 4 and 6 are originally color images, but are shown in grayscale.

[0023] As described above, in the surge protection element 1 of this embodiment, the tip portions 5a of the pair of cap electrodes 5 face each other with a gap between them, and the outer diameter of the tip portions 5a gradually increases toward the tip. Therefore, by concentrating the electric field in the space between the pair of tapered tip portions 5a that face each other and increase in diameter, damage caused by heat and shock can be reduced.

[0024] That is, the electric field is concentrated between the pair of widened and facing tip portions 5a, and the electric field is difficult to enter or exit on the outer circumferential surface side of the tapered tip portions 5a, reducing damage from heat and shock due to discharge to the outer circumferential surface side and other structures such as the insulating tube 2. Because tip portions 5a are tapered in this way, the electric field is concentrated in the space where the surfaces face each other, rather than being opposed linearly, and it is difficult for an electric field to be generated on the outer circumferential surface outside of that.

[0025] Furthermore, since the cross-sectional shape of the tip of tip portion 5a is sharp, the electric field tends to concentrate at the tip. In this way, by eliminating the conductive film and providing cap electrode 5 with the function of determining the discharge start voltage, it is also possible to suppress fluctuations in the discharge start voltage after a surge. In conventional surge protection elements, the gap between a pair of conductive films (microgap) determines the discharge start voltage, but in the surge protection element 1 of this embodiment, the gap between the pair of tip portions 5a determines the discharge start voltage.

[0026] In addition, the inner diameter of the tip portion 5a gradually expands toward the tip, and a space S is formed between the tip portion 5a and the outer peripheral surface of the insulating member 4. This makes it easier for an electric field to be generated on the insulating member 4 side, which is a dielectric, and therefore makes it easier for an electric field to be generated in the space S formed between the tip portion 5a and the outer peripheral surface of the insulating member 4, further reducing the electric field generated on the outer peripheral surface side.

[0027] Furthermore, since the tip portion 5a is formed in a trumpet shape that curves radially outward toward the tip, the outer surface of the tip portion 5a is a concave curved surface, and a larger distance and space can be secured between the outer surface of the tip portion 5a and the insulating tube 2 compared to when the tip portion 5a is uniformly expanded in diameter (when the outer surface of the tip portion 5a is inclined at a constant angle relative to the axial direction), thereby further reducing the impact of discharge on the insulating tube 2.

[0028] 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]

[0029] 1,101... surge protection element, 2,102... insulating tube, 3,103... sealed electrode, 4,104... insulating member, 5,105... cap electrode, 5a... tip portion of cap electrode, S... space between tip portion and outer peripheral surface of insulating member

Claims

[Claim 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 columnar or cylindrical insulating member that is housed in the insulating tube and is entirely made of ceramic; a pair of cap electrodes that cover both ends of the insulating member and have base ends that contact the inner surfaces of the pair of sealing electrodes; The pair of cap electrodes have tip ends facing each other with a gap therebetween, and the outer diameters of the tip ends are gradually enlarged toward the tip ends, The inner diameter of the tip portion also gradually increases toward the tip, and a space is formed between the tip portion and the outer circumferential surface of the insulating member, The surge protection element is characterized in that the tip portion is formed in a trumpet shape that is curved radially outward as it approaches the tip, and the outer peripheral surface is a concave curved surface.

Images