Surge protective element

Abstract

To provide a surge protective element capable of improving responsiveness without using a dielectric with a high dielectric constant for an insulating member.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 outer peripheral insulating member 5 that is sandwiched between tip surfaces of the pair of discharge electrodes and accommodated within the insulating tube, the outer peripheral insulating member having an outer peripheral surface formed of a dielectric 5d. The outer peripheral insulating member includes a metal body 5m at the interior thereof, and the dielectric has a relative dielectric constant of 20 or less.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] BACKGROUND ART Conventionally, surge protection elements have been known that have a structure in which an insulating member, which is a dielectric material such as alumina, is sandwiched between electrodes (for example, Patent Documents 1 and 2). It is known that in this surge protection element, increasing the dielectric constant of the dielectric promotes convergence of the electric flux, thereby increasing the locally strong electric field generated in the gap between the electrode and the dielectric. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-119198 [Patent Document 2] Patent No. 5305011 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 elements described above, in order to increase the dielectric constant of the dielectric, it is necessary to change the dielectric to a material with a higher dielectric constant than alumina, etc., but there is an inconvenience in that the material options are limited to ferroelectrics (e.g., BaTiO3, etc.). Furthermore, depending on the dielectric relaxation frequency of the dielectric constant, the response of the polarized charge may not keep up with the surge response speed, making it impossible to obtain the electric field predicted by the electrostatic field simulation, resulting in a slower response speed than expected.

[0006] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a surge protection element that can improve responsiveness without using a dielectric with a high dielectric constant for the insulating member. [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 surfaces of the sealed electrodes and whose tip ends protrude into the insulating tube and face each other, and a peripheral insulating member whose outer peripheral surface is made of a dielectric and is housed in the insulating tube and sandwiched between the tip faces of the pair of discharge electrodes, wherein the peripheral insulating member includes a metal body inside and the dielectric has a relative permittivity of 20 or less.

[0008] In this surge protection element, the peripheral insulating member has a metal body inside and the dielectric constant of the dielectric is 20 or less. Therefore, the presence of the metal body inside causes electric dipoles (polarized charges) to be generated quickly, like in a ferroelectric, and the local electric field generated in the gap between the sealed electrode and the peripheral insulating member increases, allowing the electric field to be formed quickly, thereby improving responsiveness. In the surge protection device of the present invention, it is believed that the counterpart of the charge on the discharge electrode becomes closer. That is, when the dielectric constant of the dielectric is low and a metal body is built in, the potential inside the metal body becomes the same potential, and the potential difference is the integration of the electric field over a short distance between the induced polarization charge and the charge on the discharge electrode, resulting in a high potential difference over a relatively short distance and an intensified electric field. The reason why the dielectric constant of the dielectric is set to 20 or less is that if the dielectric constant exceeds 20, the presence of a metal body will disperse the electric flux, lowering the internal electric flux density and resulting in a decrease in the electric field strength compared to when no metal body is built in.

[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 dielectric material is alumina. That is, in this surge protection element, the dielectric is alumina, which has a relative dielectric constant of 8.5 and is inexpensive, so it can be manufactured at a lower cost than ferroelectrics and can obtain a high electric field strength.

[0010] The surge protection element of the third invention is characterized in that, in the first or second invention, the outer insulating member is cylindrical with an axis perpendicular to the axis of the insulating tube. In other words, in this surge protection element, the outer insulating member is cylindrical with an axis perpendicular to the axis of the insulating tube, so that the outer surface of the outer insulating member is a curved, inclined surface, and the contact area with the tip surface of the discharge electrode is localized, allowing the electric field to be more concentrated.

[0011] The surge protection element of the fourth invention is characterized in that, in any of the first to third inventions, at the cross section between the contact portions of the peripheral insulating member with the pair of discharge electrodes, when the thickness of the metal body is Dm and the thickness of the peripheral insulating member is Dd, 0.8≦Dm / Dd<1.0. In other words, in this surge protection element, when the thickness of the metal body is Dm and the thickness of the peripheral insulating member is Dd at the cross section between the contact points with the pair of discharge electrodes of the peripheral insulating member, 0.8≦Dm / Dd<1.0, so the thickness of the dielectric is relatively thin and a higher electric field strength can be obtained.

[0012] The surge protection element of the fifth invention is characterized in that, in any of the first to fourth inventions, the outer insulating member is in contact with the outer edges of the tips of the pair of discharge electrodes and is not arranged on the axis of the pair of discharge electrodes. In other words, in this surge protection device, the peripheral insulating member is in contact with the outer edges of the tips of the pair of discharge electrodes and is not disposed on the axis of the pair of discharge electrodes, so that the converging electric flux from the center of the tip faces of the discharge electrodes is more effective, further improving the electric field. Furthermore, metal scattered from the center of the tip faces of the discharge electrodes is less likely to adhere to the peripheral insulating member. [Effects of the Invention]

[0013] According to the present invention, the following effects are achieved. In other words, in the surge protection element of the present invention, the peripheral insulating member has a metal body inside and the dielectric constant of the dielectric is 20 or less, so that the presence of the metal body inside causes electric dipoles (polarized charges) to be generated quickly like in a ferroelectric, and the local electric field generated in the gap between the sealed electrode and the peripheral insulating member increases, allowing the electric field to be formed quickly, thereby improving responsiveness. Therefore, in the surge protection element of the present invention, surge response can be improved even if the dielectric constant of the dielectric of the insulating member is not high. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a partially cutaway front view of a surge protection element according to a first embodiment of the present invention; [Figure 2] 3 is a cross-sectional view showing an insulating member disposed between a pair of discharge electrodes in the first embodiment. FIG. [Figure 3] 1 is a side view showing a surge protection element with a part broken away in the first embodiment. [Figure 4] FIG. 2 is a perspective view showing an insulating member disposed between a pair of discharge electrodes in the first embodiment. [Figure 5]FIG. 10 is a perspective view showing an insulating member disposed between a pair of discharge electrodes in a second embodiment of a surge protection element according to the present invention. [Figure 6] FIG. 10 is a perspective view showing an insulating member disposed on a discharge electrode in another example of the second embodiment. [Figure 7] 10A is a perspective view showing an insulating member arranged between a pair of discharge electrodes in a third embodiment of the surge protection element according to the present invention, and FIG. 10B is a perspective view showing an insulating member arranged on the discharge electrodes in a third embodiment of the surge protection element according to the present invention, and FIG. [Figure 8] FIG. 10 is a cross-sectional view showing an insulating member disposed between a pair of discharge electrodes in a third embodiment. [Figure 9] 10 is a graph showing the maximum electric field strength when the thickness (diameter) of the metal body is changed in examples and comparative examples of the surge protection element according to the present invention. [Figure 10] 10 is a simulation result showing the distribution of electric flux density inside a comparative example (a) without a metal body and an example of the present invention (b) with a metal body. DETAILED DESCRIPTION OF THE INVENTION

[0015] A first 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 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 outer 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 and whose outer surface is formed of a dielectric 5d. The peripheral insulating member 5 has a metal body 5m therein and a dielectric 5d having a relative dielectric constant of 20 or less.

[0017] The dielectric 5d is made of, for example, alumina. The dielectric 5d may be made of other materials as long as the relative dielectric constant is equal to or less than 20. For example, zirconia having a relative dielectric constant of equal to or less than 20 may be used as the dielectric. The outer circumferential insulating member 5 is cylindrical and has an axis AX2 in a direction perpendicular to the axis AX1 of the insulating pipe 2. The metal body 5m has the same central axis as the outer circumferential insulating member 5 and is cylindrical with a smaller diameter than the outer circumferential insulating member 5. The metal body 5m is made of, for example, copper.

[0018] Furthermore, as shown in Figure 2, in a cross section (longitudinal cross section along the axis AX1) between the contact portions of the outer peripheral insulating member 5 with the pair of discharge electrodes 4, when the thickness of the metal body 5m is Dm and the thickness of the outer peripheral insulating member 5 is Dd, it is preferable that 0.8≦Dm / Dd<1.0. That is, in this embodiment, the thickness (diameter) of the cylindrical metal body 5m is Dm and the thickness (diameter) of the cylindrical peripheral insulating member 5 is Dd, and it is preferable that 0.8≦Dm / Dd<1.0. For example, if the thickness (diameter) Dd of the outer periphery insulating member 5 is 1 mm, the range of the thickness (diameter) Dm of the metal body 5m is set to 0.8 mm≦Dm<1.0 mm. The cylindrical metal body 5m is covered with the dielectric 5d not only on its outer circumferential surface but also on both end surfaces, and is entirely covered with the dielectric 5d and is not exposed.

[0019] Since the outer peripheral insulating member 5 is cylindrical, the opposing surface 5a of the outer peripheral insulating member 5 relative to the tip surface 4a of the discharge electrode 4 has an inclined surface that is inclined at an acute angle relative to the tip surface 4a, with the contact point 5b with the tip surface 4a as the base point. That is, the outer peripheral surface of the cylindrical outer peripheral insulating member 5 forms a curved opposing surface 5a that is inclined at an acute angle relative to the tip end surface 4a of the discharge electrode 4.

[0020] The opposing surface 5a of the outer circumferential insulating member 5 preferably contacts the tip surface 4a of the discharge electrode 4 at an acute angle θ of less than 90°, and more preferably at an acute angle θ of 45° or less. Furthermore, the outer diameter of the outer insulating member 5 is smaller than the outer diameter of the discharge electrodes 4, and regions A1 are formed on both sides of the outer insulating member 5 where the tip faces of the pair of discharge electrodes 4 directly face each other.

[0021] 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.

[0022] 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.

[0023] 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. 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.

[0024] As described above, in the surge protection element 1 of this embodiment, the peripheral insulating member 5 has a metal body 5m inside and the dielectric constant of the dielectric 5d is 20 or less. Therefore, the presence of the metal body 5m inside causes electric dipoles (polarized charges) to be generated quickly like in a ferroelectric, and the local electric field generated in the gap between the sealed electrode 3 and the peripheral insulating member 5 increases, allowing the electric field to be formed quickly, thereby improving responsiveness. In particular, since the dielectric 5d is made of inexpensive alumina with a relative dielectric constant of 8.5, it can be manufactured at a lower cost than a ferroelectric material and a high electric field strength can be obtained.

[0025] Furthermore, since the outer insulating member 5 is cylindrical with an axis perpendicular to the axis of the insulating tube, the outer surface of the outer insulating member 5 is a curved, inclined surface, and the contact area with the tip surface of the discharge electrode 4 is localized, allowing the electric field to be more concentrated. Furthermore, in the cross section between the contact portions of the peripheral insulating member 5 with the pair of discharge electrodes 4, when the thickness of the metal body 5m is Dm and the thickness of the peripheral insulating member 5 is Dd, by making 0.8≦Dm / Dd<1.0, the thickness of the dielectric 5d becomes particularly thin relatively, and a higher electric field strength can be obtained. Furthermore, annular protrusions 4b are formed at the tips of the pair of discharge electrodes 4, protruding in the axial direction along the outer periphery. When the protrusions 4b come into contact with the outer insulating member 5, the contact area becomes more localized, further concentrating the electric field.

[0026] Next, second and third embodiments of the surge protection device according to the present invention will be described below with reference to Figures 5 and 6. In the following description of each embodiment, the same components as those described in the above embodiments will be denoted by the same reference numerals, and their description will be omitted.

[0027] The difference between the second embodiment and the first embodiment is that the first embodiment uses a single cylindrical peripheral insulating member 5, whereas the surge protection element of the second embodiment uses a peripheral insulating member 35 consisting of four cylindrical divided members 35a, as shown in Figure 5. The second embodiment also differs from the first embodiment in that the four divided members 35a are arranged in a line at equal intervals in the circumferential direction on the outer peripheral edge of the tip surface 4a of the discharge electrode 4, and that the inner end surfaces of the divided members face the axis of the discharge electrode 4, with spaces provided between them.

[0028] The four divided members 35a are cylindrical and shorter than the outer circumferential insulating member 5 of the first embodiment, and are arranged at 90° intervals in the circumferential direction on the outer circumferential edge of the tip end surface 4a of the discharge electrode 4. The inner end faces of the four divided members 35a are spaced apart with spaces provided therebetween, so that a cavity (space) is formed between the central portions of the opposing tip faces 4a of the pair of discharge electrodes 4. Like the outer insulating member 5 of the first embodiment, these divided members 35a each contain a cylindrical or disk-shaped metal body with the same central axis, and the outer periphery of the metal body is covered with a dielectric.

[0029] As another example of the second embodiment, the outer circumferential insulating member 35 may be made up of three columnar or cylindrical divided members 35a, as shown in Fig. 6. That is, the three divided members 35a are arranged at the outer circumferential edge of the tip surface 4a of the discharge electrode 4, spaced apart from each other at 120° intervals in the circumferential direction.

[0030] As described above, in the surge protection element of the second embodiment, the peripheral insulating member 35 is made up of three or four cylindrical divided members 35a, and the three or four divided members 35a are arranged in a line at equal intervals in the circumferential direction on the outer peripheral edge of the tip surface 4a of the discharge electrode. Therefore, since the contact surface with the discharge electrode 4 is divided into three or four by the divided members 35a, the electric field concentration portion (local electric field portion) is divided and the electric field is improved, resulting in a higher discharge inception voltage and improved responsiveness.

[0031] Furthermore, the inner end faces of the three or four divided members 35a face the axis of the discharge electrode 4, with spaces provided between them. In other words, the outer circumferential insulating member 35 is in contact with the outer edges (protrusions) of the tips of the pair of discharge electrodes 4, and is not disposed on the axis AX1 of the pair of discharge electrodes 4. This makes the converging electric flux from the center of the tip surfaces 4a of the discharge electrodes 4 more effective, further improving the electric field. Furthermore, metal scattered from the center of the tip surfaces 4a of the discharge electrodes 4 is less likely to adhere to the divided members 35a (outer circumferential insulating member 35).

[0032] Next, the difference between the third embodiment and the first embodiment is that while the first embodiment uses a single cylindrical outer insulating member 5, the surge protection element of the third embodiment has an outer insulating member 45 that is annular in shape and has the same central axis as the discharge electrode 4, as shown in Figures 7 and 8, and also has a metal body 45m built in that is also annular in shape and has the same central axis as the discharge electrode 4. That is, in the third embodiment, a doughnut-shaped outer circumferential insulating member 45 is sandwiched between a pair of discharge electrodes 4.

[0033] In the third embodiment, the thickness Dm of the metal body 45m and the thickness Dd of the outer peripheral insulating member 45 are set to satisfy 0.8≦Dm / Dd<1.0 in the cross section between the contact portions of the outer peripheral insulating member 45 with the pair of discharge electrodes 4. Here, the thickness Dm of the metal body 45m and the thickness Dd of the outer peripheral insulating member 45 are diameters indicating the thickness of the portion extending in the annular shape, rather than diameters from the center of the annular shape.

[0034] In this way, in the surge protection element of the third embodiment, even if the shape of the outer circumferential insulating member 45 changes to an annular shape, the electric field strength is significantly improved compared to when the metal body 45m is not built in. In addition, in a simulation in which the thickness Dd of the peripheral insulating member 45 was 1 mm and the thickness Dm of the metal body 45m was 0.8 mm, the maximum electric field strength was 29 MV / m when the metal body 45m was not built in, while the maximum electric field strength was 73 MV / m when the metal body 45m was built in. [Example]

[0035] For the surge protection element of the first embodiment described above, the results of a simulation of the maximum electric field strength was performed by changing the relative permittivity of the dielectric when no metal body is built in and when the thickness (diameter) of the built-in metal body is changed. These results are shown in Figure 9. As can be seen from Figure 9, compared to the case where no metal body is built in (metal body diameter 0 mm), the lower the relative permittivity of the dielectric, the lower the maximum electric field strength. However, in the case where a metal body is built in, if the relative permittivity of the dielectric is 20 or less, the greater the thickness (diameter) of the metal body (the thinner the dielectric thickness), the higher the maximum electric field strength becomes. In particular, when the thickness (diameter) of the metal body is 0.8 mm or more and less than 1.0 mm, the maximum electric field strength increases sharply.

[0036] As shown in FIG. 9, even when a metal body is built in, the maximum electric field strength decreases when the relative permittivity of the dielectric exceeds 20. This is thought to be because when the dielectric constant of the dielectric exceeds 20, the presence of a metal body disperses the electric flux, lowering the internal electric flux density and resulting in a decrease in the electric field strength compared to when no metal body is built in.

[0037] Next, Figure 10 shows the simulation results showing the distribution of internal electric flux density for a comparative example of an insulating member (diameter 1.0 mm) without a metal body and an example of a peripheral insulating member (diameter 1.0 mm) with a metal body (diameter 0.8 mm). From this distribution of electric flux density, in the comparative example (Fig. 10(a)) where there is no metal body, the inside is entirely dielectric, so a potential difference occurs over the distance between the upper and lower contact parts with the discharge electrode (diameter of the outer insulating member), whereas in the example (Fig. 10(b)) where the dielectric constant of the dielectric is low and a metal body is built in, it is thought that the counterpart of the charge on the discharge electrode is closer. In other words, the potential inside the built-in metal body becomes the same potential, and the potential difference is the integration of the electric field over the short distance between the induced polarization charge and the charge on the discharge electrode, so it is thought that a high potential difference occurs over a relatively short distance, and the electric field is strengthened.

[0038] The technical scope of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. [Explanation of symbols]

[0039] 1...surge protection element, 2...insulating tube, 3...sealed electrode, 4...discharge electrode, 4a...tip surface of discharge electrode, 4b...ridge portion, 5, 35, 45...periphery insulating member, 5b...contact portion, 5d, 45d...dielectric, 5m, 45m...metal body, AX1...axis of insulating tube, AX2...axis of peripheral insulating member

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 outer circumferential insulating member, the outer circumferential surface of which is made of a dielectric material and which is 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 peripheral insulating member has a metal body therein and the dielectric has a relative dielectric constant of 20 or less.

2. 2. The surge protection device according to claim 1, A surge protection element, characterized in that the dielectric is alumina.

3. 2. The surge protection device according to claim 1, A surge protection element, characterized in that the outer insulating member is cylindrical and has an axis perpendicular to the axis of the insulating tube.

4. 2. The surge protection device according to claim 1, In a cross section between contact portions of the outer peripheral insulating member and the pair of discharge electrodes, A surge protection element characterized in that, when the thickness of the metal body is Dm and the thickness of the peripheral insulating member is Dd, 0.8≦Dm / Dd<1.

0.

5. The surge protection device according to any one of claims 1 to 4, A surge protection element characterized in that the outer insulating member is in contact with the outer edges of the tip ends of the pair of discharge electrodes and is not disposed on the axis of the pair of discharge electrodes.

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