JP7459767B2 - surge protection element - Google Patents

Description

The present invention relates to a surge protection element that is used to protect various devices from surges generated by lightning strikes and other events, and to prevent accidents.

Surge protection elements are connected to parts of electronic equipment for communication devices such as telephones, facsimiles, and modems that are susceptible to electric shock from abnormal voltages (surge voltages) such as lightning surges and static electricity, such as where the equipment connects to communication lines, power lines, antennas, and CRT drive circuits, in order to prevent destruction by thermal damage or fire caused by abnormal voltages to the electronic equipment and the printed circuit boards on which the equipment is mounted. A surge protection element starts discharge by a glow discharge that occurs between a pair of electrodes, and this glow discharge transitions to an arc discharge, allowing the abnormal current (surge current) to pass through the surge protection element, protecting the equipment. Here, the voltage applied across both ends of the surge protection element when discharge starts by glow discharge is called the discharge inception voltage Vs.

Conventionally, as a surge protection element with good response, for example, Patent Document 1 discloses a glass tube 2 and a discharge gas sealed inside by closing the openings at both ends of the glass tube 2, as shown in FIG. a pair of sealing electrodes 103 , an insulator 8 housed in the glass tube 2 with a pair of sealing electrodes 103 arranged on both ends, and a gap between at least one of the pair of sealing electrodes 103 and the insulator 8 . A surge absorber 100 is described that includes a flat metal plate 104 interposed between the surge absorber 100 and the metal plate 104 interposed therein.

JP 2014-154528 A

The above conventional techniques still have the following problems.
3, in the conventional surge protection element, an arc discharge is generated between a pair of sealed electrodes 103, and a discharge start voltage Vs is determined by the generation of a glow discharge between the pair of sealed electrodes 103 at the start of discharge. However, if a glow discharge occurs on the creeping surface of the route D via the inner peripheral surface of the glass tube 2, there is a risk that the discharge start voltage Vs will become unstable.

The present invention was made in consideration of the above-mentioned problems, and aims to provide a surge protection element that can suppress glow discharge occurring through the inner surface of the glass tube and obtain a stable discharge start voltage Vs.

The present invention employs the following configuration to solve the above problems. That is, the surge protection element of the present invention includes a glass tube and a pair of sealing electrodes that close openings at both ends of the glass tube to seal discharge gas inside and form a discharge space. The sealed electrode includes a main body portion whose outer peripheral surface is joined to the glass tube, and a protruding portion protruding inward in the axial direction from the main body portion, the protruding portion facing inward in the axial direction. and a protrusion outer circumferential surface exposed to the discharge space between the distal end surface and the outer circumferential surface of the main body, an insulating film being formed on the protrusion outer circumferential surface, and an insulating film formed on the protrusion outer circumferential surface. It is characterized by the conductor being exposed on the surface.

In this surge protection element, the protrusion has a distal end surface facing inward in the axial direction, and an outer circumferential surface of the protrusion exposed to the discharge space between the distal end surface and the outer circumferential surface of the main body. Since an insulating film is formed on the surface and a conductor is exposed on the tip surface, the outer circumferential surface of the protruding part of the sealing electrode is covered with the insulating film, so that the outer circumferential surface of the protruding part and the inner circumferential surface of the glass tube are Creeping discharge via the capacitor is less likely to occur, and a linear glow discharge is more likely to occur between the tip surfaces of the pair of sealing electrodes, making it possible to obtain a stable discharge starting voltage Vs. Here, the conductor refers to a material having an electrical resistivity of 10 ⁻⁴ Ω·m or less, and the insulating film refers to a film formed of a material having an electrical resistivity 100 times or more that of the conductor.

The 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 protrusion has a truncated cone shape with the axis of the main body as its central axis.
That is, in this surge protection element, the protrusion is a truncated cone shape with the axis of the main body as the central axis, so that it is tapered from the main body to the tip surface, and the electric field is concentrated at the tip surface, so that the discharge occurs more stably between the tip surfaces. In addition, since the length of the outer circumferential surface of the protrusion is constant in the circumferential direction, the creeping distance between the pair of tip surfaces via the outer circumferential surface of the protrusion and the inner circumferential surface of the glass tube becomes uniform in the circumferential direction, and the occurrence of creeping discharge in the circumferential direction is eliminated, so that a more stable discharge can be obtained between the tip surfaces. Furthermore, since the tapered protrusion separates the tip surface from the inner circumferential surface of the glass tube, the discharge space becomes wider, and the conductor scattered by the discharge is less likely to adhere to the inner circumferential surface of the glass tube, so that a short circuit can be suppressed.

In the surge protection element according to a third invention, in the first or second invention, the insulating film is also formed on the outer peripheral surface of the main body, the insulating film is made of cuprous oxide, and the surge protection element is provided on the tip surface. The exposed conductor is copper.
That is, in this surge protection element, an insulating film is also formed on the outer peripheral surface of the main body, the insulating film is made of cuprous oxide, and the conductor exposed on the tip surface is made of copper. Therefore, a so-called Dumet wire on which a cuprous oxide film is formed can be used, and manufacturing costs can be reduced and a good bond between the main body and the glass tube can be obtained.

The surge protection element according to a fourth aspect of the present invention, according to any one of the first to third aspects, includes an insulator housed in the discharge space of the glass tube, and both ends of the insulator are connected to the pair of seals. It is characterized in that it is in contact with the tip end surface of the electrode.
That is, in this surge protection element, both ends of the insulator are in contact with the tip surfaces of the pair of sealing electrodes, which facilitates more stable discharge between the pair of tip surfaces via the insulator.

According to the present invention, the following effects are achieved.
That is, according to the surge protection element according to the present invention, the protrusion has a distal end surface facing inward in the axial direction, and an outer circumferential surface of the protrusion exposed to the discharge space between the distal end surface and the outer circumferential surface of the main body. An insulating film is formed on the outer circumferential surface of the protrusion, and a conductor is exposed on the tip surface, so the outer circumferential surface of the protrusion of the sealing electrode is covered with an insulating film, so that the protrusion Creeping discharge via the outer circumferential surface and the inner circumferential surface of the glass tube is less likely to occur, and a linear glow discharge is more likely to occur between the tip surfaces of the pair of sealing electrodes, making it possible to obtain a stable discharge starting electrode Vs.

1 is a front view showing one embodiment of a surge protection element according to the present invention, with a portion (glass tube) cut away. FIG. 2 is a perspective view showing a sealed electrode excluding lead wires in the embodiment. FIG. 1 is a perspective view showing a conventional example of a surge protection element according to the present invention.

Below, one embodiment of a surge protection element according to the present invention will be described with reference to Figures 1 and 2. Note that in each of the drawings used in the following description, the scale has been appropriately changed so that each component is recognizable or easily recognizable.

As shown in Figures 1 and 2, the surge protection element 1 of this embodiment comprises a glass tube 2 and a pair of sealing electrodes 3 that close both end openings of the glass tube 2 to seal in a discharge gas inside and form a discharge space.
The pair of sealed electrodes 3 include a main body 4 whose outer circumferential surface is joined to the glass tube 2, and a protruding portion 5 protruding inward in the direction of the axis C from the main body 4.

The protrusion 5 has a distal end surface 5a facing inward in the direction of the axis C, and an outer circumferential surface 5b of the protrusion exposed to the discharge space between the distal end surface 5a and the outer circumferential surface of the main body 4. That is, the tip surface 5a becomes a plane perpendicular to the axis C.
Further, in the protrusion 5, an insulating film 7 is formed on the outer peripheral surface 5b of the protrusion, and a conductor is exposed on the tip surface 5a. Note that the insulating film 7 in FIGS. 1 and 2 is hatched.
The protruding portion 5 has a truncated conical shape (a trapezoidal cross section) with the axis C of the main body portion 4 as the central axis.

An insulating film 7 is also formed on the outer peripheral surface of the main body 4 .
The insulating film 7 is made of cuprous oxide, and the conductor exposed at the tip surface 5a is made of copper.
The surge protection element 1 of this embodiment also includes an insulator 8 housed within the glass tube 2 and having a pair of sealed electrodes 3 disposed on both ends.
Both ends of the insulator 8 are in contact with the tip faces 5 a of the pair of sealed electrodes 3 .

The main body portion 4 is formed into a cylindrical shape.
In this embodiment, one end of the lead wire 9 is connected to the outside of the main body 4 by welding, soldering, embedding, or the like.
The sealing electrode 3 is fitted into the glass tube 2 and fused by heat treatment, so that the main body 4 and the glass tube 2 are fixed in close contact.

The sealed electrode 3 is formed of a nickel alloy (Fe-Ni alloy) whose surface is covered with a thin copper (Cu) film, and as described above, an insulating film 7 is further formed on the thin Cu film on the outer peripheral surface of the main body 4 and on the outer peripheral surface 5b of the protrusion 5.
For example, the sealing electrode 3 is made of a dumet wire, and a thin Cu film having a thickness of 20 μm or less is formed on the tip surface 5 a of the protruding portion 5 in an exposed state.

The discharge gas sealed in the glass tube 2 is an inert gas, such as He, Ar, Ne, Xe, Kr, _SF6 , _{CO2 , C3F8 , C2F6} , CF4 _. , H ₂ , atmosphere, etc., and mixed gases thereof are employed.
The glass tube 2 is formed of lead glass or the like into a substantially cylindrical shape, and the center portion thereof bulges outward in the radial direction.

The insulator 8 is formed into a thin plate shape from a ceramic material such as alumina, mullite, or corundum mullite. Note that the insulator 8 of this embodiment is made of alumina.
The end of this insulator 8 is formed into a convex shape.
Further, the end of the insulator 8 has approximately the same width as the inner diameter of the end of the glass tube 2, and the width of the intermediate portion is set narrower than the inner diameter of the end of the glass tube 2. That is, the middle portion of the insulator 8 is narrowed.
Furthermore, a trigger portion 8a made of a conductive material such as carbon is provided in the middle between the front and back surfaces of the insulator 8. This trigger portion 8a is formed as necessary.

Next, a method of manufacturing this surge protection element 1 will be explained.

First, in a discharge gas atmosphere, one of the sealed electrodes 3 is fitted into the lower opening of the glass tube 2 with its protruding part 5 facing inward to close it, and then the insulator 8 is inserted into the glass tube 2 from the upper opening of the glass tube 2 and stored in the glass tube 2. At this time, since the end of the insulator 8 is set to the same width as the inside diameter of the glass tube 2, the end is positioned by abutting against the inner surface of the glass tube 2, and the insulator is stored in the center of the glass tube 2 in a self-supporting state.
Furthermore, the upper opening of the glass tube 2 is closed with the other sealing electrode 3, and the openings at both ends of the glass tube 2 are closed with the other sealing electrode 3, respectively, to seal the discharge gas inside and complete the assembly.

Next, in the above-mentioned assembled state, the glass tube 2 is heated above the softening point of the glass tube 2 to soften it, and the external pressure is lowered than the internal pressure of the glass tube 2 to soften the intermediate portion of the glass tube 2. Expand outward. That is, a negative pressure state is created by reducing the pressure on the outside of the glass tube 2, and the softened glass tube 2 is expanded radially outward due to the pressure difference between the inside and outside of the glass tube 2.
Thereafter, by cooling, the intermediate portion of the glass tube 2 is hardened in a bulged state, and the main body portions 4 of the pair of sealing electrodes 3 are fused to both ends of the glass tube 2 to form the surge protection element 1. is produced.

1 between the trigger portion 8a of the insulator 8 and the tip surface 5a of the sealed electrode 3. At this time, since the insulating film 7 is formed on the outer peripheral surface 5b of the protrusion, trigger discharge is unlikely to occur along the creeping surface of route B1 via the outer peripheral surface 5b of the protrusion and the inner peripheral surface of the glass tube 2, or along the creeping surface of route B2 via only the inner peripheral surface of the glass tube 2.
This trigger discharge causes further discharge to develop, resulting in arc discharge between the tip faces 5a of the pair of sealing electrodes 3, thereby absorbing the surge.

In this way, in the surge protection element 1 of the present embodiment, the protruding portion 5 has the distal end surface 5a facing inward in the direction of the axis C, and the protruding portion 5 exposed to the discharge space between the distal end surface 5a and the outer circumferential surface of the main body portion 4. Since the insulating film 7 is formed on the protruding outer circumferential surface 5b and the conductor is exposed on the tip surface 5a, the protruding outer circumferential surface 5b of the sealing electrode 3 is insulated. By being covered with the membrane 7,
Creeping discharge via the outer circumferential surface 5b of the protrusion and the inner circumferential surface of the glass tube 2 is less likely to occur, and a linear glow discharge is more likely to occur between the tip surfaces 5a of the pair of sealing electrodes 3, resulting in a stable discharge starting electrode. Vs can be obtained.

In addition, since the protrusion 5 has a truncated cone shape with the axis C of the main body 4 as its central axis, it has a tapered shape from the main body 4 to the tip surface 5a, and the electric field is concentrated on the tip surface 5a, so that discharge occurs more stably between the tip surfaces 5a. In addition, since the length of the outer peripheral surface 5b of the protrusion is constant in the circumferential direction, the creeping distance between the pair of tip surfaces 5a via the outer peripheral surface 5b of the protrusion and the inner peripheral surface of the glass tube 2 becomes uniform in the circumferential direction, and the occurrence of creeping discharge in the circumferential direction is eliminated, resulting in a more stable discharge between the tip surfaces 5a. Furthermore, the tapered protrusion 5 separates the tip surface 5a from the inner peripheral surface of the glass tube 2, which widens the discharge space and makes it difficult for conductors scattered by discharge to adhere to the inner peripheral surface of the glass tube 2, thereby suppressing short circuits.

In addition, an insulating film 7 is formed on the outer peripheral surface of the main body 4, and the insulating film 7 is made of cuprous oxide. Since the conductor exposed on the tip surface 5 a is made of copper, a so-called Dumet wire on which a cuprous oxide film is formed can be used, which reduces manufacturing costs and provides good bonding between the main body 4 and the glass tube 2.
Furthermore, since both ends of the insulator 8 are in contact with the tip faces 5 a of the pair of sealed electrodes 3 , discharge can be more easily and stably performed between the pair of tip faces 5 a via the insulator 8 .

Note that the technical scope of the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1,100...Surge protection element, 2...Glass tube, 3,103...Sealing electrode, 4...Body part, 5...Protrusion part, 5a...Tip surface, 5b...Protrusion part outer peripheral surface, 7...Insulating film, 8... insulator

Claims (4)

A glass tube and
a pair of sealing electrodes for sealing both end openings of the glass tube to seal a discharge gas therein and form a discharge space;
The pair of sealed electrodes includes a main body having an outer circumferential surface joined to the glass tube;
a protrusion protruding inward in the axial direction from the main body,
The protrusion has a tip surface facing inward in the axial direction,
a protrusion outer circumferential surface exposed to the discharge space between the tip surface and an outer circumferential surface of the main body,
A surge protection element, characterized in that an insulating film is formed on an outer peripheral surface of the protruding portion, and a conductor is exposed on the tip surface. 2. The surge protection device according to claim 1,
A surge protection element, characterized in that the protrusion has a truncated cone shape with the axis of the main body as its central axis. 3. The surge protection device according to claim 1,
The insulating film is also formed on the outer circumferential surface of the main body,
the insulating film is made of cuprous oxide,
A surge protection element, characterized in that the conductor exposed on the tip surface is made of copper. The surge protection device according to any one of claims 1 to 3,
an insulator housed in the discharge space of the glass tube;
A surge protection element, characterized in that both ends of the insulator are in contact with the tip faces of the pair of sealed electrodes.

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