JPH0219924Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is a lightning arrester using a zinc oxide varistor element, and when the varistor element deteriorates for some reason, the heat generated by the varistor element due to the leakage current melts the low melting point alloy. Therefore, with regard to the structure of the joint made of a low melting point alloy of the opening mechanism that disconnects the lightning arrester from the circuit, it increases the degree of adhesion of the electrode that is pressure-bonded to the varistor element to obtain good heat conduction characteristics, and also to improve the connection to the varistor element of surge current. The purpose of this is to obtain uniform flow distribution characteristics.

Varistor elements mainly made of zinc oxide are widely used as gear press arresters to protect various electrical equipment because of their excellent voltage-current characteristics and large lightning surge absorption ability. This varistor element exhibits an extremely high impedance to an applied voltage within a normal rating, operates as an insulator, and has a characteristic that its leakage current is on the order of microamperes and can be ignored. However, when a surge current that greatly exceeds the rating flows in, the voltage-current characteristics deteriorate, and a large leakage current flows even at a normal applied voltage, causing heat generation in the varistor element. If this state continues for a long time, the varistor element will undergo thermal runaway within a certain period of time, leading to short-circuit destruction. If a short-circuit breakdown occurs, this varistor element will affect other equipment by operating the fuse, breaker, etc. of the power supply connected to it. In order to avoid such a situation, a lightning arrester having a structure as shown in FIG. 1 has been commercialized. In this lightning arrester, when leakage current flows into the varistor element and the temperature of the varistor element rises above a specified value, the internal circuit of the arrester attempts to open before the varistor element is short-circuited and destroyed.

That is, in FIG. 1, 1 is a disc-shaped or cylindrical varistor element, and silver electrodes 2, 2' are arranged on both sides of the varistor element.
is burned into it. A first electrode plate 3 is pressed against the electrode 2 by a spring or the like (not shown).
A conducting wire extending from this point connects one end of the distribution line as one terminal of a lightning arrester. A second electrode plate 4 having a square-shaped through hole 5 in the center is pressed into contact with the other electrode 2'. The tip of a metal rod 6 is inserted into the through hole 5 of the second electrode plate 4, and is soldered with a low melting point alloy 7 in the square hole. The eutectic temperature of this low melting point metal is usually about 130 to 190°C. An electrical insulator 8 with a flange is stacked on the back surface of the second electrode plate 4, and the metal rod 6 passes through this insulator 8 and connects the resin molded body 12 embedded in the other end with the insulator 8. A force is constantly applied to the metal rod in a direction to separate it from the electrode plate 4 by a spring 9 interposed therebetween.
The insulator 8 insulates the second electrode plate 4 and the spring 9, and also serves as a stopper when the metal rod 6 is soldered to the second electrode plate 4 with a low melting point alloy. Further, a flexible conducting wire 10 whose one end is connected to a ground terminal 11 is connected to the end of the metal rod 6.

In the above-described lightning arrester, when the varistor element deteriorates, the element 1 generates heat due to its leakage current, and the heat is transmitted to the low melting point alloy 7 via the second electrode plate 4. When the temperature exceeds the melting point of the low melting point alloy 7, the soldered part melts, and the binding force between the second metal plate 4 and the metal rod 6 disappears, which was previously applied by the spring 9. The force in the pulling direction moves the metal rod 6, the electric wire 10, and the resin molded body 12 downward, and the second electrode plate 4 and the metal rod 6 are separated, and the first electrode plate 3 and the ground terminal 11 are separated. During this period, the circuit remains open.

What plays an important role in this mechanism is the soldered portion made of the low melting point alloy 7. An enlarged view of this part is shown in FIG. Usually this soldering is done using a soldering iron, but during this soldering work,
The molten low-melting point alloy adheres to the outside of the large-diameter opening end of the rough-shaped through hole, and the second electrode plate 4
When the heat dissipation properties of molten low melting point alloy 7 are large,
The surface tension is not sufficient, and a ring-shaped convex portion 13 as shown in the figure is generated at the boundary between the roughened portion and the plane of the second electrode plate. Since this convex portion 13 protrudes slightly from the flat surface of the second electrode plate 4, the adhesion between the second electrode plate 4 and the electrode 2' of the varistor element 1 which is pressed onto it is insufficient. As a result, the heat conduction from the varistor element 1 to the second electrode plate 4 becomes poor, and when a surge current flows, the current flows only through the convex portion 13, so the current does not flow evenly through the varistor element 1. Further, problems such as arcing occurring between the electrode 2' and the electrode plate 4 occur due to incomplete contact.

In the present invention, the square-shaped hole 5 of the second electrode 4
This is an attempt to solve the above-mentioned problems by adding some innovation to the structure.

FIG. 3 shows a sectional view of essential parts of an embodiment of the present invention. In the present invention, in the lightning arrester as explained with reference to FIG. A counterbore 14 is provided concentrically with the planar hole and having a diameter larger than the maximum diameter of the planar hole. This counterbore 1
The depth of 4 is the convex portion 13 of the solder made of low melting point alloy.
It should be larger than the height of By providing such a counterbore 14, the solder convex portion 13 does not directly touch the electrode 2', and a good pressure contact state can be obtained between the electrode 2' and the second electrode plate 4.

As described above, in the present invention, on the outside of the end near the varistor element of the planar through hole 5 of the electrode plate 4 through which the metal rod 6 has penetrated, there is a hole concentric with the planar through hole.
When a counterbore 14 with a diameter larger than the maximum diameter of the through hole is made and the depth of this counterbore is filled with a low melting point alloy into the planar through hole, the low melting point that occurs at the periphery of the planar through hole. It is deeper than the height of the convex part of the alloy, and this configuration improves the heat conduction characteristics between the varistor element 1 and the electrode plate 4, and evenly distributes surge current to the varistor element. Moreover, it is possible to prevent arcing from occurring in the gap between the electrode 2' and the second electrode plate 4, thereby increasing the reliability of the lightning arrester.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing the opening mechanism of a conventional lightning arrester, Fig. 2 is an enlarged sectional view of the soldered part of the metal rod, which is the main part, and Fig. 3 is a sectional view of the main part of the embodiment of the present invention. be. 1... Varistor element, 2, 2'... Electrode, 3,
4... Electrode plate, 5... Through hole, 6... Metal rod, 7
...Low melting point alloy, 9...Spring, 11...Earth terminal, 13...Protrusion, 14...Spot face.

Claims (1)

[Scope of utility model registration request] An electrode plate having a circular through-hole is brought into contact with a zinc oxide varistor element in an electrically and thermally conductive manner, and the tip of a metal rod is inserted into the through-hole with force applied in the direction of pulling it apart by a spring. A mechanism in which the tip of the metal rod and the electrode plate are joined with a low melting point alloy filled in a through hole, and the low melting point alloy is melted by the temperature rise of the varistor element to separate the electrode plate and the metal rod. In the lightning arrester, there is provided a seat concentrically with the varistor-shaped through hole and having a diameter larger than the maximum diameter of the through-hole on the outside of the widened end of the varistor element of the varistor-shaped through hole of the electrode plate. The depth of the counterbore is set to be deeper than the height of the convex portion of the low melting point alloy that is formed on the outside of the periphery of the planar through hole when the planar hole is filled with the low melting point alloy. A lightning arrester opening mechanism featuring: